Chapter 5Chapter 5

SOIL AND FERTILIZER NSOIL AND FERTILIZER N

DefinitionsDefinitionsOrganic-N:Organic-N: N that is bound in organic material in the form of amino acids and N that is bound in organic material in the form of amino acids and proteins.proteins.Mineral-N:Mineral-N: N that is not bound in organic material, examples are ammonium and N that is not bound in organic material, examples are ammonium and nitrate-Nnitrate-NAmmonia:Ammonia: A gaseous form of N (NH3).A gaseous form of N (NH3).Ammonium:Ammonium: A positively charged ion of N (NH4+).A positively charged ion of N (NH4+).Diatomical-N:Diatomical-N: N in the atmosphere (N2)N in the atmosphere (N2)Nitrate-N:Nitrate-N: A negatively charged ion of N (NO3-).A negatively charged ion of N (NO3-).Mineralization :Mineralization : The release of N in the inorganic form (ammonia) from organic bound N. The release of N in the inorganic form (ammonia) from organic bound N. As organic matter is decayed ammonia quickly reacts with soil water to form ammonium, As organic matter is decayed ammonia quickly reacts with soil water to form ammonium, thus the first measurable product of mineralization isthus the first measurable product of mineralization isusually ammonium-N.usually ammonium-N.Immobilization:Immobilization: Assimilation of inorganic N (NH4+and NO3- ) by microorganisms.Assimilation of inorganic N (NH4+and NO3- ) by microorganisms.Nitrification:Nitrification: Oxidation of ammonium N to nitrate N by autotrophic microorganisms in Oxidation of ammonium N to nitrate N by autotrophic microorganisms in an aerobic environment.an aerobic environment.Denitrification:Denitrification: Reduction of nitrate N to nitrous oxide (N2O) or diatomical N gases by Reduction of nitrate N to nitrous oxide (N2O) or diatomical N gases by heterotrophic microorganisms in an anaerobic environment.heterotrophic microorganisms in an anaerobic environment.Autotrophic:Autotrophic: A broad class of microorganisms that obtains its energy from the A broad class of microorganisms that obtains its energy from the oxidation of inorganic compounds (or sunlight) and carbon from carbon dioxide.oxidation of inorganic compounds (or sunlight) and carbon from carbon dioxide.Heterotrophic:Heterotrophic: A broad class of microorganisms that obtains its energy and carbon from A broad class of microorganisms that obtains its energy and carbon from preformed organic nutrients.preformed organic nutrients.Volatilization:Volatilization: Loss of gaseous N from soil, usually after N has been transformed from Loss of gaseous N from soil, usually after N has been transformed from ionic or non-gaseous chemical forms. ionic or non-gaseous chemical forms.

Where does all the N come from?Where does all the N come from?Nitrogen exists in some form or another throughout our Nitrogen exists in some form or another throughout our environment. It is no wonder all soils and most bodies of environment. It is no wonder all soils and most bodies of water contain some N. water contain some N. Atmosphere is 78% N in the form of the diatomic gas NAtmosphere is 78% N in the form of the diatomic gas N22. . The amount of NThe amount of N22 above the earth’s surface has been above the earth’s surface has been calculated to be about 36,000 ton/acre. calculated to be about 36,000 ton/acre. Soils contain about 2,000 pounds of N/acre (12-inch depth) Soils contain about 2,000 pounds of N/acre (12-inch depth) for each 1 % of organic matter content. for each 1 % of organic matter content. NN22 is chemically stable is chemically stableConsiderable energy must be expended to transform it to Considerable energy must be expended to transform it to chemical forms that plants and animals can use. chemical forms that plants and animals can use. Common presence in all living organisms of amino-N in the Common presence in all living organisms of amino-N in the form of amino acids and proteins.form of amino acids and proteins.

Web Elements

15N15N (mass 30)15N14N (mass 29)14N14N (mass 28)

Magnet

N2 gas (ionized in the source, + charge)

repeller plate (electric discharge)

accelerated beam

Beams move in this direction with increased voltage

Beams move in this direction with decreased voltage

The voltage in the source can be changed prior to reaching the repeller to work with heavier or lighter isotopes (carbon).

Newer instruments are set up to change the current onthe magnet for different elements instead of accelerating voltage (applied to everything in the source)

Anhydrous AmmoniaAnhydrous Ammonia1 ton of anhydrous ammonia fertilizer requires 1 ton of anhydrous ammonia fertilizer requires 33,500 cubic feet of natural gas. 33,500 cubic feet of natural gas. 1000 Btu’s / cubic foot 1000 Btu’s / cubic foot This cost represents most of the costs associated This cost represents most of the costs associated with manufacturing anhydrous ammonia. with manufacturing anhydrous ammonia. When natural gas prices are $2.50 per thousand When natural gas prices are $2.50 per thousand cubic feet, the natural gas used to manufacture 1 cubic feet, the natural gas used to manufacture 1 ton of anhydrous ammonia fertilizer costs $83.75. ton of anhydrous ammonia fertilizer costs $83.75. If the price rises to $7.00 per thousand cubic feet of If the price rises to $7.00 per thousand cubic feet of natural gas, the cost of natural gas used in natural gas, the cost of natural gas used in manufacturing that ton of anhydrous ammonia rises manufacturing that ton of anhydrous ammonia rises to $234.50, an increase to the manufacturer of to $234.50, an increase to the manufacturer of $150.75$150.75Natural Gas: 75-85% of the cost of anhydrousNatural Gas: 75-85% of the cost of anhydrous

Canada

Natural Gas

Current costs

N Prices, 11/2007N Prices, 11/2007

N-P-KN-P-K $/ton$/ton $/lb N$/lb N

UreaUrea 46-0-046-0-0 $430$430 0.460.46

Ammonium Nitrate NH4NO3Ammonium Nitrate NH4NO3 33-0-033-0-0 $$

UAN UAN urea ammonium nitrateurea ammonium nitrate 28-0-028-0-0 $305/ton$305/ton 0.540.54

Anhydrous AmmoniaAnhydrous Ammonia 82-0-082-0-0 $432/ton$432/ton 0.260.26

DAPDAP 18-46-018-46-0 $490/ton$490/ton

UAN 10.67 lbs/gal UAN 10.67 lbs/gal (1 part urea, 1 part ammonium nitrate, 1 part water)(1 part urea, 1 part ammonium nitrate, 1 part water)

AA 5.15 lbs/galAA 5.15 lbs/gal

Fertilizer Prices, 1990-2008Fertilizer Prices, 1990-2008

How is N2 transformed?How is N2 transformed?NaturalNatural N fixation.N fixation. First transformations of N2 to plant available-N would have been a result of First transformations of N2 to plant available-N would have been a result of oxidation to oxides of N, which are or become NOoxidation to oxides of N, which are or become NO33

--, by lightning during , by lightning during thunderstorms. thunderstorms. ““Fixation” used to identify the transformation of NFixation” used to identify the transformation of N22 to plant available-N, and to plant available-N, and lightening is believed to account for the addition to soils of about 5-10 kg/ha/year. lightening is believed to account for the addition to soils of about 5-10 kg/ha/year. Since plants could not function without water, and that water is supplied to plants Since plants could not function without water, and that water is supplied to plants by rainfall (often associated with lightening), the earliest plant forms assimilated by rainfall (often associated with lightening), the earliest plant forms assimilated NONO33-N as their source of N. -N as their source of N. Amount of N2 fixed by lightning may be estimated at about 150,000,000 tons/year, Amount of N2 fixed by lightning may be estimated at about 150,000,000 tons/year, assuming the average is about 6 kg/ha and only about ½ of the earths 51 billion assuming the average is about 6 kg/ha and only about ½ of the earths 51 billion hectares land surface receives sufficient rainfall to be considered. hectares land surface receives sufficient rainfall to be considered. Relatively insignificant compared to the seasonal N requirement for dense plant Relatively insignificant compared to the seasonal N requirement for dense plant populations.populations.Free-living and rhizobium microorganisms reduce NFree-living and rhizobium microorganisms reduce N22 to amino-N and incorporate it to amino-N and incorporate it into living cell components. into living cell components. Azotobacter, clostridium, and blue-green algae (cyanobacteria) are examples of Azotobacter, clostridium, and blue-green algae (cyanobacteria) are examples of microorganisms that are capable of transforming Nmicroorganisms that are capable of transforming N22 to organically bound N, to organically bound N, independent of a host plant. independent of a host plant. Rhizobium associated with N assimilation by legumes account for transfer of about Rhizobium associated with N assimilation by legumes account for transfer of about 90,000,000 tons of N from N2 to biological-N annually. By comparison, worldwide 90,000,000 tons of N from N2 to biological-N annually. By comparison, worldwide manufacture of N fertilizers by industrial fixation of Nmanufacture of N fertilizers by industrial fixation of N22 is estimated to be about 90 is estimated to be about 90 to 100,000,000 tons N annually.to 100,000,000 tons N annually.

What happens to “fixed” NWhat happens to “fixed” N

Biologically fixed N accumulates on the soil surface as dead plant material Biologically fixed N accumulates on the soil surface as dead plant material and animal excrement. and animal excrement. During favorable conditions, heterotrophic microorganisms decay these During favorable conditions, heterotrophic microorganisms decay these materials as a means of satisfying their carbon needs. materials as a means of satisfying their carbon needs. N is conserved and C is lost through respiration as CON is conserved and C is lost through respiration as CO22, resulting in a , resulting in a narrowing of the ratio of C to N. narrowing of the ratio of C to N. During this process organic material becomes increasingly more difficult During this process organic material becomes increasingly more difficult for the microorganisms to decay. for the microorganisms to decay. Eventually the material becomes so resistant to decay that the decay Eventually the material becomes so resistant to decay that the decay process almost stops. At this point the ratio of C to N is about 10:1, the process almost stops. At this point the ratio of C to N is about 10:1, the material no longer has any of the morphological features of the original material no longer has any of the morphological features of the original tissue (leaves, stems, etc.) and may be categorically termed humus.tissue (leaves, stems, etc.) and may be categorically termed humus.

N mineralization.N mineralization. During the decay process, and before the organic During the decay process, and before the organic material becomes humus, there is a release of N from organically bound material becomes humus, there is a release of N from organically bound forms to ammonia (NHforms to ammonia (NH33). Because NH). Because NH33 has a strong affinity for water, and has a strong affinity for water, and the decay process only occurs in moist environments, ammonium (NHthe decay process only occurs in moist environments, ammonium (NH44

++) is ) is immediately formed according to the following equilibrium reaction:immediately formed according to the following equilibrium reaction:

NH3 + H2O = = = NH4+ + OH-

MineralizationMineralization

In most environments where decay In most environments where decay occurs the entire N transformed from occurs the entire N transformed from organic-N will be present initially as organic-N will be present initially as NHNH44

++. The process of transforming . The process of transforming organic-N to inorganic (mineral) N is organic-N to inorganic (mineral) N is called N mineralizationcalled N mineralization

organic-N = = = = heterotrophic microbes = = = = NH4+

MineralizationMineralizationMineralization is favored by conditions that Mineralization is favored by conditions that support higher plant growth ( e.g., moist, support higher plant growth ( e.g., moist, warm, aerobic environment containing warm, aerobic environment containing adequate levels of essential mineral adequate levels of essential mineral nutrients), organic material that is easy to nutrients), organic material that is easy to decay, and material that is rich enough in decay, and material that is rich enough in N that it exceeds microorganism N N that it exceeds microorganism N requirements. requirements. Just as plant growth and development Just as plant growth and development takes time, significant mineralization takes time, significant mineralization usually requires 2 to 4 weeks under moist, usually requires 2 to 4 weeks under moist, warm conditions.warm conditions.

What happens to NHWhat happens to NH44-N -N

Immobilization. Immobilization. Decay of plant residue Decay of plant residue does not always result in mineralization of does not always result in mineralization of N. N. When residue does not contain enough N When residue does not contain enough N to meet the needs of microbes decaying it, to meet the needs of microbes decaying it, the microbes will utilize N in the residue the microbes will utilize N in the residue andand any additional mineral-N (NH4+ and any additional mineral-N (NH4+ and NO3-) present in the soil. NO3-) present in the soil. This process of transforming mineral-N to This process of transforming mineral-N to organic-N is called immobilization, and is organic-N is called immobilization, and is the opposite of mineralization.the opposite of mineralization.

NH4+ and NO3

- == == microbes = == = organic-N

Immobilization Immobilization Immobilization is favored by conditions Immobilization is favored by conditions similar to those for mineralization, except similar to those for mineralization, except that residue is poor in N (higher ratio of C that residue is poor in N (higher ratio of C to N). to N).

When conditions are favorable for When conditions are favorable for immobilization, and non-legume crops immobilization, and non-legume crops (turf, wheat, corn, etc.) are growing in the (turf, wheat, corn, etc.) are growing in the same soil, microbes will successfully same soil, microbes will successfully compete for the available N resulting in compete for the available N resulting in crop N deficiencies. crop N deficiencies.

Cation exchange.Cation exchange. As the concentration of NHAs the concentration of NH44

++ in the soil increases, NH in the soil increases, NH44++ will successfully will successfully

compete for exchange sites on clay and humus occupied by other cations. compete for exchange sites on clay and humus occupied by other cations. This adsorption is responsible for NHThis adsorption is responsible for NH44

++-N being immobile in the soil.-N being immobile in the soil.

Volatilization.Volatilization. If the environment is basic enough (high concentration of OH-) the If the environment is basic enough (high concentration of OH-) the equilibrium will favor the reaction to the left. equilibrium will favor the reaction to the left. When this occurs there is the potential for loss of N by volatilization of NHWhen this occurs there is the potential for loss of N by volatilization of NH33 gas. gas. Volatilization is most likely to happen in high pH soils, Volatilization is most likely to happen in high pH soils, Also occurs in acid soils when NHAlso occurs in acid soils when NH44

++ accumulates from decay of N rich crop accumulates from decay of N rich crop residue or animal manures on the soil surface. residue or animal manures on the soil surface. This condition is present in range and pasture situations as well as crop land This condition is present in range and pasture situations as well as crop land where residue is not incorportated (no-till or minimum till). Volatilization is where residue is not incorportated (no-till or minimum till). Volatilization is also promoted by surface drying, as removing Halso promoted by surface drying, as removing H22O from reaction (1) shifts O from reaction (1) shifts the equilibrium in favor of the reaction to the left. the equilibrium in favor of the reaction to the left.

NH3 + H2O = = = NH4+ + OH-

Plant UptakePlant UptakePlant uptakePlant uptake. When higher plants are actively . When higher plants are actively growing they will absorb NHgrowing they will absorb NH44

++. When plant . When plant absorption proceeds at about the same rate as absorption proceeds at about the same rate as mineralization there will be little or no mineralization there will be little or no accumulation of NHaccumulation of NH44

++ in the soil. in the soil.

However, since NHHowever, since NH44++ is not mobile in the soil, in is not mobile in the soil, in

order for all the NHorder for all the NH44++ to be absorbed it would be to be absorbed it would be

necessary for plant roots to be densely necessary for plant roots to be densely distributed throughout the surface soil. distributed throughout the surface soil. Condition represented by dense plant cover in Condition represented by dense plant cover in tropical ecosystems and in turfgrass tropical ecosystems and in turfgrass environments. environments.

NitrificationNitrificationAmmonium-N may be biologically Ammonium-N may be biologically transformed to NOtransformed to NO33

-- in a two-step in a two-step process called nitrification. process called nitrification. Nitrification proceeds at about the Nitrification proceeds at about the same rate and under similar same rate and under similar conditions as mineralization and conditions as mineralization and immobilization, but has an absolute immobilization, but has an absolute requirement for Orequirement for O22

2 NH4+ + 3 O2 === nitrosomonas = 2 NO2

- + 4 H+ + 2 H2O

NitriteNitriteNitrite (NONitrite (NO22

--) does not accumulate in ) does not accumulate in well-aerated soils because the well-aerated soils because the second step occurs at a faster rate second step occurs at a faster rate than the first, and so it is quickly than the first, and so it is quickly transformed to NOtransformed to NO33

--. Because NO. Because NO22-- is is

not normally found in soils it is toxic not normally found in soils it is toxic to plants at concentration of about to plants at concentration of about only 1-2 ppm.only 1-2 ppm.

NO2- + O2 = == nitrobacter = 2 NO3

-

SUMSUM

2 NH4+ + 4 O2 ==== == === == = 2 NO3

- + 4 H+ + 2 H2O

NO2- + O2 = == nitrobacter = 2 NO3

-

2 NH4+ + 3 O2 === nitrosomonas = 2 NO2

- + 4 H+ + 2 H2O

Production of H+Production of H+

The nitrification process is often The nitrification process is often viewed as a cause of soil acidification viewed as a cause of soil acidification because of the Hbecause of the H++ shown as a shown as a product. product.

2 moles of H+ are produced for 2 moles of H+ are produced for every mole of NHevery mole of NH44

++ that is nitrified. that is nitrified.

However, if the OHHowever, if the OH-- generated by N generated by N mineralization is considered then for mineralization is considered then for the process of mineralization and the process of mineralization and nitrification…nitrification…

Organic-N = == NH3 + H2O = == NH4+ + OH-

NH4+ + 2 O2 == === == === == NO3

- + 2 H+ + H2O

And the sum affect of these two processes, with NH3 and NH4+ as

intermediates not shown in the final reaction occuring in a moist, aerobic environment would be…..

Organic-N = == mineralization == = nitrification NO3- + H+

N and AcidityN and AcidityWhen organic forms of N are the source of When organic forms of N are the source of NONO33

-- used by plants, only one mole of H used by plants, only one mole of H++, , or acidity, is produced from each mole of or acidity, is produced from each mole of N taken up by the plants. N taken up by the plants.

As NOAs NO33- - is metabolized and reduced to is metabolized and reduced to

amino-N, the Hamino-N, the H++ is either neutralized or is either neutralized or assimilated in the process and use of assimilated in the process and use of organic-N or amino-N by plants is not an organic-N or amino-N by plants is not an acidifying process.acidifying process.

NH4 and NO3NH4 and NO3Nitrification transforms plant available-N from a soil-Nitrification transforms plant available-N from a soil-immobile form (NHimmobile form (NH44

++) to a soil-mobile form (NO) to a soil-mobile form (NO33--). ).

Important in arid and semi-arid environments, where Important in arid and semi-arid environments, where considerable water movement in soil is necessary to supply considerable water movement in soil is necessary to supply the needs of plants (large root system sorption zone). the needs of plants (large root system sorption zone). Only small concentrations (10-20 ppm) of NOOnly small concentrations (10-20 ppm) of NO33-N are -N are necessary in a large volume of soil to meet the N needs of necessary in a large volume of soil to meet the N needs of plants that may have to grow rapidly during a short rainy plants that may have to grow rapidly during a short rainy season. season. In arid and semi-arid soils, that usually are calcareous and In arid and semi-arid soils, that usually are calcareous and have pH of 7.5 or greater, N accumulated over time as a have pH of 7.5 or greater, N accumulated over time as a result of mineralization would be at high risk of loss by result of mineralization would be at high risk of loss by volatilization as NHvolatilization as NH33. . As somewhat of a safeguard against NHAs somewhat of a safeguard against NH33 being volatilized, being volatilized, acidity produced by nitrification neutralizes OH- resulting acidity produced by nitrification neutralizes OH- resulting from mineralization and tends to acidify the environment as from mineralization and tends to acidify the environment as long as NO3- is accumulating in the soil.long as NO3- is accumulating in the soil.

What happens to NOWhat happens to NO33

Immobilization.Immobilization. As in the case of NH As in the case of NH44 resulting from resulting from mineralization, NOmineralization, NO33

-- is most likely to be immobilized by is most likely to be immobilized by microorganisms that exist where the NOmicroorganisms that exist where the NO33

-- is present. is present. Immobilization will occur when organic matter being decayed Immobilization will occur when organic matter being decayed does not contain enough N to meet the needs of the active does not contain enough N to meet the needs of the active microbes. microbes. Plant uptakePlant uptake. When higher plants are actively growing they . When higher plants are actively growing they will absorb NOwill absorb NO33

--. . Movement and absorption will be promoted by mass flow in Movement and absorption will be promoted by mass flow in relation to transpiration of water by plants. relation to transpiration of water by plants. Nitrate may accumulate in soils when it is produced from Nitrate may accumulate in soils when it is produced from mineralization and nitrification during periods when plants are mineralization and nitrification during periods when plants are not actively growing. not actively growing. These conditions may periodically exist in arid and semi-arid These conditions may periodically exist in arid and semi-arid environments during seasons when plants are not growing or environments during seasons when plants are not growing or are sparsely distributed and soil conditions favor microbial are sparsely distributed and soil conditions favor microbial activity.activity.

NO3NO3Leaching.Leaching. Nitrate-N is subject to loss from the root Nitrate-N is subject to loss from the root environment with water percolating through the soil. This environment with water percolating through the soil. This is a significant problem when soils are porous (sandy) in is a significant problem when soils are porous (sandy) in high rainfall or irrigated condition. high rainfall or irrigated condition. It is not believed to be a problem in arid and semi-arid, non-It is not believed to be a problem in arid and semi-arid, non-irrigated soils.irrigated soils.

Denitrification.Denitrification. When soils become anaerobic (e.g., there When soils become anaerobic (e.g., there is little or no Ois little or no O22 present) and conditions favor microbial present) and conditions favor microbial activity, some microorganisms will satisfy their need for activity, some microorganisms will satisfy their need for oxygen by stripping it from NOoxygen by stripping it from NO33

--. As a result, gaseous forms . As a result, gaseous forms of N (nitrous oxide, Nof N (nitrous oxide, N22O, and NO, and N22) are produced that may be ) are produced that may be lost from the soil to the atmosphere above. The lost from the soil to the atmosphere above. The generalized process may be represented as:generalized process may be represented as:

2 NO3- - O2 = = 2 NO2

- - O2 = = 2 NO- - ½ O2 = = N2O - ½ O2 == N2

MicroorganismsMicroorganismsMicroorganisms responsible for denitrification are Microorganisms responsible for denitrification are generally believed to be heterotrophic facultative generally believed to be heterotrophic facultative anaerobes. anaerobes. They use organic matter as a carbon source and They use organic matter as a carbon source and can function in either aerobic or anaerobic can function in either aerobic or anaerobic environments. environments. Denitrification is promoted in soils that contain Denitrification is promoted in soils that contain NONO33

--, organic matter that is easy to decay, and , organic matter that is easy to decay, and where Owhere O22 has been depleted by respiration (root has been depleted by respiration (root or microbial) or displaced by water (waterlogged). or microbial) or displaced by water (waterlogged). In addition to the problem of N loss, the In addition to the problem of N loss, the intermediate NOintermediate NO22

-- may accumulate to toxic levels may accumulate to toxic levels when the process is incompletewhen the process is incomplete

How are these N transformations How are these N transformations interrelated?interrelated?

The product of one reaction is a reactant for anotherThe product of one reaction is a reactant for anotherThis interrelationship is illustrated in the N-cycle This interrelationship is illustrated in the N-cycle It is important to consider how change in the concentration of one It is important to consider how change in the concentration of one component of the cycle (e.g., NH4+) can have a ‘ripple’ effect (like a component of the cycle (e.g., NH4+) can have a ‘ripple’ effect (like a pebble thrown into a pond) throughout the cycle pebble thrown into a pond) throughout the cycle – temporarily affecting plant uptake of Ntemporarily affecting plant uptake of N– immobilization by microbesimmobilization by microbes– exchangeable basesexchangeable bases– NitrificationNitrification

or it may only affect one process, as in the case when NH4+ is produced as or it may only affect one process, as in the case when NH4+ is produced as a result of mineralization occurring at the surface of a moist, alkaline (high a result of mineralization occurring at the surface of a moist, alkaline (high pH) soil where it is quickly lost by volatilization when the surface dries in pH) soil where it is quickly lost by volatilization when the surface dries in an afternoon. an afternoon. As easy as it may be to illustrate the interrelationship of these processes in As easy as it may be to illustrate the interrelationship of these processes in the cycle, it is another matter (difficult) to understand how they influence the cycle, it is another matter (difficult) to understand how they influence our management of N to grow plants.our management of N to grow plants.

DENITRIFICATION

RESIDUE

SOIL ORGANIC MATTER

NH4+ + OH- HOH + NH3

HARVEST TO CITY N2, N2O,

NH3

LEACHING

VOLATILIZATION

N2O, N2 - O2 NO2

- - O2

VOLATILIZATION

MINERALIZATION

FERTILIZERS

C:N > 30:1 IMMOBILIZATION

C:N < 20:1 MINERALIZATION

NO3-

IFICATION

+O2FICATION

NO2-

IFICATION

+O2FICATION

NITRIFICATION

CO2 levels in the atmosphere have increased from 260 to 380 ppm in the last 150 years

Global Warming?Global Warming?

What % of the increase (100 ppm) has What % of the increase (100 ppm) has been due to cultivation?been due to cultivation?

CO2 levels in the atmosphere have increased from 260 to 380 ppm in the last 150 years

Global Warming?Global Warming?

What % of the increase (100 ppm) has What % of the increase (100 ppm) has been due to cultivation?been due to cultivation?

25 ppm or 25%

N ConservationN ConservationImportant aspect of the N-cycle is that it is Important aspect of the N-cycle is that it is nature’s way of conserving N. nature’s way of conserving N. In nature there is likely seldom more than In nature there is likely seldom more than a few (1-5) ppm of N present in the form of a few (1-5) ppm of N present in the form of either NHeither NH44

++ or NO or NO33--. .

Thus, although there are processes Thus, although there are processes (leaching and volatilization) that can (leaching and volatilization) that can remove excess N from the natural system, remove excess N from the natural system, these are not likely to be active except in these are not likely to be active except in extreme situations.extreme situations.

Mineralization-immobilizationMineralization-immobilization

Occurs within a growing season and influences Occurs within a growing season and influences plant growth and the need for in-season N plant growth and the need for in-season N management. management. When organic matter has a C:N ratio > than 30, When organic matter has a C:N ratio > than 30, NONO33 initially present in the soil is consumed initially present in the soil is consumed (immobilized) by microbes during the decay (immobilized) by microbes during the decay process. process. As a product of the decay process (respiration) As a product of the decay process (respiration) COCO22 content in the soil gradually increases. content in the soil gradually increases. Because C is lost and N is conserved, the C:N Because C is lost and N is conserved, the C:N ratio becomes narrower until it is finally < 20, at ratio becomes narrower until it is finally < 20, at which point nitrate begins to accumulate which point nitrate begins to accumulate (mineralization). (mineralization).

How does the N-cycle influence How does the N-cycle influence commercial plant productioncommercial plant production

When plants are harvested and removed from an area, N is When plants are harvested and removed from an area, N is also removed from the soil of that area. also removed from the soil of that area. Large removals occur with annual cereal grain productionLarge removals occur with annual cereal grain productionCultivation stimulates N mineralization and nitrification, Cultivation stimulates N mineralization and nitrification, resulting in gradual depletion of soil organic-N and soil resulting in gradual depletion of soil organic-N and soil organic matter. organic matter. Many prairie soils of the central Great Plains and corn belt Many prairie soils of the central Great Plains and corn belt regions of the US have lost one-third to three-fourths of regions of the US have lost one-third to three-fourths of their original organic matter content as a consequence. their original organic matter content as a consequence. The use of legume crops in rotation with non-legumes and The use of legume crops in rotation with non-legumes and the N fertilizer industry grew out of a need to replace the the N fertilizer industry grew out of a need to replace the depleted soil N.depleted soil N.

Mineralization of N in legume residueMineralization of N in legume residueBecause legumes seldom lack N in their growth and Because legumes seldom lack N in their growth and development, their residue is rich in N (high protein), development, their residue is rich in N (high protein), C:N ratio is < 20:1 and N mineralization will be favored. C:N ratio is < 20:1 and N mineralization will be favored. When non-legumes, like corn, are rotated with a legume, such When non-legumes, like corn, are rotated with a legume, such as soybeans (common in the corn belt of the US), soybean as soybeans (common in the corn belt of the US), soybean residue may contribute 30 to 50 lb N/acre to the corn needsresidue may contribute 30 to 50 lb N/acre to the corn needsSoybean-corn system, without N, yields about the same as the Soybean-corn system, without N, yields about the same as the 40 lb N rate for the corn-corn system.40 lb N rate for the corn-corn system.

0

50

100

150

200

250

0 40 80 120 160 200 240Fertilizer-N rate (lb/acre)

Yie

ld (

bu

/acr

e)

corn-cornsoybean-corn

RotationsRotationsCorn planted following alfalfa…Corn planted following alfalfa…Perennial legume has usually been growing for 4 to 10 years, Perennial legume has usually been growing for 4 to 10 years, Accumulated residue, and existing growth when the alfalfa was Accumulated residue, and existing growth when the alfalfa was destroyed by cultivation, provides a large amount of N-rich destroyed by cultivation, provides a large amount of N-rich organic residue. organic residue. Sufficient to meet N needs of the first year of corn production Sufficient to meet N needs of the first year of corn production following alfalfa. following alfalfa. As the residual contribution from alfalfa becomes less and less As the residual contribution from alfalfa becomes less and less each year, there is an increasing corn response to the application each year, there is an increasing corn response to the application of fertilizer-N. of fertilizer-N. Response of non-legumes to mineralization of N from legume Response of non-legumes to mineralization of N from legume residue is commonly observedresidue is commonly observedResult is entirely due to the high protein or N-rich residue of the Result is entirely due to the high protein or N-rich residue of the legume. legume. Inter-seeding legumes into non-legume forages will also increase Inter-seeding legumes into non-legume forages will also increase crude protein content of the mixture. crude protein content of the mixture. Not a result of the legume somehow providing available plant N Not a result of the legume somehow providing available plant N directly to adjacent non-legume plants. directly to adjacent non-legume plants.

Legume residue: narrow C:N ratio because it was grown in a N-rich environmentLegume residue: narrow C:N ratio because it was grown in a N-rich environmentN not limitingN not limitingN-rich residue is created whenever non-legumes are grown in a N-rich environment as a result of fertilizer N-rich residue is created whenever non-legumes are grown in a N-rich environment as a result of fertilizer input at levels that exceed crop requirement. input at levels that exceed crop requirement.

Response is not linear, as might be predicted for a mobile soil nutrient according to Bray’s mobility concept. Response is not linear, as might be predicted for a mobile soil nutrient according to Bray’s mobility concept.

Why? Why? Some of the fertilizer-N is immobilized when the soil is enriched with mineral NSome of the fertilizer-N is immobilized when the soil is enriched with mineral NSome of the mineral N is lost from the system because of the mineral N enrichment. Some of the mineral N is lost from the system because of the mineral N enrichment.

N-cycle is effective in conserving N in a natural ecosystem, when large quantities of N are introduced N-cycle is effective in conserving N in a natural ecosystem, when large quantities of N are introduced When excesses exist, system is not as efficientWhen excesses exist, system is not as efficientSystem should be viewed as one that System should be viewed as one that buffersbuffers against mineral N changes and one that against mineral N changes and one that leaksleaks when mineral N is when mineral N is present in excess. present in excess. Most efficient N fertilization program would be one that most closely resembles the natural supply of N from Most efficient N fertilization program would be one that most closely resembles the natural supply of N from the soil to the growing plants. the soil to the growing plants. This system would add minute amounts of mineral N to the soil at a location where the plant could absorb it This system would add minute amounts of mineral N to the soil at a location where the plant could absorb it each day. Such a system is usually not economically feasible because of the high cost of daily application.each day. Such a system is usually not economically feasible because of the high cost of daily application.

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Mineralization of N from non-Mineralization of N from non-legume residuelegume residue

N ResponseN Response

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3rd yr corn corn-corn

Mineralization of Soil-NMineralization of Soil-NCorn yield of about 70 bushels/acre when no fertilizer-N is Corn yield of about 70 bushels/acre when no fertilizer-N is applied to a field that grows corn year after year, without a applied to a field that grows corn year after year, without a legume in rotation. legume in rotation. N to support this yield is believed to come primarily from N to support this yield is believed to come primarily from soil-N in the organic fraction, that is, N mineralized since soil-N in the organic fraction, that is, N mineralized since the last crop was grown and during the growing season. the last crop was grown and during the growing season. For this example the mineralized, or non-fertilizer N, For this example the mineralized, or non-fertilizer N, supports about one-third of the maximum yield. supports about one-third of the maximum yield. Less difference between fertilized and unfertilized yields for Less difference between fertilized and unfertilized yields for dryland than for irrigated systems in arid and semi-arid dryland than for irrigated systems in arid and semi-arid environments. environments. Large differences in plant response between fertilized and Large differences in plant response between fertilized and unfertilized areas are common, for example, in irrigated turf unfertilized areas are common, for example, in irrigated turf where clippings are removed.where clippings are removed.

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Chlorophyll Content

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Midfield bermudagrass turf response to fertilizer N (rates are equivalent to 0.5, 1, 1.5, 2, 4, and 6 lb N/1000 square feet. From Howell, OSU M.S. thesis, 1999).

Characteristics of N fertilizer responsesCharacteristics of N fertilizer responsesNitrogen Use EfficiencyNitrogen Use Efficiency

No-N treatment to be slightly more than one-half (60 %) of the maximum yields of N No-N treatment to be slightly more than one-half (60 %) of the maximum yields of N fertilized plots, when averaged over the past 30 yearsfertilized plots, when averaged over the past 30 years

Yield response is non-linear. Yield response is non-linear. Maximum yield: 42 bushels/acre at 80 lb N/acre rate, Maximum yield: 42 bushels/acre at 80 lb N/acre rate, Supports “rule of thumb” of 2 lb N required per bushel of wheat yield. Supports “rule of thumb” of 2 lb N required per bushel of wheat yield. Nitrogen Use Efficiency: measure of the percentage of fertilizer applied that is Nitrogen Use Efficiency: measure of the percentage of fertilizer applied that is

removed in the harvest (grain in this situation).removed in the harvest (grain in this situation).

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NUE = (grain N uptake treated – grain N uptake check)Rate of N applied

NUENUENUE = 50 % at the lowest input of fertilizer NUE = 50 % at the lowest input of fertilizer

Decreases to about 35 % at maximum Decreases to about 35 % at maximum yield. yield.

Low NUE is believed to result from Low NUE is believed to result from increasingly large “excesses” of mineral N increasingly large “excesses” of mineral N being present because all fertilizer was being present because all fertilizer was applied preplant, without knowledge of applied preplant, without knowledge of yield potential or supply of non-fertilizer N.yield potential or supply of non-fertilizer N.

How profitable is it to fertilize for How profitable is it to fertilize for maximum yield? maximum yield?

Using 31-year Using 31-year averageaverage yield response data profitability of each 20-lb/acre yield response data profitability of each 20-lb/acre addition of N can be examined by considering different prices (value) for addition of N can be examined by considering different prices (value) for wheat and fertilizer-N (cost). wheat and fertilizer-N (cost). Using $0.25/lb N cost: most profitable rate may easily vary by 20 lb N/acre Using $0.25/lb N cost: most profitable rate may easily vary by 20 lb N/acre depending upon value of the wheat. depending upon value of the wheat. Since the 31-year average yield response data fit a quadratic response Since the 31-year average yield response data fit a quadratic response model, the law of diminishing returns applies, and the last 20 lb N model, the law of diminishing returns applies, and the last 20 lb N increment that increases yield (60 to 80 lb) always has less economic increment that increases yield (60 to 80 lb) always has less economic return. return. When the value of wheat is $2.00/bushel the maximum economic rate of N When the value of wheat is $2.00/bushel the maximum economic rate of N is 60 lb/acre, even though the maximum grain yield is from 80 lb N/acre.is 60 lb/acre, even though the maximum grain yield is from 80 lb N/acre.

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Fertilizer N rate (lb/acre)

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ize

r c

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$3.50 $3.00 $2.50 $2.00

How variable are crop N needs from year to year? How variable are crop N needs from year to year?

EONR versus YieldEONR versus YieldExperiment 502Experiment 502

Since crop N needs are related to concentration of N in the Since crop N needs are related to concentration of N in the crop and yield (Bray concept for mobile nutrients), it is crop and yield (Bray concept for mobile nutrients), it is important to reliably estimate what the yield will be in order important to reliably estimate what the yield will be in order to determine N needs. to determine N needs. Maximum yield from fertilized plots is found to be highly Maximum yield from fertilized plots is found to be highly variable from year-to-year, and tends to increase slightly variable from year-to-year, and tends to increase slightly over time (0.24 bu/acre/year). This variability in maximum over time (0.24 bu/acre/year). This variability in maximum yield, together with the variability in supply of non-fertilizer yield, together with the variability in supply of non-fertilizer N, makes it difficult to estimate how much fertilizer-N N, makes it difficult to estimate how much fertilizer-N should be applied in a given year.should be applied in a given year.

Indexing N responsesIndexing N responsesVariability in crop requirements for N fertilizer from year-to-Variability in crop requirements for N fertilizer from year-to-year is most easily seen when maximum yields of the year is most easily seen when maximum yields of the fertilized plots are divided by the yields of unfertilized plots fertilized plots are divided by the yields of unfertilized plots for the same years. for the same years. Response index (RI) Response index (RI) When the RI is near 1.0, there is little response to N fertilizer When the RI is near 1.0, there is little response to N fertilizer and its application may have questionable economic value. and its application may have questionable economic value. RI is large (e.g., >1.5) there is great economic opportunity RI is large (e.g., >1.5) there is great economic opportunity from fertilizing. It is important to note that most farmer’s from fertilizing. It is important to note that most farmer’s fields do not have a history of zero fertilizer-N input, and a fields do not have a history of zero fertilizer-N input, and a smaller response index should be expected if an unfertilized smaller response index should be expected if an unfertilized area is compared to that with adequate N.area is compared to that with adequate N.

Estimating fertilizer-N needs Estimating fertilizer-N needs from yield goalsfrom yield goals

Conventional approachConventional approachYield goal, that is a realistic yield expectation, Yield goal, that is a realistic yield expectation, and then multiply this yield (bushels/acre) times 2 and then multiply this yield (bushels/acre) times 2 to get the total N requirement. to get the total N requirement. Avg yield of the last 5 years + 20%Avg yield of the last 5 years + 20%Attempts to assure adequate N for years of better Attempts to assure adequate N for years of better than average yields than average yields Good approach to N fertilizer management, and Good approach to N fertilizer management, and easy to carry out easy to carry out Does not take into consideration the year-to-year Does not take into consideration the year-to-year variability in maximum yield obtained and in how variability in maximum yield obtained and in how much of that yield may be supported by non-much of that yield may be supported by non-fertilizer N.fertilizer N.

Year to Year VariabilityYear to Year VariabilityImportance of considering year-to-year variability in maximum Importance of considering year-to-year variability in maximum

yield and plant available non-fertilizer N is found by yield and plant available non-fertilizer N is found by comparing yields for 1994 and1995. comparing yields for 1994 and1995.

Unfertilized yields for these years were 11 bushels (1994) and Unfertilized yields for these years were 11 bushels (1994) and 29 bushels (1995). 29 bushels (1995).

Maximum yield obtained by adding fertilizer-N was about 45 Maximum yield obtained by adding fertilizer-N was about 45 bushels for each year. bushels for each year.

Yield response to N fertilizer is quite different, 34 bushels in Yield response to N fertilizer is quite different, 34 bushels in 1994 and only 16 bushels in 1995. 1994 and only 16 bushels in 1995.

In 2000, unfertilized yield was 41 bushels/acre and the In 2000, unfertilized yield was 41 bushels/acre and the fertilized yield was only 47 bushels/acre (60 lb N/acre)fertilized yield was only 47 bushels/acre (60 lb N/acre)

If year-to-year variability in maximum yields and supply of If year-to-year variability in maximum yields and supply of non-fertilizer N can be managed, such a strategy has the non-fertilizer N can be managed, such a strategy has the potential to pay good economic benefits.potential to pay good economic benefits.

LossLossApproximately $10/acre/year loss in unrealized yield or Approximately $10/acre/year loss in unrealized yield or excess fertilizer application when 80 lb N/acre is applied each excess fertilizer application when 80 lb N/acre is applied each year instead of the optimum rate for maximum yield. year instead of the optimum rate for maximum yield. 1994 to 1999, Maximum yield obtained from 100 lb N/acre 1994 to 1999, Maximum yield obtained from 100 lb N/acre rate. Approximately the requirement calculated for a yield rate. Approximately the requirement calculated for a yield goal identified by the average yield plus 20%. goal identified by the average yield plus 20%. Loss associated with this rate applied each of the 31 years Loss associated with this rate applied each of the 31 years would be about $15/acre compared to the rate of N that just would be about $15/acre compared to the rate of N that just matched the requirement for maximum yield each year.matched the requirement for maximum yield each year.

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)

Yld Loss Excs N Loss Total LossAve Loss/ac/yr = $9.77

How can uncertainty be managed? How can uncertainty be managed? 1. Apply full rate to a strip running the length of the field (N Rich Strip)1. Apply full rate to a strip running the length of the field (N Rich Strip)2. Small amount applied to the rest of the field2. Small amount applied to the rest of the fieldFor crops whose management allows for in-season adjustment of N needs by fertilization. For crops whose management allows for in-season adjustment of N needs by fertilization. N-Rich Strip evaluated during the growing season and used to guide N FertilizationN-Rich Strip evaluated during the growing season and used to guide N FertilizationNo differences: no need for NNo differences: no need for NN-Rich Strip is markedly different from the rest of the field: N neededN-Rich Strip is markedly different from the rest of the field: N needed

Rate of fertilizer: Difference in crop conditions between the N-Rich Strip and the rest of the field. Rate of fertilizer: Difference in crop conditions between the N-Rich Strip and the rest of the field.

Turfgrass: N Rich Strip in inconspicuous areas Turfgrass: N Rich Strip in inconspicuous areas N-Rich Strip Observed over time and used as a guide for future fertilization. N-Rich Strip Observed over time and used as a guide for future fertilization.

OSU ResearchOSU Research

How does the sensor work?How does the sensor work?

Optical sensors provide an index of biomass and active chlorophyll (normalized difference vegetative index, or NDVI) from ratios of near infrared and red light reflectance from the crop Optical sensors provide an index of biomass and active chlorophyll (normalized difference vegetative index, or NDVI) from ratios of near infrared and red light reflectance from the crop canopy. canopy.

Predicting YieldPredicting Yield

Response IndexResponse Index

Nitrogen Fertilization Optimization AlgorithmNitrogen Fertilization Optimization Algorithm

Sensor Based N Rate CalculatorSensor Based N Rate Calculator

Sources of N fertilizers and how are Sources of N fertilizers and how are they managed?they managed?

Animal waste. Animal waste. Early civilizations observed increased Early civilizations observed increased yields resulting from application of animal waste to fields yields resulting from application of animal waste to fields where they had domesticated plants for food production. where they had domesticated plants for food production.

NRCSNRCS

History of ManureHistory of Manure

Animal waste, including sewage sludge (biosolids) from Animal waste, including sewage sludge (biosolids) from cities, continues to be an important source of N and other cities, continues to be an important source of N and other nutrients for improving nutrient availability in soils. nutrients for improving nutrient availability in soils. On a macro-scale, N management could be improved and N On a macro-scale, N management could be improved and N could be better conserved if all animal waste would be could be better conserved if all animal waste would be returned to the fields that produced the feed and food for returned to the fields that produced the feed and food for animals and humans consuming it. animals and humans consuming it.

ANIMAL WASTE AND BIOSOLIDS

SOIL ORGANIC MATTER

NH4+ + OH- HOH + NH3

HARVEST TO CITY N2

MINERALIZATION

FERTILIZERS

C:N > 30:1 IMMOBILIZATION

NO3-

IFICATION

+O2FICATION

NO2-

IFICATION

+O2FICATION

NITRIFICATION

RESIDUE

Waste ManagementWaste ManagementIncreasing # of people in citiesIncreasing # of people in cities

Confinement of animals that produce meat to feed themConfinement of animals that produce meat to feed them

Resultant concentration of animal waste and biosolids to fewer Resultant concentration of animal waste and biosolids to fewer locations on the landscape. locations on the landscape.

As waste accumulates to larger and larger amounts, society becomes As waste accumulates to larger and larger amounts, society becomes more sensitive to its existence and measures are taken to manage it more sensitive to its existence and measures are taken to manage it for beneficial uses (e.g. crop production) and decreased impact on the for beneficial uses (e.g. crop production) and decreased impact on the environment. environment. Applications to cropland at rates that restore native fertility.Applications to cropland at rates that restore native fertility.

Nutrient content of animal manures varies, but is in the order of (plus Nutrient content of animal manures varies, but is in the order of (plus or minus 50%) 50-50-50 for poultry, 20-20-20 for beef, and 10-10-10 or minus 50%) 50-50-50 for poultry, 20-20-20 for beef, and 10-10-10 for swine, where the analysis is for swine, where the analysis is lblb N, P N, P22OO55, and K, and K22O per ton of material.O per ton of material.

Organic food productionOrganic food productionThere are groups within our society that believe There are groups within our society that believe food should be raised “organic”, meaning food should be raised “organic”, meaning ‘without the benefit of external inputs of synthetic ‘without the benefit of external inputs of synthetic materials’ (e.g. chemical fertilizers), materials’ (e.g. chemical fertilizers),

The soundness of this approach can be quickly The soundness of this approach can be quickly examined by considering the amount of animal examined by considering the amount of animal manure required to replace the current 300,000 manure required to replace the current 300,000 tons of N, from commercial inorganic fertilizer, tons of N, from commercial inorganic fertilizer, used in Oklahoma to maintain current crop used in Oklahoma to maintain current crop production levels. production levels.

Using beef manure, the tons of manure Using beef manure, the tons of manure required would berequired would be

300,000 tons N x 2,000 lb/ton = 6 x 10300,000 tons N x 2,000 lb/ton = 6 x 1088 lb N lb N requiredrequired6 x 106 x 1088 lb N required lb N required 1 ton (2000 lbs) has 20 lb N1 ton (2000 lbs) has 20 lb N6 x 106 x 1088 lb N required/20 lb N /ton lb N required/20 lb N /ton= 3.0 x 10= 3.0 x 1077 tons of manure tons of manureAverage manure production of 1,000 lb steers in Average manure production of 1,000 lb steers in a confined feedlot will produce 3.212 tons per a confined feedlot will produce 3.212 tons per year.year.3.0 x 103.0 x 1077 ton manure x 1.0 animals/3.212 ton per ton manure x 1.0 animals/3.212 ton per year = 9,339,975 steersyear = 9,339,975 steersThe Oklahoma Agricultural Statistics 430,000 The Oklahoma Agricultural Statistics 430,000 cattle on feed as of January 1, 1998 cattle on feed as of January 1, 1998

Cattle ManureCattle Manure

The Oklahoma Agricultural Statistics for 1997 The Oklahoma Agricultural Statistics for 1997 reported 430,000 cattle on feed as of January 1, reported 430,000 cattle on feed as of January 1, 1998 (this does not mean the number was constant 1998 (this does not mean the number was constant throughout the year). throughout the year).

A 21A 21XX increase in feedlot beef cattle to produce the increase in feedlot beef cattle to produce the required N in the form of animal manure. required N in the form of animal manure. What would we do with all the meat?What would we do with all the meat?

It is also important for the promoters of ‘organic’ It is also important for the promoters of ‘organic’ farming to realize that even the best recycling farming to realize that even the best recycling efforts are not 100% efficient. efforts are not 100% efficient.

# of Cattle # of Cattle USA 39,500,000 (feedlot) total 96,000,000USA 39,500,000 (feedlot) total 96,000,000– 14 Million-TX (feedlot)14 Million-TX (feedlot)– 7.4 Million-NE (feedlot)7.4 Million-NE (feedlot)– 1.2 Million-KY (feedlot)1.2 Million-KY (feedlot)– 1.0 Million-IA (feedlot)1.0 Million-IA (feedlot)– 0.5 Million-OK (feedlot) (5.5 total)0.5 Million-OK (feedlot) (5.5 total)

Japan 4,530,000 Japan 4,530,000 USSR (former area of) 35,227,000 USSR (former area of) 35,227,000 Australia 27,588,000 (total, not feedlot)Australia 27,588,000 (total, not feedlot)New Zealand 9,700,000 New Zealand 9,700,000 Southern Africa 5,625,000 Southern Africa 5,625,000 Eastern Europe 16,495,536 Eastern Europe 16,495,536 Argentina 50,000,000 Argentina 50,000,000

Synthetic N fertilizersSynthetic N fertilizersDevelopment of the fertilizer industry after the Development of the fertilizer industry after the second World War in the mid 1940’s coincided second World War in the mid 1940’s coincided with other technological improvements in with other technological improvements in agricultural production (i.e. improved varieties) agricultural production (i.e. improved varieties) and a general increase in yield. and a general increase in yield.

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Changes in winter wheat yield and fertilizer tonnage sold in Oklahoma

N FertilizersN FertilizersAll N fertilizer materials are All N fertilizer materials are synthesized while P and K fertilizers synthesized while P and K fertilizers are processed, natural deposits. are processed, natural deposits.

Of the synthesized N fertilizers, urea Of the synthesized N fertilizers, urea is an organic fertilizer and the others is an organic fertilizer and the others are not.are not.

(NH(NH22))22COCO

Anhydrous ammonia (82-0-0)Anhydrous ammonia (82-0-0)

The leading N fertilizer in terms of The leading N fertilizer in terms of tons sold nationwide is anhydrous tons sold nationwide is anhydrous ammonia (82-0-0). It is manufactured ammonia (82-0-0). It is manufactured by combining atmospheric Nby combining atmospheric N22 with H with H in an environment of high pressure in an environment of high pressure and temperature that includes a and temperature that includes a catalyst.catalyst.

N2 + 3 H2 ==500-atm pressure, 1000 C and a catalyst 2 NH3

NHNH33

The common source of H is from The common source of H is from natural gas (CHnatural gas (CH44). Important ). Important properties of anhydrous ammonia properties of anhydrous ammonia are listed beloware listed below

– Very hygroscopic (water loving)Very hygroscopic (water loving)

3CH4 + 3O2 + 2N2 4NH3 + 3CO2

High temp (1200°C)High pressure (200-1000 atm)(magnetite, Fe3O4) catalyst

Methane Anhydrous Ammonia

Haber-Bosch: (Germany, 1910)

NH3NH3

The strong attraction of anhydrous The strong attraction of anhydrous ammonia for water is identified ammonia for water is identified chemically by the equilibrium chemically by the equilibrium reactionreaction

NH3 + H2O === NH4+ + OH- Keq = 10-4.75

(NH4+)(OH-) = 10-4.75 (NH3)

(OH-)=10-14/H+

pH = 14-4.75

pH = 9.25

NH4+ + OH- ---> NH4OH ---->NH3 + H2ONH4+ + OH- ---> NH4OH ---->NH3 + H2OpH = pKa + log [(base)/(acid)]pH = pKa + log [(base)/(acid)]At a pH of 9.3 (pKa 9.3) 50% NH4 and 50% NH3At a pH of 9.3 (pKa 9.3) 50% NH4 and 50% NH3pHpH Base (NH3)Base (NH3) Acid (NH4)Acid (NH4)7.37.3 11 99998.38.3 1010 90909.39.3 5050 505010.310.3 9090 101011.311.3 9999 11

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4+N H

NHNH33

pH 7: ratio of NH4pH 7: ratio of NH4++/ NH3 is about 200:1, / NH3 is about 200:1, Strong tendency for the reaction to go to the right. Strong tendency for the reaction to go to the right. Undissociated NHUndissociated NH44OH does not exist in aqueous OH does not exist in aqueous solutions of NHsolutions of NH33 at normal temperature and pressure. at normal temperature and pressure. If undissociated NHIf undissociated NH44OH did exist, it would provide a OH did exist, it would provide a form of N, other than NOform of N, other than NO33

-- that would be mobile in the that would be mobile in the soil.soil.Anhydrous ammonia is a hazardous material and Anhydrous ammonia is a hazardous material and special safety precautions must be taken in its use. special safety precautions must be taken in its use. Most important among these is to avoid leaks in hoses Most important among these is to avoid leaks in hoses and couplings, and to always have a supply (5 gallons and couplings, and to always have a supply (5 gallons or more) of water available for washing.or more) of water available for washing.Anhydrous ammonia injected: reacts immediately with Anhydrous ammonia injected: reacts immediately with soil-water. soil-water.

NHNH33Dry soils: sufficient hygroscopic water present to cause Dry soils: sufficient hygroscopic water present to cause reaction [1] to take place. When there is insufficient reaction [1] to take place. When there is insufficient water present (e.g. dry, sandy soil) to react with all the water present (e.g. dry, sandy soil) to react with all the NHNH33 (high rate of N, shallow application depth), some (high rate of N, shallow application depth), some NHNH33 may be lost to the atmosphere by volatilization. may be lost to the atmosphere by volatilization. Losses are minimized by injecting NHLosses are minimized by injecting NH33 at least 4” deep at least 4” deep in loam soils and 6” deep in sandy soils for N rates of in loam soils and 6” deep in sandy soils for N rates of 50 lb N/acre. 50 lb N/acre. As rates increase, depth of injection should be As rates increase, depth of injection should be increased and/or spacing between the injection points increased and/or spacing between the injection points decreased. decreased. In all application situations it is important to obtain a In all application situations it is important to obtain a good “seal” as soil flows together behind the shank or good “seal” as soil flows together behind the shank or injection knife moving through the soil. Packing injection knife moving through the soil. Packing wheels are sometimes used to improve the seal and wheels are sometimes used to improve the seal and minimize losses.minimize losses.

Blue Jet

NH3NH3

Anhydrous Anhydrous

H2SO4 (NH4)2SO4 20%Nammonium sulfate

HNO3 NH4NO3 33%Nammonium nitrate

CO2 (NH2)2CO 45%Nurea

H3PO4 NH4H2PO4 11-18%Nammoniated phosphates11-48-018-46-0

HNO3/rock phosphate nitric phosphates

NH3 +

NHNH33Least expensive source of N. Least expensive source of N. Cost of natural gas strongly influences the price of anhydrous Cost of natural gas strongly influences the price of anhydrous ammoniaammoniaN source for manufacturing other N fertilizers N source for manufacturing other N fertilizers Widest use in corn and wheat productionWidest use in corn and wheat productionNot recommended for use in deep, sandy soils because of the risk of Not recommended for use in deep, sandy soils because of the risk of leaching associated with the deeper injection requirement and lower leaching associated with the deeper injection requirement and lower CEC of these soils. CEC of these soils. Sometimes used with a nitrification inhibitor, such as N-Serve (also Sometimes used with a nitrification inhibitor, such as N-Serve (also called called nitrapyrinnitrapyrin) or fall applied when soil temperatures are cold ) or fall applied when soil temperatures are cold enough to minimize nitrification and leaching loss and risk of enough to minimize nitrification and leaching loss and risk of groundwater contamination. groundwater contamination. Good source of N for no-till systems since immobilization is minimized Good source of N for no-till systems since immobilization is minimized by band injections. Does not cause hard pans, acid soils, or reduced by band injections. Does not cause hard pans, acid soils, or reduced populations of microorganisms and earthworms, as is sometimes populations of microorganisms and earthworms, as is sometimes suggested.suggested.

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US Gas Price

US NH3 Price

$5.00 per MMBtu (million metric British thermal units)

33.5 MMBtu (million metric British thermal units) per ton NH3

At $5.00 per MMBtu, the production cost is about $200 per ton (current sale price of $340/ton)

Soil Fertility & Nat. GasSoil Fertility & Nat. Gas

Urea (46-0-0)Urea (46-0-0) Most popular (based on sales) solid N fertilizer.Most popular (based on sales) solid N fertilizer.Produced as either a crystal or prill (small bead-Produced as either a crystal or prill (small bead-like shape). like shape). Very soluble in water, highest analysis solid Very soluble in water, highest analysis solid material sold commercially. material sold commercially. Not hazardous and has low corrosive propertiesNot hazardous and has low corrosive propertiesHygroscopic (attracts water) and requires storage Hygroscopic (attracts water) and requires storage free of humid air. free of humid air. Mobile in soil because it remains an uncharged Mobile in soil because it remains an uncharged molecule after it dissolves. molecule after it dissolves. After it dissolves it hydrolyzes to ammonium, After it dissolves it hydrolyzes to ammonium, bicarbonate and hydroxide in the presence of the bicarbonate and hydroxide in the presence of the enzyme ureaseenzyme urease

UreaUreaUrease is present in all soil and plant Urease is present in all soil and plant materialmaterialHydrolysis of urea will occur on the surface Hydrolysis of urea will occur on the surface of moist soil, plant residue, or living plant of moist soil, plant residue, or living plant material if the moist environment is material if the moist environment is maintained for about 24 hours. maintained for about 24 hours. If, after hydrolysis has taken place, the If, after hydrolysis has taken place, the environment dries, N may be lost environment dries, N may be lost (volatilized)(volatilized)

CO(NH2)2 + H2O = urease enzyme == 2 NH4+ + HCO3

- + OH-

NH3 + H2O === NH4+ + OH-

UreaUrea

Environments that are already basic (high pH soil) Environments that are already basic (high pH soil) and lack exchange sites to hold NHand lack exchange sites to hold NH44

++ (sandy, low (sandy, low organic matter soils) will favor lossorganic matter soils) will favor lossEasy to blend with other fertilizers, but should be Easy to blend with other fertilizers, but should be incorporated by cultivation, irrigation or rain incorporated by cultivation, irrigation or rain within a few hours of application if the surface is within a few hours of application if the surface is moist and temperatures are warm (>60°F)moist and temperatures are warm (>60°F)There apparently is little or no loss of ammonia There apparently is little or no loss of ammonia when urea is surface applied during cool weather when urea is surface applied during cool weather or remains dry during warm weatheror remains dry during warm weather

Ammonium Nitrate (33-0-0)Ammonium Nitrate (33-0-0)

Use of ammonium nitrate fertilizers decreased with increasing use of urea Use of ammonium nitrate fertilizers decreased with increasing use of urea in the 1980’s. in the 1980’s. Preferred for use on sod crops, like bermudagrass hayfieldsPreferred for use on sod crops, like bermudagrass hayfieldsSince the bombing of the Federal Building in Oklahoma City April 19, 1995, Since the bombing of the Federal Building in Oklahoma City April 19, 1995, fertilizer dealers are even more reluctant to include it in their inventory of fertilizer dealers are even more reluctant to include it in their inventory of materials. Because ammonium nitrate has been popular for homeowners, materials. Because ammonium nitrate has been popular for homeowners, some retailers continue to carry a 34-0-0 material that is a blend of urea some retailers continue to carry a 34-0-0 material that is a blend of urea and ammonium sulfate or other materials. and ammonium sulfate or other materials. Thus, they are able to sell a fertilizer of the same analysis, but which has Thus, they are able to sell a fertilizer of the same analysis, but which has no explosive properties. Although ammonium nitrate is widely used as an no explosive properties. Although ammonium nitrate is widely used as an explosive in mining and road building, the fertilizer grade (higher density) explosive in mining and road building, the fertilizer grade (higher density) is not considered a high risk, hazardous material and accidental explosions is not considered a high risk, hazardous material and accidental explosions of the fertilizer grade are extremely rare.of the fertilizer grade are extremely rare.Ammonium nitrate is hygroscopic, like urea, and will form a crust or cake Ammonium nitrate is hygroscopic, like urea, and will form a crust or cake when allowed to take on moisture from the atmosphere. when allowed to take on moisture from the atmosphere. Unlike urea, loss of N as NHUnlike urea, loss of N as NH33 volatilization is not a problem with ammonium volatilization is not a problem with ammonium nitrate. This fertilizer is corrosive to metal and it is important to clean nitrate. This fertilizer is corrosive to metal and it is important to clean handling equipment after use. handling equipment after use. A major advantage of ammonium nitrate fertilizer is that it provides one-A major advantage of ammonium nitrate fertilizer is that it provides one-half of the N in a soil-mobile form. This is often justification for use in half of the N in a soil-mobile form. This is often justification for use in short-season, cool weather, vegetable crops and greens like spinach. short-season, cool weather, vegetable crops and greens like spinach.

N FertilizersN FertilizersUAN (urea-ammonium nitrate) solutionsUAN (urea-ammonium nitrate) solutions Urea and ammonium nitrate are combined with water in a 1:1:1 ratio by weight =28 Urea and ammonium nitrate are combined with water in a 1:1:1 ratio by weight =28 %N solution. %N solution. Popular for use as a topdressing (application to growing crop) for winter wheat and Popular for use as a topdressing (application to growing crop) for winter wheat and bermudagrass hayfields. bermudagrass hayfields. Because it has properties of both urea and ammonium nitrate, its use is discouraged for Because it has properties of both urea and ammonium nitrate, its use is discouraged for topdressing during humid, warm, summer periods when volatilization of NHtopdressing during humid, warm, summer periods when volatilization of NH33 from the from the urea portion could occur. urea portion could occur. Can serve as a carrier for pesticidesCan serve as a carrier for pesticidesSolution 32 is a similar material that simply is more concentrated (contains less water) Solution 32 is a similar material that simply is more concentrated (contains less water) Precipitates (salts out) when temperatures are below about 28°F. Precipitates (salts out) when temperatures are below about 28°F. Solution 28 does not salt out until temperatures reach about 0°F.Solution 28 does not salt out until temperatures reach about 0°F.

Ammonium sulfate (21-0-0)Ammonium sulfate (21-0-0)Dry granular material that is the most acidifying of the common N fertilizer materials Dry granular material that is the most acidifying of the common N fertilizer materials because the N is in the ammonium form. because the N is in the ammonium form. When urea is hydrolyzed to form NHWhen urea is hydrolyzed to form NH44

++, there are two ‘basic’ anions (OH, there are two ‘basic’ anions (OH-- and HCO and HCO33--) )

Neutralizes some of the HNeutralizes some of the H++, formed when NH, formed when NH44++ is nitrified to NO is nitrified to NO33

--. . Because the analysis of N is relatively low, compared to other dry materials, there is Because the analysis of N is relatively low, compared to other dry materials, there is not much market for ammonium sulfate and its cost/lb of N is relatively high. As a not much market for ammonium sulfate and its cost/lb of N is relatively high. As a result its use is limited to specialty crops, lawns and gardens, and in blended result its use is limited to specialty crops, lawns and gardens, and in blended formulations that need S.formulations that need S.

Slow-release fertilizersSlow-release fertilizersTwo to three (or more) times more expensive than urea or Two to three (or more) times more expensive than urea or ammonium nitrateammonium nitrateNot used in conventional agriculture, but rather in production Not used in conventional agriculture, but rather in production systems that are less sensitive to fertilizer costs and which systems that are less sensitive to fertilizer costs and which desire a somewhat uniform supply of N to the plants over the desire a somewhat uniform supply of N to the plants over the cyclecycleTurfgrass systems: Turfgrass systems: Advantage of these materials is that one application may Advantage of these materials is that one application may provide a uniform supply of N to the plants for several weeks.provide a uniform supply of N to the plants for several weeks.Urea-formaldehyde (38 %N) is a synthetic organic material of Urea-formaldehyde (38 %N) is a synthetic organic material of low solubility, whose N release depends upon microbial low solubility, whose N release depends upon microbial breakdown and thus is temperature dependent.breakdown and thus is temperature dependent.IBDU (isobutylidene diurea, 31 %N) is another synthetic IBDU (isobutylidene diurea, 31 %N) is another synthetic organic material. N release from this fertilizer depends upon organic material. N release from this fertilizer depends upon particle size, soil moisture content and pH.particle size, soil moisture content and pH.S-coated urea (32-36 %N) is urea that has been encapsulated S-coated urea (32-36 %N) is urea that has been encapsulated with elemental S in the prilling process. Release of N depends with elemental S in the prilling process. Release of N depends upon breakdown of the S coat (physical barrier)upon breakdown of the S coat (physical barrier)

N FertilizersN Fertilizers

Milorganite Milorganite (Milwaukee sewage sludge, 6 %N) is an organic fertilizer (Milwaukee sewage sludge, 6 %N) is an organic fertilizer that has a very low N content. that has a very low N content.

Popular in turf maintenance because there is little or no turf Popular in turf maintenance because there is little or no turf response from its application.response from its application.

The most obvious trend of the last 25 years has been for a The most obvious trend of the last 25 years has been for a decline in anhydrous ammonia (AA) and ammonium nitrate decline in anhydrous ammonia (AA) and ammonium nitrate (AN) while urea and urea-ammonium nitrate (UAN) (AN) while urea and urea-ammonium nitrate (UAN) solutions have increased. solutions have increased.

Diammonium phosphate (DAP), although a major source of Diammonium phosphate (DAP), although a major source of P, contributes only minor to the total N (about 300,000 lb N) P, contributes only minor to the total N (about 300,000 lb N) sold each year in Oklahomasold each year in Oklahoma

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Sales activity of common fertilizer materials in Oklahoma over time

Managing fertilizer inputsManaging fertilizer inputsN loss from the soil-plant system increases in proportion to the amount of excess N loss from the soil-plant system increases in proportion to the amount of excess mineral N present in the soil. mineral N present in the soil. Important to apply fertilizer-N as close to the time the plant needs, or will Important to apply fertilizer-N as close to the time the plant needs, or will respond to itrespond to itMost efficient use of fertilizer-N is usually accomplished with ‘Most efficient use of fertilizer-N is usually accomplished with ‘split split applicationsapplications’, whereby more than one application is applied to meet the ’, whereby more than one application is applied to meet the seasonal N needs. seasonal N needs.

The desire to improve NUE, or fertilizer recovery, by the crop is offset by the cost The desire to improve NUE, or fertilizer recovery, by the crop is offset by the cost of making several applications. Additionally, in the case of cereal grain of making several applications. Additionally, in the case of cereal grain production, the cost per pound of N may be higher for materials used in-season production, the cost per pound of N may be higher for materials used in-season than the material used pre-season.than the material used pre-season.

82-0-0 @ $340/ton = $340/1640 lb N = 82-0-0 @ $340/ton = $340/1640 lb N = $0.21/ lb N$0.21/ lb N46-0-0 @ $285/ton = $285/920 lb N = 46-0-0 @ $285/ton = $285/920 lb N = $0.31/ lb N$0.31/ lb N

Cost of N from anhydrous ammonia is less than ½ the cost of N from urea. Cost of N from anhydrous ammonia is less than ½ the cost of N from urea. Farmers may choose to apply anhydrous ammonia pre-plant for wheat and corn Farmers may choose to apply anhydrous ammonia pre-plant for wheat and corn production even though it is not as efficiently used as an in-season application of production even though it is not as efficiently used as an in-season application of urea. Decreased efficiency of the pre-plant application is often overcome, urea. Decreased efficiency of the pre-plant application is often overcome, economically, by its much lower cost per pound of N. economically, by its much lower cost per pound of N.