Chapter 1Chapter 1IntroductionIntroduction

Population and Food ProductionPopulation and Food Production

Increasing population needing to be Increasing population needing to be fed will fuel interest in finding and fed will fuel interest in finding and developing new practices to improve developing new practices to improve food productionfood production

Interest in improved soil nutrient Interest in improved soil nutrient management today as world management today as world population growspopulation grows

World PopulationWorld Population

World FoodWorld FoodCurrent world food supplies are Current world food supplies are estimated to be more than adequate estimated to be more than adequate at about 2,500 to 3,000 calories per at about 2,500 to 3,000 calories per day per person. day per person. Nonetheless, hunger is still quite Nonetheless, hunger is still quite common in developing countries common in developing countries because of the lack of resources to because of the lack of resources to purchase and/or redistribute purchase and/or redistribute available foodstuffs. available foodstuffs.

World Food (www.fao.org)World Food (www.fao.org)

Grain SourceGrain Source Cal/kgCal/kg Production, Mt, 2004Production, Mt, 2004 Total CaloriesTotal Calories

Wheat grain, wholeWheat grain, whole 33943394 624093306624093306 2.11802E+152.11802E+15

Cornmeal, wholeCornmeal, whole 36253625 705293226705293226 2.55682E+152.55682E+15

Rice, white, Rice, white, cookedcooked 12191219 608496284608496284 7.41497E+147.41497E+14

SoybeansSoybeans 17341734 206409525206409525 3.57837E+143.57837E+14

PotatoesPotatoes 10921092 328865936328865936 3.59195E+143.59195E+14

TotalTotal 6.13336E+156.13336E+15

World PopulationWorld Population 6,500,000,0006,500,000,000

/ 6.5 billion / / 6.5 billion / 365365

Calories per person/day from grainCalories per person/day from grain 25852585

Beef, Fish, Dairy, PotatoBeef, Fish, Dairy, Potato242 million tons of beef produced in 2002

242 million tons845 calories per pound

pounds of beef5.324E+11

total calories from beef, 2002 calories/person from beef/day4.49878E+14 189.6219

120 million tons of fish produced in 2002

pounds of fish2.64E+11

total calories from fish, 2002 calories/person from fish/day2.22816E+14 93.91612

512.7 million tones of dairy milk produced

pounds of milk1.1264E+12

total calories from milk, 2002 calories/person from milk/day3.26656E+14 137.6843

328 million tons of potatoes produced in 2004

328495 calories per pound

pounds of potatos7.216E+11

total calories from potatoes, 2004 calories/person from potato/day3.57192E+14 150.5551

Beef

Fish

Dairy

Potato

Beef

Fish

Dairy

Potato

POP

6.5 Billion

POP

6.5 Billion

World FoodWorld Food

10-17 calories in animal feed to produce 1 10-17 calories in animal feed to produce 1 calorie of flesh (beef, pork, or chicken). calorie of flesh (beef, pork, or chicken).

So who can afford to invest 10-17 calories So who can afford to invest 10-17 calories of badly needed wheat and corn grain to of badly needed wheat and corn grain to produce 1 calorie?produce 1 calorie?

– Intentional loss of 9 to 16 calories Intentional loss of 9 to 16 calories – Grass fed versus confinement (% grass fed Grass fed versus confinement (% grass fed

beef in the USA?)beef in the USA?)

““With great power comes great responsibility”With great power comes great responsibility”

WikipediaWikipedia

““The Price of Greatness is Responsibility” The Price of Greatness is Responsibility” Winston ChurchillWinston Churchill

"In a democratic world, as in a democratic "In a democratic world, as in a democratic Nation, power must be linked with Nation, power must be linked with responsibility... ." Franklin Delano Rooseveltresponsibility... ." Franklin Delano Roosevelt

““Much will be required of the person Much will be required of the person entrusted with much and still more will be entrusted with much and still more will be demanded of the person entrusted with demanded of the person entrusted with more.” more.”

““Pressure is a privilege (Billie Jean King)Pressure is a privilege (Billie Jean King)Luke 12:48

Ability of the Soil to SupplyAbility of the Soil to SupplyOne important fact remains--soils have finite One important fact remains--soils have finite reserves of the nutrient elements essential for plant reserves of the nutrient elements essential for plant growth. growth. As these nutrients become depleted, by crops that As these nutrients become depleted, by crops that are harvested and shipped for use in other regions, are harvested and shipped for use in other regions, crop yields and food supplies ultimately decrease. crop yields and food supplies ultimately decrease. Loss of plant nutrient elements from the soil cannot Loss of plant nutrient elements from the soil cannot be overcome by genetically engineered new be overcome by genetically engineered new varieties, different tillage systems, new pesticides or varieties, different tillage systems, new pesticides or more water. more water. When soil nutrient depletion occurs, it will be When soil nutrient depletion occurs, it will be important to identify which of the 13 plant food important to identify which of the 13 plant food elements supplied through the soil are deficient, and elements supplied through the soil are deficient, and how to most effectively correct the deficiency. how to most effectively correct the deficiency.

Does soil nutrient management Does soil nutrient management impact the environment?impact the environment?

Concern for protecting, maintaining, and improving the Concern for protecting, maintaining, and improving the environment is a luxury only affluent societies can afford to act environment is a luxury only affluent societies can afford to act upon. upon. Soil erosion and sedimentation in the US increased several fold Soil erosion and sedimentation in the US increased several fold when the more than 100 million acres that are now farmland when the more than 100 million acres that are now farmland were first converted from forest and native grass by were first converted from forest and native grass by cultivation. cultivation. IOWA 3 lbs soil lost/1lb corn grain producedIOWA 3 lbs soil lost/1lb corn grain producedGreatest concern has been for the impact of Greatest concern has been for the impact of excessexcess nutrients nutrients in the environment, particularly nitrate-nitrogen (NO3-N) in in the environment, particularly nitrate-nitrogen (NO3-N) in excess of 10 ppm in drinking water, and water-soluble excess of 10 ppm in drinking water, and water-soluble phosphate levels that promote algae growth in surface water. phosphate levels that promote algae growth in surface water. The challenge in nutrient management is to provide adequate, The challenge in nutrient management is to provide adequate, but not excessive, availability of nutrients to achieve the yield but not excessive, availability of nutrients to achieve the yield (food crops), growth rate (turf), and appearance (ornamentals) (food crops), growth rate (turf), and appearance (ornamentals) of plants we manage.of plants we manage.

What is our general knowledge What is our general knowledge of nutrient management?of nutrient management?

Water, the sole nutrientWater, the sole nutrient

An Englishman, van Helmont (1577-1644), planted a 5-pound willow An Englishman, van Helmont (1577-1644), planted a 5-pound willow tree in a pot containing 200 pounds of soil. After five years he found the tree in a pot containing 200 pounds of soil. After five years he found the tree weighted about 170 pounds and the soil still weighted about 200 tree weighted about 170 pounds and the soil still weighted about 200 pounds. Quite naturally, he concluded that plants obtained their pounds. Quite naturally, he concluded that plants obtained their nutrients from water (since that was the only thing he had added in the nutrients from water (since that was the only thing he had added in the five years). five years).

Earth for plantsEarth for plants

Jethro Tull (1674-1741) observed that plants grew better if the soil they Jethro Tull (1674-1741) observed that plants grew better if the soil they were growing in was “pulverized”. He is credited with the invention of were growing in was “pulverized”. He is credited with the invention of the cultivator and grain drill. Observing that plants grew better in the cultivator and grain drill. Observing that plants grew better in cultivated soil, he concluded the benefit of cultivation was to pulverize cultivated soil, he concluded the benefit of cultivation was to pulverize the soil and make it a “pabulum for the lacteal mouths of roots”. His the soil and make it a “pabulum for the lacteal mouths of roots”. His conclusion was wrong, since we now know plants do not ingest soil conclusion was wrong, since we now know plants do not ingest soil particles, but his contribution of the cultivator and drill were significant. particles, but his contribution of the cultivator and drill were significant.

Air, water, and elements from soil.Air, water, and elements from soil.

Justis von Liebig (1803-1873) “Father of agricultural Justis von Liebig (1803-1873) “Father of agricultural chemistry”, is credited with correctly concluding that chemistry”, is credited with correctly concluding that plants obtained their carbon (C) from carbon dioxide plants obtained their carbon (C) from carbon dioxide (CO2) in the atmosphere and hydrogen (H) and (CO2) in the atmosphere and hydrogen (H) and oxygen (O) from water (H2O). oxygen (O) from water (H2O).

Suggested that phosphorus (P) was necessary for Suggested that phosphorus (P) was necessary for seed formation and that alkaline metal elements seed formation and that alkaline metal elements were necessary to neutralize plant acids. were necessary to neutralize plant acids.

Incorrectly promoted the notion that plants absorb Incorrectly promoted the notion that plants absorb all the ions in soil water indiscriminately and excrete all the ions in soil water indiscriminately and excrete what they don’t need. We now know that plants what they don’t need. We now know that plants preferentially absorb needed ions, but not at the preferentially absorb needed ions, but not at the complete exclusion of unnecessary ions.complete exclusion of unnecessary ions.

Law of the MinimumLaw of the Minimumvon Liebig postulated that the yield of a plant von Liebig postulated that the yield of a plant would be directly proportional to the most limiting would be directly proportional to the most limiting growth factor, even if several other growth growth factor, even if several other growth factors might be limiting to a lesser degree. His factors might be limiting to a lesser degree. His “Law of the Minimum” = water barrel made up of “Law of the Minimum” = water barrel made up of different length barrel staves. Each stave different length barrel staves. Each stave represents the existing level of a growth factor, represents the existing level of a growth factor, such as light, heat, nutrients, etc. The level of such as light, heat, nutrients, etc. The level of water in the barrel (yield) is limited to the height water in the barrel (yield) is limited to the height of the shortest barrel stave (most limiting growth of the shortest barrel stave (most limiting growth factor).factor).

Father of Agricultural Chemistry

SCIENCE-WORLD

Agricultural Experiment StationsAgricultural Experiment StationsEarliest effort to maintain a “field laboratory” for the purpose of Earliest effort to maintain a “field laboratory” for the purpose of conducting scientific research to improve our understanding of how conducting scientific research to improve our understanding of how plants grow and interact with the soil occurred in England in 1843 with plants grow and interact with the soil occurred in England in 1843 with the establishment of the Rothamsted Experiment Station. the establishment of the Rothamsted Experiment Station. (Rothamsted Farms)(Rothamsted Farms)Two scientists, Lawes and Gilbert are credited with this effort. They Two scientists, Lawes and Gilbert are credited with this effort. They concluded from some of their work that plants needed both concluded from some of their work that plants needed both phosphorus (P) and potassium (K), and that non-legumes needed phosphorus (P) and potassium (K), and that non-legumes needed nitrogen (N). They showed that the benefit of fallow (cultivating, but nitrogen (N). They showed that the benefit of fallow (cultivating, but not growing a crop for one season) was from improved N availability not growing a crop for one season) was from improved N availability and that soil fertility could be maintained by addition of chemical and that soil fertility could be maintained by addition of chemical fertilizers.fertilizers.Rothamsted SustainabilityRothamsted SustainabilityIn 1862, shortly after the Rothamsted station was started, the US In 1862, shortly after the Rothamsted station was started, the US congress passed the Morrill Act and established the Department of congress passed the Morrill Act and established the Department of Agriculture. This legislation provided for Land Grant Universities in Agriculture. This legislation provided for Land Grant Universities in every state. These universities, and the associated agricultural every state. These universities, and the associated agricultural experiment stations, were instrumental in the continued search for, experiment stations, were instrumental in the continued search for, and improved understanding of, soil fertility.and improved understanding of, soil fertility.Magruder Plots, 1892-present, Oldest Long-term Continuous Magruder Plots, 1892-present, Oldest Long-term Continuous Winter Wheat Experiment Winter Wheat Experiment

How do plants respond to How do plants respond to growth factors?growth factors?

Initially there is little growth as the plant is in the Initially there is little growth as the plant is in the seedling stage and largely dependent on nutrition seedling stage and largely dependent on nutrition from reserves in the seed. As leaves develop and from reserves in the seed. As leaves develop and capacity to capture sunlight and photosynthesis capacity to capture sunlight and photosynthesis increases, there is a rapid increase in growth or increases, there is a rapid increase in growth or biomass. Growth diminishes as the plant enters biomass. Growth diminishes as the plant enters the reproductive phase and begins seed the reproductive phase and begins seed development, stopping with full maturity. Growth development, stopping with full maturity. Growth (G) may be expressed as a function of each (G) may be expressed as a function of each growth factor (x) bygrowth factor (x) byG = f (x1, x2, x3,….., xn)G = f (x1, x2, x3,….., xn)

[1][1]

Growth

Time

Growth

N UptakeN Uptake

How much N is accumulated at V10 How much N is accumulated at V10 in corn? F5 in winter wheat?in corn? F5 in winter wheat?

http://www.nue.okstate.edu/http://www.nue.okstate.edu/Nitrogen_Uptake.htmNitrogen_Uptake.htm

If the precise cause and effect relationship If the precise cause and effect relationship of each growth factor is known, then the of each growth factor is known, then the growth response to each factor can be growth response to each factor can be mathematically predicted. These mathematically predicted. These mathematical expressions, or models, can mathematical expressions, or models, can be useful in management of plants when be useful in management of plants when the growth factors can be controlled. the growth factors can be controlled.

Use of fertilizers is an example of how we Use of fertilizers is an example of how we might manage nutrients as a growth might manage nutrients as a growth factor, and in turn, plant growth.factor, and in turn, plant growth.

How do plants respond to How do plants respond to growth factors?growth factors?

How do growth factors interact?How do growth factors interact?Whenever a growth factor is limiting, it Whenever a growth factor is limiting, it lessens the plant’s need for other growth lessens the plant’s need for other growth factors. factors. Example: when cool weather limits plant Example: when cool weather limits plant growth there is less demand by the plant growth there is less demand by the plant for nutrients and water. for nutrients and water. Whenever two or more growth factors are Whenever two or more growth factors are limiting and one of these is input at an limiting and one of these is input at an adequate level there will be increased adequate level there will be increased demand for the other growth factorsdemand for the other growth factors

Growth Factor

Nutrient Uptake

Growth FactorsGrowth FactorsWhen a limiting growth factor, such When a limiting growth factor, such as water, is removed by installing an as water, is removed by installing an irrigation system it will generally irrigation system it will generally improve plant response to fertilizer improve plant response to fertilizer used to correct nutrient deficiencies used to correct nutrient deficiencies that are also limiting growth that are also limiting growth

Irrigated

Non-irrigated

Increasing nutrient availability (fertilizer use)

Yield

Useful models for nutrient Useful models for nutrient management?management?

German scientist Mitscherlich, and the US scientist Bray. German scientist Mitscherlich, and the US scientist Bray. Mitscherlich law of diminishing returns.Mitscherlich law of diminishing returns.In 1906, E.A. Mitscherlich published work showing yields In 1906, E.A. Mitscherlich published work showing yields diminished more with each added increment of a growth-diminished more with each added increment of a growth-limiting factor. Mitscherlich expressed the relationship limiting factor. Mitscherlich expressed the relationship mathematically asmathematically as dy/dx = (A - y) cdy/dx = (A - y) cWhere:Where:1. dy/dx is the change in yield 1. dy/dx is the change in yield y1 from an increment (x) y1 from an increment (x) addition of a single limiting growth factor, or nutrient.addition of a single limiting growth factor, or nutrient.2. A is the maximum yield when all growth factors are at their 2. A is the maximum yield when all growth factors are at their optimum.optimum.3. y is the yield initially or from the last addition of the limiting 3. y is the yield initially or from the last addition of the limiting nutrient.nutrient.4. c is a proportionally constant or efficiency factor.4. c is a proportionally constant or efficiency factor.

MitscherlichMitscherlichIf a growth factor is deficient (not necessarily the If a growth factor is deficient (not necessarily the most limiting as identified in Liebig’s “Law of the most limiting as identified in Liebig’s “Law of the Minimum”), increasing the level of the growth factor Minimum”), increasing the level of the growth factor present can increase yield. present can increase yield. The The yield increase will be proportional to the yield increase will be proportional to the difference between maximum yield obtained by difference between maximum yield obtained by adding the growth factor and yield at the given level adding the growth factor and yield at the given level of the growth factorof the growth factor. . When the deficient growth factor is first added, the When the deficient growth factor is first added, the difference in yield without any deficiency (A) and difference in yield without any deficiency (A) and yield (y) supported by the current level of the growth yield (y) supported by the current level of the growth factor is at its largest value. factor is at its largest value.

y2

y1

A-y for x1 and y1 Yield

(y)

Increasing level of growth factor (nutrient, x)

x1 x2 x3 x4 x5 x6 x7 x8 x9 x10

A-y for x2 and y2

Law of Diminishing ReturnsLaw of Diminishing ReturnsBecause the crop response was always less from each Because the crop response was always less from each successive increment of growth factor, the relationship was successive increment of growth factor, the relationship was also referred to as the “Law of diminishing returns”. also referred to as the “Law of diminishing returns”. If a growth factor is limiting, growth response will be If a growth factor is limiting, growth response will be greatest for the first increment added and least for the last greatest for the first increment added and least for the last increment added. increment added. This is not unlike our response to satisfying a hunger for ice This is not unlike our response to satisfying a hunger for ice cream or a thirst for water. The first spoonful of ice cream cream or a thirst for water. The first spoonful of ice cream or swallow of water will usually be the most satisfying. or swallow of water will usually be the most satisfying. Each additional spoonful of ice cream or swallow of water Each additional spoonful of ice cream or swallow of water will be less satisfying than the previous, until at last there is will be less satisfying than the previous, until at last there is no satisfaction from additional ice cream or water. no satisfaction from additional ice cream or water.

y2

y1

A-y for x1 and y1 Yield

(y)

Increasing level of growth factor (nutrient, x)

x1 x2 x3 x4 x5 x6 x7 x8 x9 x10

A-y for x2 and y2

MitscherlichMitscherlichResearchers found that the Mitscherlich Researchers found that the Mitscherlich response could be used to describe yield, at response could be used to describe yield, at any deficient level of a growth factor, as a any deficient level of a growth factor, as a percentage of the maximum yield possible. percentage of the maximum yield possible. When this is done, the level of the deficient When this is done, the level of the deficient growth factor can be expressed as a percent growth factor can be expressed as a percent sufficiency levelsufficiency level

Yie

ld (

% o

f M

axim

um)

Increasing level of growth factor (nutrient, x)

x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 x10

100

80

60

40

MitscherlichMitscherlichWithout any external inputs of the growth factor x, the yield is Without any external inputs of the growth factor x, the yield is about 50 % of maximum. about 50 % of maximum. Whatever the level of the growth factor when it is present at Whatever the level of the growth factor when it is present at the x0 amount, it is only about 50 % sufficient. the x0 amount, it is only about 50 % sufficient. The x1 level of growth factor is about 70 % sufficientThe x1 level of growth factor is about 70 % sufficientThe x2 level of growth factor is about 80 % sufficientThe x2 level of growth factor is about 80 % sufficientThe x3 level of growth factor is about 85 % sufficientThe x3 level of growth factor is about 85 % sufficient““Diminishing returns” the increase in each percentage Diminishing returns” the increase in each percentage sufficiency results in smaller and smaller increases in yield sufficiency results in smaller and smaller increases in yield (e.g. 20, 10, and 5)(e.g. 20, 10, and 5)Mitscherlich response model is also referred to as the “Percent Mitscherlich response model is also referred to as the “Percent Sufficiency Response” or more commonly as the “Percent Sufficiency Response” or more commonly as the “Percent Sufficiency Concept”. Sufficiency Concept”. For immobile nutrientsFor immobile nutrients

Yie

ld (

% o

f M

axim

um)

Increasing level of growth factor (nutrient, x)

x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 x10

100

80

60

40

How does the Mitscherlich Sufficiency How does the Mitscherlich Sufficiency Concept work in practice?Concept work in practice?

An example of how the Mitscherlich Sufficiency Concept is applied to An example of how the Mitscherlich Sufficiency Concept is applied to plant growth-nutrient management situations is illustrated by plant growth-nutrient management situations is illustrated by considering the following hypothetical data for wheat grain yields as considering the following hypothetical data for wheat grain yields as influenced by available soil phosphorus (P). influenced by available soil phosphorus (P).

Soil test P (STP) is expressed as pp2m, which is approximately equal Soil test P (STP) is expressed as pp2m, which is approximately equal to pounds per acre, and yield is in units of bushels per acre.to pounds per acre, and yield is in units of bushels per acre.

Yield (bu/acre) Soil Test P (pp2m) Percent Sufficiency 10 0 25 18 10 45 32 20 80 36 40 90 40 65 100 40 90 100

Relationship of wheat grain yield, soil test P and Relationship of wheat grain yield, soil test P and percent sufficiency of soil P.percent sufficiency of soil P.

How can 0 pp2m be 25% sufficient?

How does this help in the “real world”?How does this help in the “real world”?By using this relationship of soil test P and percent sufficiency By using this relationship of soil test P and percent sufficiency of soil P, we can estimate the impact of growing plants in a P of soil P, we can estimate the impact of growing plants in a P deficient environment if we have some reliable estimate of deficient environment if we have some reliable estimate of maximum yield. maximum yield. Most experienced crop or plant managers have some Most experienced crop or plant managers have some knowledge of what a realistic yield goal or yield maximum for knowledge of what a realistic yield goal or yield maximum for the growing environment should be. the growing environment should be. If the yield maximum is 50 bu/acre and the soil test P is 30, If the yield maximum is 50 bu/acre and the soil test P is 30, then the yield without added P will be 85 % of 50, or 42.5 then the yield without added P will be 85 % of 50, or 42.5 bu/acre (soil test P of 30 is 85 % sufficient).bu/acre (soil test P of 30 is 85 % sufficient).

0

10

20

30

40

50

60

70

80

90

100

110

0 10 20 30 40 50 60 70 80 90 100

Soil Test P (pp2m)

So

il P

Su

ffic

ien

cy

(%

)

Bray “Nutrient Mobility ConceptBray “Nutrient Mobility Concept

In 1954, the US scientist Bray proposed that plant In 1954, the US scientist Bray proposed that plant response to availability of soil nutrients should be response to availability of soil nutrients should be strongly influenced by how easily the nutrient is moved strongly influenced by how easily the nutrient is moved with water in the soil. with water in the soil. He considered nutrients as relatively mobile or He considered nutrients as relatively mobile or immobile in the soil. immobile in the soil. On that basis, he stated that On that basis, he stated that as the mobility of a as the mobility of a nutrient in soil decreases the amount needed in the nutrient in soil decreases the amount needed in the soil increases from a value equal to the product of soil increases from a value equal to the product of maximum yield and optimum plant composition to a maximum yield and optimum plant composition to a constantconstant. . In other words, for a nutrient that is 100% mobile the In other words, for a nutrient that is 100% mobile the amount required is simply a product of yield and plant amount required is simply a product of yield and plant composition. composition.

Bray’s mobility concept was a combination of the Bray’s mobility concept was a combination of the Mitscherlich percent sufficiency concept and Liebig’s Mitscherlich percent sufficiency concept and Liebig’s Law of the Minimum. Law of the Minimum. Bray showed that Liebig’s Law of the Minimum Bray showed that Liebig’s Law of the Minimum concept applied for concept applied for mobile nutrientsmobile nutrients like NO3-N, like NO3-N, and that Mitscherlich’s percent sufficiency concept and that Mitscherlich’s percent sufficiency concept worked for worked for immobile nutrientsimmobile nutrients like P and K. like P and K. In Liebig’s theory of plant response, if all nutrients In Liebig’s theory of plant response, if all nutrients were adequate except one (only one short stave in were adequate except one (only one short stave in the barrel), then yield would increase in direct the barrel), then yield would increase in direct proportion to increasing the availability of the proportion to increasing the availability of the deficient nutrient (straight-line response). deficient nutrient (straight-line response).

Bray “Nutrient Mobility ConceptBray “Nutrient Mobility Concept

Bray illustrated the difference in how plants extracted mobile Bray illustrated the difference in how plants extracted mobile and immobile nutrients from the soil by showing that mobile and immobile nutrients from the soil by showing that mobile nutrients would be extracted from a large volume of soil (root nutrients would be extracted from a large volume of soil (root system sorption zone) and immobile nutrients from a much system sorption zone) and immobile nutrients from a much smaller volume of soil (root surface sorption zone). smaller volume of soil (root surface sorption zone).

Bray “Nutrient Mobility ConceptBray “Nutrient Mobility Concept

Mobile Nutrient (root system sorption zone)

Immobile Nutrient (root surface sorption zone)

BrayBrayBray’s concept of how plants responded to soil nutrient Bray’s concept of how plants responded to soil nutrient availability could be represented as a straight-line response availability could be represented as a straight-line response for a nutrient that is 100% mobile in the soil and a for a nutrient that is 100% mobile in the soil and a curvilinear response for relatively immobile nutrientscurvilinear response for relatively immobile nutrientsComplete mobility probably does not exist in soils, except Complete mobility probably does not exist in soils, except for water itself, which is an important consideration. for water itself, which is an important consideration.

Mitscherlich, or Bray (immobile nutrient)

Liebig, or Bray (mobile nutrient)

Nutrient Availability

% Yield

100

How does Bray’s concept apply in How does Bray’s concept apply in practice?practice?

When plants are grown close together, as in an When plants are grown close together, as in an intensive agriculture, it becomes clear that the intensive agriculture, it becomes clear that the volumes of soil that each plant extracts mobile volumes of soil that each plant extracts mobile nutrients from may overlap while soil volumes nutrients from may overlap while soil volumes supplying immobile nutrients for plants do notsupplying immobile nutrients for plants do not

Soil volume where plants compete for mobile nutrients.

Distance, cm 35 45 84 99 137Distance, cm 35 45 84 99 137

Mobility of NMobility of N

http://www.nue.okstate.edu/Spatial_N_Variability.htm

Long term N-P-K Experiments(1969-2004)Long term N-P-K Experiments(1969-2004)

Mobility of NMobility of N

Impact of among-plant competition Impact of among-plant competition for mobile nutrientsfor mobile nutrients

Plants will compete among each other for mobile nutrients if Plants will compete among each other for mobile nutrients if they are spaced close enough together. they are spaced close enough together. As cropping systems increase yield by planting more densely, As cropping systems increase yield by planting more densely, there will be a direct increase in demand by the crop for the there will be a direct increase in demand by the crop for the mobile nutrient(s).mobile nutrient(s).if both plants are going to grow normally it will be necessary to if both plants are going to grow normally it will be necessary to add more of the mobile nutrient to eliminate the competition add more of the mobile nutrient to eliminate the competition among plants. among plants.

Impact of among-Impact of among-plant competition for plant competition for immobile nutrientsimmobile nutrients

When plants are growing close together there is no competition among When plants are growing close together there is no competition among plants for extracting immobile nutrients from the soil. This is because the plants for extracting immobile nutrients from the soil. This is because the plant root is extracting immobile nutrients from an extremely small volume plant root is extracting immobile nutrients from an extremely small volume of soil, often only the soil within a millimeter or two from the root surface. of soil, often only the soil within a millimeter or two from the root surface. As plants grow, they obtain additional supplies of an immobile nutrient by As plants grow, they obtain additional supplies of an immobile nutrient by developing more roots that will explore new volumes of soil. However, developing more roots that will explore new volumes of soil. However, even with a large number of hair-roots developing for each plant, there is even with a large number of hair-roots developing for each plant, there is seldom found any common soil volume being explored by hair-roots of seldom found any common soil volume being explored by hair-roots of adjacent plants. adjacent plants. Immobile nutrients are extracted from only a fraction of the total surface Immobile nutrients are extracted from only a fraction of the total surface soil volume.soil volume.If a soil is 100 % sufficient in supplying an immobile nutrient for a dry-land If a soil is 100 % sufficient in supplying an immobile nutrient for a dry-land crop yield goal of 60 bushels corn per acre, then it will also be 100 % crop yield goal of 60 bushels corn per acre, then it will also be 100 % sufficient if the field is irrigated and the yield goal can be increased to 180 sufficient if the field is irrigated and the yield goal can be increased to 180 bushels per acre. bushels per acre.

Sufficiency: INDEPENDENT OF YIELD LEVELSufficiency: INDEPENDENT OF YIELD LEVEL

Combined effects of mobile and Combined effects of mobile and immobile nutrient deficienciesimmobile nutrient deficiencies

The most limiting of the mobile nutrients will determine the maximum The most limiting of the mobile nutrients will determine the maximum possible yield (as in Liebig’s “Law of the Minimum”). possible yield (as in Liebig’s “Law of the Minimum”). Deficiencies of immobile nutrients reduce the potential yield of a site, or Deficiencies of immobile nutrients reduce the potential yield of a site, or field, by a “percent sufficiency” factor, and identify the ultimate potential field, by a “percent sufficiency” factor, and identify the ultimate potential yield. yield. In non-irrigated production systems, water is usually the most limiting In non-irrigated production systems, water is usually the most limiting mobile nutrient (hydrogen) source. mobile nutrient (hydrogen) source. Environment will support a yield of 5 ton per acre of forage and all Environment will support a yield of 5 ton per acre of forage and all nutrients are adequate except one mobile nutrient and one immobile nutrients are adequate except one mobile nutrient and one immobile nutrient. nutrient. If the amount of mobile nutrient present will only support a yield of 3 ton, If the amount of mobile nutrient present will only support a yield of 3 ton, then 3 ton per acre becomes the maximum possible yield. then 3 ton per acre becomes the maximum possible yield. If the If the imimmobile nutrient were present at a 75 % sufficiency level then the mobile nutrient were present at a 75 % sufficiency level then the “adjusted” (both nutrients deficient) maximum possible yield would be only “adjusted” (both nutrients deficient) maximum possible yield would be only 75 % of 3 ton, or 2.25 ton. 75 % of 3 ton, or 2.25 ton. Correcting only the mobile nutrient deficiency would raise the possible Correcting only the mobile nutrient deficiency would raise the possible yield to 3.75 ton (5 ton x 0.75) and correcting only the immobile nutrient yield to 3.75 ton (5 ton x 0.75) and correcting only the immobile nutrient deficiency would raise the possible yield to 3 ton (3 ton x 1.00).deficiency would raise the possible yield to 3 ton (3 ton x 1.00).

When two immobile nutrients are deficient, the When two immobile nutrients are deficient, the expected yield will be the product of their percent expected yield will be the product of their percent sufficiencies times the maximum possible yield. sufficiencies times the maximum possible yield. Example, if one immobile nutrient is 90 % Example, if one immobile nutrient is 90 % sufficient and another is 80 % sufficient, their sufficient and another is 80 % sufficient, their combined effect will be that the expected yield combined effect will be that the expected yield will be 72 % (.90 x .80) of the maximum possible will be 72 % (.90 x .80) of the maximum possible yield.yield.

If one is 70% sufficient, and another 50% If one is 70% sufficient, and another 50% Expected YIELD = Expected YIELD =

Models used to describe yield Models used to describe yield response to nutrientsresponse to nutrients

Models used by scientists and general agronomists today Models used by scientists and general agronomists today are often simple mathematical expressions of yield in are often simple mathematical expressions of yield in relation to nutrient availability, but may also be very relation to nutrient availability, but may also be very complex. complex. Simple models are created using correlation-regression Simple models are created using correlation-regression analysis that results in output of a regression equation, or analysis that results in output of a regression equation, or model. Examples of these models are illustrated by model. Examples of these models are illustrated by considering simple linear and polynomial models. considering simple linear and polynomial models. Linear response model?Linear response model?The linear response is described by the general expressionThe linear response is described by the general expressiony = a + bxy = a + bxwhere y is yieldwhere y is yielda is a constant (y-intercept)a is a constant (y-intercept)b is the slope of the line b is the slope of the line x is the level of nutrient inputx is the level of nutrient input

y = 0.266x + 21.443

R2 = 0.998

0

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60

0 20 40 60 80 100 120

Nitrogen Rate (lb N/acre)

Whe

at Y

ield

(bu

/acr

e)

Polynomial modelsPolynomial modelsPolynomial models have two or more terms where a constant (like Polynomial models have two or more terms where a constant (like

the slope in the linear model) is multiplied times the value the slope in the linear model) is multiplied times the value representing the level of available nutrient. representing the level of available nutrient.

y = a + b1x + b2x2y = a + b1x + b2x2

Terms similar to those defined for the linear model. Terms similar to those defined for the linear model. Two coefficients (b1 and b2). Two coefficients (b1 and b2). Coefficients describe the slope of the line, which is not constant, Coefficients describe the slope of the line, which is not constant, but instead changes with change in the value of x. The but instead changes with change in the value of x. The magnitude of the value for b1 identifies how strong yield magnitude of the value for b1 identifies how strong yield responds linearly to the nutrientresponds linearly to the nutrient

y = -2.06E-03x2 + 3.62E-01x + 2.53E+01

R2 = 9.91E-01

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25

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45

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N Rate (lb N/acre)

Yie

ld (

bu

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Importance of crop response Importance of crop response modelsmodels

Help identify the potential yield for a particular crop and locationHelp identify the potential yield for a particular crop and locationHow much of specific nutrient might be required to support that yield. How much of specific nutrient might be required to support that yield. 40 bushels/acre wheat grain can be produced with 80 pounds/acre. 40 bushels/acre wheat grain can be produced with 80 pounds/acre. Average yield without N fertilizer is about 25 bushels/acre, so the Average yield without N fertilizer is about 25 bushels/acre, so the addition of 80 pounds of N fertilizer is associated with increasing yield addition of 80 pounds of N fertilizer is associated with increasing yield by 15 bushels/acre. by 15 bushels/acre. Realistic costs for N are about $0.50/lb and wheat has a value of at Realistic costs for N are about $0.50/lb and wheat has a value of at least $6.00/bushel. Thus, for a cost of $40.00 for N (80 lb x $0.50/lb) least $6.00/bushel. Thus, for a cost of $40.00 for N (80 lb x $0.50/lb) there is an increase in crop value of $90.00 (15 bushels x there is an increase in crop value of $90.00 (15 bushels x $6.00/bushel). 10 yrs ago $16 and $45.$6.00/bushel). 10 yrs ago $16 and $45.These ASSUME all other growth factors are at a constant or non-These ASSUME all other growth factors are at a constant or non-limiting, and do not consider 2 simultaneouslylimiting, and do not consider 2 simultaneously

y = -2.06E-03x2 + 3.62E-01x + 2.53E+01

R2 = 9.91E-01

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N Rate (lb N/acre)

Yie

ld (

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Nutrient interaction responsesNutrient interaction responses

When one growth factor is supplied at a higher level, it influences When one growth factor is supplied at a higher level, it influences how plants will respond to a second, limiting growth factor. how plants will respond to a second, limiting growth factor. Plants supplied with more water responded to fertilizer differently. Plants supplied with more water responded to fertilizer differently. Interaction between two nutrients may be either positive or Interaction between two nutrients may be either positive or negative. negative. Sometimes the addition of the two nutrients has no interactive Sometimes the addition of the two nutrients has no interactive effect.effect.General polynomial expression to identify interaction responses General polynomial expression to identify interaction responses for N and P may be given asfor N and P may be given as y = a + b1N + b2P + b3NPy = a + b1N + b2P + b3NPwhere y is yield, a is the y-intercept, b1,2,3 are coefficients where y is yield, a is the y-intercept, b1,2,3 are coefficients describing the magnitude of response from associated inputs of N, describing the magnitude of response from associated inputs of N, P, and the interactive effect (NP) of N and P.P, and the interactive effect (NP) of N and P.

b3 = 0

N P N N P P

b3 > 0 b3 < 0

YieldYield

YieldYield

YieldYield

b3 = 0

N P N N P P

b3 > 0 b3 < 0

YieldYield

YieldYield

YieldYield

Yield response to N and P when there Yield response to N and P when there is no NxP interaction is no NxP interaction

P Availability N Availability 0 20 40 60

Yield 0 10 12 14 16 20 12 14 16 18 40 14 16 18 20 60 16 18 20 22

b3 = 0

N P N N P P

b3 > 0 b3 < 0

YieldYield

YieldYield

YieldYield

Yield response to N and P when there Yield response to N and P when there is a positive NxP interaction is a positive NxP interaction

b3 = 0

N P N N P P

b3 > 0 b3 < 0

YieldYield

YieldYield

YieldYield

P Availability N Availability 0 20 40 60

Yield 0 10 12 14 16 20 12 16 20 24 40 14 20 26 32 60 16 24 32 40

Yield response to N and P when there Yield response to N and P when there is a negative NxP interaction is a negative NxP interaction

b3 = 0

N P N N P P

b3 > 0 b3 < 0

YieldYield

YieldYield

YieldYield

P Availability N Availability 0 20 40 60

Yield 0 10 12 14 16 20 12 13 14 15 40 14 14 13 12 60 16 15 12 10

What evidence do we have that What evidence do we have that the mobility concept works?the mobility concept works?

Natural distribution of plants in relation to availability of the mobile Natural distribution of plants in relation to availability of the mobile nutrient water, as influenced by annual rainfall. nutrient water, as influenced by annual rainfall. Desert environment:Desert environment: sparse spacing, plants will not compete for available sparse spacing, plants will not compete for available water even in the driest years. water even in the driest years. The volume of soil that receives, stores and then provides water for plants The volume of soil that receives, stores and then provides water for plants is relatively large for each plant because this volume is only occasionally is relatively large for each plant because this volume is only occasionally refilled (rain is scarce)refilled (rain is scarce)Tropical environment: dense spacing, water not limiting Tropical environment: dense spacing, water not limiting Volume of soil serving each plant is refilled frequently (rains often), & does Volume of soil serving each plant is refilled frequently (rains often), & does not need to be very large.not need to be very large.

a.

b.

Desert Plant CompetitionDesert Plant Competition

Tropical PlantsTropical Plants

What can we infer from the mobility What can we infer from the mobility concept?concept?

Mobile and immobile nutrients must be managed differently. Mobile and immobile nutrients must be managed differently. Requirement for mobile nutrients is directly related to yield (or Requirement for mobile nutrients is directly related to yield (or growth rate).growth rate).Requirement for immobile nutrients is related to the Requirement for immobile nutrients is related to the concentration at the root surface, and not related to yield goal.concentration at the root surface, and not related to yield goal.In-season deficiencies of mobile nutrients can be corrected by In-season deficiencies of mobile nutrients can be corrected by soil addition, soil addition, In-season fertilization of immobile nutrient is usually of no In-season fertilization of immobile nutrient is usually of no benefit.benefit.Availability of mobile nutrients, in the root system sorption Availability of mobile nutrients, in the root system sorption zone (or bulk soil), changes dramatically during the growing zone (or bulk soil), changes dramatically during the growing season and from one season to another depending on the season and from one season to another depending on the balance between external nutrient input (fertilization) and yield balance between external nutrient input (fertilization) and yield (harvest).(harvest).

What can we infer from the mobility What can we infer from the mobility concept?concept?

Soil availability of immobile nutrients, in the bulk soil, is Soil availability of immobile nutrients, in the bulk soil, is relatively constant during and among seasons (e.g. soil test relatively constant during and among seasons (e.g. soil test values for immobile nutrients should not change much from values for immobile nutrients should not change much from one year to the next, whereas soil test values for mobile one year to the next, whereas soil test values for mobile nutrients may change greatly from one year to the next.).nutrients may change greatly from one year to the next.).Mobile nutrients may be lost by leaching in high rainfall Mobile nutrients may be lost by leaching in high rainfall environments environments Leaching has little impact on availability of immobile Leaching has little impact on availability of immobile nutrients.nutrients.Accurate assessment of soil supply of mobile nutrients must Accurate assessment of soil supply of mobile nutrients must include surface and subsoil measurement. include surface and subsoil measurement. Availability of immobile nutrients in the subsoil is of little Availability of immobile nutrients in the subsoil is of little value in meeting crop needs.value in meeting crop needs.Plant response to fertilizer additions of immobile nutrients Plant response to fertilizer additions of immobile nutrients will be maximized by placing the fertilizer where roots will will be maximized by placing the fertilizer where roots will be growing.be growing.

SummarySummaryManagement of soil nutrients required by plants is Management of soil nutrients required by plants is important because plants are the foundation of our important because plants are the foundation of our food supply. food supply. Projected doubling of world population in the next 50 Projected doubling of world population in the next 50 years will double the demand for a barely adequate years will double the demand for a barely adequate food supply. food supply. Depletion of soil nutrients by food harvesting will Depletion of soil nutrients by food harvesting will need to be replenished from external sources need to be replenished from external sources (fertilizers) by ever increasing amounts. (fertilizers) by ever increasing amounts. Understanding how plants respond to soil nutrient Understanding how plants respond to soil nutrient deficiencies and the input of fertilizer forms will be deficiencies and the input of fertilizer forms will be critical to efficient food production and minimizing its critical to efficient food production and minimizing its impact on the environment.impact on the environment.

SummarySummaryAvailable soil nutrients are most commonly under the control of Available soil nutrients are most commonly under the control of farmers, crop production managers, and other non-food plant farmers, crop production managers, and other non-food plant managers. managers. Plant response to correcting deficient soil nutrients can be Plant response to correcting deficient soil nutrients can be generally described by considering whether nutrients are mobile generally described by considering whether nutrients are mobile or immobile in the soil. or immobile in the soil. Mobile soil nutrients, like water, impose the first limit to plant Mobile soil nutrients, like water, impose the first limit to plant growth. growth. Maximum crop yield is determined by the most limiting of any Maximum crop yield is determined by the most limiting of any deficient mobile nutrients. deficient mobile nutrients. Deficiencies of immobile nutrients impose a secondary yield limit Deficiencies of immobile nutrients impose a secondary yield limit as a percentage of the maximum yield possible. as a percentage of the maximum yield possible. The ease with which computers have allowed evaluation of how The ease with which computers have allowed evaluation of how crops respond to changing levels of nutrients and other growth crops respond to changing levels of nutrients and other growth factors, has led to the generation of many types of models, or factors, has led to the generation of many types of models, or mathematical expressions describing the responses. These mathematical expressions describing the responses. These models help managers estimate yield potential and the degree to models help managers estimate yield potential and the degree to which their crop may respond to increases in nutrient input.which their crop may respond to increases in nutrient input.

Movement of Nutrients to the RootsMovement of Nutrients to the Roots

Mass FlowMass Flow

DiffusionDiffusion

Contact Exchange? (Root Contact Exchange? (Root Interception)Interception)

UMN PresentationUMN Presentationhttp://www.soils.umn.edu/academics/http://www.soils.umn.edu/academics/classes/soil3416/lecture3.htmclasses/soil3416/lecture3.htm

Monocots versus dicots

Mass FlowMass FlowNutrients in soil solution move to the Nutrients in soil solution move to the roots, driven mostly by plant transpirationroots, driven mostly by plant transpirationMechanism is considered movement to Mechanism is considered movement to roots by mass flow. In some cases, this is roots by mass flow. In some cases, this is an adequate explanation for all the plants an adequate explanation for all the plants requirements of nutrients. requirements of nutrients.

Mass flow to roots is driven by plant Mass flow to roots is driven by plant transpiration, however, mass flow is not a transpiration, however, mass flow is not a major pathway of P movement to plants. major pathway of P movement to plants.

DiffusionDiffusion - the flow from higher to lower - the flow from higher to lower concentrationsconcentrations

Ficks Law of diffusionD is the diffusion constant SI unit m2s-1L

CDA

t

m

Examples of Diffusion:Examples of Diffusion:• Drop of ink in water

• Perfume diffusing across room.

Root InterceptionRoot InterceptionRoots occupy 1-3% of the soil volume of Roots occupy 1-3% of the soil volume of the root zone. By this mechanism, plants the root zone. By this mechanism, plants are thought to take up nutrients that they are thought to take up nutrients that they encounter as roots grow into unexplored encounter as roots grow into unexplored soil volume. soil volume.

In truth, plant roots grow in the voids In truth, plant roots grow in the voids between soil particles, either avoiding the between soil particles, either avoiding the solids or pushing them aside, and plants solids or pushing them aside, and plants take up nutrients from solution rather than take up nutrients from solution rather than from solids. from solids.