Soil carbon levels in irrigated Western Corn Belt rotations

Authors: Varvel, Gary; Wilhelm, Wallace

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2008
Publication Date: 7/1/2008
Citation: Varvel, G.E., Wilhelm, W.W. 2008. Soil carbon levels in irrigated Western Corn Belt rotations. Agronomy Journal. 100:1180-1184.

Interpretive Summary: Recent reports conclude that US agriculture and forest lands have the capacity to produce immense amounts of lignocellulosic material needed for domestically produced biofuels, but can these residues be utilized sustainably. Our objective was to evaluate the effects of crop rotation and N fertilizer management and their stover production characteristics on soil organic carbon (SOC) levels, one measure of sustainability, in a long-term high yielding irrigated study in the western Corn Belt. An irrigated monoculture corn, monoculture soybean, and soybean-corn cropping systems study was initiated in 1991 on a uniform site in the Platte Valley near Shelton, Nebraska. Soil samples were collected in 1991 prior to initiation of the study and in the spring of 2005 and analyzed for SOC. Significant differences in total SOC values were obtained between rotations and N rates at the 0 to 7.5 and 0 to 15 cm depths in 2005 and all total SOC values were equal to or greater than SOC values obtained in 1991. Residue production was greater than 6 Mg ha-1, a level that appears to be sufficient to maintain SOC levels, in all systems. Can residue amounts above this level be harvested sustainably for biofuel production in cropping systems similar to these? Though these results suggest that a portion of corn stover could be harvested without reducing SOC under the conditions of this investigation, the direct impact of stover removal remains to be evaluated.

Technical Abstract: Proposals promoting the use of massive amounts of crop residues and other lignocellulosic biomass for biofuel production have increased need for evaluation of the sustainability of cropping practices and their effect on environment quality. Our objective was to evaluate the effects of crop rotation and N fertilizer management and their stover production characteristics on soil organic carbon (SOC) levels in a long-term high yielding irrigated study in the western Corn Belt. An irrigated monoculture corn, monoculture soybean, and soybean-corn cropping systems study was initiated in 1991 on a uniform site in the Platte Valley near Shelton, Nebraska. Soil samples were collected in 1991 prior to initiation of the study and in the spring of 2005 and analyzed for SOC. Significant differences in total SOC values were obtained between rotations and N rates at the 0 to 7.5 and 0 to 15 cm depths in 2005 and all total SOC values were equal to or greater than SOC values obtained in 1991. Residue production was greater than 6 Mg ha-1, a level that appears to be sufficient to maintain SOC levels, in all systems. Can residue amounts above this level be harvested sustainably for biofuel production in cropping systems similar to these? Though these results suggest that a portion of corn stover could be harvested without reducing SOC under the conditions of this investigation, the direct impact of stover removal remains to be evaluated. [REAP and GRACEnet Publication]