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Greenhouse Gas Emissions from Crop Production Systems and Fertilizer Management Effects. C.S. Snyder, T.W. Bruulsema, T.L. Jensen, and P. E. Fixen. Background. N is essential to the survival of all life

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greenhouse gas emissions from crop production systems and fertilizer management effects

Greenhouse Gas Emissions from Crop Production Systems and Fertilizer Management Effects

C.S. Snyder, T.W. Bruulsema, T.L. Jensen, and P. E. Fixen

  • N is essential to the survival of all life
  • Over 40% of the people on Earth owe their existence to the food production made possible by N fertilizers
  • “Human alterations of the N cycle have caused a variety of environmental and human health problems ranging from too little to too much reactive N in the environment.” (Woods Hole Research Center)
  • half the synthetic N fertilizer ever used has been utilized since 1985 (Howarth, 2005).



Dedicated to improved nutrient use effectiveness and reductions in environmental footprints: including GHG emissions

United Nations Educational, Scientific, and Cultural Organization

& Scientific Committee on Problems of the Environment

world population growth in more and less developed countries
World Population Growth in More and Less Developed Countries


20% more people in ~ 20 years

Less Developed Regions

Food, fiber, and fuel demands will continue to increase

…… what will the environmental impacts be?

More Developed Regions

Source: United Nations, World Population Prospects: The 2004 Revision (medium scenario), 2005.


Best Management Practices to Minimize Greenhouse Gas Emissions

Associated with Fertilizer Use

IPNI Review Paper

IPNI Better Crops article, Issue 4 of 2007

Greenhouse Gas Emissions from Cropping Systems and the Influence of Fertilizer Management$webindex/6F2F57CBF1C5209685257394001B2DD0/$file/07-4p16.pdf

greenhouse gases ghgs and their sources
Greenhouse Gases (GHGs)and their sources
  • Carbon Dioxide (CO2): fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of other chemical reactions (e.g., manufacture of cement).
  • Methane (CH4): production and transport of coal, natural gas, and oil; livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.
  • Nitrous Oxide (N2O): agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.
  • Fluorinated Gases: (Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride): synthetic, powerful greenhouse gases from a variety of industrial processes.
    • Sometimes used as substitutes for ozone-depleting substances (i.e., CFCs, HCFCs, and halons). Typically emitted in smaller quantities, but because they are potent GHGs, they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”).

GWP = Global Warming Potential

N2O x 296 = CO2 equivalent

CH4 x 21 = CO2 equivalent

Sources: U.S. EPA, IPCC 3rd assessment

estimates of n 2 o emissions from cropland in 1995 adapted from ifa fao 2001
Estimates of N2O Emissions from Cropland in 1995 (adapted from IFA/FAO, 2001)

Recently published reports suggest terrestrial and aquatic N2O-N emissions may range from 3 to 5% of “new N”

(Crutzen et al., 2008. Atmos. Chem. Phys. 8:389-395)

consumption of n sources
Consumption of N Sources

Data source: IFA, AAPFCO & TFI

range of n 2 o emission among n sources can vary greatly
Range of N2O Emission Among N Sources can Vary Greatly
  • Report 1 (Stehfest & Bouwman, 2006)
    • 0 to 46% of applied N
  • Report 2 (Granli & Bockman, 1994)
    • 0 to 7% of applied N
  • Report 3 (Eichner, 1990)
    • 0 to 7% of applied N
  • Report 1
    • Median among N sources ranged from: 0.26 to 1.56 kg of N/ha
nitrogen use efficiency
Nitrogen Use Efficiency
  • “…… estimated NUE for cereal production ranges from 30 to 35%.” 

Improving Nitrogen Use Efficiency for Cereal Production

( 1999 Agronomy Journal 91:357-363)


Food Yield/










n loss consequences requiring management attention
N Loss Consequences Requiring Management Attention
  • Decreased crop production and profitability
    • Inefficient land use, reduced performance of other crop inputs, reduced water use efficiency
  • Water resource contamination
    • eutrophication: lakes, streams, rivers, estuaries
    • groundwater contamination
    • coastal water contamination - urea and harmful algal blooms (neurotoxin poisoning)
  • Air pollution
    • Ammonia and particulates, nitrous oxide and NOx (global warming, stratospheric ozone depletion, acid rain)
loss of no 3 n to water resources may also impact n 2 o emissions
Loss of NO3 -N to Water Resources May Also Impact N2O Emissions

SPARROW - Modeled Estimate of N and P Discharge in Watersheds of the Mississippi R. Basin



.01- 0.1

0.1 to 1

1 to 5

5 to 10


Alexander et al., 2008.

Environ. Sci. Technol. 42: 822–830


Nutrient Use Efficiency and Effectiveness:

Indices of Agronomic and Environmental Benefit


post-harvest evaluation of N effectiveness in cropping systems$FILE/Revised%20NUE%20update.pdf


F-amt. nutrient applied, Y- yield of harvested portion with applied nutrient, Y0- yield of harvested portion with no applied nutrient, UH –nutrient content of harvested portion of crop, U –total nutrient uptake in aboveground biomass with nutrient applied, U0 –total nutrient uptake in aboveground biomass with no nutrient applied

increased farmer interest in better n management
Increased Farmer Interest in Better N Management
  • Increased N costs
  • Better crop prices
  • Calibration and verification of newer technologies
  • Improved farmer skills, and availability of professional guidance by crop advisers

“The Market” Nov.1, 2007

corn grain produced in the u s per unit of fertilizer n used 1964 to 2005

51% increase in N efficiency

12% increase in N fertilizer use

Since 1975:

Corn grain produced in the U.S. per unit of fertilizer N used, 1964 to 2005.




*Application rate for 2004 estimated as avg of 2003 & 2005.

Data sources: USDA Ag Chem Use Survey & Annual Crop Production.

fertilizer n in california and ghg emission
Fertilizer N in California and GHG Emission

802,682 x 0.01= 8,027 metric tons N2O–N emitted

(assuming IPCC 1% factor)

N x 1.57 = 12,602 metric tons of N2O

N2O x 296 = 3.73 million metric tons GWP CO2 equivalent

All GHGs in CA in 2004 (CA EPA, ARB 2007) :

479.74 million metric tons CO2 equivalent

Portion of total that is “fertilizer N induced”

= (3.73/479.74) x 100 = 0.78% of all GWP in California

Source: AAPFCO


Fertilizer N BMPs can help minimize potential for residual NO3-N accumulation & losses

  • N source, rate, placement , and timing …. which may include
    • Urease inhibitors
    • Nitrification inhibitors
    • Slow-release materials
    • Controlled-release materials
  • In combination with appropriate, site-specific cropping system and conservation practices
    • (e.g. conservation tillage, cover crops, vegetative buffers, managed drainage, wetlands, bioreactors, etc.)

  • Appropriate fertilizer N helps increase crop biomass to restore & maintain soil organic matter (SOM)
  • Tillage practices with the least soil disturbance help maintain SOM
  • Intensive crop management can help minimize GHG emissions, and lower GHG emission/unit of crop or food produced
  • Fertilizer N contributions to agricultural GHG emissions can range widely, BUT agricultural emissions are relatively small compared to other source emissions
  • We must continue to strive to improve NUE

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