The myth of nitrogen fertilization for soil carbon sequestration.
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 CO(2) enrichment, and NO(3)(-) 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.
Khan
S A
SA
Department of Natural Resources and Environmental Sciences, Turner Hall, 1102 S. Goodwin Ave., University of Illinois, Urbana, IL 61801, USA. mpcnlink@gmail.com
Mulvaney
R L
RL
Ellsworth
T R
TR
Boast
C W
CW
D002244:Carbon / Q000378:metabolism*; D005308:Fertilizers; D015146:Midwestern United States; D009584:Nitrogen / Q000378:metabolism*; D012987:Soil / Q000032:analysis*; D013997:Time Factors; D003313:Zea mays / Q000378:metabolism
D005308:Fertilizers; D012987:Soil; D002244:Carbon; D009584:Nitrogen