2004.. fertilizer nutrient recovery in sustainable cropping systems

7/27/2019 2004.. Fertilizer Nutrient Recovery in Sustainable Cropping Systems

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Better Crops/Vol. 88 (2004, No. 4) 15

CCCCC

urrent estimates of recovery efficien-cies for nitrogen (N), phosphorus (P),

and potassium (K) fertilizers used inNorth American crop production vary con-siderably. They vary largely because of dif-ferences in definition. Recovery by thecrops response differs from recovery by thecropping system.

RRRRRecoecoecoecoecovvvvvererererery efy efy efy efy efffffficiencicienciciencicienciciency is defy is defy is defy is defy is defined as theined as theined as theined as theined as theamount ofamount ofamount ofamount ofamount of nnnnnutrient in the crutrient in the crutrient in the crutrient in the crutrient in the crop as a rop as a rop as a rop as a rop as a raaaaatiotiotiotiotioofofofofof the amount athe amount athe amount athe amount athe amount applied or applied or applied or applied or applied or avvvvvailaailaailaailaailabbbbblelelelele..... Itscalculation varies widely depending on the

system being considered: the soil-plant sys-tem, the whole plant, the above-groundportion of the plant, or the harvested por-tion of the plant may be considered thevessel of recovery. The inputs may or maynot include: applied manures, mineraliza-tion of soil nutrients, atmospheric deposi-tion, and contribution of soil micro-organ-isms, in addition to applied fertilizers.Recovery can be calculated for each single

source or for the total of all sources.

Recovery from a single source is oftenestimated from the single-year response:

the difference in nutrient uptake betweenfertilized and unfertilized plants. It canalso be measured using tracers. Both meth-ods are subject to error.

Error arises in the difference methodbecause plants respond to nutrient defi-ciencies by altering root growth and thecapacity of roots to acquire nutrients.These mechanisms may not be operativeinor compatible withthe type of plant

growth associated with the higher yieldlevels of fertilized plants.

Recovery estimates using tracers areconfounded by internal cycling of nutri-ents in the soil. For example, the rapiduptake and release of ammonium and ni-trate forms of N (mineralization-immobi-lization turnover) generally reduces theconcentration of the tracer in the N madeavailable to plants.

A recent study measured the differencebetween N uptake in fertilized and unfer-tilized plots in 55 producer-managed cornfields in the north central U.S. (Cassmanet al., 2002). Recovery of N in above-ground plant biomass averaged only 37%of fertilizer N applied. This is a disturb-ingly low figure. Assuming a typical N har-vest index (portion of above-ground N ingrain) of 56%, it implies that as little as21% of the fertilizer N applied is removedin the grain. In actual practice, this levelof efficiency would be difficult to match,since optimum rate was selected inhindsight from a rate study. Where is the

Fertilizer Nutrient Recovery in

Sustainable Cropping SystemsBy T.W. Bruulsema, P.E. Fixen, and C.S. Snyder

While single-year crop responses often recover less than half the nutrients appliedas fertilizers, cropping systems are more efficient. Nutrient additions support themaintenance of soil organic matter and fertility as well as crop yields.

FFFFFererererertilizer N eftilizer N eftilizer N eftilizer N eftilizer N efffffficiencyiciencyiciencyiciencyiciency is influenced by long-term

dynamics of a soils organic matter.


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16 Better Crops/Vol. 88 (2004, No. 4)

rest of the fertilizer going?LetLetLetLetLets look mors look mors look mors look mors look more ce ce ce ce closellosellosellosellosely ay ay ay ay at the mean-t the mean-t the mean-t the mean-t the mean-

ing ofing ofing ofing ofing of 37% r37% r37% r37% r37% recoecoecoecoecovvvvvererererery in this ey in this ey in this ey in this ey in this examplexamplexamplexamplexample.....What it means is that in these fields, whenfertilizer was added at an optimum rate(which averaged 92 lb/A), it boosted the

uptake of N into the above-ground por-tion of the plant by 34 lb/A (37% of 92).

The fertilized corn took up an averageof 164 lb N/A: 130 from the soil and 34from the fertilizer. The total amount of Nin its grain would be 56% of 164 = 92 lb/A:equal to the amount of fertilizer applied.So is the recovery 21% (as estimated bysingle-year-response recovery in grain) or100% (assuming the observed balance of

input and output is sustainable long-term)?

The answer cannot be known unless thelonger-term dynamics of the soils organicmatter are understood. If the croppingsystem is maintaining organic matter, andif the 130 lb/A of N from the soil camefrom mineralization of organic matter, anequivalent amount of N must be returnedin the form of crop residues, and also sta-

bilized to protect it from loss.If the soil is gaining organic matter,

even more N is required. The crop con-verted at least 164 lb/A of mineral N intoorganic forms; more if below-ground as-similation by roots and associated micro-flora is considered. How much will be heldin that form depends on the dynamics ofdecomposition, controlled to some degreeby tillage management.

MinerMinerMinerMinerMineralizaalizaalizaalizaalization oftion oftion oftion oftion of N frN frN frN frN from soil orom soil orom soil orom soil orom soil orggggganicanicanicanicanicmamamamamatter is a lartter is a lartter is a lartter is a lartter is a larggggge be be be be but unsustainaut unsustainaut unsustainaut unsustainaut unsustainabbbbble sourle sourle sourle sourle sourcececececefffffor the ror the ror the ror the ror the reeeeeplacement ofplacement ofplacement ofplacement ofplacement of crcrcrcrcrop rop rop rop rop remoemoemoemoemovvvvval.al.al.al.al .Depletion of organic matter eventuallyreduces the productivity of soils. In a sus-tainable cropping system, N contributedby mineralization needs to be returned torebuild soil organic matter. Crop residuesexudates, roots, and stoverreturn this N.

In recent years, through a combinationof reduced tillage and the return of in-creased residues from higher-yieldingcrops, many areas have reversed the trendof organic matter decline. Since 1970, soilsof the central U.S. Corn Belt are

sequestering N at the rate of 20 lb/A/yearas their organic matter increases throughreduced tillage (Lal et al., 1998). As con-servation tillage expands, requirements forN can be expected to increase, and part ofthe reason is that a source of N is needed

for soil organic matter accumulation.NitrNitrNitrNitrNitrooooogggggen boosts the ren boosts the ren boosts the ren boosts the ren boosts the returetureturetureturn ofn ofn ofn ofn of crcrcrcrcropopopopop

residue to the soil and enhances its con-residue to the soil and enhances its con-residue to the soil and enhances its con-residue to the soil and enhances its con-residue to the soil and enhances its con-vvvvvererererersion to stasion to stasion to stasion to stasion to stabbbbble soil orle soil orle soil orle soil orle soil orggggganic maanic maanic maanic maanic matterttertterttertter..... Manyexperiments have shown that fertilizingcrops with N results in higher levels of soilcarbon over time. An example from Min-nesota is shown in TTTTTaaaaabbbbble 1le 1le 1le 1le 1. Paustian et al.(1997) documented 20 sites worldwide thatgained soil carbon (C) in response to appli-

cation of N fertilizers over periods rang-ing from 7 to 120 years. As shown in Fig-Fig-Fig-Fig-Fig-ururururure 1e 1e 1e 1e 1, N is integral to the chemical struc-ture of soil organic matter, and is stabi-lized within it.

TTTTThe conhe conhe conhe conhe convvvvvererererersion ofsion ofsion ofsion ofsion of N into orN into orN into orN into orN into orggggganicanicanicanicanicffffforororororms bms bms bms bms by plants and associay plants and associay plants and associay plants and associay plants and associated soilted soilted soilted soilted soil

TTTTTable 1.able 1.able 1.able 1.able 1. Soil organic carbon (SOC) accumulatedfrom 1965 to 1995 in the top foot of asoil cropped to continuous corn.

Applied N, SOC derived from cornlb/A/yr tons/A %

150 7.6 2175 5.8 170 4.5 12

Source: Wilts et al., 2004

FFFFFigurigurigurigurigure 1.e 1.e 1.e 1.e 1. Chemical structure of soil organicmatter (Schulten and Schnitzer, 1997).The element colors are: N-blue, C-cyan,hydrogen-white, oxygen-red, sulfur-yellow.


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Better Crops/Vol. 88 (2004, No. 4) 17

microflora gives the mobile nutrientmicroflora gives the mobile nutrientmicroflora gives the mobile nutrientmicroflora gives the mobile nutrientmicroflora gives the mobile nutrientN properties similar to the relativelyN properties similar to the relativelyN properties similar to the relativelyN properties similar to the relativelyN properties similar to the relativelyimmobile nimmobile nimmobile nimmobile nimmobile nutrients P and K.utrients P and K.utrients P and K.utrients P and K.utrients P and K. Recov-ery of all three nutrients is greater in thelong term than in the short term. Whilesingle-year-response recovery of fertilizer

P often ranges from 15 to 25%, longer-termrecovery in cropping systems is more typi-cally 50 to 60%, and for some systems ashigh as 70 to 90% (Smil, 2000).

Among the producer-managed fieldsdescribed above, five had single-year-re-sponse recovery efficiencies in excess of60% even when fertilized at rates of 160lb N/A or more. This suggests that highrates of nutrient application can be com-

patible with high recovery efficiencies.A study in France reported recovery of

71% of labeled fertilizer N in corn, with26% of the remainder recovered as soil or-ganic N and only 3% as inorganic formssubject to losses.

Recent data for U.S. corn suggest thatthe harvested grain removes amountsequivalent to 81, 122, and 77% of the N, Pand K applied as fertilizers. Removals rela-

tive to applications have increased signifi-cantly in recent decades (FigurFigurFigurFigurFigure 2e 2e 2e 2e 2).

Removal by all North American cropsrelative to nutrients supplied in the formof fertilizers and manures amounts to 95%and 143% for P and K, respectively. Thecomparable figure for N is 77%, but con-sidering non-legume crops only, it declinesto 64%. The lower recovery for N could betaken as an indication of priority for

efforts at enhancement, or more thoroughdocumentation of its role in contributingto increased soil organic matter. Appropri-ate management of P and K can contrib-ute to improved N recovery.

ConcConcConcConcConclusionlusionlusionlusionlusionLow nutrient recovery in a single-year

response does not imply that the remain-der is permanently lost. We need to im-prove short-term response recovery, but notat the expense of long-term sustainability.Nutrient inputs to cropping systems haveimportant roles in supporting the mainte-nance of soil organic matter and fertility,in addition to directly supporting crop

yield. Enhancement of use efficiency ofEnhancement of use efficiency ofEnhancement of use efficiency ofEnhancement of use efficiency ofEnhancement of use efficiency ofnnnnnutrients mutrients mutrients mutrients mutrients must be inteust be inteust be inteust be inteust be integggggrrrrraaaaated with thated with thated with thated with thated with that oft oft oft oft ofall rall rall rall rall resouresouresouresouresources essential to sustainaces essential to sustainaces essential to sustainaces essential to sustainaces essential to sustainabbbbble crle crle crle crle cropopopopopproduction.production.production.production.production. BC

Dr. Bruulsema is PPI Northeast RegionDirector, located at Guelph, Ontario; e-mail:[email protected]. Dr. Fixen is PPISenior Vice President, North American ProgramCoordinator and Director of Research, located atBrookings, South Dakota. Dr. Snyder is PPISoutheast Region Director, located at Conway,Arkansas.

0%

20%

40%

60%

80%

100%

120%

140%

1963 1973 1983 1993 2003

NPK

Figure 2.Figure 2.Figure 2.Figure 2.Figure 2. Grain nutrient removal as percentageof fertilizer use on corn in the U.S.

RRRRRefefefefeferererererencesencesencesencesences

Cassman, K.G., A. Dobermann, and D.T. Waters.2002. Agroecosystems, nitrogen use efficiency,and nitrogen management. Ambio 31(2), 132-140.

Lal, R., J.M. Kimble, R.F. Follett, and C.V. Cole.1998. The SOC pool in U.S. soils and SOC lossfrom cultivation. In The potential of U.S. crop-land to sequester carbon and mitigate the green-house effect. Ann Arbor Press, Chelsea, MI. 128p.

Paustian, K., H.P. Collins, and E.A. Paul. 1997.Management controls on soil carbon. p. 39-41,Chpt. 2. In E.A. Paul, K. Paustian, E.T. Elliot,C.V. Cole (eds.) Soil Organic Matter in Temper-ate Agroecosystems, CRC Press, Inc.

Schulten, Hans-Rolf, and Morris Schnitzer. 1997.Chemical model structures for soil organic mat-ter and soils. Soil Science 162(2):115-130.

Smil, V. 2000. Phosphorus in the environment: natu-ral flows and human interferences. Annu. Rev.Energy Environ. 25:53-88.

Wilts, A.R., D.C. Reicosky, R.R. Allmaras, and C.E.Clapp. 2004. Long-term corn residue effects: har-vest alternatives, soil carbon turnover, and root-derived carbon. Soil Sci. Soc. Am. J. 68:13421351.

2004.. fertilizer nutrient recovery in sustainable cropping systems

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