Agro-Climatic Regions and Crop Zones in M.P. The State is divided in 11 Agro-climatic regions and 5 crop zones. District-wise classification alongwith soil type and normal rainfall range is as below : S.N o. CROP/ ZONES AGRO- CLIMAT IC REGION S SOIL TYPE RAINFA LL (Range in m.m.) DISTRICTS COVERED DETAILS OF PARTLY COVERED DISTRICTS 1. 1 Rice zone Chhattisga rh plains Red & Yellow (Medium) 1200 to 1600 Balaghat. 2 -do- Northe rn Hill Region of Chhatt isgarh Red & Yellow Medium black & skeltal (Medium/ light) 1200 to 1600 ,Shahdol,Mandla, Dindori, Anuppur, Sidhi(Partly), Umaria Sidhi :-Singroli Tehsil(Bedhan) 3 2 Wheat Rice Zone Kymore Platea u & Satpur a Hills Mixed red and black soils (Medium) 1000 to 1400 Rewa,Satna,Panna ,Jabalpur, Seoni, Katni, Sidhi (except Singroli tehsil ) 4 3 Wheat zone Centra l Narmad a Valley Deep black (deep) 1200 to 1600 Narsinghpur, Hoshangabad Sehore(Partly),R aisen(Partly) Sehore :- Budni Tehsil. Raisen :- Bareli Tehsil. 5 -do- Vindhya Plateau Medium black & deep black (Medium/ Heavy) 1200 to 1400 Bhopal,Sagar,Dam oh,Vidisha, Raisen(except Bareli Teh.), Sehore(except Budni Teh.), Guna(Partly). Guna :- Chanchoda,Ra ghogarh & Aron Tehsils. 6 4Wheat- Jowar Gird Region Alluvial (Light) 800 to 1000 Gwalior,Bhind,Mo rena, Sheopur- Kala,Shivpuri,
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Agro-Climatic Regions and Crop Zones in M.P.
The State is divided in 11 Agro-climatic regions and 5 crop zones.District-wise classification alongwith soil type and normal rainfall range is as below :
S.No.
CROP/ZONES
AGRO-CLIMATIC REGIONS
SOIL TYPE
RAINFALL (Range in m.m.)
DISTRICTS COVERED DETAILS OF PARTLY COVERED DISTRICTS
Cropping systemThe cropping pattern used on a farm and its interactions with farm resources, other farm enterprises, and available technology which determine their makeup.
Mixed farmingCropping pattern which involve the raising of crops, animals and or trees.
Ratooning One of the important methods of intensive cropping, allowing the stubbles of the original crop to strike again after harvesting and to raise another crop.
Live mulch systemLive mulch crop production involves planting a food crop directly into a living cover of an established cover crop without tillage or the destruction of the fallow vegetation.
Mixed croppingGrowing of two or more crops simultaneously and intermingled without row arrangements, where there is significant amount of intercrop competition.
IntercroppingGrowing of two or more crops simultaneously in alternate rows or otherwise in the same area, where there is significant amount of inter crop competition.Advantages of intercropping are a)greater stability of yield over different seasons,b) better use of growth resources,c) better control of weeds, pests and diseases,d) one crop provides physical support to the other crop,e) one crop provides shelter to the other crop,f) erosion control through providing continuous leaf cover over the ground surface, and g) it is the small farmers of limited means who is most likely to benefit.
Thereare some disadvantages as well,as for eg.a)yield decrease because of adverse competition effect,b)allelopathic effect,c)creates obstruction in the free use of machines for intercultural operations and d)large farmers with adequate resources may likely to get less benefit out of intercropping.
Relay planting is inter planting or inter sowing of seeds/seedlings of the following crop in the preceding/maturing crop.Multiple cropping is defined as the growing of more than one crop on the same land in one year.
There are some other terms related to multiple cropping are the following.Sole cropping-One crop variety grown alone in pure stands at normal density. Also known as solid planting.Monoculture-The repetitive growing of the same sole crop on the same land.Crop rotation-The repetitive cultivation of an ordered succession of crops or crops and fallow on the same land.
Soil Structure
Soil conditions and characteristics such as water movement, heat transfer, aeration, and porosity are much influenced by structure. In fact, the important physical changes imposed by the farmer in ploughing, cultivating, draining, liming, and manuring his land are structural rather than textural. Definition of Soil Structure: The arrangement and organization of primary and secondary particles in a soil mass is known as soil structure. Soil structure controls the amount of water and air present in soil. Plant roots and germinating seeds require sufficient air and oxygen for respiration. Bacterial activities also depend upon the supply of water and air in the soil. Formation of soil structure: Soil particles may be present either as single individual grains or as aggregate i.e. group of particles bound together into granules or compound particles. These granules or compound particles are known as secondary particles. A majority of particles in a sandy or silty soil are present as single individual grains while in clayey soil they are present in granulated condition. The individual particles are usually solid, while the aggregates are not solid but they possess a porous or spongy character. Most soils are mixture of single grain and compound particle. Soils, which predominate with single grains are said to be structure less, while those possess majority of secondary particles are said to be aggregate, granulated or crumb structure. Mechanism of Aggregate Formation: The bonding of the soil particles into structural unit is the genesis of soil structure. The bonding between individual particles in the structural units is generally considered to be stronger than the structural units themselves. In aggregate formation, a number of primary particles such as sand, silt and clay are brought together by the cementing or binding effect of soil colloids. The cementing
materials taking part in aggregate formation are colloidal clay, iron and aluminium hydroxides and decomposing organic matter. Whatever may be the cementing material, it is ultimately the dehydration of colloidal matter accompanied with pressure that completes the process of aggregation. Colloidal clay: By virtue of high surface area and surface charge, clay particles play a key role in the formation of soil aggregates. Sand and silt particles can not form aggregates as they do not possess the power of adhesion and cohesion. These particles usually carry a coating of clay particles; they are enmeshed in the aggregates formed by the adhering clay particles. Colloidal particles form aggregates only when they are flocculated. There is vast difference between flocculation and aggregation. Flocculation is brought about by coalescence of colloidal particles and is the first step in aggregation. Aggregation is some thing more than flocculation involving a combination of different factors such as hydration, pressure, dehydration etc. and required cementation of flocculated particles. The cementation may be caused by cations, oxides of Fe and Al, humus substances and products of microbial excretion and synthesis. Clay particles form aggregates only if they are wetted by a liquid like water whose molecules possess an appreciable dipole moment.
The aggregation also depends upon the nature of clay particles, size and amount of clay particles, dehydration of clay particles, cations like calcium and anions like phosphate. Fe and Al oxides: The colloidal Fe oxides act as cementing agent in aggregation. Al oxides bind the sand and silt particles. These act in two ways. A part of the hydroxides acts as a flocculating agent and the rest as a cementing agent.
Organic matter: It also plays an important role in forming soil aggregates.
1. During decomposition, cellulose substances produce a sticky material very much resembling mucus or mucilage. The sticky properly may be due to the presence of humic or humic acid or related compounds produced.
2. Certain polysaccharides formed during decomposition.
3. Some fungi and bacteria have cementing effect probably due to the presence of slimes and gums on the surface of the living organisms produced as a result of the microbial activity
Classification of Soil Structure: The primary particles sand, silt and clay usually occur grouped together in the form of aggregates.
Natural aggregates are called peds where as clod is an artificially formed soil mass. Structure is studied in the field under natural conditions and it is described under three categories 1. Type - Shape or form and arrangement pattern of peds 2. Class - Size of Peds 3. Grade - Degree of distinctness of peds
Types of Soil Structure: There are four principal forms of soil structure
Plate-like (Platy): In this type, the aggregates are arranged in relatively thin horizontal plates or leaflets. The horizontal axis or dimensions are larger than the vertical axis.
When the units/ layers are thick they are called platy. When they are thin then it is laminar. Platy structure is most noticeable in the surface layers of virgin soils but may be present in the subsoil.
This type is inherited from the parent material, especially by the action of water or ice.
Prism-like: The vertical axis is more developed than horizontal, giving a pillar like shape. Vary in length from 1- 10 cm. commonly occur in sub soil horizons of Arid and Semi arid regions. When the tops are rounded, the structure is termed as columnar when the tops are flat / plane, level and clear cut prismatic.
Block like: All three dimensions are about the same size. The aggregates have been reduced to blocks. Irregularly six faced with their three dimensions more or less equal. When the faces are flat and distinct and the edges are sharp angular, the structure is named as angular blocky. When the faces and edges are mainly rounded it is called sub angular blocky. These types usually are confined to the sub soil and characteristics have much to do with soil drainage, aeration and root penetration.
Spheroidal (Sphere like): All rounded aggregates (peds) may be placed in this category. Not exceeding an inch in diameter. These rounded complexes usually loosely arranged and readily separated. When wetted, the intervening spaces generally are not closed so readily by swelling as may be the case with a blocky structural condition.
Therefore in sphere like structure, infiltration, percolation and aeration are not affected by wetting of soil. The aggregates of this group are usually termed as granular which are relatively less porous. When the granules are very porous, it is termed as crumb. This is specific to surface soil particularly high in organic matter/ grass land soils.
Classes of Soil Structure: Each primary structural type of soil is differentiated into 5 size classes depending upon the size of the individual peds.
The terms commonly used for the size classes are:
1. 1. Very fine or very thin2. 2. Fine or thin
3. 3. Medium
4. 4. Coarse or thick
5. 5. Very Coarse or very thick
The terms thin and thick are used for platy types, while the terms fine and coarse are used for other structural types.
Grades of Soil Structure: Grades indicate the degree of distinctness of the individual peds. It is determined by the stability of the aggregates. Grade of structure is influenced by the moisture content of the soil. Grade also depends on organic matter, texture etc. Four terms commonly used to describe the grade of soil structure are:
1. Structure less: There is no noticeable aggregation, such as conditions exhibited by loose sand.
2. Weak Structure: Poorly formed, indistinct formation of peds, which are not durable and much unaggregated material.
3. Moderate structure: Moderately well developed peds, which are fairly durable and distinct.
4. Strong structure: Very well formed peds, which are quite durable and distinct.
Soil Structure Naming: For naming a soil structure the sequence followed is grade, class and type; for example strong coarse angular blocky, moderate thin platy, weak fine prismatic.
Role of soil organic matter in crop productivity
a. Cation exchange capacity
b. Nutrient retention and release
c. Soil structure and bulk density
d. Water-holding and snow/drain catchment
e. Biological activity
The roles of soil organic matter can be classified into three broad categories: biological, physical, and chemical.
As pointed out by Krull (19), there are many and varied interactions that occur between these aspects of SOM.
Additionally, the active and stable fractions will play different roles in specific SOM functions.
2a. Cation Exchange Capacity
Cation exchange capacity (CEC) is the total sum of exchangeable cations (positively charged ions) that a soil can
hold (4). Cation exchange capacity determines a soil’s ability to retain positively charged plant nutrients, such as
NH4+, K+, Ca2+, Mg2+, and Na+. As CEC increases for a soil, it is able to retain more of these plant nutrients and
reduces the potential for leaching. Soil CEC also influences the application rates of lime and herbicides required
for optimum effectiveness. The stable fraction (humus) of SOM is the most important fraction for contributing to
the CEC of a soil.
Different soil textures have differing CEC (Table 1). In most soils, organic matter contributes more to exchange
capacity than the soil texture. The interaction of texture and organic matter components in soil has a tremendous
influence on CEC potential (9).
Table 1. The range of CEC for each soil texture and organic
matter.
Texture CEC (cmol/kg)
Organic matter 40-200
Sand 1-5
Sandy loam 2-15
Silt loam 10-25
Clay loam/silty clay loam 15-35
Clay 25-60
Vermiculite 150
2b. Nutrient Retention and Release
As stated in the previous section, humus plays an important role in regulating the retention and release of plant
nutrients. Humus has a highly negatively charged soil component, and is thus capable of holding a large amount
of cations. The highly charged humic fraction gives the SOM the ability to act similarly to a slow release fertilizer.
Over time, as nutrients are removed from the soil cation exchange sites, they become available for plant uptake.
Predictions of the amount of nutrients released from SOM are complicated and there are no widely agreed upon
methods in use. Prediction of N release to the soil from SOM is difficult but can be estimated by the pre-plant soil
profile nitrate (PPNT) or pre-sidedress nitrate (PSNT) tests. Many land grant universities have conducted trials to
estimate the N release from SOM for plant growth. In Minnesota, a soil with a SOM content greater than 3% will
have a lower fertilizer N requirement compared to a soil with less than 3% SOM (26).
2c. Soil Structure and Bulk Density
Figure 2. Water runoff on a poorly structured soil.Photo courtesy of Jodi DeJong-Hughes, UMN.Soil structure refers to the way that individual soil mineral particles (sand, silt, and clay) are arranged and
grouped in space. Soil structure is stabilized by a variety of different binding agents. Soil organic matter is a
primary factor in the development and modification of soil structure (9).
While binding forces may be of organic or inorganic origins, the organic forces are more significant for building
large, stable aggregates in most soils. Examples of organic binding agents include plant- and microbially-derived
polysaccharides, fungal hyphae, and plant roots. Inorganic binding agents and forces include charge attractions
between mineral particles and/or organic matter and freezing/thawing and wetting/drying cycles within the soil as
well as compression and deformation forces. Both the stable and the active fraction of SOM contribute to and
maintain soil structure and resist compaction.
2d. Water-Holding and Snow/Drain Catchment
Increasing SOM is an effective method for increasing drought-resistance in arid areas. The effect that drought
has to reduce crop yields is not only due to irregular or insufficient rainfall, but also because a large proportion of
rainfall is lost from fields as a result of runoff (6) (Fig. 2). Some factors in inefficient water usage are out of a
grower’s hands, for example slope, rainfall intensity, soil texture, and water that moves below rooting depth. But
some factors, especially those that reduce SOM, such as burning crop residues, excessive tillage, and
eliminating windrows reduce water infiltration and increase water runoff. SOM affects the amount of water in a
soil by influencing 1) water infiltration and percolation, 2) evaporation rates, and 3) increasing the soil water
holding capacity.
Factors that reduce water infiltration and percolation are compaction in surface soils, lack of surface residue,
poor soil structure, surface crusting due to salinity, and steep slopes that facilitate high volumes of water runoff. If
water is running off of a field at a high velocity, it cannot overcome the lateral force of water movement and thus
will not move vertically down into the soil profile. Erosion of valuable topsoil is a common result of water runoff.
Surface residues physically impede water runoff, resulting in reduced velocity of water movement. As water
movement across the soil surface slows down, water has more time to move downward into the soil profile,
rather than across the soil surface. In this way, increasing SOM and leaving residue on the soil surface can
increase water infiltration.
soil types of M.P
Soils are porous and open bodies, yet they retain water. They contain mineral particles of many shapes and sizes and organic material which is colloidal (particles so small they remain suspended in water) in character. The solid particles lie in contact one with the other, but they are seldom packed as closely together as possible.
Texture
The size distribution of primary mineral particles, called soil texture, has a strong influence on the properties of a soil. Particles larger than 2 mm in diameter are considered inert. Little attention is paid to them unless they are boulders that interfere with manipulation of the surface soil. Particles smaller than 2 mm in diameter are divided into three broad categories based on size. Particles of 2 to 0.05 mm diameter are called sand; those of 0.05 to 0.002 mm diameter are silt; and the <0.002 mm particles are clay. The texture of soils is usually expressed in terms of the percentages of sand, silt, and clay. To avoid quoting exact percentages, 12 textural classes have been defined. Each class, named to identify the size separate or separates having the dominant impact on properties, includes a range in size distribution that is consistent with a rather narrow range in soil behavior. The loam textural class contains soils whose properties are controlled equally by clay, silt and sand separates. Such soils tend to exhibit good balance between large and small pores; thus, movement of water, air and roots is easy and water retention is adequate. Soil texture, a stable and an easily determined soil characteristic, can be estimated by feeling and manipulating a moist sample, or it can be determined accurately by laboratory analysis. Soil horizons are sometimes separated on the basis of differences in texture.
Structure
Anyone who has ever made a mud ball knows that soil particles have a tendency to stick together. Attempts to make mud balls out of pure sand can be frustrating experiences because sand particles do not cohere (stick together) as do the finer clay particles. The nature of the arrangement of primary particles into naturally formed secondary particles, calledaggregates, is soil structure. A sandy soil may be structureless
because each sand grain behaves independently of all others. A compacted clay soil may be structureless because the particles are clumped together in huge massive chunks. In between these extremes, there is the granular structure of surface soils and the blocky structure of subsoils. In some cases subsoils may have platy or columnar types of structure. Structure may be further described in terms of the size and stability of aggregates. Structural class is based on aggregate size, while structural grade is based on aggregate strength. Soil horizons can be differentiated on the basis of structural type, class, or grade.
What causes aggregates to form and what holds them together? Clay particles cohere to each other and adhere to larger particles under the conditions that prevail in most soils. Wetting and drying, freezing and thawing, root and animal activity, and mechanical agitation are involved in the rearranging of particles in soils--including destruction of some aggregates and the bringing together of particles into new aggregate groupings. Organic materials, especially microbial cells and waste products, act to cement aggregates and thus to increase their strength. On the other hand, aggregates may be destroyed by poor tillage practices, compaction, and depletion of soil organic matter. The structure of a soil, therefore, is not stable in the sense that the texture of a soil is stable. Good structure, particularly in fine textured soils, increases total porosity because large pores occur between aggregates, allowing penetration of roots and movement of water and air.
Consistence
Consistence is a description of a soil's physical condition at various moisture contents as evidenced by the behavior of the soil to mechanical stress or manipulation. Descriptive adjectives such as hard, loose, friable, firm, plastic, and sticky are used for consistence. Soil consistence is of fundamental importance to the engineer who must move the material or compact it efficiently. The consistence of a soil is determined to a large extent by the texture of the soil, but is related also to other properties such as content of organic matter and type of clay minerals.
Color
The color of objects, including soils, can be determined by minor components. Generally, moist soils are darker than dry ones and the organic component also makes soils darker. Thus, surface soils tend to be darker than subsoils. Red, yellow and gray hues of subsoils reflect the oxidation and hydration states or iron oxides, which are reflective of predominant aeration and drainage characteristics in subsoil. Red and yellow hues are indicative of good drainage and aeration, critical for activity of aerobic organisms in soils. Mottled zones, splotches of one or more colors in a matrix of different color, often are indicative of a transition between well drained, aerated zones and poorly drained, poorly
aerated ones. Gray hues indicate poor aeration. Soil color charts have been developed for the quantitative evaluation of colors.
Major Elements
Eight chemical elements comprise the majority of the mineral matter in soils. Of these eight elements, oxygen, a negatively-charged ion (anion) in crystal structures, is the most prevalent on both a weight and volume basis. The next most common elements, all positively-charged ions (cations), in decreasing order are silicon, aluminum, iron, magnesium, calcium, sodium, and potassium. Ions of these elements combine in various ratios to form different minerals. More than eighty other elements also occur in soils and the earth's crust, but in much smaller quantities.
Soils are chemically different from the rocks and minerals from which they are formed in that soils contain less of the water soluble weathering products, calcium, magnesium, sodium, and potassium, and more of the relatively insoluble elements such as iron and aluminum. Old, highly weathered soils normally have high concentrations of aluminum and iron oxides.
The organic fraction of a soil, although usually representing much less than 10% of the soil mass by weight, has a great influence on soil chemical properties. Soil organic matter is composed chiefly of carbon, hydrogen, oxygen, nitrogen and smaller quantities of sulfur and other elements. The organic fraction serves as a reservoir for the plant essential nutrients, nitrogen, phosphorus, and sulfur, increases soil water holding and cation exchange capacities, and enhances soil aggregation and structure.
The most chemically active fraction of soils consists of colloidal clays and organic matter. Colloidal particles are so small (< 0.0002 mm) that they remain suspended in water and exhibit a very large surface area per unit weight. These materials also generally exhibit net negative charge and high adsorptive capacity. Several different silicate clay minerals exist in soils, but all have a layered structure. Montmorillonite, vermiculite, and micaceous clays are examples of 2:1 clays, while kaolinite is a 1:1 clay mineral. Clays having a layer of aluminum oxide (octahedral sheet) sandwiched between two layers of silicon oxide (tetrahedral sheets) are called 2:1 clays. Clays having one tetrahedral sheet bonded to one octahedral sheet are termed 1:1 clays.
Cation Exchange
Silicate clays and organic matter typically possess net negative charge because of cation substitutions in the crystalline structures of clay and the loss of hydrogen cations from functional groups of organic matter. Positively-charged cations are attracted to these negatively-charged particles, just as opposite poles of magnets attract one another. Cation exchange is the ability of soil clays and organic matter to adsorb and exchange cations with those in soil solution (water in soil pore space). A dynamic equilibrium exists between adsorbed cations and those in soil solution. Cation adsorption is reversible if other cations in soil solution are sufficiently concentrated to displace those attracted to the negative charge on clay and organic matter surfaces. The quantity of cation exchange is measured per unit of soil weight and is termed cation exchange capacity. Organic colloids exhibit much greater cation exchange capacity than silicate clays. Various clays also exhibit different exchange capacities. Thus, cation exchange capacity of soils is dependent upon both organic matter content and content and type of silicate clays.
Cation exchange capacity is an important phenomenon for two reasons:
1. exchangeable cations such as calcium, magnesium, and potassium are readily available for plant uptake and
2. cations adsorbed to exchange sites are more resistant to leaching, or downward movement in soils with water.
Movement of cations below the rooting depth of plants is associated with weathering of soils. Greater cation exchange capacities help decrease these losses. Pesticides or organics with positively charged functional groups are also attracted to cation exchange sites and may be removed from the soil solution, making them less subject to loss and potential pollution.
Calcium (Ca++) is normally the predominant exchangeable cation in soils, even in acid, weathered soils. In highly weathered soils, such as oxisols, aluminum (Al+3) may become the dominant exchangeable cation.
The energy of retention of cations on negatively charged exchange sites varies with the particular cation. The order of retention is: aluminum > calcium > magnesium > potassium > sodium > hydrogen. Cations with increasing positive charge and decreasing hydrated size are most tightly held. Calcium ions, for example, can rather easily replace sodium ions from exchange sites. This difference in replaceability is the basis for the application of gypsum (CaSO4) to reclaim sodic soils (those with > 15% of the cation exchange capacity occupied by sodium ions). Sodic soils exhibit poor structural characteristics and low infiltration of water.
The cations of calcium, magnesium, potassium, and sodium produce an alkaline reaction in water and are termed bases or basic cations. Aluminum and hydrogen ions produce acidity in water and are
called acidic cations. The percentage of the cation exchange capacity occupied by basic cations is called percent base saturation. The greater the percent base saturation, the higher the soil pH.
Soil pH
Soil pH is probably the most commonly measured soil chemical property and is also one of the more informative. Like the temperature of the human body, soil pH implies certain characteristics that might be associated with a soil. Since pH (the negative log of the hydrogen ion activity in solution) is an inverse, or negative, function, soil pH decreases as hydrogen ion, or acidity, increases in soil solution. Soil pH increases as acidity decreases.
A soil pH of 7 is considered neutral. Soil pH values greater than 7 signify alkaline conditions, whereas those with values less than 7 indicate acidic conditions. Soil pH typically ranges from 4 to 8.5, but can be as low as 2 in materials associated with pyrite oxidation and acid mine drainage. In comparison, the pH of a typical cola soft drink is about 3.
Soil pH has a profound influence on plant growth. Soil pH affects the quantity, activity, and types of microorganisms in soils which in turn influence decomposition of crop residues, manures, sludges and other organics. It also affects other nutrient transformations and the solubility, or plant availability, of many plant essential nutrients. Phosphorus, for example, is most available in slightly acid to slightly alkaline soils, while all essential micronutrients, except molybdenum, become more available with decreasing pH. Aluminum, manganese, and even iron can become sufficiently soluble at pH < 5.5 to become toxic to plants. Bacteria which are important mediators of numerous nutrient transformation mechanisms in soils generally tend to be most active in slightly acid to alkaline conditions.
Soil Biota
The soil contains a vast array of life forms ranging from submicroscopic (the viruses), to earthworms, to large burrowing animals such as gophers and ground squirrels. Microscopic life forms in the soil are generally called the "soil microflora" (though strictly speaking, not all are plants in the true sense of the word) and the larger animals are called macrofauna.
Soil animals, especially, the earthworms and some insects tend to affect the soil favorably through their burrowing and feeding activities which tend to improve aeration and drainage through structural modifications of the soil solum. In general, they affect soil chemical properties to a lesser extent though their actions indirectly enhance microbial activities due to creation of a more favorable soil environment.
Soil Microorganisms
Soil microorganisms occur in huge numbers and display an enormous diversity of forms and functions. Major microbial groups in soil are bacteria (including actinomycetes), fungi, algae (including cyanobacteria) and protozoa.
Because of their extremely small cell size (one to several micrometers), enormous numbers of soil microbes can occupy a relatively small volume, hence space is rarely a constraint on soil microbes. Soil microbes can occur in numbers ranging up to several million or more in a gram of fertile soil (a volume approximately that of a red kidney bean). Note that the bacteria are clearly the most numerous of the soil microbes. Perhaps more important than the numbers of the various soils microbes is the microbial biomass contributed by the respective groups. It is the soil fungi which tend to contribute the most biomass among the microbial groups. In fact, it is because of their large contribution to the biomass that they are generally regarded as being the dominant decomposer microbes in the soil. You might find it surprising that there are literally "tons" of microbes beneath your feet as you walk across a grassland in Africa or Australia or through a cornfield in the American Midwest. Interestingly, a fungus discovered in the state of Michigan may be one of the largest living organ-isms on the planet.
A fungus, Armillaria bulbosa, discovered in the U.S. in the state of Michigan, could turn out to be earth's largest creature or at least among the largest. Scientists discovered the fungus growing among the roots of
hardwood trees in a forest. The microscopic, branched filaments (called hyphae) of the fungus occupy a 14.8 ha (37-acre) area of land. Careful genetic analysis has shown the filaments constitute a single organism. Fungi generally radiate outward in a circular pattern as they grow through the soil. In fact, the fairy rings of mushrooms (named because ancient peoples thought they represented the paths of fairies dancing in the night) often seen in lawns or on golf courses actually represent the outer boundary of a developing fungus. Scientists estimate that the portion of the Michigan fungus they have been able to identify may weigh as much as 100 tons, slightly less than a blue whale. Imagine the biochemical capacity of a soil microorganism this large!
The significance of these large amounts of microbial biomass in the soil lies not only in their large biochemical capacity, but in the phenomenal diversity of biochemical reactions attributed to the soil microbial population. It is worth remembering that soil microbes not only interact with other members of their own group, they also interact with other microbial groups. It is quite common to find, for example, that degradation of plant materials occurs much more quickly in the presence of the mixed soil population than it does when one or more groups of soil microbes have been eliminated from the system.
Soil life can be divided into trophic (i.e. feeding) levels. At the base of the trophic levels lies the soil microbial population which degrades plant, animal and microbial bodies, and also serves as the food source for some of the levels above it. For example, soil protozoa consume enormous numbers of bacteria and even some fungal spores. These in turn are consumed by still larger soil animals (nematodes, mites, etc.) which in turn are eaten by still larger animals (e.g. worms and insects). Thus, nutrients flow through this microbial food web which lies at the heart of controlling soil fertility and plant productivity in the absence of external inputs such as fertilizers. In fact, the role of soil microbes in degrading organic materials and thereby regenerating a supply of carbon dioxide for plants is perhaps their most vital global function.
Nutrient Cycling by Soil Microbes
Soil microbes exert much influence in controlling the quantities and forms of various chemical elements found in soil. Most notable are the cycles for carbon, nitrogen, sulfur and phosphorus, all of which are elements important in soil fertility, and as we know today, may be involved in global environmental phenomena. The mineralization (i.e. the conversion of organic forms of the elements to their inorganic forms) of organic materials by soil microbes liberates carbon dioxide, ammonium (which is rapidly converted to nitrate by soil microbes), sulfate, phosphate and
inorganic forms of other elements. This is the basis of nutrient cycling in all major ecosystems of the world. John Burroughs once said, "Without death and decay, how could life go on?" No doubt, he was referring to the mineralization of nutrients from dead animals and plants. We now know that soil microbes accomplish this task with remarkable zeal and that in the process a substantial part (perhaps as much as one third) of the decomposing materials are converted to the bodies of soil microbes. This pool of microbial biomass constitutes a portion of the soil organic matter which turns over (cycles) fairly quickly and therefore represents a "fertility buffer" in the soil. Don't forget that the liberation of carbon dioxide through microbial respiration makes possible the continued photosynthesis (i.e. carbon dioxide fixation) by algae and green plants which in turn produce more organic materials which may ultimately reach the soil, thereby completing the cycle.
In the world's agricultural soils, the source of our food supply, mineralization of nitrogen by soil microbes is a most important process. In those soils not receiving external inputs of fertilizer nitrogen (e.g. most forested lands and many grasslands) the liberation of ammonium from organic debris makes possible the continued growth of new plant matter. Therefore, it is the soil microbial population which controls the productivity of these soils if other environmental factors (moisture, temperature) are suitable. In fact, fertilization of a soil represents our attempt to balance the competition between plants and soil microbes for available soil nitrogen. Nitrogen tied-up (assimilated into cell constituents) in microbial cells is not available for plants or other microbes until that tissue has been decomposed by other microbes. In other words, nitrogen contained in tissues is said to be immobilized. Microbes are the keys for the remobilization of these nutrients. These mineralization/immobilization phenomena are common to all the elements but typically they are only agriculturally important for the macronutrients such as nitrogen, phosphorus and sulfur.
Aside from their role in controlling the rates of production of inorganic forms of nitrogen and sulfur, soil microbes, in particular soil bacteria, can control the forms of the ions in which these nutrients occur. For example, ammonium (NH4
+) in the soil is usually rapidly oxidized by bacteria first to nitrite (NO<sub<2< sub="">-) and then to nitrate (NO3
-) which may readily leach through soil. Ammonium is oxidized to nitrite and then to nitrate by the bacteria Nitrosomonas and Nitrobacter, respectively. Thus, bacteria can influence the form and, thereby, the retention of nitrogen in the soil. Similarly, reduced sulfur compounds such as thiosulfate, elemental sulfur and even iron pyrite (FeS2, "Fool's Gold") can be oxidized to sulfuric acid by soil bacteria. The bacteria which accomplish the oxidation of reduced nitrogen and sulfur compounds use these materials as energy sources to drive their metabolism. Unlike the decomposer microbes which use organic carbon compounds from organic matter for energy and to make cell matter (e.g. they are called heterotrophs), these specialized bacteria called chemoautotrophs obtain their carbon
for cell synthesis from carbon dioxide or from dissolved carbonate.</sub<2<>
There are many genera of bacteria that can oxidize reduced sulfur compounds. However, much of this activity, especially the oxidation of sulfur and pyrite, can be attributed to bacteria of the genus Thiobacillus (thio = sulfur; bacillus = rod-shaped bacterium). Thiobacillus thiooxidans can oxidize elemental sulfur to sulfuric acid. Sulfur, therefore, can be used to decrease the pH of an alkaline soil. Thiobacillus ferrooxidans attacks both the iron and sulfur in iron pyrite, generating sulfuric acid and dissolved iron in the process. This is also the basis of acid mine drainage associated with the mining of coal throughout the world.
The long-term application of ammonium-based fertilizers can likewise result in the acidification of agricultural soils through bacterial nitrification (the conversion of ammonium to nitrate with the concurrent production of acidity). Thus, we see that certain environmental problems can arise from the activities of these chemoautotrophic soil bacteria.
Another important aspect of nutrient cycling is that under certain circumstances nitrogen and sulfur may be converted to gaseous forms (volatilized) and lost to the atmosphere. Nitrogen in the form of nitrate can be converted to gases such as nitrous oxide (N2O) and dinitrogen (N2) through the process of denitrification (the bacterial reduction of NO3
- to N2O or N2) by soil bacteria under anaerobic conditions. A consequence of denitrification is that nitrogen, a precious nutrient for plants, is lost from the soil. On the other hand, this process is a useful way to remove excess nitrate from wastewater.
Sulfur in the form of sulfate (SO4-2) is used by anaerobic bacteria like the
genus Desulfovibrio which convert it to hydrogen sulfide gas (H2S). Hydrogen sulfide reacts with metal ions and forms very insoluble metallic sulfides like pyrite (Fe2S). In fact, it is probable that the pyrites associated with coal seams were deposited by the action of these bacteria eons ago. The black color of salt marsh soils and the rotten egg smell associated with them are a result of the activities of the sulfate-reducing bacteria in these habitats. They attest to the occurrence of anaerobic conditions. Sulfur volatilization from soil represents loss of a plant nutrient as well as a contribution of atmospheric sulfur which may contribute to the phenomenon of acid precipitation.
We mentioned above that nitrogen can be lost from agricultural soils as well as from other ecosystems. Fortunately, this "leak" in the terrestrial nitrogen cycle can be at least partially replaced through another important biological process called biological nitrogen fixation. In this process, which is unique to bacteria and a few other microbes, notably the cyanobacteria (blue-green algae), atmospheric dinitrogen (N2) is captured and converted to plant-available forms. Biological nitrogen fixation is
carried out by free-living bacteria and cyanobacteria and by symbiotic microorganisms in a wide variety of mutualistically symbiotic associations with higher plants.
The most useful and probably the most widely recognized example of symbiotic nitrogen fixation is that of the Rhizobium - legume root-nodule symbiosis. Soil bacteria belonging to the genera Rhizobium and Bradyrhizobium (and a few others) are capable of inducing the formation of nodules on roots of specific legumes (plants like peas, beans, peanuts, soybeans, alfalfa etc.) and fixing large quantities of nitrogen in these structures. In the nodule, the bacteria are supplied with carbon sources (photosynthate from the plant) that they need in order to fix nitrogen. In return for this carbon, the bacteria fix atmospheric nitrogen which is converted to amino acids used by the plant for growth. The result of this unique plant-microbe partnership is that many legumes are self-sufficient for nitrogen, that is, they are nearly independent of a supply of nitrogen from the soil. It is no wonder that these plants are cultivated all over the world as sources of food, fiber and forage. Nearly two-thirds of the world's nitrogen supply is from biological nitrogen fixation. Legumes have been used since the beginning of recorded history as "soil improving" crops known as "green manures". Green manuring is the practice of growing a legume species for the sole purpose of returning it to the soil to serve as a source of nitrogen for an ensuing crop.
Soil Microbes and Bioremediation
We have touched on the remarkable metabolic diversity and capacity of the soil microflora. This capacity is increasingly being harnessed and put to good use by humans. A most beneficial spin-off from our understanding of the metabolism of soil microbes has been the development of methods for the bioremediation of soils contaminated by hazardous wastes or spilled petroleum products both on land and sea. Bioremediation may be defined as the controlled use of microorganisms for the destruction of chemical pollutants. A large number of processes have been developed to handle various wastes and for the cleanup of spilled organic materials. At the heart of all of these processes lies the premise that the metabolic activities of bacteria or fungi can be used to degrade many of the organic chemicals of commerce (solvents, pesticides, hydrocarbon fuels, etc.).
Either of two forms of bioremediation is commonly employed. In biostimulation the environment into which the material has been spilled or otherwise introduced is made favorable for the rapid development of microbes. Typically, this process involves adding sufficient nitrogen and phosphorus fertilizer to overcome nutrient limitations to microbial growth and providing some mechanism for increased aeration of the system. These practices encourage development of the indigenous microbial population which usually contains microbes able to degrade the compounds of interest. In the practice of bioaugmentation, an external microbial population is added in order to speed up the degradation process. Numerous microbes have been developed for such purposes. However, the full measure of the usefulness of such microbial products is not yet known. Some inoculants have reportedly enhanced the remediation process and others have had little or no effect on the process. It is probable that in due time useful microbial products or processes will be developed for use in the clean-up of oil or other chemical spills. What is certain is that successful bioremediation will require detailed knowledge of the factors which make some microbes more competitive than others in a given environment. Only when these details are established will we know how to use sound ecological principles to add microbes to these complex environments to insure their establishment and function in the clean-up process.
In March 1989, the Exxon Valdez oil tanker hit a reef in Prince William Sound, Alaska (USA) and released over 40 million liters of crude oil into the Sound within a 5-hour period. Over 1500 km (932 miles) of shoreline in the Sound and the Gulf of Alaska were contaminated to varying degrees by crude oil. The Exxon Valdez oil spill was a historic event because of the magnitude of the spill, the vastness and isolation of the area to be treated, and the large number of personnel and vehicles ultimately involved. The success of bioremediation, particularly in a climate as cold as Alaska’s, prompted regulatory agencies in the United States to view bioremediation much more favorably over previous strategies of physical or chemical “entombment” (storage in cement tombs).
Because oil is inherently high in carbon and low in nitrogen and phosphorus, a portion of the shoreline was selected for biostimulation. After several potential fertilizer candidates were evaluated, a microemulsion, Inipol EAP22™ (henceforth, Inipol), was selected. Inipol (an “oleophilic” fertilizer) is a stable water-in-oil formulation that yields an N-P-K ratio of 7.3:0.8:0. The nitrogen source is urea and the phosphorus source is trilaureth (4)-phosphate. At room temperature, Inipol has the consistency and appearance of honey, and it must be heated to 90oC (194oF) before it can be sprayed on the soil. Inipol was applied as a thin coat to the shore at a rate of 306 ml m-2 (0.27 quart per square yard). As the microemulsion mixed with the weathered crude oil, the crude oil destabilized Inipol to release its urea-N. In addition, a surface-active organic material (oleic acid) in Inipol served as a readily degradable carbon and energy source to increase the activity and number of indigenous hydrocarbon-degrading bacteria. When the oleic acid was depleted, the increased biomass of hydrocarbon-degrading bacteria supported enhanced biodegradation of the petroleum. Visual observations and chemical assays showed dramatic evidence that biostimulation contributed to the remediation of the site. Although passive bioremediation also undoubtedly occurred in the absence of the fertilizer nitrogen and phosphorus, the accelerated rate of biodegradation observed with Inipol was critical to a successful bioremediation effort.
Sixteen chemical elements are recognized as being essential for the growth of all plants. Five others, silicon, sodium, cobalt, vanadium, and nickel, have been recognized as necessary for the growth of some plant species. Although certain essential elements can exist in nature in a number of ionic forms, plants can use only specific ones.
Nitrogen
Other than carbon, hydrogen, and oxygen, nitrogen is the nutrient required by plants in the greatest quantity. The nitrogen concentration of plants ranges from about 0.5 to 5% on a dry weight basis. Since most plants have a rather high nitrogen requirement and most soils can't supply sufficient nitrogen to meet this demand, nitrogen normally must be supplemented from organic or inorganic fertilizer sources.
The ultimate source of all nitrogen in soils is the atmosphere, which is approximately 78% N2. Although this quantity represents an almost unlimited supply, nitrogen as N2 is not directly available for uptake by most plants. Recall that legumes in symbiosis with particular species of the bacterial genus, Rhizobium, transform gaseous N2 to plant available form, with capacities to fix N2 ranging from about 40 to greater than 300 lbs N/acre/year. Nonsymbiotic fixation of N2 by free living soil microorganisms also occurs but quantities are usually less than 10 lbs N/acre/year. Lightning discharge in thunderstorms can oxidize atmospheric N2 to plant available nitrate, but quantities are generally less than 20 lbs N/acre/year. N2 can also be transformed to plant available forms through the fertilizer manufacturing process. The chemical triple bond that exists between the two N atoms in N2 is very strong. All the above processes that convert N2 to plant useable forms, therefore, are highly energy intensive.
Nitrogen is an extremely reactive element with many of its possible transformations being depicted in the nitrogen cycle. The nitrogen cycle is the dynamic system in which nitrogen is transformed, or cycled, from one form to another. Total nitrogen in the soil-plant-water-atmosphere continuum is conserved, but amounts existing in various "pools", or forms, of nitrogen change with time and environmental conditions. The vast majority of soil nitrogen (approximately 95%) is found in soil organic matter. This organically-combined nitrogen is not immediately plant available, but can be converted to inorganic, available forms through the actions of soil microorganisms. This process, as previously discussed, is termed nitrogen mineralization. Prior to the production of inorganic nitrogen fertilizers, most nitrogen for plant growth was supplied through
leguminous N2 fixation and nitrogen mineralization of added animal manures and indigenous soil organic nitrogen. Sole reliance on nitrogen mineralization from soil organic matter normally is not sufficient for crop production and may result in soil deterioration associated with the loss of organic matter. Nitrogen supplementation, whether from organic or inorganic fertilizer sources, is normally necessary for crop production.
Nitrogen, primarily in the form of nitrate, may be lost from soils through leaching. Nitrate, being an anion, is repelled by the negatively-charged cation exchange sites in soils. Since the ion is not adsorbed and is highly water soluble, it will move downward in soils with percolating water. Nitrate leaching is most common in coarse, sandy soils receiving excess rainfall or irrigation. Nitrate losses may also be increased by applying nitrogen fertilizers, whether inorganic or organic, in excess of a crop's requirement. Nitrate leaching should be prevented not only from economic, but also from environmental and health standpoints. Ingestion of waters high in nitrate has been implicated in gastrointestinal problems in adults and methemoglobinemia ("blue baby syndrome") in infants, though confirmed cases are rare. Near-surface aquifers normally are the most susceptible. Nitrate contamination of waters is usually localized and can be decreased through proper management.
Denitrification is the bacterial reduction of nitrate under anaerobic conditions to N2 or N2O gases. Under anaerobic conditions, most nitrate in soils may be denitrified in a period of a few days. Some scientists theorize that atmospheric N2 is the result of denitrification over geologic time. Evidence also indicates that N2O may be partially responsible for depletion of the protective ozone layer and is also a potent “greenhouse gas”. Thus, loss of nitrate through denitrification not only results in an economic loss of plant available nitrogen, but may also have other detrimental effects. Combustion of fossil fuels also produces nitrous oxides that may contribute to this effect.
Nitrogen is an essential ingredient for the production of sufficient food for an expanding world population. Proper nitrogen management can decrease the potential for negative environmental impacts.
Phosphorus
Phosphorus in soil organic matter accounts for about 20 to 65% of the total phosphorus found in soils. Therefore, phosphorus mineralization from soil organic matter is an important source of available phosphorus for plant growth. Phosphorous ranks second to nitrogen as a limiting nutrient for plant growth. Although plant available forms of this element are anionic, phosphorus is immobile in soils with appreciable colloid content because it tends to be tightly bound to these tiny particles. Phosphorus may also form water insoluble compounds such as insoluble calcium phosphates in alkaline soils and insoluble iron and aluminum phosphates in acid soils. The concentration of phosphorus in soil solution is normally
much less than one part per million (ppm), even in fertilized soils, and often is only hundredths of a ppm in unfertilized soils.
Phosphorus fertilizers are normally produced through acidification of the mineral, apatite, found in high concentrations in some sedimentary deposits. Organic phosphorus sources, such as manure, may also be used. Manures, however, usually contain relatively large quantities of phosphorus relative to nitrogen. Care must be taken with manure additions so that excess phosphorus doesn't result in deficiencies of other nutrients, such as zinc, or contribute to soluble phosphorus in runoff waters.
Soluble phosphorus can be lost in surface runoff waters, but is usually found adsorbed to soil particles transported by erosion. Phosphorus in runoff has been implicated in eutrophication (excessive algal growth) of lakes and streams.
Potassium
Potassium is required by plants in amounts second only to nitrogen. Unlike nitrogen and phosphorus, potassium is not organically combined in soil organic matter. Different potassium-containing minerals, such as micas and feldspars, therefore, are the principal sources of potassium in soils. Clay-sized micas weather more rapidly to release potassium than feldspars because of their much greater surface area. Soils that contain considerable micaceous clays may be able to supply all of a crop's potassium requirement without fertilization. Acid, weathered soils are those most likely to be deficient in available potassium.
Calcium and Magnesium
Calcium is the predominant exchangeable cation in soils, even in the majority of acid soils, followed by magnesium. This occurs because of the large number of minerals in soils that contain calcium and/or magnesium. Actual plant deficiencies of these elements are infrequent because problems associated with soil acidity, such as aluminum toxicity, become limiting first.
Sulfur
Approximately 85% of total soil sulfur is found in soil organic matter. Microbial mineralization of the soil organic fraction is an important source of available sulfur for plant growth. Reactions of sulfur in soils are very similar to those of nitrogen. Sulfides, such as pyrite and other reduced forms of sulfur, are commonly unearthed in metal and coal mining. Upon exposure to oxygen, sulfuric acid which is produced through chemical and biological oxidation can result in soil acidification and acid mine drainage. Soils may also receive sulfur through atmospheric deposition. Soils near large metropolitan areas may receive greater than 150 lbs S/acre/year
from the combustion of fossil fuels. Volcanic eruptions can also emit large quantities of sulfur gases. Soils most commonly deficient in available sulfur are sandy, leached soils that are low in organic matter.
Micronutrients
Iron, zinc, manganese, copper, chlorine, boron, and molybdenum are classified as micronutrients. Micronutrients are plant essential elements that are required by plants in much smaller amounts than the other essential nutrients. Generally, less than 1 lb/acre of each micronutrient will be present in the aboveground portion of crops. This small quantity contrasts with the 200 lb/acre or more of nitrogen.
The total quantity of many micronutrients in soils doesn't necessarily relate to plant availability. Most soils, for example, will contain from 20,000 to 200,000 lbs total iron/acre to a depth of six inches, but may not be able to supply a crop with sufficient available iron for uptake of 1 lb/acre. Iron deficiency is usually associated with highly alkaline soils because iron solubility roughly decreases 1000-fold for each one unit increase in soil pH.
Zinc, manganese, and copper availabilities are also decreased by alkalinity and by high organic matter concentrations (> 10%). These three elements form very stable bonds with soil organic matter which decrease their availability.
Plant micronutrient deficiencies are becoming more widespread because of greater quantities required by higher yields and decreasing micronutrient impurities in fertilizers.
In addition to the essential mineral elements are the beneficial elements, elements which promote plant growth in many plant species but are not absolutely necessary for completion of the plant life cycle, or fail to meet Arnon and Stout's criteria on other grounds. Recognized beneficial elements are:
Silicon, sodium, cobalt, and selenium
Other elements that have been proposed as candidates for essential or beneficial elements include chromium, vanadium, and titanium, although strong evidence is lacking at this time.
Another group is the essential nonmineral elements, elements taken up as gas or water, which are:
Hydrogen, oxygen, and carbon
Out of all of the many natural elements, essential mineral elements, essential nonmineral elements, and beneficial elements are not randomly scattered, but instead cluster in several groups on the periodic chart.
Various classification schemes for essential elements include:
Macronutrients and Micronutrients
Plant concentrations of essential elements may exceed the critical concentrations, the minimum concentrations required for growth, and may vary somewhat from species to species. Nonetheless, the following table gives the general requirements of plants:
Typical concentrations sufficient for plant growth. After E. Epstein. 1965. "Mineral metabolism" pp. 438-466. in: Plant Biochemistry (J.Bonner and J.E. Varner, eds.) Academic Press, London.
Element Symbol mg/kg percentRelative number
of atoms
Nitrogen N 15,000 1.5 1,000,000
Potassium K 10,000 1.0 250,000
Calcium Ca 5,000 0.5 125,000
Magnesium Mg 2,000 0.2 80,000
Phosphorus P 2,000 0.2 60,000
Sulfur S 1,000 0.1 30,000
Chlorine Cl 100 -- 3,000
Iron Fe 100 -- 2,000
Boron B 20 -- 2,000
Manganese Mn 50 -- 1,000
Zinc Zn 20 -- 300
Copper Cu 6 -- 100
Molybdenum Mo 0.1 -- 1
Nickel Ni 0.1 -- 1
Please note that concentrations, whether in mg/kg (=ppm, parts per million) or Percent (%), are always based on the weight of dry matter, instead of the fresh weight. Fresh weight includes both the weight of the dry matter and the weight of the water in the tissue. Since the percentage of water can vary greatly, by convention, all concentrations of elements are based on dry matter weights.
Somewhat arbitrarily, a dividing line is drawn between those nutrients required in greater quantities, macronutrients, and those elements required in smaller quantities, micronutrients. This division does not mean that one nutrient element is more important than another, just that they are required in different quantities and concentrations. On the table above, the dividing line is typically drawn between S and Cl, meaning that:
Macronutrients: N, K, Ca, Mg, P, and S, and Micronutrients: Cl, Fe, B, Mn, Zn, Cu, Mo, and Ni
The prefix "micro" is well-understood from its use in terms such as "microscope". The term "macro" is somewhat less common, but indicates objects of a somewhat large size. Intermediate sizes are sometimes indicated by "meso". For example, the fauna (animal life) of soil may be divided into macrofauna (moles, mice, etc.), mesofauna (earthworms, burrowing insects, etc.), and microfauna (nematodes, etc.)
Essential Elements for Plant Growth
Primary and Secondary Nutrients
All essential elements are by definition required for plant growth and completion of the plant life cycle from seed to seed. Some essential elements are needed in large quantities and others in much smaller quantities. However, from a practical standpoint, three of the six essential macronutrients are most often "managed" by the addition of fertilizers to soils, while the others are most often found in sufficient quantities in most soils and no soil amendments are required to supply adequate supplies.
From a management perspective only, the primary nutrients are N, P, and K, because they are most often limiting from a crop production standpoint. All of the other essential macronutrient elements are secondary nutrients because they are rarely limiting, and more rarely added to soils as fertilizers.
The ability of soils to supply secondary nutrients to plants indefinitely is is subject to the law of conservation of matter and is therefore dependent upon nutrient cycling. Continued crop removal of Ca, Mg, and S requires replentishment just as surely as primary nutrients, but most likely less frequently. Calcium and magnesium are often supplied by mineral weathering, either of natural soil materials or of aglime, ground limestone added to correct soil acidity. Sulfur is often added to soil as either atmospheric deposition (associated with air pollution) or as impurities in fertilizers, particularly common P fertilizers.
To demonstrate that this classification is more responsive to soil ability to supply nutrients than plant requirements, it should be noted that plant requirements for Ca, a secondary nutrient element, is greater than for P. Calcium is found as a principle exchangeable cation in most soils and an important soluble cation in the soil solution. Phosphorus, on the other hand, is only slightly soluble in most soils, and many soils (particularly acid soils and alkaline soils) have the potential for causing phosphorus deficiencies.
Whether a macronutrient or micronutrient, or whether a primary or secondary nutrient, the Law of the Minimum holds: the most growth-limiting nutrient will limit growth, no matter how favorable the nutrient supply of other elements. For example, a deficiency of Fe or Mn (most common in soils containing calcium carbonate) can severely limit plant growth in spite of adequate N, P, and K.
Deficiencies of nutrients in plants have various visual symptoms that are usually similar regardless of the species. The most common deficiency symptom is reduced growth, which is difficult to detect and diagnose at a glance. Other visual symptoms usually involve changes in coloration following a specific pattern, such as from the leaf tip down the midrib towards the base of the leaf or from the leaf margin toward the midrib, or between the veins of the leaf. Such symptoms may appear in new leaves or old leaves, indicating the phloem-mobility of the deficient nutrient and the ability of the plant to translocate existing stocks of the deficient nutrient. In many cases, internodal distances will shorten as well.
Many nutrient deficiency symptoms are ambiguous unless they are well-developed, and a visual diagnosis can be regarded as an educated guess until tissue samples are gathered and chemical analyses are used to compare elemental composition with healthy leaf tissue. In fact, many types of environmental and management damage can masquerade as visual nutrient deficiency symptoms.
Lest we become too centered on what plants require and their deficiencies, it may be remembered that plants are autotrophs, gathering solar energy for fixation of atmospheric carbon into energy-rich compounds consumed by heterotrophs, which gather the energy-rich plants for consumption and completion of their (and our) life cycles. In addition to energy, plants also harvest the mineral nutritients required by animal life. For the most part, the essential elements required by higher animals are similar to those of plants. However, animals require sodium (only beneficial in plants), selenium (beneficial to only a small group of Se-hyperaccumulating plants, iodine (essential only to certain marine alga), silicon (beneficial to a number of plant species), and cobalt (essential to N2-fixing Rhizobium symbiotically associated with leguminous plants). Yet other trace elements essential to animal and human nutrition, but apparently neither essential nor beneficial for plants, are chromium, lithium, fluorine, and vanadium (although some propose that chromium and vanadium might be essential or beneficial to plants as well but are required at levels too low to demonstrate the effect of their absence.) Were it not for the fact that plants accumulate not only the elements essential to plants but also incidentally accumulate the elements required by animals, life on earth would be quite different!
Essential Elements for Plant Growth
Nitrogen
Biological function of N
Protein (one or more N per amino acid) Base pairs for RNA/DNA
Prosthetic groups for protein (ex.: heme group of chlorophyll)
Hormones (ABA, cytokinins)
Metal uptake (phytosiderophores) and transport in xylem & phloem (ex: Cu with amines)
Osmoregulation (ex.: lettuce and spinach, which may accumulate 0.1 M NO3
Note that plants do not use nitrate and ammonium, directly but must reduce nitrate and assimilate them into organic compounds (with the minor exception of osmoregulation using nitrate above.) Reduction of nitrate takes place in both the root and the shoot. Particularly at high rates of nitrate supply or low photosynthetic activity, physiological limits to root reduction of nitrate will mean that increasing amounts of nitrate will be in the xylem flow, where it will be end up in shoots and ultimately be reduced in the leaves.
Nitrate reduced in the roots will be reduced first to nitrite by nitrate reductase and then to ammonium by nitrite reductase. Ammonium will undergo reaction with glutamate to form glutamine by the action of glutamine synthase. Glutamine may then undergo additional transformations before entering the xylem flow as reduced N, depending upon the plant species.
Deficiency:
Mild N deficiency will restrict plant growth, but often in a subtle manner that can only be assessed by comparison to plants grown with an adequate N supply. Moderate N deficiency will cause leaves to be light green or yellowish. Severe symptoms include necrosis (tissue death) starting at the tips of older leaves, with the tissue death developing a V-pattern down the midrib toward the base of the leaf.
Essential Elements for Plant Growth
Phosphorus
The biological functions of P in living organisms is most notable in the ubiquitious ATP/ADP energy transport and storage compounds. Additionally, sugar phosphates form the "rails" of the nucleic acids DNA and RNA (which N-containing bases forming the "rungs"). Phospholipids are an important constituent of membrane chemistry and phosphoproteins are essential for life functions.
Phosphorus is phloem-mobile and the physiological results of P deficiency are spread more or less evenly around the plant, usually with no glaring visual deficiency symptom except for stunted growth and late maturity. Grassy species, including corn, will show reddening of leaves if P is severely deficient.
Fertilizer Types
Soil amendments are made by adding fertilizer to the soil but there are different types of fertilizers. There is bulky organic fertilizer such as cow manure, bat guano, bone meal, organic compost and green manure crops. And then there is also chemical fertilizer which is also referred to as inorganic fertilizer and is made up with different formulations to suit a variety of specified uses. Though many governments and agricultural departments go to great lengths to increase the supply of organic fertilizers, such as bulky organic manures and composting materials, there is just not enough of these fertilizers available to meet the existing and future fertilizer needs. Compared to organic compost, chemical or inorganic fertilizers also have the added advantage of being less bulky. Being less bulky makes chemical fertilizer easier to transport, both overland and from the soil into the plants itself, because they get to be available to the plant relatively quickly when incorporated as part of the plant-food constituents. Chemical fertilizer usually comes in either granular or powder form in bags and boxes, or in liquid formulations in bottles. The different types of chemical fertilizers are usually classified according to the three principal elements, namely Nitrogen (N), Phosphorous (P) and Potassium (K), and may, therefore, be included in more than one group.
ORGANIC AND INORGANIC CHEMICAL NITROGENOUS FERTILIZER TYPES
This type of fertilizer is divided into different groups according to the manner in which the Nitrogen combines with other elements. These groups are:
Sodium Nitrates,
Ammonium Sulphate and ammonium salts,
Chemical compounds that contains Nitrogen in amide form, and
Animal and plant by products.
Sodium Nitrates
Sodium Nitrates are also known as Chilates or Chilean nitrate. The Nitrogen contained in Sodium Nitrate is refined and amounts to 16%. This means that the Nitrogen is immediately available to plants and as such is a valuable source of Nitrogen in a type of fertilizer. When one makes a soil amendment using Sodium Nitrates as a type of fertilizer in the garden, it is usually as a top- and side-dressing. Particularly when nursing young plants and garden vegetables. In soil that is acidic Sodium Nitrate is quite useful as a type of fertilizer. However, the excess use of Sodium Nitrate may cause deflocculation.
Ammonium Sulphate
This fertilizer type comes in a white crystalline salt form, containing 20 to 21% ammonia cal nitrogen. It is easy to handle and it stores well under dry conditions. However, during the rainy season, it sometimes, forms lumps. (TIP: When these lumps do occur you should grind them down to a powered form before use.) Though this fertilizer type is soluble in water, its nitrogen is not readily lost in drainage, because the ammonium ion is retained by the soil particles. A note of caution: Ammonium sulphate may have an acid effect on garden soil. Over time, the long-continued use of this type of fertilizer will increase soil acidity and thus lower the yield. (TIP: It is advisable to use this fertilizer type together with bulky organic manures to safeguard against the ill effects of continued application of ammonium sulphate.)
The application of Ammonium sulphate fertilizer can be done before sowing, at sowing time, or even as a top-dressing to the growing crop. Do however take care NOT to apply it along with, or too close to, the seed, because in concentrated form, it affects seed germination very adversely.
Ammonium Nitrate
This fertilizer type also comes in white crystalline salts. Ammonium Nitrate salts contains 33 to 35% nitrogen, of which half is nitrate nitrogen and the other half in the ammonium form. As part of the ammonium form, this type of fertilizer cannot be easily leached from the soil. This fertilizer is quick-acting, but highly hygroscopic thus making it unfit for storage. (TIP: Coagulation and Granulation of this fertilizer can be combated with a light coating of the granules with oil.) On a note of caution: Ammonium Nitrate also has an acid effect on the soil, in addition this type of fertilizer can be explosive under certain conditions, and, should thus be handled with care.
'Nitro Chalk' is the trade name of a product formed by mixing ammonium nitrate with about 40% lime-stone or dolomite. This fertilizer is granulated, non-hazardous and less hygroscopic. The lime content of this fertilizer type makes it useful for application to acidic garden soils.
Ammonium Sulphate Nitrate
This fertilizer type is available as a mixture of ammonium nitrate and ammonium sulphate and is recognizable as a white crystal or as dirty-white granules. This fertilizer contains 26% nitrogen, three-fourths of it in the ammoniac form and the remainder (i.e. 6.5%) as nitrate nitrogen. Ammonium Sulphate Nitrate is non-explosive, readily soluble in water and is very quick-acting. Because this type of fertilizer keeps well, it is very useful for all crops. Though it can also render garden soil acidic, the acidifying effects is only one-half of that of ammonium sulphate on garden soil. Application of this fertilizer type can be done before sowing, at sowing time or as a top-dressing, but it should not be applied along the seed.
Ammonium Chloride
This fertilizer type comes in a white crystalline compound, which contains a good physical condition and 26% ammoniac nitrogen. In general, Ammonium Chloride is similar to ammonium sulphate in action. (TIP: Do not use this type of fertilizer on crops such as tomatoes because the chorine may harm your crop.)
Urea
This type of fertilizer usually is available to the public in a white, crystalline, organic form. It is a highly concentrated nitrogenous fertilizer and fairly hygroscopic. This also means that this fertilizer can be quite difficult to apply. Urea is also produced in granular or pellet forms and is coated with a non-hygroscopic inert material. It is highly soluble in water and therefore, subject to rapid leaching. It is, however, quick-acting and produces quick results. When applied to the soil, its nitrogen is rapidly changed into ammonia. Similar to ammonium nitrate, urea supplies nothing but nitrogen and the application of Urea as fertilizer can be done at sowing time or as a top-dressing, but should not be allowed to come into contact with the seed.
Ammonia
This fertilizer type is a gas that is made up of about 80% of nitrogen and comes in a liquid form as well because under the right conditions regarding temperature and pressure, Ammonia becomes liquid (anhydrous ammonia). Another form, 'aqueous ammonia', results from the absorption of Ammonia gas into water, in which it is soluble. Ammonia is used as a fertilizer in both these forms. The anhydrous liquid form of Ammonia can be applied by introducing it into irrigation water, or directly into the soil from special containers. Not really suitable for the home gardener as this renders the use of ammonia as a fertilizer very expensive.
Organic Nitrogenous Fertilizers
Organic Nitrogenous fertilizer is the type of fertilizer that includes plant and animal by-products. These by-products can be anything from oil cakes, to fish manure and even to dried blood. The Nitrogen available in organic nitrogenous fertilizer types first has to be converted before the plants can use it. This conversion occurs through bacterial action and is thus a slow process. The upside of this situation is that the supply of available nitrogen lasts so much longer AND the amounts of this type of fertilizer may contain small amounts of organic stimulants that contain other minor elements that might also be needed by the plants that are being fertilized. Furthermore, they may also small amounts of organic stimulants that they may contain, or of some of the minor elements needed by plant. Oil-cakes contain not only nitrogen but also some phosphoric and potash, besides a large quantity of organic matter. This type of fertilizer is used in conjunction with quicker-acting chemical fertilizers.
Then there is also blood meal which contains 10 to 12% highly available Nitrogen as well as 1 to 2% Phosphoric acid. Blood meal, used in much the same way as oilcakes, makes for a quick remedy and can effectively be used on all types of soil as a type of fertilizer.
Fish meal which can be dried fish, fish-meal or even powder is extracted in areas where fish oil is extracted. The resulting residue is used as a fertilizer type. Obviously depending on the type of fish used, the available Nitrogen can be between 5 and 8% and the Phosphoric content can be from 4 to 6%. Fish meal also constitutes a fast-acting fertilizer type which is suitable for most soil types and crops. (TIP: In powder form it is at its best.)
ORGANIC AND INORGANIC CHEMICAL PHOSPHATE FERTILIZER TYPES
The Phosphate fertilizers are categorized as natural phosphates, either treated or processed, and also by products of phosphates and chemical phosphates.
Rock Phosphate
As a type of fertilizer, rock phosphate occurs as natural deposits in some countries. This fertilizer type has its advantages and disadvantages. The advantage is that with adequate rainfall this fertilizer results in a long growing period which can enhance crops. Powdered phosphate fertilizer is an excellent remedy for soils that are acidic and has a phosphorous deficiency and requires soil amendments.
However, the disadvantage is that although phosphate fertilizer such as rock phosphate contains 25 to 35% phosphoric acid, the phosphorous is insoluble in water. It has to be pulverized to be used as a type of fertilizer before rendering satisfactory results in garden soil. Thus it is not surprising that Rock Phosphate is used to manufacture superphosphate which makes the Phosphoric acid water soluble.
Superphosphate
Superphosphate is a fertilizer type that most gardeners are familiar with. As a fertilizer type one can get superphosphate in three different grades, depending on the manufacturing process. The following is a short description of the different superphosphate fertilizer grades:
Single superphosphate containing 16 to 20% phosphoric acid;
Dicalcium phosphate containing 35 to 38% phosphoric acid; and
Triple superphosphate containing 44 to 49% phosphoric acid.
Triple superphosphate is used mostly in the manufacture of concentrated mixed fertilizer types.
The greatest advantage to be had of using Superphosphate as a fertilizer is that the phosphoric acid is fully water soluble, but when Superphosphate is applied to the soil, it is converted into soluble phosphate. This is due to precipitation as calcium, iron or aluminum phosphate, which is dependent on the soil type to which the fertilizer is added, be it alkaline or acidic garden soil. All garden soil types can benefit from the application of Superphosphate as a fertilizer. Used in conjunction with an organic fertilizer, it should be applied at sowing or transplant time.
Slag
Basic slag is a by-product of steel mills and is used as a fertilizer to a lesser extent than Superphosphate. Slag is an excellent fertilizer that can be used to amend soils
that are acidic because of its alkaline reaction. For slag application to be an effective fertilizer it has to be pulverized first.
Bonemeal
Bonemeal as a fertilizer type needs no introduction. Bone-meal is used as a phosphate fertilizer type and is available in two types: raw and steamed. The raw bone-meal contains 4% organic Nitrogen that is slow acting, and 20 to 25% phosphoric acid that is not soluble in water. The steamed bone-meal on the other hand has all the fats, greases, nitrogen and glue-making substances removed as a result of high pressure steaming. But it is more brittle and can be ground into a powder form. In powder form this fertilizer is of great advantage to the gardener in that the rate of availability of the phosphoric acid depends on its pulverization. This fertilizer is particularly suitable as a soil amendment for acid soil and should be applied either at sowing time or even a few days prior to sowing. (TIP: As a fertilizer type, bone-meal is slow acting and should be incorporated into the soil and not as a top-dressing.)
ORGANIC AND INORGANIC CHEMICAL POTASSIUM FERTILIZER TYPES
Chemical Potassium fertilizer should only be added when there is absolute certainty that there is a Potassium deficiency in your garden soil. Potassium fertilizers also work well in sandy garden soil that responds to their application. Crops such as chilies, potato and fruit trees all benefit from this type of fertilizer since it improves the quality and appearance of the produce. There are basically two different types of potassium fertilizers:
Muriate of potash (Potassium chloride) and
Sulphate of potash (Potassium sulphate).
Both muriate of potash and sulphate of potash are salts that make up part of the waters of the oceans and inland seas as well as inland saline deposits.
Muriate Of Potash
Muriate of potash is a gray crystal type of fertilizer that consists of 50 to 60% potash. All the potash in this fertilizer type is readily available to plants because it is highly soluble in water. Even so, it does not leach away deep into the soil since the potash is absorbed on the colloidal surfaces. (TIP: Apply muriate of potash at sowing time or prior to sowing.)
Sulphate Of Potash
Sulphate of potash is a fertilizer type manufactured when potassium chloride is treated with magnesium sulphate. It dissolves readily in water and can be applied to the garden soil at any time up to sowing. Some gardeners prefer using sulphate of potash over muriate of potash.
DIFFERENT TYPES OF FERTILIZERS
The different types of fertilizers with all its specifications and cautions that should be kept in mind should not detract us from the joys of gardening. Thus to make it easier on most gardeners and since this website is dedicated to the home gardener and growing our own gardens the following section is geared towards the home gardener.
The different types of chemical and organic fertilizers that are usually commercially available in most countries can be categorized further into:
Complete inorganic fertilizers: – these types of inorganic fertilizers contain all three major macronutrients, Nitrogen (N), Phosphorous (P) and Potassium (K). On the containers you will find that these macronutrients are depicted as a ratio, e.g. 2:3:2 (22). Complete inorganic fertilizers are usually applied at a rate of 60g/m2 or roughly 4 tablespoons per square meter.
Special purpose fertilizer: – these types of fertilizer are formulated especially to target certain plants' requirements or certain soil deficiencies. Of the examples that come to mind here are the Blue Hydrangea Food, and straight fertilizer that is made up of one particular plant nutrient for example lawn fertilizer.
Liquid fertilizers: – these types of fertilizer come in a variety of formulations and even include organic fertilizer, complete fertilizer as well as special purpose fertilizer. Some examples of liquid fertilizer are Nitrosol and African Violet Food.
Slow-release fertilizer: – these types of fertilizer are formulated to release their nitrogen at a steady pace. On the packs of this fertilizer that are available commercially it will usually be depicted as 3:1:5 (SR) where the SR indicates slow-release.
Fertilizer with insecticide: – these types of fertilizer that are prepared and combined with an insecticide. One such example is Wonder 4:1:1 (21) + Karbaspray.
The reason why there are so many different types of chemical fertilizers in different formulations is because different plants require different nutrients and different pH levels in the soil. However, organic fertilizers have more diversity, and these types of fertilizers do not burn plant roots, get into ground water, or
affect surrounding growth as is the case when using the different types of chemical fertilizer and NPK amendments.
Organic Manures
1. What are organic manures?
Organic manures are natural products used by farmers to provide food (plant nutrients) for the crop plants. There are a number of organic manures like farmyard manure, green manures, compost prepared from crop residues and other farm wastes, vermicompost, oil cakes, and biological wastes - animal bones, slaughter house refuse.
2. How are organic manures beneficial in the cultivation of crops?
Organic manures increase the organic matter in the soil. Organic matter in turn releases the plant food in available from for the use of crops. However, organic manures should not be seen only as carriers of plant food. These manures also enable a soil to hold more water and also help to improve the drainage in clay soils. They provide organic acids that help to dissolve soil nutrients and make them available for the plants.
3. How are organic manures differing from fertilizers?
Organic manures have low nutrient content and therefore need to be applied in larger quantities. For example, to get 25 kg of NPK, one will need 600 to 2000 kg of organic manure where as the same amount of NPK can be given by 50 kg of an NPK complex fertilizer.
The nutrient content of organic manures is highly variable from place to place, lot to lot, and method of preparation. The composition of fertilizers is almost constant. For example, urea contain 46% N regardless of which factory makes it any where in the world.
4. How much of plant nutrients are provided by organic manures?
Just as different fertilizers contain different amounts of plant nutrients, organic manures are also not alike.
Average quality of farmyard manure provides 12 kg nutrients per ton and compost provides 40 kg per ton.
Most of the legume green manures provide 20 kg of nitrogen per ton.
Each ton of sorghum/rice/maize straw can be expected to add 26 kg of nutrients.
5. What is green manuring?
Green manuring is the practice of growing a short duration, succulent and leafy legume crop and ploughing the plants in the same field before they form seeds.
6. What is green leaf manuring?
Green leaf manuring refers to adding the loppings from legume plants or trees to a field and then incorporating them into the soil by ploughing.
7. What green manure crops are beneficial?
Sesbania, Crotalaria, ‘Pillipesara’, Cowpea etc are good for green manuring.
Sesbania Crotalaria Cowpea
8. What are the popular green leaf manuring plants?
Glyricidia, Pongamia, Leucina are common green leaf manuring plants.
Glyricidia Pongamia Leucaena
9. What is compost?
Compost is well decomposed organic wastes like plant residues, animal dung, and urine earth from cattle sheds, waste fodder etc.
Compost
10. How good compost is prepared?
Compost making is the process of decomposing organic wastes in a pit. Site for compost making is selected should be at a high level and water should not pond during monsoon season. Pit should be of 3’ depth and 6’ to 8’ width. Length may be of any convenient size. The process is as follows:
1. Make slurry of the cattle dung with water.2. Prepare 6” layer of organic wastes – plant residues, sweepings from the cattle shed, waste fodder, dried
plants stalks and leaves etc. and sprinkle water to just moisten it. (Over watering should be avoided).
3. Cover with the layer with urine earth and cattle dung slurry.
4. Add 5 to 10 kg of super phosphate for every 10 tons of organic wastes.
5. Repeat the process of putting such layers till the pit is full.
6. Close the pit with urine earth, waste fodder and then heap the soil till it gets convex shape (about 1 to 1.5’ above the ground) so that the rainwater rolls away.
7. After six months compost is ready to apply to the fields.
The pit can be filled up if sufficient organic wastes are available. Otherwise a temporary partition can be made in the pit with bamboos or stalks and the pit can be filled up over time filling each partitioned area as and when the material is available for composting.
Compost making
11. Why super phosphate is added in compost making?
Due to quick heating and drying during the decomposition of organic wastes, nitrogen in the organic wastes will be lost due to volatilization. Addition of super phosphate decreases such nitrogen losses. It will also increase the phosphate content of compost.
12. What is vermicomposting?
Vermicomposting is a type of compost making in which earthworms are used to convert organic wastes into valuable material to supply nutrients for crops.
Earthworms Vermicomposting
INTEGRATED NUTRIENT MANAGEMENT
Integrated Nutrient Management refers to the maintenance of soil fertility and of plant nutrient supply at an optimum level for sustaining the desired productivity through optimization of the benefits from all possible sources of organic, inorganic and biological components in an integrated manner.
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Inorganic Fertilizers Organic Manures+ +
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Green manures Biofertilizers
Concepts
1. Regulated nutrient supply for optimum crop growth and higher productivity.2. Improvement and maintenance of soil fertility.
3. Zero adverse impact on agro – ecosystem quality by balanced fertilization of organic manures, inorganic fertilizers and bio- inoculant
Determinants
1. Nutrient requirement of cropping system as a whole.2. Soil fertility status and special management needs to overcome soil problems, if any
3. Local availability of nutrients resources (organic, inorganic and biological sources)
4. Economic conditions of farmers and profitability of proposed INM option.
5. Social acceptability.
6. Ecological considerations.
7. Impact on the environment
Advantages
1. Enhances the availability of applied as well as native soil nutrients2. Synchronizes the nutrient demand of the crop with nutrient supply from native and applied sources.
3. Provides balanced nutrition to crops and minimizes the antagonistic effects resulting from hidden
deficiencies and nutrient imbalance.
4. Improves and sustains the physical, chemical and biological functioning of soil.5. Minimizes the deterioration of soil, water and ecosystem by promoting carbon sequestration,
reducing nutrient losses to ground and surface water bodies and to atmosphere
Components:
Soil Source:
Mobilizing unavailable nutrients and to use appropriate crop varieties, cultural practices and cropping system.
Mineral Fertilizer :
Super granules, coated urea, direct use of locally available rock PO4 in acid soils, Single Super Phosphate (SSP),
MOP and micronutrient fertilizers.
Organic Sources :
By products of farming and allied industries. FYM, droppings, crop waste, residues, sewage, sludge, industrial waste.
In the context of agricultural problem soils, calcareous soils are soils in which a high amount of calcium carbonate dominates the problems related to agricultural land use. They are characterized by the presence of calcium carbonate in the parent material and by a calcic horizon, a layer of secondary accumulation of carbonates (usually Ca or Mg) in excess of 15% calcium carbonate equivalent and at least 5% more carbonate than an underlying layer. In the World Reference Base (WRB) soil classification system calcareous soils may mainly occur in the Reference Soil Group of Calcisols.
FERTILIZER MANAGEMENT ON CALCAREOUS SOILS
Nitrogen.
Regardless of the initial form applied, essentially all N fertilizer ultimately exists as NO3 because nitrification
proceeds uninhibited in calcareous soils. Rather than attempt to slow this process, citrus grove management
practices should emphasize irrigation and fertilizer application scheduling strategies that decrease N leaching.
These include irrigating based on tensiometer readings or evapotranspiration measurements and using split
applications of N fertilizer. Applying a portion of the required N fertilizer with irrigation water (i.e., through
fertigation) and scheduling irrigations to maintain the N in the root zone is a sound method to prevent large N
leaching losses. Using controlled-release N also can increase N fertilizer efficiency.
Management of N fertilizer also should involve practices that minimize its loss through ammonia volatilization.
Following an application of ammoniacal-N to the surface of a calcareous soil, the fertilizer should be moved into
the soil profile with irrigation water if rainfall is not likely. Urea applied to the surface of any soil, regardless of its
pH value, should be moved into the soil via rainfall or irrigation. Fertigation using either of these N sources is a
suitable application method, provided that there is ample time to flush the fertilizer out of the lines and into the
soil.
Phosphorus. To maintain P availability to citrus on calcareous soils, water-soluble P fertilizer should be applied
on a regular, but not necessarily frequent, basis. Since phosphorus accumulates in the soil, it is at least partially
available as it converts to less soluble compounds with time. Phosphorus deficiency has never been found in
citrus grown on Florida calcareous soils where P fertilizer has been applied regularly.
Phosphorus fertilizer should be applied each year in newly planted groves, at a rate based on the recommended
rate for young trees, until the groves begin to bear fruit. As the trees approach maturity, P applications can be
limited to once every few years. Diagnostic information from leaf and soil testing can help determine whether P
fertilization is necessary. Citrus yields have not been correlated with the results of soil tests measuring P levels in
calcareous soils; however, soil testing with Mehlich 3, sodium bicarbonate, or another suitable extractant still can
be useful in estimating the magnitude of accumulated P. An increased level of P measured by soil tests following
periodic fertilization would indicate an increase in available P above the native soil level.
Leaf tissue testing can be used to determine whether soil P is available to citrus trees. For best results, the leaf P
concentration of 4- to 6-month-old spring flush leaves from mature trees should be evaluated. The optimum
range for leaf P in mature citrus leaves is from 0.12% to 0.16% on a dry weight basis. A decline in leaf P
concentration from optimum to low over several years indicates declining soil P availability and justifies a P
The total area of land in our country is around 300 million hectares. The water in our country
mainly comes from the Himalayas. Around half of this is considered to be a waste land. The
water from Himalayas has high sedimentation rate and the creation of slopes has created a big
trouble for existence in the plains of our country. It may lead to floods, injury to the water
reservoirs and irrigation system. There are many ways by which the land and water can be
managed. The catchment area must be maintained. It starts from the top most layer and the
trees are planted for conservation and must be socially and economically viable. There are
certain grasses which are used to bind the soil depending upon the local needs, edaphic factors
and environment. The presence of suitable outlet channels which can carry the water and the
sowing of certain crops also keep a check on the productivity of land. The salinity must also be
checked at the regular intervals and should be treated with the leaching where the ground water
is not sufficient. The ground water has many advantages as it is economical, it is easy to tap,
there is no evaporation and sewage loss, and it lowers the water table in the areas where the
water table is high. It is present in the large amount in deserts. So, the ground water must be
conserved. The land production has been affected by the degradation but as the population of
human is increasing the wasteland is becoming more and more. It is essential and covers around
half of the land. It can be culturable and non culturable. The culturable wastelands include the
water logged, marsh, saline, forest, strip, mining and industrial land. The non culturable
wastelands include the barren area, steep slopes, snow capped mountains and rocky glaciers.
The culturable wasteland gives more land for agriculture. The waste land must be reclaimed and
should be under taken immediately
irrigation methods
Irrigation is the the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall. Crop irrigation is vital throughout the world in order to provide the world's ever-growing populations with enough food. Many different irrigation methods are used worldwide, including:
Center-Pivot: Automated sprinkler irrigation achieved by automatically rotating the sprinkler pipe or boom, supplying water to the sprinkler heads or nozzles, as a radius from the center of the field to be irrigated. Water is delivered to the center or pivot point of the system. The pipe is supported above the crop by towers at fixed spacings and propelled by pneumatic, mechanical, hydraulic, or electric power on wheels or skids in fixed circular paths at uniform angular speeds. Water is applied at a uniform rate by progressive increase of nozzle size from the pivot to the end of the line. The depth of water applied is determined by the rate of travel of the system. Single units are ordinarily about 1,250 to 1,300 feet long and irrigate about a 130-acre circular area.
Drip: A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure with the applicators being placed either on or below the surface of the ground.
Flood: The application of irrigation water where the entire surface of the soil is covered by ponded water.
Furrow: A partial surface flooding method of irrigation normally used with clean-tilled crops where water is applied in furrows or rows of sufficient capacity to contain the designed irrigation system.
Gravity: Irrigation in which the water is not pumped but flows and is distributed by gravity.
Rotation: A system by which irrigators receive an allotted quantity of water, not a continuous rate, but at stated intervals.
Sprinkler: A planned irrigation system in which water is applied by means of perforated pipes or nozzles operated under pressure so as to form a spray pattern.
Subirrigation: Applying irrigation water below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system that discharges directly into the root zone.
Traveling Gun: Sprinkler irrigation system consisting of a single large nozzle that rotates and is self-propelled. The name refers to the fact that the base is on wheels and can be moved by the irrigator or affixed to a guide wire.
Supplemental: Irrigation to ensure increased crop production in areas where rainfall normally supplies most of the moisture needed.
Surface: Irrigation where the soil surface is used as a conduit, as in furrow and border irrigation as opposed to sprinkler irrigation or subirrigation.
Types of soil erosionThere are several ways of classifying erosion. One general way is to distinguish between accelerated and geologic erosion. Geological erosion occurs where soil is in its natural environment surrounded by its natural vegetation without human disturbance. Geologic erosion has been taking place naturally for millions of years and it helps to create balance in uncultivated soil that enables plant growth. It’s a relatively a slow continuous process that often goes on unnoticed. Accelerated erosion is a concept referring to an essentially natural process occurring at an increased rate under conditions of ecological disequilibrium. Accelerated erosion is the most dangerous type and it needs concerted efforts through careful planning and implementation of appropriate control measures. Another distinction is between rill, sheet and gully.
Splash erosion
Splash erosion is the first stage of the erosion process. It occurs when raindrops hit bare soil. The explosive impact breaks up soil aggregates so that individual soil particles are ‘splashed’ onto the soil surface. The splashed particles can rise as high 60cm above the ground and move up to 1.5 metres from the point of impact. The particles block the spaces between soil aggregates, so that the soil forms a crust that reduces infiltration and increases runoff.
Sheet erosion
Sheet erosion refers to the uniform movement of a thin layer of soil across an expanse of land devoid of vegetative cover. Raindrops detach soil particles, which go into solution as runoff occurs and are transported downstream to a point of deposition. Deposition occurs when runoff slows to the point where soil particles can no longer remain in suspension. Tilled agricultural fields and construction sites are subject to sheet erosion.
Rill erosion
When sheet flows begin to concentrate on the land surface, rill erosion occurs. While sheet erosion is generally invisible, rill erosion leaves visible scouring on the landscape. This type of erosion occurs when the duration or intensity of rain increases and runoff volumes accelerate. Rills may become stable through soil consolidation; however, they are still the major sediment transport route for soil detached on the interrill areas. Improved understanding of the ability of rain-impacted flows in rills to transport sediment is needed to improve our estimates of sediment transport and delivery.
Gully erosion
Rill erosion evolves into gully erosion as duration or intensity of rain continues to increase and runoff volumes continue to accelerate. A gully is generally defined as a scoured out area that is not crossable with tillage or grading equipment.
Stream channel erosion
Stream channel erosion consists of both stream bed and stream bank erosion. Stream bed erosion occurs as flows cut into the bottom of the channel, making it deeper. This erosion process will continue until the channel reaches a stable slope. The resulting slope is dependant on the channel materials, and flow properties. As the stream bed erodes, and the channel deepens, the sides of the channel become unstable and slough off; resulting in stream bank erosion. Stream bank erosion can also occur as soft materials are eroded from the stream bank or at bends in the channel. This type of stream bank erosion results in meandering waterways. One significant cause of both steam bed and stream bank erosion is due to the increased frequency and duration of runoff events that are a result of urban development.
Tunnel erosion
Tunnel erosion occurs when surface water moves into and through dispersive subsoils. Dispersive soils are poorly structured so they erode easily when wet.The tunnel starts when surface water moves into the soil along cracks or channels or through rabbit
Severe sheet and rill erosionsoils in northwest Iowa (USA) after heavy rains. These soils had no protection against soil erosion.Source: Lynn Betts, NRCS
Ephemeral gully erosionerosionwashes young corn plants from the ground as well as topsoil and nutrients from loess soils.Source: Lynn Betts, NRCS
burrows and old tree root cavities. Dispersive claysare the first to be removed by the water flow. As the space enlarges, more water can pour in and further erode the soil. As the tunnel expands, partsof the tunnel roof collapse leading to potholes and gullies.Indications of tunnel erosion include water seepage at the foot of a slope and fine sediment fans downhill of a tunnel outlet.Remediation actions include breaking open existing tunnels, revegetation, and increasing soil organic matter. Extensive earthworks may be required.
Tillage erosion
Tillage erosion moves soil from the top of the field downward, exposing subsoil at the crest while burying soil at the bottom. After many years of tillage, topsoil accumulates at the bottom of the slope. No soil leaves the field due to tillage erosion, but the effects for productivity and increased yield variability can be huge.
Gully erosion is evident in this unprotected field following a storm.Soure: Tim McCabe, NRCS
Stream erosion and deposition
Source: Albert Copley, Oklahoma University
Causes of soil erosion
Erosion is an incluxive term for the detachment and removal of soil and rock by the action ofrunning water, wind, waves, flowing ice, and mass movement. on hillslopes in most parts of the world the dominant processes are action by raindrops, running water, subsurface water, and mass wasting. The activity of waves, ice, or wind may be regarded as special cases restricted to particular environment.
Climate and geology are the most important influences on erosion with soil character and vegetation being dependent upon them and interrelated with each other. The web of relationships between the factors which influence erosion is extremly complex. Vegegation, for example, is dependent upon climate, especially rainfall and temperature, and upon the soil which is derived from the weathered rock forming the topography. Vegetation in its turn influences the soil through the action of roots, take-up of nutrients, and provision of organic matter, and it protect the soil from erosion. The importance of this feedback is most obvious when the vegetation cover is inadequate to protect the soil, for eroded soil cannot support a close vegetation cover. The operation of the factors which influence erosion is most readily seen in their effect upon the disposition of storm rainfall. By comparison with the high runoff from an eroded catchment a well-
vegetated catchment with a permeable soil will experience higher infiltration, lower surface runoff, and less surface erosion.
Erosion is a function of the eroding power of raindrops, running water, and sliding or flowing earth masse, and the erodibility of the soil, or:
Erosion=f(Erosivity, Erodibility).
Climate factor
The major climatic factors which influence runoff and erosion are precipitation, temperature, and wind. Precipitation is by far the most important. Temperature affects runoff by contributing to changes in soil moisture between tains, it determines whether the precipitation will be in the form of rain or snow, and it changes the absorptive properties of the soil for sater by causing the soil to freeze. Ice in the soil, particularly needle ice, can be very effective in raising part of the surface of bare soil and thus making it more asily removed by rnuoff or wind. The wind effect includes the power to pick up and carry fine soil particles, the influence it exerts on the angle and impact of raindrops and, more rarely, its effect on vegetation, especially by wind-throw of trees.
Many reports of soil erosion phenomena have their value limited by uncertainties in the terminology used, consequently the key terms are defined here.
Raindrop erosion is recognized as being responsible for four effects: (1) disaggregation of soil aggregates as a result of impact; (2) minor lateral displacement of soil particles (a process sometimes referred to as creep );(3) splashing of soil particles into the air (sometimes called saltation); (4) selection or sorting of soil particles by raindrop impact which may occur as a result of two effects-(a) the forcing of fine-grained particles into soil voids causing the infiltration rate to be reduced and (b)selective splashing of detached grains. wash is the
process in which soil particles are entrained and transported by shallow sheet flows (overland flow). Rainwash is the combined effect from raindrops falling into a sheet flow.
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Soil feature factor
The soil factor is expressed in the erodibility of the soil. Erodibility, unlike the determination of erosivity of rainfall, is difficult to measure and no universal method of measurement has been developed. The main reason for this deficiency is that into two groups: those which are the actual physical features of the soil; and those which are the result of human use of the soil.
The resistance of soil to detachment by raindrop impact depends upon its shear strength, that is its cohesion (c) and angle of friction. It is difficult, in practice, to measure the appropriate values of c and for grains at the suface of a soil or soil crust, partly because of variability in the size, packing, and shape of particles and partly because of the varying degrees of wetting and submergence of grains by water. More success has been achieved with simplw rotational shear vanes than with most other methods.
Many attempts have been made to relate the amount of erosion from a soil to its physical characterisics. Pinoneer work in this field was done in North American in the 1930s. Bouyoucos (1935) suggested that erodibility is related to the sizes of the particles of the soil in the ratio:
This factor is evident in the steepness and length of slopes. Nearly all of the experimental work on the slope effect has assumed that the slopes are undercultivation. In such conditions raindrop splash will move material further down steep slopes than down gentle ones, there is likely to be more runoff, and runoff velocities will be faster. Because of this combination of factors the amount of erosion is not just proportional to the steepness of the slope, but rises rapidly with increasing angle. Mathematically the ralaationship is: EµS2
where E is the erosion, S the slope in per cent, and a is an exponent. Values of a derived experimental range from 1.35 to 2.
The lengh of slope has a similar effect upon soil loss, because on a long slope there can be a greater depth and velocity of overland flow, and rills can develop more readily than on short slopes. Because there is a greater area of land on long than on short slope facets of the same width, it is necessary to distinguish between total soil loss and soil loss per unit area. The relationship between soil loss and slope length may be expressed as: EµLb
Where E is the soil loss per unit area, L is the length of slope, and b is an exponent. In a series of experiments Zingg found that the values of b are around 0.6 but experiments elsewhere indicated that a rather higher value is more representative.
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Biological factor
Vegetation offsets the effects on erosion of the other factors-clmate, topography, and soil characteristics. The major effects of vegetation fall into at least seven main categories:
(1) the interception of rainfall by the vegetation canopy;
(2) the decreasing of velocity of runoff, and hence the cutting action of water and its capacity to entrain sediment;
(3) root effects in increasing soil strength, granulation, and porosity;
(4) biological activityies associated with vegetative growth and their influence on soil porosity;
(5) the transpiration of water, leading to the subsequent drying out of the soil;
(6) insulation of the soil against high and low temperatures which cause cracking or frost heaving and needle ice formation;
(7) compaction of underlying soil.
The importance of plantsPlants provide protective cover on the land and prevent soil erosion for the following reasons: plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground;Plant roots hold the soil in position and prevent it from being washed away;Plants break the impact of a raindrop before it hits the soil, thus reducing its ability to erode;Plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion.
The loss of protective vegetation through deforestation, over-grazing, ploughing, and fire makes soil vulnerable to being swept away by wind and water. In addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded. Erosion will remove the top-soil first. Once this nutrient-rich layer of soil is gone, few plants will grow in the soil again. Without soil and plants the land becomes desert-like and unable to support life - this process is called desertification. It is very difficult and often impossible to restore desertified land.
How to control soil erosion1. COVER methods
These methods all protect the soil from the damaging effects of rain-drop impact. Most will also improve soil fertility.
MulchingBare soil between growing plants is covered with a layer of organic matter such as straw, grasses, leaves and rice husks - anything readily available. Mulching also keeps the soil moist, reduces weeding, keeps the soil cool and adds organic matter. If termites are a problem, keep the mulch away from the stems of crops.
Cover crops and green manuresCover crops are a kind of living mulch. They are plants - usually legumes - which are grown to cover the soil, also reducing weeds. Sometimes they are grown under fruit trees or taller, slow maturing crops. Sometimes they also produce food or fodder. Cowpeas, for example may be used both as a cover crop and a food crop.
Green manures - also usually legumes - are planted specially to improve soil fertility by returning fresh leafy material to the soil. They may be plants that are grown for 1-2 months between harvesting one crop and planting the next. The leaves may be cut and left on the surface of the soil as a mulch or the whole plant dug into the soil. Green manures may also be trees or hedges which may grow for many years in a cropping field from which green leaves are regularly cut for use as mulch (alley cropping).
Mixed cropping and inter-croppingBy growing a variety of crops - perhaps mixed together, in alternate rows, or sown at different times - the soil is better protected from rain splash.
Early plantingThe period at the beginning of the rainy season when the soil is prepared for planting, is when the damage from rain splash is often worst. Sowing early will make the period when the soil is bare, as short as possible.
Crop residuesAfter harvest, unless the next crop is to be immediately replanted, it is a good idea to leave the stalks, stems and leaves of the crop just harvested, lying on the soil. They will give some cover protection until the next crop develops.
AgroforestryPlanting trees among agricultural crops helps to protect the soil from erosion, particularly after crops are harvested. The trees will give some protection from rain splash. Fruit, trees, legume trees for fodder or firewood and alley cropping all help reduce soil erosion.
Minimum cultivationEach time the soil is dug or ploughed, it is exposed to erosion. In some soils it may be possible to sow crops without ploughing or digging, ideally among the crop residue from the previous crop. This is most likely to be possible in a loose soil with plenty of organic matter.
2. BARRIER methods
Barrier methods all slow the flow of water down a slope. This greatly reduces the amount of soil which run-off water can carry away and conserves water. Any kind of barrier should work. To be effective any barrier must follow the contour lines.
Man-made terracesIn some countries terracing has been successfully practised for centuries - the Philippines, Peru and Nepal, for example. Well-built terraces are one of the most effective methods of controlling soil erosion,
especially on steep slopes. However, terraces require skill and very hard work to build. Each terrace is levelled - first by levelling the sub-soil, then the top soil - and firm side supports are built, often of rock. Man-made terraces are unlikely to be an appropriate method in countries with no tradition of terrace building.
Contour ploughingWhenever possible all land should be ploughed along the contour line - never up and down, since this simply encourages erosion. In some cultures this may be very difficult due to the pattern of land inheritance. For example the Luo people in Western Kenya inherit land in long strips running down to the river valleys, making contour ploughing extremely difficult. Soil conservation programmes may need to consider land redistribution schemes, or neighbouring farmers will have to work together.
Contour barriersAlmost any available material can be used to build barriers along the contours. Here are some examples: old crop stalks and leaves, stones, grass strips, ridges and ditches strengthened by planting with grass or trees.
Natural terracesDavid Stockley encourages the use of grass strips. He writes...‘Why do so much hard work (building terraces) when nature can do it for less? Let us make use of natural erosion. We planted grass along the contour lines. We used fibrous grasses with a dense root system such as Napier grass, Guatemala grass and Guinea grass. The strips of land in between were cultivated. As the soil is cultivated, nature moves the soil to form a natural terrace. The rainwater passes through the grass strip, depositing any soil carried behind the grass. In our experience in Bangladesh and Brazil, rains formed natural terraces within five years. Once well established, the grass barrier can be planted with banana, pineapple, coffee, fruit or firewood trees.’
Vetiver grass has been very effective in grass strips. It does not spread onto cultivated soil, it produces sterile seeds, has few pest problems and can survive in a wide range of climates.
For more information about Vetiver grass, write to:Vetiver Information Network, World Bank,1818 High Street NW,Washington DC 20433, USA
Medias lunasThis is a helpful system for reclaiming badly eroded land which has been used successfully in Bolivia. Medias lunas or crescent shaped depressions are built on sloping land. The crescent shapes are built at the end of the rainy season so the ridges made can be compacted well. The crescent collects the rainwater and soil. Trees - usually legumes - are planted when the next rainy season begins and protected by thorn branches from grazing animals. After 3 or 4 years each media luna will be covered with vegetation. Later, as the soil continues to improve, crops may be grown in the medias lunas.
Crop & Residue Cover
The benefits of growing the appropriate crops on specific soils are important. Crops help reduce the erosive forces of water and wind by means of their canopy intercepting rain, and acting as a windbreak. Root systems stabilize the soil and reduce losses. Crop residues perform similar functions and, in addition, form small dams that help retain runoff water, thereby reducing erosion.
Crop RotationsFallow land has the highest erosion potential in any cropping system. Row crops such as corn or beans reduce this potential by half, which is still considered to be excessive. Sod crops such as hay and permanent pasture keep soil erosion to a minimum and should, therefore, be used in rotation with other crops where erosion is a problem. Compared to continuous corn, hay or pasture crops reduce soil loss by about 90% (Table 3). A rotation involving row crops and grain crops, while not as effective as a sod-based rotation, may reduce soil losses by 30% compared to continuous row crops.
Rotation of 1 year corn, 1 year grain, 2 years hay pasture or 3 years corn, 3 years hay pasture 60
Rotation of 2 years corn, 4 years hay pasture 70
Hay pasture 87
Permanent pasture 93
Table 3. Reduction in soil loss compared to continuous corn or beans*
* Values from parameters used in Universal Soil Loss Equation.
A crop rotation that includes forages can reduce soil loss by water erosion and, at the same time, slow the build up of insect and disease problems encountered with a continuous cropping program. On farms where crop rotations are not adequate to control soil erosion, other conservation practices should be considered.
Tillage PracticesProper tillage practices, employed separately or in combination with crop rotations, can be very effective in reducing soil erosion losses. Compared to conventional fall plowing, a mulch tiller used in the fall can reduce soil loss by up to 40%. On sandy soils, planting can be done without any previous tillage or following discing only. Compared to fall plowing, water-related soil losses can be reduced by up to 80% by practising the methods listed in Table 4. The objective with any tillage practice is to leave the soil surface in a rough condition, and, where practical, protected with crop residues. These conditions facilitate easier infiltration of water by slowing surface water runoff, and minimize soil erosion. Choice of a tillage program depends on many factors, which are described in OMAFRA tillage factsheets.
Tillage Practice % Reduction
Spring plowing 15
Spring chisel 30
Fall mulch tiller 40
Disk-plant 70
No-till plant 80
Table 4. Reduction in soil losses compared to fall plowing*
* Values from parameters used in Universal Soil Loss Equation.
Tillage and planting of the crop across, rather than with the slope, can reduce soil loss by 25%. (Value from parameters used in Universal Soil Loss Equation). Strip cropping þ alternate hay and grain strips þ is an erosion control measure that can be used on long, smooth slopes where forages are part of the rotation. Strip cropping across the slope can reduce soil losses by 50% when compared to up-down slope cropping. Contour strip cropping will reduce soil losses even further. Strip cropping, ideally, involves alternating strips of forage and a row crop on the contour. In situations where forage is not being grown, cereal crops are a reasonable substitute to be alternated with corn or soybeans.
Figure 2. Strip cropping can reduce soil losses by 50%.
Wind Erosion Control
Management practices to control wind erosion are critical on sandy, muck, or peat soils, and should also be considered on clay or silty soils. Maintaining good soil structure and residue cover provides good resistance to wind erosion. Where little or no residue is left on the soil surface, (e.g., corn silage), a cover crop of winter rye may be sown to protect the surface of wind-susceptible soils until spring. Fencerows and snowfencing also provide good protection. Strip cropping, or even planting crops at right angles to prevailing winds is a method of controlling wind erosion on land susceptible to strong winds.
Tree windbreaks should be planted along the north and west boundaries of fields, and may be planted all around fields where wind erosion is a particular problem. On very steep slopes or areas where blowouts or rills/gullies frequently occur, permanent sod or tree cover should be maintained, and may in fact provide better financial returns.
Structural Erosion Control PracticesWhen surface water concentrates, rills develop. If these rills are not addressed with appropriate control practices, a gully may result. Water runoff may continue to be a
problem on some areas even after conservation tillage and cropping practices are followed. A properly constructed and maintained waterway with good vegetative cover can be a practical way to prevent this type of water erosion. Waterways must have a shallow, saucer-shaped cross- section and an erosion-resistant vegetative cover to carry water safely. A wide, shallow waterway shape will facilitate machinery crossing. See OMAFRA Factsheet, Grassed Waterways, Order No. 09-021.
Figure 3. A properly constructed and maintained grassed waterway.
Water and sediment control basins, or channel terraces, can achieve the same objective as grassed waterways. They are used to pond surface water from small upland areas (less than 20 hectares) for short periods of time (less than 24 hours), and direct these flows into subsurface tile systems. These structures effectively reduce the peak flows of surface runoff and control rill and gully erosion. For more information, see OMAFRA Factsheet, Water and Sediment Control Basins, Order No. 89-167.
Buffer strips along the banks of drainage ditches and streams stabilize the banks by preventing slumping and washouts as well as subsequent siltation. The buffer strips should be maintained with grass cover. Ditch or stream banks should have proper side slopes based on the soil type and be permanently vegetated. Properly installed and maintained buffer strips and vegetated banks will reduce maintenance costs for ditch cleaning. See OMAFRA Factsheet, Considerations for Stable Open Ditch Construction, Order No. 85-067.
Concentrated flows of surface water must be directed to protected points along the ditch bank where they may enter the watercourse. Drop structures such as rock chute spillways or drop pipe inlets will safely convey this water to the ditch or stream bottom. For more information, see OMAFRA Factsheet,Drop Inlet Spillways, Order No. 85-057.
Tile drainage systems can also be an effective means of reducing surface runoff. By maintaining the water table at a constant, desired level, the soil surface will remain in a drier condition to more effectively accept water without eroding. Tile drainage systems complement surface water control measures such as grassed waterways, water and sediment control basins, terracing and water inlet systems.
Tile drainage outlets should be protected from erosion at the point where tile systems enter ditches and streams. Proper installation of rock riprap or other
erosion-resistant materials will ensure that tile water is safely discharged into watercourses. Refer to OMAFRA Factsheet, Tile Drainage Outlets, Order No. 90-223.
Controlling livestock access to streams and ditches can be an effective means of maintaining bank stability, decreasing sedimentation, and improving water quality. Several OMAFRA Factsheets address this subject.
In summary, wind and water erosion control practices are based on maintaining a good soil structure, protecting the soil surface and making use of erosion control structures. Adherence to these practices will do much to enable farmers to continue to maximize crop yields, minimize soil erosion, and enhance the quality of surface water.
Rainfed Farming
Growing of crops on natural preciption without irrigation.
Dry farming areas : Dry farming areas (as per the IV five year plan) are those areas receiving an annual rainfall ranging from 375 to 1125 mm and very limited irrigation facilities. Areas which receive less than 375 mm of average rainfall are considered as absolutely arid or desert areas, which require special treatment. As many as 128 districts in the country falls under category of dry farming areas as defined above. Out of these 25 dists from the states of Rajasthan, Sourashtra and rainshado region of Maharashtra and Karnataka belong to very high intensity dryfarming areas (i.e. rainfall ranges from 375 to 750 mm and irrigated area belong 10% of the cropped area.)
As the Encylopedia Britanmputs Dry land farming consists of making the best use of limited water supply by storing in the soil and much of the rainfall as possible and by going suitable crop plants those make the best use of this moisture. The major physiographic regions observed in India namely
i) Mountain region ii) Indogangatic alluvial plains iii) Peninsular or Deccan plateau & iv) Coastal plains.
National Agricultural Research Project (NARP) launched in 1979 by ICAR with soft loan support from International Development Agency (IDA) of World Bank. Where in state Agricultural Universities were advised to divide each zone / state into subzons (NARP). Accordingly 120 sub zone map based primarily on rainfall, existing cropping pattern and administrative units was prepared. Although the agro climatic regional approach considers an agro - climatic zone having a greater degree of commonality of the relevant basic fetures of soils, topography, climate and water resources. Yet in practice this approach neighter gave adequate consideration to soils and environmental conditions nor had a uniform criterion. Moreover, the use of state as a unit for sub - division may not be reconciled with, as it resulted is the creation of many sub - divisions having similar agro - climation characteristics, occurring in different states.Since the agro - climatic regional planning a approach was intended take an integrated view of agricultural economy in relation to resource bas and linkage with other sectors, further development should be specific agro - ecoregions and considered to generate an agro ecological region my of the country giving due recognition to climatic conditions, length growing period, land form & soils.
ii. Piling method – piling method is a compost making process on the surface. It is an appropriate
method for areas where there is excess moisture through high rain and irrigation. If the
compost making is in a pit, excess moisture may enter into the pit and change the
decomposition of the compost from a good smelling aerated process into a sour or ammoniasmelling process.
2. Some principles to be followed
For effective compost training, there are some principles, which have been identified from the
training ISD has conducted for more than 12 years. These are:
1
Institute for Sustainable Development, PO Box 171–code 1110, Addis Ababa, Ethiopia. Tel: 0116-186774
(office); 0911-246046 (mobile); e-mail [email protected] (office); <[email protected]>i. The training should give opportunity for a free dialogue among the trainees and the trainer.
This will allow both to create an open relationship so that concerns and misunderstandings
are quickly resolved.
ii. Farmers develop confidence and are convinced when they see and participate directly in the
training in practice because most farmers are convinced by what they see rather than what
they hear. Therefore, training has to be practical.
iii. To get an effective and sustainable result out of the training, the trainees should be a
mixture of different social groups such as farmers, women, youth, DAs, experts, priests, etc
iv. The number of trainees should be limited to a maximum of 30 people so all participants can
be active and not just passive watchers.
v. Training should be in a simple straight forward language that can be readily understood by
all the trainees; i.e. there should not be a mix of English technical terms with the local
language.
vi. Each of the participants in the training should be given a copy of the compost making
manual/booklet in Amharic and allowed to make their own comments, etc in the booklet.
They will keep the booklet with them after the training is completed.
3. Choosing a compost pit location
Selection of a compost pit site is very important for a better compost-making process. A compost
pit should be under the shade of a tree to help retain moisture and flood water should not enter
the pit.
Trainees should be taken for an outdoor practice in selecting compost pit sites and should discuss
about the location among themselves before reporting back to the trainer.
Note: If they do not find a good place with shade and appropriate slope in the area during their
outdoor training the question is: "are they going to drop preparing compost?" The answer is: "No."
A compost pit can be dug with some safeguards. These are, first, to make a shade with plastic,
grasses, old sacks, etc similar to the shade used in a seedling nursery and second, make structures
to divert possible flood water from entering into the pit. Both these safeguards should be put in
place after the pit has been completely filled with composting materials.
4. Digging a compost pit
Compost can be prepared using one pit, two pits or three pits. This depends on the farmers’ need
and/or capacity to prepare compost. If there is only one pit, the amount of compost to be made will
be less, while if there are three pits, more compost can be made and stored ready to be used. The
width and length of a compost pit is not limited except its depth, which should not be deeper than 1.5 meters. This is because it is difficult to control the temperature in a deeper pit; it may be too hot
and therefore, it can easily loose moisture, and this stops the decomposition process.
It is recommended that pit for the training exercise is dug 1.5 x 1.5 x 1.0 m and is made in the
compound of a Farmers' Training Center or a home of a disadvantaged family (elderly, sick, poor
women-headed) so they can make use of the compost.
5. Preparing biomass for compost preparation
All clean organic recyclable materials can be used for compost making. But listing all for a trainee
does not help, even it confuses her/him. It is best if the composting materials are grouped into four
categories, and then the trainees can suggest materials they know that fit each category. These are:
- Dry stalks (stover) – maize, sorghum, grasses with thicker stems, or thin branches from trees,
which could not decompose easily. These are put in the bottom of the compost pit to make
sure there is a good circulation of air and moisture inside the pit.
- Dry plant materials – this refers to all kinds of dry biomass such as straw of field crops, all
kinds of weeds, grasses, etc. It is preferred if these materials are the leftovers from animal
feed and bedding. This is because there is no need to compete with clean straw and grass
needed for animal feed. These leftovers also have the advantage of already being mixed with
urine and fresh animal dung produced by the animals while they are in the barn. The urine
and dung are very good for improving decomposition of the straw and the establishment of
compost making micro-organisms.
- Green plant materials - all kinds of green plant material; such as leaves and soft branches,
weeds, grasses, etc. Troublesome weeds such as Parthenium and spiny/thorny plants can also
be included.
- Qmemaqmem - Starter material = "spices" – is a mixture of other naturally decomposable
materials other than stalks, dry and green plant materials mentioned above. Farmers called it
"qmemaqmem" because it is used at every step of compost making. Dry qmemaqmem is a dry
starter, which includes any animal manure (figh-Amharic), bird and chicken droppings, ash,
fertile soil, etc; and wet qmemaqmem is a fresh or wet starter including fresh animal dung,
urine (human and animal) and water. This mixture contains the micro-organisms (worms,
beetles) as well as the fungi and bacteria that do the work of turning the plant and animal
materials into compost.
- Testing stick – it is used to test the condition inside the composting materials in a pit.
The trainees are divided into groups to collect these different materials, and bring them to beside
the pit. A jerry can be placed in a toilet to collect human urine. It is also recommended that the
trainer also arranges to have compost materials collected 1 or 2 days before the training is to take
place. It is important to make sure there are enough materials to properly fill a pit of 1.5 x 1.5 x 1.0
meters, which are the width, length and depth respectively.6. Materials not part of compost
In any part of a training program and/or follow-up the trainer should make it possible for all
participants to forward their comments, questions and concerns. During trainings and discussions
the trainer’s recommendations in listing materials not to be included in the compost making should
be based on his/her knowledge and experience. He/she should only make comments and/or
statements in which he/she is fully confident, or invite the farmers already making compost to
forward their own experiences. Farmers are innovative and may disprove comments from trainers
through their own daily practices and this can affect relations in other extension work.
However, the following materials should not be part of the compost preparation: fuel (kerosene,
diesel, petrol), engine oil, stones, pieces of iron, broken glass, plastic materials, any pieces of clothes
(especially nylon or plastic cloth), hyena or dog droppings, any type of wax, any type of fat,
hide/skin, etc.
7. Preparing the compost pit
The next step is preparing the compost pit before filling it with the available materials. All sides of a
pit must be dry i.e., there should not be any moisture (e.g. a small spring) leaking into the compost
pit. Then the sides need to be painted with a mixture of fresh animal dung and urine mixed
thoroughly with water. If there is a shortage of fresh animal dung using only water to moisten the
sides is another option. This helps macro- and micro-organisms (the decomposers) to work faster
and stops moisture leaking out of the pit into the surrounding earth.
8. Filling a compost pit
During the filling of the compost pit, trainees should be grouped into 3-5 groups i.e. according to
the available materials and work. Each group should be a mixture of experts, DAs and farmers
regardless of background and/or qualifications. The groups are: 1. Compost pit preparation group;
2. Stalk group; 3. Dry composting material group; 4. Green composting material group; and 5.
Qmemaqmem group (if necessary this can be subdivided into two, one for adding dry
qmemaqmem and the other for wet qmemaqmem). This grouping helps in minimizing a mix-up of
the work, ensures full participation of all the trainees, and opens up discussion during training on
whose turn comes next and why. All groups should be asked to estimate the amount of biomass
available for the compost pit. During filling a compost pit the following steps are followed:
1. Preparing compost pit is the first step.
The sides are painted with a mixture of fresh manure, urine and water.2. Filling a compost pit needs time and care. First, all the dry stalks are put to cover the
bottom of the compost pit. The layer should not be thicker than one hand deep (15-20
cm).
The bottom layer is sprayed with water and a mixture of fresh animal dung and water i.e.
according to farmers it is a mixture of wet qmemaqmem. If possible, also put in some dry
qmemaqmem – a mixture of dry animal dung, ash, bird and chicken droppings, fertile soil, and
even crushed and burnt bones if possible. Then spray well with water.
3. The next layer to be added is a mixture of all available dry plant material: straw and hay
from animal bedding, all kinds of dry weeds, grasses, etc. The layer should not be thicker
than one hand deep (15-20 cm).
Then spray with sufficient water, and a mixture of fresh animal dung and water i.e. wet
qmemaqmem. If possible, also put in some dry qmemaqmem. Then spray well with water.
4. The next layer to be added is green plant material. It should not be thicker than one hand
deep (15-20 cm).
This layer does not need to be sprayed with water or a mixture of cow dung and water because
it is moist. However, if possible, add some dry qmemaqmem over the top of the layer. Then
spray with a small amount of water.
5. This sequence, steps 2-4, completes one round of layering. But the pit will not be filled in
one round.
6. The addition of this set of layers (2-4) is repeated twice more to completely fill the pit and
have a raised, dome-shaped top, nearly 50 cm above the ground level next to the pit.
7. Put in a testing stick by pushing a straight stick, 2-2.5m or about half a meter above the
completed dome, down into and through the layers in the pit. This is useful for follow-up on
the compost making process. It is used to test the moisture and temperature of the inside
part of the compost pit. It is better if it is not perpendicular because nobody should stand on
the pit when pulling it up. It is preferable to put in the stick when the pit is half full.
8. Filling the compost pit is completed by sealing the top with cow dung, mud or a mixture of
soil and cow dung (chika) and then protected with large wide leaves such as those of enset
and banana. If large leaves are not available, the top can be covered with plastic, sacks,
cartoon, cloth, card-board.9. If the pit is in a place where there is no shade, a shade is made and ditches dug to prevent
flood water getting into the pit.
9. Follow up and turning over
Follow-up with the compost making process needs to be given strong emphasis, as it is often
weak. If the compost pit has been filled correctly and it is shaded and protected from floods,
usually the farmer can find good compost when he opens the pit 3-6 months later. However,
regular follow-up is important to identify problems quickly (e.g. compost too dry or too wet) and
deal with the problem promptly. In reality most farmers do not turn-over their compost, but all
farmers should test the progress in the decomposition process.
The testing stick is a medium-sized piece of dry and straight wood i.e., between 2-2.5m long. It
tests the moisture and temperature of the inside part of the compost pit. About 3 weeks after
filling the compost pit, the testing stick is pulled out, the material on the stick is smelled and it is
then put on the back of the hand. If the stick is watery and cold, and the material smells sour or
like ammonia it shows that there is excess water in the compost. Therefore, the materials should
be taken out and more dry matter added while turning-over the compost materials back into the
pit. If the stick is dry, it shows that more moisture and/or green matter should be added to the
materials.
10.Storing compost
Matured compost should be stored either in its original compost pit or taken out and put under
shade and covered until it is taken and used in a field. A sunny and windy place is not good for
storing compost because many of the nutrients, particularly nitrogen, will be lost.
11.Compost application
There are different views about how and when to apply compost. It is true that the nutrients in
compost are released to plants slowly. However, if compost is applied earlier than the crop is
planted the nutrients will escape to the air. As soon as the compost is added to the soil, small
amounts of nutrients are available to the germinating/growing plants. Therefore, compost
application should be during planting time. This is because when applied at the same time the
releasing process will be inside the soil.
If compost is applied before planting, it should not lie on the surface of the soil. It has to be
ploughed or dug into the soil. If farmers use row planting, the compost should be put in the row
with the seeds and then covered.12. Important points to be considered
Many farmers are afraid of MICH (sickness when they open the compost pit during
the day time). Therefore, the suggestion is to turn-over the compost in the evening or
during the night.
Many people are not convinced about the availability of sufficient biomass but the
farmers preferred time for making compost is immediately after the main rainy
season before they start harvesting. It can be prepared the year round in irrigated
areas, and particularly where vegetables are grown.
If the materials are not decomposed well enough there is high probability that weed
seeds will be put back into the field with the compost. Therefore, it is important to
make sure the compost process has been completed with a temperature high enough
to kill weed seeds, diseases (pathogens) and other pests.
Vermicompost is the product or process of composting utilizing various species of worms, usually red
wigglers, white worms, and earthworms to create aheterogeneous mixture of decomposing vegetable or
food waste, bedding materials, and vermicast. Vermicast, similarly known as worm castings, worm humus
or worm manure, is the end-product of the breakdown of organic matter by a species of earthworm.[1]
Containing water-soluble nutrients, vermicompost is an excellent, nutrient-rich organic fertilizer and soil
conditioner.[2] The process of producing vermicompost is called vermicomposting.
What is Vermicompost?
Put simply, vermicompost is the castings of earthworms. Organic waste gets decomposed by micro-organizms and is consumed by earth worms. The castings of these worms is popularly known as vermicompost.
Vermicompost can be prepared easily. The essentials are space, cowdung, organic wastes, and epigeic phytophagous earthworms. Vermicompost is a good organic manure as it improves soil quality. Conversely, over time, inorganic fertilisers can deprive the soil of fertility.
Sources of organic waste for manure production:
The organic wastes that are available in agricultural areas include cattle dung, sheep dropping, biogas slurry, stubble from harvested crops, husks and corn shells, weeds, kitchen waste etc. All these materials can be used to produce vermicompost.
Requirements
Housing: Sheltered culturing of worms is recommended to protect the worms from excessive sunlight and rain. All the entrepreneurs have set up their units in vacant cowsheds, poultry sheds, basements and back yards.
Containers: Cement tanks were constructed. These were separated in half by a dividing wall. Another set of tanks were also constructed for preliminary decomposition.
Bedding and feeding materials: During the beginning of the enterprises, most women used cowdung in order to breed sufficient numbers of earthworms. Once they have large populations, they can start using all kinds of organic waste. Half of the entrepreneurs have now reached populations of 12,000 to 15,000 adult earthworms.
Process
The bedding and feeding materials are mixed, watered and allowed to ferment for about two to three weeks in the cement tanks. During this period the material is overturned 3 or 4 times to bring down the temperature and to assist in uniform decomposition. When the material becomes quite soft, it is transferred to the culture containers and worms ranging from a few days to a few weeks old are introduced into them.
A container of 1 metre by 1 metre by 0.3 metres, holds about 30-40 kgs of the bedding and feeding materials. In such a container, 1000 - 1500 worms are required for processing the materials. The material should have 40 to 50 percent moisture, a Ph of 6.3 to 7.5, and a temperature range of 20 to 30 degree celsius.
The earthworms live in the deeper layers of the material. They actively feed and deposit granular castings on the surface of the material. The worms should be allowed to feed on the material until it is converted into a highly granular mass.
The earthworms take 7 weeks to reach adulthood. From the 8th week onwards they deposit cocoons. One mature worm can produce two cocoons per week. Each cocoon produces 3-7 young after an incubation period of 5-10 days depending on the species of worms, quality of feed, and general conditions. The resulting increase is about 1200-1500 worms per year. The population doubles in about a months time.
Harvesting of Vermicompost
The harvesting of vermicompost involves the manual separation of worms from the castings. For this purpose, the contents of the containers are dumped on the ground in the form of a mound and allowed to stand for a few hours. Most of the worms move to the bottom of the mound to avoid light. The worms collect at the bottom in the form of a ball. At this stage, the vermicompost is removed to get the worms. The worms are collected for new culture beds. The vermicompost collected is dried, passed through a 3 mm sieve to recover the cocoons, young worms, and unconsumed organic material. The cocoons and young worms are used for seeding the new culture beds. The vermicompost recovered is rich in macro-nutrients, microbes such as actinomycetes and nitrogen fixers, and is used as a manure.
Pests and Predators
Earth worms have a large number of predators, including: birds, fowl, rodents, frogs, toads, snakes, ants, leeches, and flat worms such as bipalium. To avoid attacks of these predators vermiculture should be practised in protected places.
Benefits
By establishing vermiculture units entrepreneurs can recycle their own resources and create an effective fertiliser in the process. The extra worms that are produced can be used as feed for poultry and fish. The advantages of this technology include:
1. Recycling of organic wastes.2. Production of energy rich resources.
3. Reduction of environmental pollution.
4. Provision of job opportunities for women and jobless people.
5. Improvement of soil pH. (vermicompost acts as a buffering agent).
6. Improvement in the percolation property of clay soils (from the compost's granular nature).
7. Improvement of the water holding capacity in sandy soils.
8. Release of exchangeable and available forms of nutrients.
9. Increase of oxidizable carbon levels, improving the base exchange capacity of the soil.
10. Improvement of the nitrate and phosphate levels.
11. Encouragement of plant root system growth.
12. Improvement in the size and girth of plant stems.
13. Early and profuse plant flowering
14. Creation of a substitute protein in poultry and fish feed.
One disadvantage of this technology is that pesticides and heavy metals accumulate in the bodies of the worms that are raised on contaminated organic wastes. If such worms are used as protein source in animal feeds, health hazards may result.
