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Synthetic Fertilizer

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Synthetic Fertilizer

Synthetic Fertilizer Degrades Soil Carbon and Nitrogen

University of Illinois scientists Richard Mulvaney, Saeed Khan, and Tim Ellsworth published studies in 2007 and 2009 with findings that synthetic fertilizer use degrades soil carbon and nitrogen.

"The degradation of soil C and Ν resources necessarily in­creases reliance on synthetic Ν fertilization (e.g., Singh et al., 1998), but given the value of organic matter for improving the chemical, physical, and microbial properties of soil, this strategy cannot be expected to maintain current levels of productiv­ity (Cassman et al., 2003; Tong et al., 2003). Despite ongoing genetic and cultural improvements, a 66% global decrease has occurred over the past 40 yr in the agronomic efficiency of fertilizer N (Tilman et al., 2002; Raun and Schepers, 2008). Excessive Ν fertilization no doubt contributes to the latter trend, but soil degradation is a more important concern for sustaining world food supplies (Tong et al., 2003)."[1][2][3][4][5][6]

Following publication of their study, the scientists lost their grant funding from the Illinois Department of Agriculture Fertilizer Research and Education Council. ("They cut us off cold turkey," said Mulvaney.[7]) The studies have been the subject of controversy, but the scientists maintain the accuracy of their findings.[8]

The degradation of soil organic matter with the application of chemical fertilizer was first recorded in the 1920s, when it was found that "Attempts to increase and maintain an abnormally high organic matter content through the excessive applications of farm manure has met with failure and resulted in excessive loss of organic carbon and nitrogen" and that "Liberal use of mineral nitrogen as measured by long-time field experiments has stimulated the decay of organic matter in excess of such action by mineral fertilizer without nitrogen."[9]

Likewise, a 1939 paper found that:

"The lowest supply of organic matter after fifty years occurs in Plot No. 2 under continuous wheat given heavy additions of commercial fertilizer. This seems to suggest that the addition of the nitrogen and minerals has supplied a microbiological deficiency, and that fertilizers served thus to deplete the organic matter further here than on any other plot. With over 750 pounds of mixed fertilizers, of which no small part was mineral nitrogen, the carbon supply of the soil has been extensively burned out. That the phosphate and potassium are essential contributions toward increased microbiological activity is testified to by the higher content of organic matter in the continuous wheat plots given ammonium sulfate and sodium nitrate. These are still higher at this time in organic matter than the plot given complete fertilizer."[10]

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  1. R.L. Mulvaney, S.A. Khan, and T.R. Ellsworth, "Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production," Journal of Environmental Quality, November/December 2009.
  2. Cassman, K.G., A. Dobermann, D.T. Walters, and H. Yang. 2003. Meeting cereal demand while protecting natural resources and improving environmental quality. Ann. Rev. Environ. Resour. 28:315-358.
  3. Raun, W.R. and J.S. Schepers. 2008. Nitrogen Management for Improved Use Efficiency. p. 675-693. In J.S. Schepers and W. R. Raun (ed.) Nitrogen in agricultural systems. Agron. Monogr. 49. ASA and SSSA. Madison, WI.
  4. Sing, Y., S.P. Singh, and A.K. Bhardwaj. 1998. Long-term effects of nitrogen, phosphorus, and potassium fertilizers on rice-wheat productivity and properties of Mollisols in Himalayan foothills. p. 238-246. In A. Swarup et al (ed.) Proc. Natl. Workshop on Long-term Soil Fertil. manage. Integr. Plant Nutr. Supply. Indian Inst. Soil Sci., Bhopal, India.
  5. Tilman, D., K.G. Cassman, P.A. Matson, R. Naylor, and S. Polasky. 2002. Agricultural sustainability and intensive production practices. Nature 418:671-677.
  6. Tong, C., C.A.S. Hall and H. Wang. 2003. Land use change in rice, wheat, and maize production in China (1961-1998). Agric. Ecosyst. Environ. 95:523-536.
  7. Phone interview with Jill Richardson, April 20, 2012.
  8. D.S. Powlson, D.S. Jenkinson, A.E. Johnston, P.R. Poulton, M. J. Glendining, and K.W.T. Goulding, Comments on “Synthetic Nitrogen Fertilizers Deplete Soil Nitrogen: A Global Dilemma for Sustainable Cereal Production,” by R.L. Mulvaney, S.A. Khan, and T.R. Ellsworth in the Journal of Environmental Quality 2009 38:2295–2314.
  9. J.W. White, "Soil Organic Matter and Manurial Treatment," Paper read as a part of the symposiumon "Soil Organic Matter" at the meeting of the Society held in Washington D.C., November 19, I926. Contribution from the Department of Agronomy, Pennsylvania State College.
  10. Wm. A. Albrecht, "Variable Levels of Biological Activity in Sanborn Field after Fifty Years of Treatment," Department of Soils, Missouri Agricultural Experiment Station, Columbia, Mo., Journal Series No. 584, 1939.

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