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Manure Happens: Altering the Global Nitrogen 
Cycle by Feeding About Seven Billion Carnivorous 
Humans 
Eric A. Davidson 
...
The History of Nitrogen 
7,000 
6,000 
5,000 
4,000 
3,000 
2,000 
1,000 
0 
200 
150 
100 
50 
0 
Invention of Haber Bosc...
The Haber-Bosch process is 
one of the greatest public 
health boons in human history
The Fate of Haber-Bosch Nitrogen 
N Fertilizer 
Produced 
N Fertilizer 
Applied 
N 
in Crop 
N 
Harvested 
N 
in Food 
N 
...
The Fate of Haber-Bosch Nitrogen 
N Fertilizer 
Produced 
N Fertilizer 
Applied 
N 
in Crop 
N 
Harvested 
N 
in Food 
N 
...
People and Animals 
7,000 
6,000 
5,000 
4,000 
3,000 
2,000 
1,000 
0 
250 
200 
150 
100 
50 
0 
1800 1850 1900 1950 200...
Increasing consumption of animal protein 
Westhoek et al. (2011) “The Protein Puzzle” 
Reay et al. (2011) European Nitroge...
The Fate of Haber-Bosch Nitrogen 
N Fertilizer 
Produced 
N Fertilizer 
Applied 
N in 
Crop 
N in 
Feed 
N in 
Livestock 
...
Consumed 
Animal 
Products 
N inputs: 
synthetic N 
fertilizers 
manure 
& natural N 
fixation 
Consumed 
Crops 
Nitrogen:...
Natural N Fixation 
N in Products 
Energy 
12% 
Food 
51% 
Industrial 
products 
35% 
Fiber 
2% 
Intentional N Fixation 
N...
The upper photo shows a site in Southern California 
dominated by exotic annual grasses five years after a burn, 
and the ...
Reactive N in the atmosphere causes several 
forms of air pollution (as well as the GHG N2O) 
 O3 
 Fine Particulate Mat...
Drinking Water Nitrate 
 U.S. standard of 10 ppm 
 In place because of 
methylglobinemia 
 The need for 
maintaining th...
Davidson et al. 2012. Issues in Ecology, Report 
Number 15, Ecological Society of America. 
WHO International 
Agency for ...
Birth defect risks 
 Prenatal exposure to 
nitrate in drinking water 
is associated with neural 
tube defects, oral cleft...
USGS findings for 2001-2004: 
• The federal MCL drinking-water 
standard was exceeded 
in >20% of shallow (<30m 
below the...
Hog production 
NH3 emissions 
Costal 
eutrophication 
Grain production
Hypoxic Zones & Eutrophic Coastal Area 
http://www.vims.edu/research/topics/dead_zones/
A German family with food for one week AA Sno Ammaeliraicnafna mfaimlyi lwyi twhi tfho ofodo fdo rf oorn oen we eweekek 
H...
NATURE|Vol 461|24 September 2009 
“Editor’s note Please note that this 
Feature and the Commentaries are not 
peer-reviewe...
EPA. 2006. Global Anthropogenic Non-CO2 Greenhouse Gas 
Emissions: 1990-2020.
Crutzen et al. Atmos. Chem. Phys. 8, 389-395 (2008) 
Pre-industrial: 
Stratospheric photochemical sink of N2O  total N2O ...
320 
Atmospheric N 2O (ppb) Observed 
310 
300 
290 
280 
270 
Crutzen model 
1860 1880 1900 1920 1940 1960 1980 2000 
The...
320 
310 
300 
290 
280 
270 
1860 1880 1900 1920 1940 1960 1980 2000 
Atmospheric N 2O (ppb) 
Observed 
Crutzen model 
16...
 Time-course analysis of sources and sinks of atmospheric N2O since 1860, 
using both top-down and bottom-up constraints ...
 For each year, the anthropogenic biological source was 
calculated as follows: 
 Anthro-Bio source = Atmospheric growth...
 Anthro-Bio source = 0.0203*manure-N + 0.0254*fertilizer-N 
(p < 0.0001 for each coefficient; adjusted R2 = 0.98) 
 The ...
Atmospheric N2O-N Growth (TgN/yr) Total Source Model 
6 
5 
4 
Manure 
3 
was the 
dominant 
2 
source in 
1 
the 19th 
ce...
Where does the N in manure 
come from? It may not all be 
newly fixed N. 
Mining of soil N due to 
expansion of livestock ...
Units are Gg N yr-1 
David, M. B., McIsaac, G. F., Royer, T. V., 
Darmody, R. G. & Gentry, L. E. Estimated 
historical and...
http://www.unep.org/publications/ebooks/ 
UNEPN2Oreport/
What are the technical, economic, and social impediments 
and opportunities for increased nitrogen use efficiency in 
crop...
Nitrogen Use Efficiency in 
Nebraska’s Central Platte 
Valley 
Richard B. Ferguson 
Hog production 
NH3 emissions 
Profess...
Stakeholder input on 
performance 
indicators 
They have power - 
ballot box and the 
super market 
Paul Fixen 
Applying t...
Trends in the Central Platte Valley 
y = ‐0.1523x + 321.41 
R² = 0.824 
y = ‐2.1092x + 4289.4 
R² = 0.6312 
20 
19 
18 
17...
Balanced 
rations 
Total mix-ed 
rations 
bST 
Milk 3x/d 
A study of 54 dairy farms in Wisconsin demonstrated that more of...
Estimated shares of variable costs per 
acre for rotation corn in Indiana in 2013 
Mixed economic signals 
From 2013 Purdu...
Estimated costs for adopting several currently available management practices across the 
Ceder Creek Watershed, Iowa, for...
RECOMMENDATIONS: 
 Develop partnerships & networks between industry, 
universities, governments, NGOs, crop advisors, and...
PAN AFRICAN SOIL NUTRIENT DEPLETION 
1995-97 2002-04 
Source: IFDC 
kg nutrient ha-1
Initial Goal of African Green Revolution 
Moving from 1 to 3 tons per hectare 
0 N added 
1 ton/ha of maize 
50 kg N ha-1 ...
Manure happens: Altering the global nitrogen cycle by feeding about seven billion carnivorous humans
Manure happens: Altering the global nitrogen cycle by feeding about seven billion carnivorous humans
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Manure happens: Altering the global nitrogen cycle by feeding about seven billion carnivorous humans

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Presented by Eric A. Davidson at the Livestock Systems and Environment (LSE) Seminar, ILRI, Nairobi, 9 September 2014

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Manure happens: Altering the global nitrogen cycle by feeding about seven billion carnivorous humans

  1. 1. Manure Happens: Altering the Global Nitrogen Cycle by Feeding About Seven Billion Carnivorous Humans Eric A. Davidson September 9, 2014
  2. 2. The History of Nitrogen 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 200 150 100 50 0 Invention of Haber Bosch Nitrogen N-Discovered N-Nutrient BNF N2 + H2 → NH3 1750 1800 1850 1900 1950 2000 2050 Humans, millions Haber Bosch, Tg N
  3. 3. The Haber-Bosch process is one of the greatest public health boons in human history
  4. 4. The Fate of Haber-Bosch Nitrogen N Fertilizer Produced N Fertilizer Applied N in Crop N Harvested N in Food N Consumed 100 94 47 31 26 14 -6 -47 -12 -5 -16 14% of the N produced in the Haber-Bosch process enters the human mouth……….
  5. 5. The Fate of Haber-Bosch Nitrogen N Fertilizer Produced N Fertilizer Applied N in Crop N Harvested N in Food N Consumed 100 94 47 31 26 14 -6 -47 -12 -5 -16 14% of the N produced in the Haber-Bosch process enters the human mouth……….if you are a vegetarian.
  6. 6. People and Animals 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 250 200 150 100 50 0 1800 1850 1900 1950 2000 2050 Humans, millions Meat,Total Millions of people Millions of metric tons of meat 140 Manure-N 1860 1880 1900 1920 1940 1960 1980 2000 Nitrogen Inputs (Tg N yr-1) 120 100 80 60 40 20 0 Fertilizer-N NOx-N
  7. 7. Increasing consumption of animal protein Westhoek et al. (2011) “The Protein Puzzle” Reay et al. (2011) European Nitrogen Assessment
  8. 8. The Fate of Haber-Bosch Nitrogen N Fertilizer Produced N Fertilizer Applied N in Crop N in Feed N in Livestock N Consumed 100 94 47 31 7 4 -6 -47 -3 -24 -16 4% of the N produced in the Haber-Bosch process and used for animal production enters the human mouth.
  9. 9. Consumed Animal Products N inputs: synthetic N fertilizers manure & natural N fixation Consumed Crops Nitrogen: A Very Leaky Element NH3 N2O NOX N2 Crop production NH3 N2O NOX N2 Groundwater & surface waters NH4 + NO3 - DON Npart NH4 + NO3 - DON Npart Atmosphere feed Agriculture 14% 4% Animal production
  10. 10. Natural N Fixation N in Products Energy 12% Food 51% Industrial products 35% Fiber 2% Intentional N Fixation Natural 19% C‐BNF 29% 24.7 Tg N Intentional 67% Unintentional N Fixation Unintentional 14% Total N Fixation Vehicles 63% Utility and Industry 35% Other 2% H‐B Fertilizer 46% H‐B Industry 25% Lightning 2% BNF 98% 6.5 Tg N 4.8 Tg N 13.7 Tg N 23.3 Tg N N lost to the Environment N2O 3% Hydrologic N NOx 20% NH3 13% 21% Unknown 20 – 40% N2 3 –23% Fates of intentional N fixation in the U.S. for 2007. C-BNF = crop biological N fixation; H-B = Haber-Bosch. Alteration of N Flows in the U.S. • Intentional Nr creation accounts for 2/3rds of total N2 fixation in the U.S. • Nearly 2/3rds of unintentional Nr is from vehicle use, while a majority of the remainder is from stationary power plants and industrial boilers. • About 3/4ths of intentional Nr enters US agricultural systems. Synthetic fertilizer comprises 2/3rds of Nr input to U.S. agriculture, with the remainder originating from C-BNF. Industrial products like nylon and explosives account for the remaining 25% of intentionally fixed Nr in the U.S. • About 1/3rd of total Nr is incorporated into products, about 1/3rd is lost as Nr to the broader environment, about 1/3rd is denitrified or lost to unknown sinks. • Nitrogen use efficiency is about 38% for agriculture and about 55% for all intentional Nr. From chapter by Benjamin Z. Houlton, Elizabeth Boyer, Adrien Finzi, James Galloway, Allison Leach, Daniel Liptzin, Jerry Melillo, Todd S. Rosenstock, Dan Sobota, and Alan R. Townsend Biogeochemistry (2013) 114:11-23
  11. 11. The upper photo shows a site in Southern California dominated by exotic annual grasses five years after a burn, and the lower shows a site immediately post-burn. Climate-N Interactions and Biodiversity  Both empirical studies and modeling indicate that N and climate change can interact to drive losses in biodiversity greater than those caused by either stressor alone.  In arid ecosystems of southern California, elevated N deposition and changing precipitation patterns have promoted the conversion of native shrub communities to communities dominated by a few species of annual non-native grasses.  A change in biodiversity can also affect ecosystem function, such as increasing fire risk where fuel accumulation was previously rare. From chapter by E. Porter, W. D. Bowman, C. M. Clark, J. E. Compton, L. H. Pardo and J. Soong Biogeochemistry 114: 93-120 Photos by Edith Allen
  12. 12. Reactive N in the atmosphere causes several forms of air pollution (as well as the GHG N2O)  O3  Fine Particulate Matter (PM2.5)  NO2 EPA 2005 estimates for US: • PM2.5 exposure caused 130,000 annual premature deaths • Ozone exposure caused another 4,700 annual premature deaths . • Hundreds of thousands of hospital visits and millions of additional respiratory symptoms each year are also attributed to this pollution
  13. 13. Drinking Water Nitrate  U.S. standard of 10 ppm  In place because of methylglobinemia  The need for maintaining the standard is a matter of recent controversy Methemoglobinemia “blue baby syndrome”
  14. 14. Davidson et al. 2012. Issues in Ecology, Report Number 15, Ecological Society of America. WHO International Agency for Research on Cancer expert working group:  “ingested nitrate or nitrite under conditions that result in endogenous nitrosation is probably carcinogenic to humans”  NOCs are potent carcinogens and teratogens in animals including non-human primates.
  15. 15. Birth defect risks  Prenatal exposure to nitrate in drinking water is associated with neural tube defects, oral cleft defects, and limb deficiencies.  These birth outcome risks occurred at exposures below the current MCL for public water supplies.  However, nitrate may occur in conjunction with other contaminants (e.g., arsenic, pesticides).
  16. 16. USGS findings for 2001-2004: • The federal MCL drinking-water standard was exceeded in >20% of shallow (<30m below the water table) domestic wells in agricultural areas, an increase from 16% a decade earlier. • About 1.2 million Americans use private drinking wells with [NO3-] between 5 and 10 mgN L-1 and about 0.5 million use wells that exceed 10 mgN L-1. • The [NO3-] in deep groundwater increased from 1.2 to 1.5 mgN L-1, indicating that municipal water sources may be at risk in the future. Davidson et al. 2012. Issues in Ecology, Report Number 15, Ecological Society of America.
  17. 17. Hog production NH3 emissions Costal eutrophication Grain production
  18. 18. Hypoxic Zones & Eutrophic Coastal Area http://www.vims.edu/research/topics/dead_zones/
  19. 19. A German family with food for one week AA Sno Ammaeliraicnafna mfaimlyi lwyi twhi tfho ofodo fdo rf oorn oen we eweekek Hungary Planet: What the World Eats Faith D'Aluisio and Peter Menzel, Random House, 2005
  20. 20. NATURE|Vol 461|24 September 2009 “Editor’s note Please note that this Feature and the Commentaries are not peer-reviewed research. This Feature, the full paper and the expert Commentaries can all be accessed from http://tinyurl.com/planetboundaries.”
  21. 21. EPA. 2006. Global Anthropogenic Non-CO2 Greenhouse Gas Emissions: 1990-2020.
  22. 22. Crutzen et al. Atmos. Chem. Phys. 8, 389-395 (2008) Pre-industrial: Stratospheric photochemical sink of N2O  total N2O source  10.2 TgN2O-N/yr Natural source from land and coastal zones = 6.2 to 7.2 TgN2O-N/yr New annual N fixation = 141 Tg N/yr N2O yield = 6.2 to 7.2 TgN2O-N/yr  141 Tg N/yr “new” fixed N = 4.4 – 5.1% 1990-2000 Stratospheric photochemical sink of N2O: 11.9 TgN2O-N/yr Total N2O source = photochemical sink (11.9 TgN2O-N/yr) + atmospheric growth (3.9 TgN2O-N/yr) = 15.8 TgN2O-N/yr Anthropogenic N2O source = total source (15.8 TgN2ON/yr) - current natural source (9.3 to 10.2 TgN2O-N/yr) = 5.6–6.5 TgN2O-N/yr Agricultural contribution = 5.6–6.5 TgN2O-N/yr - industrial source (0.7–1.3 TgN2O-N/yr) = 4.3–5.8 TgN2O-N/yr New anthropogenic fixed N = 86 Tg N Haber-Bosch fertilizer + 24.2 Tg N fixed due to fossil fuel combustion + 3.5 Tg new BNF = 114 Tg N/yr Anthropogenic N2O yield = 4.3–5.8 TgN2O-N/yr  114 Tg N/yr “new” fixed N = 3.8 – 5.1%
  23. 23. 320 Atmospheric N 2O (ppb) Observed 310 300 290 280 270 Crutzen model 1860 1880 1900 1920 1940 1960 1980 2000 The Crutzen et al. (2008) model, based on 4% of annual newly fixed N, underestimates atmospheric N2O from about 1880 to 1980. To match the observed rate of atmospheric accumulation in the 1950s, 10% of annual newly fixed N would have to have been converted to N2O. Davidson, E.A. 2009. Contribution of manure and fertilizer nitrogen to increasing atmospheric nitrous oxide since 1860. Nature Geoscience, 2:659-662.
  24. 24. 320 310 300 290 280 270 1860 1880 1900 1920 1940 1960 1980 2000 Atmospheric N 2O (ppb) Observed Crutzen model 160 140 120 100 80 60 40 20 0 1860 1880 1900 1920 1940 1960 1980 2000 Nitrogen (Tg/year) Manure Synthestic N Fertilizer NOx Holland, E. A., Lee-Taylor, J., Nevison, C., & Sulzman, J. Global N cycle: fluxes and N2O mixing ratios originating from human activity. Data set available on-line [http://daac.ornl.gov/CLIMATE/g uides/N_Emiss.html] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. (2005).
  25. 25.  Time-course analysis of sources and sinks of atmospheric N2O since 1860, using both top-down and bottom-up constraints  Previously compiled database (Holland et al. 2005) of: • atmospheric N2O concentrations • manure production • fertilizer-N use • legume cultivation • NOx emissions  New annual estimates of N2O production from: • fossil fuel N2O sources • nylon production • biomass burning • tropical deforestation • temporal estimates of the stratospheric sink for N2O
  26. 26.  For each year, the anthropogenic biological source was calculated as follows:  Anthro-Bio source = Atmospheric growth – industrial & transport sources + anthropogenic sink + reduced natural tropical forest soil source  The fractions of annual manure-N production (Fm) and annual synthetic fertilizer-N production (Ff) that are released as N2O were estimated by multiple linear regression, using historical data for manure-N and fertilizer-N production:  Anthro-Bio source = Fm*manure-N + Ff*fertilizer-N
  27. 27.  Anthro-Bio source = 0.0203*manure-N + 0.0254*fertilizer-N (p < 0.0001 for each coefficient; adjusted R2 = 0.98)  The entire 19th-20th century pattern of increasing atmospheric N2O can be fit to a regression model related to human food production systems, assuming that 2.0% of annual manure production and 2.5% of annual synthetic fertilizer-N production are released as N2O.  Sensitivity analyses of uncertainties in input data suggest that these coefficients likely fall within these ranges:  Manure-N production: 1.6% - 2.7%  Fertilizer-N production: 1.7% - 2.7%  These yield percentages are within the ranges of uncertainty of IPCC average emission factors.  However, these results differ from the Crutzen et al. (2008) model, because manure-N is not necessarily newly fixed N.
  28. 28. Atmospheric N2O-N Growth (TgN/yr) Total Source Model 6 5 4 Manure 3 was the dominant 2 source in 1 the 19th century 0 NylonN2O TransportN2O FertilizerN2O ManureN2O Biomass Burning 1860 1880 1900 1920 1940 1960 1980 2000 Manure still dominates, but fertilizers are also important
  29. 29. Where does the N in manure come from? It may not all be newly fixed N. Mining of soil N due to expansion of livestock and agricultural production from 1860 to 1960, before synthetic fertilizer-N could replace lost soil N, could explain why atmospheric N2O increased from 1860 to 1960 at a faster rate than predicted from a model of 4% of annual new N fixation. David, M. B., McIsaac, G. F., Royer, T. V., Darmody, R. G. & Gentry, L. E. Estimated historical and current nitrogen balances for Illinois. The Scientific World 1, 597-604. DPO 10.1100/tsw.2001.283 (2001).
  30. 30. Units are Gg N yr-1 David, M. B., McIsaac, G. F., Royer, T. V., Darmody, R. G. & Gentry, L. E. Estimated historical and current nitrogen balances for Illinois. The Scientific World 1, 597-604. DPO 10.1100/tsw.2001.283 (2001).
  31. 31. http://www.unep.org/publications/ebooks/ UNEPN2Oreport/
  32. 32. What are the technical, economic, and social impediments and opportunities for increased nitrogen use efficiency in crop and animal production systems?
  33. 33. Nitrogen Use Efficiency in Nebraska’s Central Platte Valley Richard B. Ferguson Hog production NH3 emissions Professor of Soil Science Costal eutrophication Department of Agronomy & Horticulture University of Nebraska-Lincoln Grain production
  34. 34. Stakeholder input on performance indicators They have power - ballot box and the super market Paul Fixen Applying the Right Source at the Right Rate at the Right Time and in the Right Place, where Right is defined by practice impact on system performance
  35. 35. Trends in the Central Platte Valley y = ‐0.1523x + 321.41 R² = 0.824 y = ‐2.1092x + 4289.4 R² = 0.6312 20 19 18 17 16 15 14 13 12 11 Average of values from producer reports in GWMA, representing ~ 300,000 acres 200 180 160 140 120 100 80 60 40 20 0 10 1985 1990 1995 2000 2005 2010 2015 Soil Residual NO3‐N (lb/acre) Groundwater NO3‐N(ppm)
  36. 36. Balanced rations Total mix-ed rations bST Milk 3x/d A study of 54 dairy farms in Wisconsin demonstrated that more of the N fed to cows ends up in the milk and less in the manure when: • the feed is modified to be more balanced • hormones are managed • when milking is done three times per day. Adapted from Powell et al. 2006. J. Dairy Sci. 89,2268-2278
  37. 37. Estimated shares of variable costs per acre for rotation corn in Indiana in 2013 Mixed economic signals From 2013 Purdue Crop Cost & Return Guide. Purdue Extension publication ID-166-W.  N fertilizer costs are high enough for many farmers to want to improve NUE.  But most also agree that the economic risk of applying too little N is high.  N application provides an important economic margin of safety, like relatively inexpensive insurance.
  38. 38. Estimated costs for adopting several currently available management practices across the Ceder Creek Watershed, Iowa, for a 35% load reduction, implemented over a 20 year period. The total cost is $71 million per year, or $7.78 kg-1 N removed yr-1, or $42 ha-1 yr-1 (from Dan Jaynes, USDA-ARS, and Mark David, Univ. Illinois). Davidson et al. 2012. Issues in Ecology, Report Number 15, Ecological Society of America.
  39. 39. RECOMMENDATIONS:  Develop partnerships & networks between industry, universities, governments, NGOs, crop advisors, and farmers to demonstrate the most current, economically feasible, best management practices.  Provide improved, continuing education to private sector retailers and crop advisors through professional certification programs by university and government extension  Provide science-based recommendations through trusted sources of information to help reduce the perception of risk and the perceived need to apply additional N Linda for Prokopy “insurance” purposes. Purdue Univ.
  40. 40. PAN AFRICAN SOIL NUTRIENT DEPLETION 1995-97 2002-04 Source: IFDC kg nutrient ha-1
  41. 41. Initial Goal of African Green Revolution Moving from 1 to 3 tons per hectare 0 N added 1 ton/ha of maize 50 kg N ha-1 3 tons/ha maize

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