To Cut Nitrogen Pollution, Move Past the Synthetic-Organic Debate

There's No Silver Bullet Solution
  1. Lassaletta, L., Billen, G., Garnier, J., Bouwman, L., Velazquez, E., Mueller, N. D., & Gerber, J. S. (2016). Nitrogen use in the global food system: past trends and future trajectories of agronomic performance, pollution, trade, and dietary demand.Environmental Research Letters, 11(9), 95007. doi.org/10.1088/1748-9326/11/9/095007. p. 1 and 6.

  2. Zhang, X., Davidson, E. A., Mauzerall, D. L., Searchinger, T. D., Dumas, P., & Shen, Y. (2015). Managing nitrogen for sustainable development. Nature, 528(7580), 51. p.5 Table 1 Note: The nitrogen use efficiency (NUE) of 0.42 corresponds to a loss of 58% of the nitrogen inputs.

  3. Fowler, D., Coyle, M., Skiba, U., Sutton, M. A., Cape, J. N., Reis, S., ... & Vitousek, P. (2013). The global nitrogen cycle in the twenty-first century. Phil. Trans. R. Soc. B, 368(1621), 20130164. p. 2 Calculation: X Teragrams of current N estimated in Lassaletta et al. (2016)

  4. Calculation: 251 MtCO2e from agricultural soil management / 522.3 MtCO2e total from agricultural sector. (2017). Inventory of US greenhouse gas emissions and sinks: 1990-2015: Chapter 5. Environmental Protection Agency.https://www.epa.gov/sites/production/files/2017-02/documents/2017_chapter_5_agriculture.pdf p. 5-1

  5. Robertson, G. P., Vitousek, P. M., & Kellogg, W. K. (2009). Nitrogen in Agriculture: Balancing the Cost of an Essential Resource. Annual Review of Environment and Resources, 34(1), 97–125. doi.org/10.1146/annurev.environ.032108.105046. p. 103.

  6. The first number is calculated using the median values, the second using the mean. U.S. Department of Agriculture, Natural Resources Conservation Service. 2017. Effects of Conservation Practices on Nitrogen Loss from Farm Fields: A National Assessment Based on the 2003-06 CEAP Survey and APEX Modeling Databases.www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcseprd1365657.pdf, p. 48

  7. But see contrary finding of lower eutrophication potential per unit area on organic farms from Tuomisto, H. L., Hodge, I. D., Riordan, P., & Macdonald, D. W. (2012). Does organic farming reduce environmental impacts?--a meta-analysis of European research. Journal of Environmental Management, 112(834), 309–20. doi.org/10.1016/j.jenvman.2012.08.018, p. 314

  8. "...farmers often apply manure N at rates much higher than they would apply fertilizer N to achieve similar total plant-available N." Han, Z., Walter, M. T., & Drinkwater, L. E. (2017). N2O emissions from grain cropping systems: a meta-analysis of the impacts of fertilizer-based and ecologically-based nutrient management strategies. p. 345

  9. U.S. Department of Agriculture, Natural Resources Conservation Service. 2017. Effects of Conservation Practices on Nitrogen Loss from Farm Fields: A National Assessment Based on the 2003-06 CEAP Survey and APEX Modeling Databases.www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcseprd1365657.pdf, p. 48. Note: This is the difference between “Nitrogen applied as commercial fertilizer and manure,” omitting N from biological fixation or deposition.

  10. “We found that N fertilizer rate had the most significant impact on N2O emissions...this relationship between the quantity of N applied and N2O emissions is congruent with studies linking N rates to the size of soil inorganic N pools, nitrate leaching and total N losses.” Boy- Roura et al. 2016 in Han, Z., Walter, M. T., & Drinkwater, L. E. (2017). N2O emissions from grain cropping systems: a meta-analysis of the impacts of fertilizer-based and ecologically-based nutrient management strategies. Nutrient Cycling in Agroecosystems, 107(3), 335–355. doi.org/10.1007/s10705-017-9836-z, p. 343

  11. Leaching and runoff rates are similar for manure and synthetic fertilizer, estimated at 12-17% of applied nitrogen over 80 years: Sebilo, M., Mayer, B., Nicolardot, B., Pinay, G., & Mariotti, A. (2013). Long-term fate of nitrate fertilizer in agricultural soils. Proceedings of the National Academy of Sciences, 110(45), 18185-18189. See also the higher estimate of ~20% from Millennium Ecosystem Assessment (MA). 2005. Ecosystems and Human Wellbeing: Policy Responses Volume 3. Chapter 9: Nutrient Management: pp. 295-311 in www.wri.org/our-work/project/eutrophication-and-hypoxia/sources-eutrophication

  12. Webb, J., Sørensen, P., Velthof, G., Amon, B., Pinto, M., Rodhe, L., … Reid, J. (2013). An Assessment of the Variation of Manure Nitrogen Efficiency throughout Europe and an Appraisal of Means to Increase Manure-N Efficiency. In Advances in Agronomy (Vol. 119, pp. 371–442), p. 390

  13. Ibid.

  14. Sawyer, J. (2007). Is Manure the Same as Fertilizer as a Crop Nutrient Resource? p.2

  15. Lassaletta et al.

  16. Lory, J. A., & Massey, R. (2006). Using Manure as a Fertilizer for Crop Production. In Mississippi Basin Symposia. Retrieved from https://www.epa.gov/sites/production/files/2015-07/documents/2006_8_25_msbasin_symposia_ia_session8.pdf, p. 3

  17. Ibid.

  18. e.g. MacDonald, James M. Manure use for fertilizer and for energy: report to congress. DIANE Publishing, 2009.

  19. “...the quantity of N added was a more significant driver of N2O fluxes than was the form of N.” Han, Z., Walter, M. T., & Drinkwater, L. E. (2017). p. 335

  20. Sainju, U. M. (2016). A global meta-analysis on the impact of management practices on net global warming potential and greenhouse gas intensity from cropland soils. PloS one, 11(2), e0148527 p. 1

  21. Stehfest, E., & Bouwman, L. (2006). N2O and NO emission from agricultural fields and soils under natural vegetation: summarizing available measurement data and modeling of global annual emissions. Nutrient Cycling in Agroecosystems, 74(3), 207–228. doi.org/10.1007/s10705-006-9000-7. p. 207, 211

  22. But note that a smaller portion of the nitrogen in manure than in most synthetic fertilizers is emitted as nitrous oxide. Davidson, E. A. (2009). The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860. Nature Geoscience, 2(9), 659-662.

  23. These values are for tons of CO2e per ton Nitrogen contained in the fertilizer for the average facility in Europe. Stork, M., & Bourgault, C. (2015). Fertilizers and Climate Change. Retrieved fromwww.fertilizerseurope.com/fileadmin/documents/ETS/1._Fertilizers_Europe_documents/Ecofys_Fertilizers_and_Climate_Change_FinalReport21092015_b.pdf

  24. Clark, M., & Tilman, D. (2017). Comparative analysis of environmental impacts of agricultural production systems, agricultural input efficiency, and food choice. Environmental Research Letters, 12(6), 64016. https://doi.org/10.1088/1748-9326/aa6cd5, p. 4

  25. Tuomisto et al. (2012). p. 314

  26. This can be demonstrated through calculations of average values as well. Default emission factors for synthetic N fertiliser is 0.01 kg N2O-N/kg N for direct N2O emission, 0.01 kg N2O-N/kg for indirect N2O emission from volatilization and 0.0075 kg N2O-N/kg N for indirect leached/runoff emissions (IPCC, 2006). Assuming the fraction of synthetic N fertiliser volatised is 0.1 and the fraction of synthetic N fertiliser leached/runoff is 0.3, gives us 0.01325 kg N2O-N/kg N total. N2O-N emissions are typically converted to N2O using a multiplier of 44/28 and then converted to CO2-eq by multiplying them with a global warming potential of 298. This gives us a final CO2-eq value of 6.205 kg CO2/kg N, although it should be noted that N2O emissions have been observed to increase exponentially with application rates. Adding the 2-4 kg CO2/kg N from manufacturing would increase emissions by ~33-50%.

  27. e.g. Baggs, Watson, & Rees, 2000, p. 154

  28. Peigné, J., Casagrande, M., Payet, V., David, C., Sans, F. X., Blanco-Moreno, J. M., ... & Bigongiali, F. (2016). How organic farmers practice conservation agriculture in Europe. Renewable Agriculture and Food Systems, 31(1), 72-85. Abstract.

  29. Basche, A. D., Miguez, F. E., Kaspar, T. C., & Castellano, M. J. (2014). Do cover crops increase or decrease nitrous oxide emissions? A meta-analysis. Journal of Soil and Water Conservation, 69(6), 471-482. Abstract

  30. Kaye, J. P., & Quemada, M. (2017). Using cover crops to mitigate and adapt to climate change. A review. Agronomy for Sustainable Development, 37(1), 4. doi.org/10.1007/s13593-016-0410-x p. 9

  31. Ibid, p. 5

  32. Han, Z., Walter, M. T., & Drinkwater, L. E. (2017). N2O emissions from grain cropping systems: a meta-analysis of the impacts of fertilizer-based and ecologically-based nutrient management strategies. Nutrient Cycling in Agroecosystems, 107(3), 335–355. https://doi.org/10.1007/s10705-017-9836-z p. 350-351

  33. https://www.sare.org/Learning-Center/From-the-Field/North-Central-SARE-From-the-Field/2017-Cover-Crop-Survey-Analysis

  34. Lory, J. A., & Massey, R. (2006). Using Manure as a Fertilizer for Crop Production. In Mississippi Basin Symposia. Retrieved from https://www.epa.gov/sites/production/files/2015-07/documents/2006_8_25_msbasin_symposia_ia_session8.pdf, p. 3

  35. Manure N to fertilizer ratio 1970-2012 was 0.50–0.77, with the ratio decreasing over time. Therefore, manure amounted to 33 - 43% of total manure available. Calculation: Percent of total = ratio / (1 ratio). Yang, Q., Tian, H., Li, X., Ren, W., Zhang, B., Zhang, X., & Wolf, J. (2016). Spatiotemporal patterns of livestock manure nutrient production in the conterminous United States from 1930 to 2012. Science of the Total Environment, 541, 1592-1602, p. 1594

  36. csanr.wsu.edu/can-manure-supply-n-and-p-to-ag/

  37. Mueller, N. D., Gerber, J. S., Johnston, M., Ray, D. K., Ramankutty, N., & Foley, J. A. (2012). Closing yield gaps through nutrient and water management. Nature, 490, 254–257. doi.org/10.1038/nature11420, p. 2

  38. Cui, Z., Zhang, H., Chen, X., Zhang, C., Ma, W., Huang, C., … Dou, Z. (2018). Pursuing sustainable productivity with millions of smallholder farmers. Nature. Retrieved from dx.doi.org/10.1038/nature25785

  39. http://www.croplife.com/equipment/2017-precision-dealership-survey-making-the-turn-toward-decision-agriculture/Fig. 1, statistics for UAVs

  40. Less than 5% of operations in the U.S. currently use anaerobic digesters. 250 anaerobic digester projects out of 8,000 hog and dairy operations EPA estimates could technically install a system. https://www.epa.gov/agstar/agstar-data-and-trends

  41. Pape, D., Lewandrowski, J., Steele, R., Man, D., Riley-Gilbert, M., Moffroid, K., … Moffroid, K. (2016). Managing Agricultural Land for Greenhouse Gas Mitigation within the United States. Retrieved fromhttps://www.usda.gov/oce/climate_change/White_Paper_WEB_Final_v3.pdf, p. 18

  42. This process still produces product that can be used as fertilizer. http://articles.extension.org/pages/30310/uses-of-solids-and-by-products-of-anaerobic-digestion

  43. Gorrie, Peter (August 2014) Capitalizing On Digester Coproducts. BioCycle. Accesed 11/29/17https://www.biocycle.net/2014/08/13/capitalizing-on-digester-coproducts/

  44. Recommended rates may need to be different for leachate, however, given that nutrients in digestate (the byproduct) are more prone to runoff and leaching when applied than those in manure.

  45. Compost: Enhancing the Value of Manure. An assessment of the environmental, economic, regulatory, and policy opportunities of increasing the market for manure compost. (2017). Retrieved from http://suscon.org/wp-content/uploads/2017/10/Sustainable-Conservation_Manure-Compost-Report.pdf, p. 16

  46. Ibid., p. 19.

  47. e.g. https://www.ag.ndsu.edu/manure/documents/nm1478.pdf

  48. Compost: Enhancing the Value of Manure, p. 15.

  49. Gaskell, M., & Smith, R. (2007). Nitrogen Sources for Organic Vegetable Crops, 4461(December), 431–441

  50. suscon.org/project/managing-dairy-manure

  51. Liquid Manure Injection. (2015). (Agronomy Fact Sheet Series No. 87). Retrieved fromhttp://nmsp.cals.cornell.edu/publications/factsheets/factsheet87.pdf, p. 1-2

  52. e.g. MacDonald, J. M. (2009)

  53. Yang, Q., Tian, H., Li, X., Ren, W., Zhang, B., Zhang, X., & Wolf, J. (2016). Spatiotemporal patterns of livestock manure nutrient production in the conterminous United States from 1930 to 2012. Science of the Total Environment, 541, 1592-1602, p. 1598

  54. Hilimire, K. (2011). Integrated crop/livestock agriculture in the United States: A review. Journal of Sustainable Agriculture, 35(4), 376-393. p. 382-384. http://www.tandfonline.com/doi/abs/10.1080/10440046.2011.562042

  55. MacDonald, J. M. (2009).

  56. Ribaudo M, Marshall E, Aillery M, Scott S (2016) Reducing the dead zone in the Gulf of Mexico: Assessing the costs to agriculture. Selected Paper Prepared for Presentation at the 2016 Agricultural & Applied Economics Association Annual Meeting, Boston, MA, July 31–August 2. http://ageconsearch.umn.edu/record/235197/files/Seclectedpaper_2016c.pdf, p. 11