‣ Soil & Agriculture

‣ Shaping the Planet‣ The main forces that shape the surface of the

Earth are:* Weathering and erosion* Deposition

‣ Weathering and Erosion‣ Weathering is the breaking down of rocks on the surface

by local conditions with no movement. ‣ Erosion is the break up and removal of those rocks. The

movement deposits them elsewhere.‣ Weathering and erosion come in two forms:

* Chemical: rocks are dissolved by the action of acids or other reactive chemicals. This includes leaching.

* Physical: rocks are broken down into smaller and smaller pieces by mechanical forces such as wind or water.

‣ Deposition‣ Deposition, the process by which material is

added to land, also occurs by both chemical and physical means:* Chemical deposition: chemicals (often pure

elements or compounds) precipitate out of solution and form crystalline structures.

* Physical deposition: sediments are laid down by wind or water in large areas and may form strata, showing the different types of sediment and mode of deposition.

‣ The character and composition of the parent material is important in determining the properties of a soil.

‣ Parent materials include volcanic deposits, and sediments deposited by wind, water, or glaciers.

‣ The occurrence of freeze-thaw and wet-dry cycles, as well as average temperature and moisture levels are important in the development of soils.

‣ Climate also affects vegetation, influencing soil development.

‣ Plants, animals, fungi, and bacteria help to create a soil both through their activities and by adding to the soil's organic matter when they die.

‣ Moist soils with a high organic content tend to be higher in biological activity because of the opportunity for shelter and food.

‣ The topography of the land influences soil development by affecting soil moisture and tendency towards erosion.

‣ Soils in steep regions are more prone to loss of the topsoil and erosion of the subsoil.

‣ Soil Formation‣ Soils are a complex mixture of unconsolidated

weathered rock and organic material. ‣ Soils are essential to terrestrial life as plants

require soil and the microbial populations, responsible for recycling organic wastes, live in the soil and contribute to its fertility.

‣ They are named and classified on the basis of physical and chemical properties in their horizons (layers). Besides the O horizon, soils have three basic horizons A, B and C.‣ The O horizon is the layer that includes the

organic material like leaf litter or relatively undecomposed humus. Most biological activity occurs in the O horizon.

‣ The A horizon is the topsoil, which is rich in organic matter. The dark color of the topsoil is due to the carbon in the decomposing organic material.

‣ The B horizon is a subsoil containing clay and soluble minerals. The horizon of illuviation where the dissolved minerals accumulate.

‣ The C horizon comprises weathered parent material and rock fragments.

‣ Soil Formation ‣ The parent rock is broken down by weathering to

form a regolith which overlies the solid bedrock. ‣ The soil that forms is part of the regolith. ‣ The first portions of soil formation are also the

first portions of primary succession.‣ Plants begin to establish and organic material

builds up on the surface. ‣ The organic material aids the disintegration of

the parent material.

‣ As different organisms begin to respire they release CO2 which combines with H2O to form Carbonic Acid H2CO3

‣ Horizons form as the mineral and organic content mix.

‣ Humus rich layers are at the surface and mineral rich layers are at the base.

‣ Humus is any organic material that has reached the point of stability.

‣ Soil Formation ‣ Horizons are well developed in mature soils. ‣ The final characteristics of the soil are

determined by the regional conditions and the rock type.

‣ The soil type determines the water holding capacity. Water holding capacity is affected by the addition of sand silt, clay or humus in varying amounts.

‣ The degree of infiltration and leaching is thus affected by the formation of the soil.‣ Infiltration: the downward movement of water

through soil.‣ Leaching: dissolving of minerals and organic matter

in upper layers carrying them to lower layers.‣ Climatic Influence on Soil‣ Climatic Influence on Soil‣ Particle Size

‣ Soils are made of many different sized mineral particles and other material, but the grains in them can be placed into categories based on size.

‣ The combination of sizes gives the soil its texture.‣ Sand (largest) feels gritty, silt (med.) feels smooth, and

clay (small) feels smooth‣ Soil Texture‣ Soil texture depends upon the amount of sand, silt and

clay present. ‣ Soil Texture‣ Permeability is the rate at which water and air

moves from upper to lower soil layers. ‣ Porosity is the measure of the volume of soil and

the average distances between the spaces.‣ Some soils, like clays, swell when H2O gets in

them, then they dry and crack because they have a high water holding capacity.

‣ Soil Nutrition‣ Food‣ Although food production is generally adequate

to meet human needs there are problems with distribution. Along with distribution there is: * A loss of or decline in arable land* Increasing population growth and increasing poverty

‣ Over 1 billion people remain undernourished, which could change by simply consuming more vegetable protein in place of meat protein

‣ Overfishing of key fish stocks to levels where recovery is unlikely has occurred in many fishing grounds.

‣ Agricultural Ecosystems ‣ Intensive Agriculture‣ Advantages of Intensive Agriculture‣ Irrigation Technique‣ Irrigation is the artificial application of water to the soil.

Most intensive agriculture requires irrigation to assist in the growing of crops..

‣ Three main types of irrigation are used in agriculture today. * Surface irrigation or flood irrigation allows water to

move across the land by simple gravity flow* Drip irrigation or trickle irrigation delivers water at or

near the root of the plant. High water application efficiency, low water loss to evaporation.

* Sprinkler irrigation uses high-pressure overhead sprinklers to deliver water to the plant. Most common type is center-pivot

‣ Factory Farming‣ Factory farming is the practice of raising livestock in

confinement at high stocking density. Industrial farming produces meat, milk, and eggs for human consumption.

‣ Besides the ethics some of the environmental problems include deforestation, water pollution from fertilizers and waste, and loss of biodiversity.

‣ The impact on human or animal health can include the incorporation of antibiotics into feeding regimens of densely concentrated livestock.

‣ Most industrial countries consume beef and by simply converting to eating vegetarian could solve many environmental problems like the problem associated with land use.

‣ Crop Harvest‣ Crop harvesting interrupts normal nutrient cycles and

removes nutrients from the land. If the soil is left unreplenished it becomes nutrient deficient. The addition of fertilizers restores soil fertility.* Organic fertilizers (carbon based) include animal manures,

green manure, and compost.* Inorganic fertilizers contain simple inorganic chemicals

immediately available to the plant because exact compositions are known.

‣ Because the soil is laid bare after harvest, erosion of topsoil occurs, with the loss of habitat for important soil organisms.

‣ Fertilizers‣ Nutrients lost through cropping can be replaced by the

addition of fertilizers: materials that supply nutrients to plants.

‣ Plants require a variety of minerals which are normally obtained from the soil. Minerals required in large amounts are called macronutrients (e.g. phosphorus, nitrogen, sulfur). Phosphorous and nitrogen are limiting factors for plant growth and thus low levels can limit plant growth.

‣ Those needed in small amounts are called trace elements or micronutrients.

‣ The use of fertilizers contributed to the world’s first green revolution, which greatly increased crop yields between 1950 and 1970.

‣ Pesticides

‣ Any substances or mixture of substances intended for preventing, destroying, repelling or mitigating and pest is called a pesticide.

‣ Pesticides are classified by the effect on their target organism, the chemical structure and the physical statea gradual deterioration of soil quality.* Organophosphates and carbamates have an acute

toxicity that is less persistent.* Organochlorines or chlorinated hydrocarbons like

DDT are persistent pesticides that stay in the environment for a long period of time. The mode of action is endocrine disruption which poses many risks to non-target organisms.

‣ DDT was discovered to prevent fish-eating birds from reproducing because of bioaccumuation. The threat was brought to light by Rachel Carson in the book Silent Spring which increased public awareness of the risks of using pesticides.

‣ Chemical Contamination‣ Intensive agricultural practices, which call for high

inputs of herbicides, pesticides, and fertilizers, can lead to a gradual deterioration of soil quality.* Inorganic chemicals (nitrogen and phosphorous)

can accumulate in the soil and enter ground water through leaching.

* Persistent chemicals like DDT used in one region of Earth can circulate through the biosphere and affect other regions.

‣ The problem of disposing of unwanted agrichemicals has reached major proportions in developed countries. * Chemical dumps may be unstable: storage vessels

deteriorate and

their contents escape to enterground and surface waters.

‣ Regulations for Pesticides‣ The Federal Insecticide, Fungicide, and Rodenticide

Act (or FIFRA) was established in 1947 and amended in 1996 to require the specific labeling and registration of all pesticides.

‣ Federal Food, Drug, and Cosmetic Act (FFDCA) gave authority to the USDA to oversee the safety of food, drugs, and cosmetics. Also, set maximum residue levels, or tolerances, for pesticides used in or on foods or animal feed.

‣ The Food Quality Protection Act (FQPA) of 1996 amended the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Federal Food Drug, and Cosmetic Act (FFDCA), which changed how the EPA regulates pesticides. The requirements included a new safety standard to all pesticides used on foods.

‣ Bhopal, India‣ The world’s worst industrial accident occurred in 1984

at a pesticide plant in Bhopal, India.‣ An explosion at Union Carbide pesticide plant in an

underground storage tank released a large quantity of highly toxic methyl isocyanate (MIC) gas.* 15,000-22,000 people died and over 500,000 were

exposed to pesticides.* Indian officials claim that simple upgrades could have

prevented the tragedy‣ Factors that determine the harm caused by exposure to

a chemical can include:

* The amount of exposure (dose), frequency, effectiveness of immune or detoxification system, and genetics.

‣ Bioaccumulation‣ Bioaccumulation (also called biological

magnification) occurs when highly persistent pesticides, which cannot be metabolized or excreted, are stored and accumulate in the fatty tissues of the body.

‣ There is a progressive concentration of the pesticides with increasing trophic level; higher order consumers are at greater risk because they eat a large number of lower order consumers.

‣ Global Soil Degradation‣ Especially in the tropics, deforestation, overgrazing,

overcultivation, and poor irrigation practices can lead to desertification and salinization.

‣ Soil Degradation‣ Salinization‣ Salinization is caused by the excess

accumulation of salts especially in the surface of the soil.

‣ The excess salt can result from high soil salt content, the movement of the water table, climate trends and land clearing. * Soil salinity can occur from irrigation over time. Almost

all water contains some dissolved salts. Poor drainage and use of saline water to irrigate crops can add additional salt to the soil.

* Salt can affect plant growth, corrode infrastructure, cause sedimentation problems, and lead to soil erosion.

* Addition of large amounts of water can often leach out the excess salts.

‣ Desertification‣ Desertification is a complex process involving

multiple natural and human-related causes. In desertification, the productive potential of arid and semi-arid lands falls by 10% or more, and topsoil is lost or degraded.* Desertification results mainly from a combination of

natural climate changes causing prolonged drought and unsustainable human activities, including overgrazing and deforestation.

* Desertification may lead to the formation of a desert or the encroachment of an existing desert onto formerly arable land.

‣ The Green Revolution‣ Crop Production‣ The second green revolution (or the gene revolution) is

occurring in response to the use of fast growing, high yielding varieties of rice, corn, and wheat, specially bred or genetically modified for the tropical and subtropical climates.

‣ Providing adequate nutrition by distribution, effective irrigation, new food crops, and dedicating more land to grain production are methods to feed a growing population.

‣ Rice, corn, and wheat provide the major source of nutrients for the human population.

‣ Global Wheat Production

‣ Wheat (Triticum spp.) is the most important world cereal crop and is extensively grown in temperate regions.

‣ Key areas for wheat production are the prairies of Canada and the USA, Europe, and Russia (the former Soviet Union wheat belt).

‣ Global Maize Production‣ The USA corn belt produces nearly half the world’s maize

(Zea mays). Some is exported, but 85% is used within the USA as animal feed (as grain and silage). It is also a major cereal crop in Africa and second only to rice in importance in Asia.

‣ Maize is poor in the essential amino acids tryptophan and lysine and as the diversity of corn decreases the susceptibility to plant disease increases.

‣ Maize‣ Maize grows well where temperature and light

intensity are high, and its adaptations include:* A slightly different biochemical pathway for

photosynthesis than that in most cooler climate plants. This C4 pathway allows the plant to fix CO2 (even at low levels) as a 4C compound, which is used to boost CO2 levels for the regular C3 pathway. As a result, in warmer regions, C4 plants can achieve very high photosynthetic rates.

* Maize roots are shallow, so the plants often have small aerial roots at the base of the stem to increase their ability to withstand buffeting by wind.

‣ Global Rice Production‣ Rice (Oryza sativa) is the basic food crop of monsoon

Asia, and is highly nutritious. Both paddy and indica (upland) varieties are grown.

‣ Most rice is grown in China, mainly for internal consumption. Other major producers include India, Pakistan, Japan, Thailand, and Vietnam.

‣ Rice‣ Most of the rice in SE Asia is grown partly

submerged in paddy fields. Its adaptations include:* The stem has large air spaces running the length of

the stem which allows oxygen to penetrate through the submerged roots.

* Shallow roots allow access to the oxygen that diffuses into the surface layer of waterlogged soil.

* When oxygen levels fall too low, the root cells respire anaerobically, producing ethanol. The root cells have a high tolerance to this normally toxic product. So, rice plantations are a significant contributor to methane in the atmosphere.

‣ Global Sorghum Production‣ Sorghum (Sorghum bicolor) is a nutritious grain used as a

human foodstuff in Asia and Africa. In other regions it is used mainly as animal feed and as an industrial raw material (for oil, starch, and fiber).

‣ Sorghum is widely cultivated in Africa, the middle East to India and Myanmar, and parts of Australia, the Americas, and Southern Europe.

‣ Sorghum‣ Sorghum is able to grow well in the very hot, dry regions of

tropical Africa and central India. Its adaptations include:* The presence of special motor cells on the underside of the leaf

that cause the leaf to roll inwards in dry conditions. This traps moist air in the rolled leaf and reduces water loss.

* A thick waxy cuticle and a reduced number of sunken stomata prevent evaporative water loss through the leaf surface.

* A dense root system that is efficient at extracting water from the soil.

‣ New Crop Developments‣ Wheat has a selection of cultivars for particular

nutritional qualities or high yield in local conditions. Research focuses on breeding hardy, disease resistant, and high yielding varieties.

‣ Maize has high lysine hybrid varieties with better disease resistance and higher yields. Most countries have cultivars suited to local conditions.

‣ New Crop Developments‣ Rice has fast growing, disease resistant, high yielding

cultivars which crop up to three times a season. Genetic engineering to increase the tolerance to high salinity is extending the range for cultivation.

‣ Sorghum has high-yielding, low-growing and uniformly ripening new hybrids. Further breeding aims to improve grain quality and combine high yield properties with the disease resistance of the African wild stocks.

‣ Artificial Ecosystems‣ Humans can provide conditions that can maximize

crop yield by:* Providing enclosures, e.g tunnel houses and

glasshouses.* Regulating the abiotic factors important for growth,

e.g. temperature, light intensity, and carbon dioxide concentration.

‣ Hydroponics

‣ Hydroponics is a technology for growing plants in nutrient solutions with or without the use of an artificial soil medium, such as sand or vermiculite, to provide support.* Like all controlled-environment

agriculture, it is expensive to establish and operate, but it is highly productive, conservative of water and land, and protective of the environment.

‣ Hydroponic culture has been practised for centuries but it has been used on a commercial basis for only 40 years or so. Mostly in the growth of tomatoes and cranberries.

‣ Fish Farming‣ Fish farming (aquaculture), once thought to be

the solution to the world’s over-fishing problems, actually accelerates the decline of wild fish stocks.* Many farmed fish are fed meal made from wild fish,

but it takes about one kilo of wild fish to grow 300g of farmed fish.

‣ Some forms of fish farming destroy natural fish habitat and produce large scale effluent flows.

‣ Managing Farm Fisheries‣ Besides helping with demands on wild fisheries and

overfishing the criticisms of fish farms include:* New water must be used as the recycled water will become

polluted because of the high densities of the fish populations and the high concentrations of feces.

* Escape from habitats can occur, especially when the habitats are located in controlled ponds or streams.

* Risk of infections by parasites like fish lice, fungi, intestinal worms, and protozoa in high population densities.

‣ Tragedy of the Commons‣ The Tragedy of the Commons is an essay written in

1968 dealing with the management of a common resource.* Because the resource is not owned by any particular

person it is in the best interests of the individual to use it as much as possible.

* In this way their benefit is maximized while the damage is shared by others.

* The result however, is the eventual destruction of the commons.

‣ Sustainable Agriculture‣ The components of sustainable, low input

agriculture are applicable to any type of cropping or harvesting system.

‣ Advantages of Organic Farming

‣ The advantages of organic farming include:* Farmers can still make use of new high yielding crop

varieties (right).* Produce is pesticide free and produced sustainably.* Crop type is more closely matched to the appropriate

season and soil.* It increases crop diversity and disrupts disease and

pest cycles.

* It improves soil quality and structure, reducing nutrient and water loss.

‣ The disadvantages of organic farming include:* Yields are lower and more land is required for the

same yield.* Produce may be more expensive to buy, of reduced

quality and with a shorter shelf life. Consumer choice may be restricted if out of season.

* There may be considerable bacterial contamination of produce due to high use of manures.

‣ The Impact of Farming‣ Shelterbelts & Hedgerows‣ The conversion of many traditional, mixed

farms, which required hedgerows or shelterbelts to contain livestock, have been converted to arable farms with large fields to accommodate modern machinery.

‣ Hedgerows and shelterbelts are economically and ecologically important because they: * Reduce wind erosion and

maintain soil moisture* Provide food and habitats

for birds and other animals.* Provide habitats for predators

of pest species.* Act as corridors for wildlife

to move along.‣ Crop Rotation

‣ Crop rotation is a farm practice where crops with different nutrient demands are cultivated in succession on the same ground in successive years.

‣ Its purpose is to maintain soil fertility and reduce pest infestation. This avoids the need for chemical pesticides.

‣ A typical rotation is of three to six years. Legumes (e.g. clover, beans) are important in the rotation as they restore nitrogen to the soil. These alternate with root and cereal crops.

‣ Conservation Tillage‣ Conservation (minimum) tillage describes the practice of

leaving crop residue in place and mixing it into the surface layers of the soil. Conservation tillage and no-tillage improves the soil structure through allowing for aeration and the return of nutrients to the soil. * It is best suited to crop rotations where the crop residue

changes seasonally. In continuous cropping systems, conservation tillage leaves the same type of residue in the soil all year round, and this may harbor pests and disease.

‣ Traditional Farming‣ Traditional farming, such as that practised by the Amish

people of Pennsylvania, USA, uses low-input agricultural methods similar to those used in modern organic farming.

‣ Currently, low input agriculture occurs on less than 1% of the world’s cropland (0.2% in the USA, but 6-10% in parts of Europe), but this type of farming is growing rapidly.

‣ Traditional farming practices are sustainable in the long term and improve soil health and fertility.

‣ Managing Grasslands‣ Natural grasslands are diverse and productive

ecosystems, but currently cultivated grasslands may contain as few as three species.

‣ In order to conserve grassland ecosystems, management practices that promote grassland species diversity must be implemented, even though many of these practices often conflict with modern farming methods.

‣ Managing Grasslands‣ The increase in urban sprawl and the pressure on farmers

to increase the productivity of their land and are having a detrimental effect on the once common flowering plants of Britain’s grasslands.* Conservation of grasslands is not only important for

maintaining plant diversity. Many birds, reptiles, invertebrates, and mammals also rely on these ecosystems for food and shelter.

‣ Integrated Pest Management

‣ Integrated pest management (IPM) describes pest control practices where each crop and its pests are evaluated as part of an ecological system. A program is developed that includes crop management(e.g. intercropping or polyculture where multiple types of plants are planted together), and biological and chemical controls.* The aim is not to eradicate pest

populations, but to reduce cropdamage to an economicallytolerable level.

‣ An increasing number of pestcontrol experts and farmersbelieve IPM is the best way tocontrol crop pests because of the many different methods that are used.

‣ Stages in IPM‣ IPM involves several phases. Crop management and

monitoring of pest levels are ongoing. When crop damage becomes unacceptable, farmers implement the following control measures in sequence and with the proper timing.* Stage 1: Cultivation controls, such as hand weeding and

vacuuming crops to remove insect pests.* Stage 2: Biological controls, such as pheromone traps, and

natural predators, parasites, and disease organisms.* Stage 3: Targeted pesticide use (chemical controls), mostly

based on natural insecticides. Different chemicals are used to slow the development of resistance.

‣ Biological Pest Control‣ Biological control (biocontrol) is a management

tool for controlling pests using parasites, predators, disease organisms.

‣ Control agents with a botanical or microbial origin (e.g. Bt toxin) are classified as biopesticides.

‣ Biological control is an important part of IPM but it is not risk free. Some biocontrol agents may even become pests themselves attacking beneficial species. The cane toad (right) was introduced to Australia to control gray cane beetle and is now a

major threat to native wildlife by displacing native species.

‣ Biocontrol of Whitefly‣ Adult whitefly resemble tiny moths. The young

appear as scales on the undersides of many glasshouse crops where they suck the sap.

‣ Two biocontrol agents are in common use: the ladybird Delphastus, which feeds on eggs and larvae, and the parasitic wasp Encarsia.

‣ Both adult and larval Delphastus feed on whitefly; individuals may consume 150 whitefly eggs a day.

‣ Biocontrol of Prickly Pear‣ Prickly pear cactus (Opuntia stricta) was introduced to

Australia as an ornamental plant in the 1800s. It dispersed rapidly to cover an estimated 250,000 km2 by 1925, much of it so densely that the land could not be used.

‣ The caterpillar of the moth Cactoblastis cactorum is a natural enemy of the prickly pear cactus and, as a biocontrol agent, it succeeded in clearing the 250,000 km2

of prickly pear cactus over several years.

‣ Biocontrol of Scotch Thistle

‣ The scotch thistle (Onopordum acanthium) was accidentally introduced into the US and Australia from Europe. The seeds survive in soil for more than 20 years and are distributed by livestock which have spread this weed across 1 million hectares of Australian farmland.

* The biocontrol program, launched in 1987, involves three established weevil species, each of which attacks a different part of the thistle: flower head, stem, or rosettes. This multi-pronged approach offers effective control.

‣ European Rabbit Control‣ The European rabbit (Oryctolagus cuniculus) has reached

plague proportions in parts of New Zealand, Australia and other islands.* Early attempts at biological control involved the Myxoma pox

virus (introduced in the 1950s). This was ineffective in the long term.

* Calicivirus (the infective agent for Rabbit Hemorrhagic Disease or RHD) escaped from quarantine in Australia in 1995 and then spread both naturally and with assistance. It was introduced illegally into New Zealand in 1997, although at the wrong season for maximum effect.

‣ Effects of Biocontrol‣ The European rabbit (Oryctolagus cuniculus) was

successfully introduced into Britain by the Normans for their meat and fur.

‣ By the 1950s, they were considered a pest. The introduction of the Myxoma virus killed 99% of Britain’s rabbit population. The cascade effects of this event are still evident today.

‣ World Seed Banks‣ Seed banks are designed for the long term

storage of seeds.‣ They are built to guard global seed supplies

against war, climate change, earthquakes and other possible future disasters.

‣ Rare plants also have seeds stored to protect biodiversity.

‣ Most seeds store come from important crop plants.

‣ The genetic diversity of seeds can be increased by crossing crop plants with ancestral varieties, thus the need for saving and storing seeds.

‣ The Svalbard International Seed Vault on the Norwegian island of Spitsbergen, 1000km from the North pole is one of the world’s newest seed vaults.* It accepted its first seeds on the 26th of February

2008.‣ It is built into the side of a sandstone mountain,

surrounded by permafrost and cooled to -18oC. ‣ The vault has meter thick walls, two air locks and

blast-proof doors.