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TECHNICAL REPORTS

Plant and Environment Interactions

The Myth of Nitrogen Fertilization for Soil Carbon Sequestration

Department of Natural Resources and Environmental Sciences, Turner Hall, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61801. This study was performed with partial funding under Project 875397, Illinois Agric. Exp. Stn., and with support generated through the ¹⁵N Analysis Service

^* Corresponding author (mpcnlink{at}gmail.com).

Received for publication February 2, 2007. Intensive use of N fertilizers in modern agriculture is motivated by the economic value of high grain yields and is generally perceived to sequester soil organic C by increasing the input of crop residues. This perception is at odds with a century of soil organic C data reported herein for the Morrow Plots, the world's oldest experimental site under continuous corn (Zea mays L.). After 40 to 50 yr of synthetic fertilization that exceeded grain N removal by 60 to 190%, a net decline occurred in soil C despite increasingly massive residue C incorporation, the decline being more extensive for a corn–soybean (Glycine max L. Merr.) or corn–oats (Avena sativa L.)–hay rotation than for continuous corn and of greater intensity for the profile (0–46 cm) than the surface soil. These findings implicate fertilizer N in promoting the decomposition of crop residues and soil organic matter and are consistent with data from numerous cropping experiments involving synthetic N fertilization in the USA Corn Belt and elsewhere, although not with the interpretation usually provided. There are important implications for soil C sequestration because the yield-based input of fertilizer N has commonly exceeded grain N removal for corn production on fertile soils since the 1960s. To mitigate the ongoing consequences of soil deterioration, atmospheric CO₂ enrichment, and NO₃^– pollution of ground and surface waters, N fertilization should be managed by site-specific assessment of soil N availability. Current fertilizer N management practices, if combined with corn stover removal for bioenergy production, exacerbate soil C loss.

Abbreviations: HI, harvest index • HNPK, high NPK • ISNT, Illinois soil N test • NPK, fertilization with commercial N, P, and K • RSR, root-to-shoot ratio • SOC, soil organic C • SOM, soil organic matter

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				Reply: Comment on "The Myth of Nitrogen Fertilization for Soil Carbon Sequestration", by S.A. Khan et al. in the Journal of Environmental Quality 36:1821-1832 J. Environ. Qual., May 1, 2008; 37(3): 739 - 740. [Full Text] [PDF]