Study Shows Nitrogen Fertilizers Decrease Soil Organic Carbon

The intensive use of nitrogen fertilizers in agriculture is believed to benefit the soil by building organic carbon. A group of researchers from the University of Illinois, however, disputes this view based on analyses of soil samples from the Morrow Plots, the oldest experimental field in the USA. Despite the greater inputs of nitrogen fertilizers,  there has been a 20 percent decrease in corn growth and yield during the past 50 years in the plots.

The findings of the study implicate excessive nitrogen fertilizer use, especially starting in the 1970’s with the yield-based nitrogen recommendations, in promoting the decomposition of crop residues and soil organic matter. After decades of massive inputs of residue carbon, the scientists learned that all the residue carbon disappeared, with a net decrease in soil carbon that averaged 4.9 tons per acre. Regardless of crop rotation, the decline became much greater with the higher nitrogen rate. Because soils differ in their capacities to supply nitrogen, the researchers stress the need for soil testing, ideally on a site-specific basis, as a prerequisite to soil-based nitrogen management that optimizes fertilizer rates.

Read more athttp://www.aces.uiuc.edu/news/internal/preview.cfm?NID=4185&CFID=1627523&CFTOKEN=53360267 The full paper published by the Journal of Environmental Quality is available at http://jeq.scijournals.org/cgi/reprint/36/6/1821