Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2005
Publication Date: 1/4/2007
Citation: Huggins, D.R., Allmaras, R.R., Clapp, C.E., Lamb, J.A., Randall, G.W. Corn-soybean sequence and tillage effects on soil carbon dynamics and storage. Soil Science Society of America Journal 71:145-154. 2007. Interpretive Summary: Background: Worldwide, agricultural soils have a large potential to sequester carbon that is derived from the atmosphere, thereby mitigating climate change. Carbon storage in agricultural soils is largely controlled by tillage and crop rotation. The interactions of these regulators, however, is not well understood, particularly where large amounts of soil carbon storage occur. Description: After 14 years of a tillage and crop sequence study, we used natural C-13 abundance to evaluate the effects of tillage treatment (moldboard plow, chisel plow and no-tillage) and crop sequence (fallow, corn and soybean) on soil organic carbon storage and dynamics. We found marked interactive effects of tillage and crop sequence on soil carbon. Fallow, and treatments with moldboard plowing or continuous soybean decreased soil carbon from an estimated 187 Mg C ha-1 to an average of 135 Mg C ha-1, while chisel plowing with continuous corn and corn-soybean sequences, and no-tillage with continuous corn averaged 164 Mg C ha-1. Impact: We concluded that: (1) Under high initial levels of soil carbon, losses of soil carbon are rapid and substantial with fallow, moldboard plow and continuous soybean treatments; and (2) conservation tillage will slow soil carbon losses, but more carbon inputs from alternative cropping systems are needed to achieve or maintain high levels of soil carbon.
Technical Abstract: Carbon dynamics of agroecosystems are largely regulated by soil disturbance (cultivation) and crop rotation. Interactions between cultivation and crop rotation may be significant in the sub-humid region of the U.S. Corn Belt. Our objectives were to assess tillage and crop sequence effects on soil organic carbon (SOC) storage and dynamics using natural C-13 abundance in corn (Zea mays L., a C-4 species) and soybean [Glycine max (L.), Merr., a C-3 species]. A randomized, split-plot design (four replications) with main plots consisting of tillage treatment: moldboard plow (MP), chisel plow (CP) and no-tillage (NT) and subplots of crop sequence: continuous corn (CC), continuous soybean (SS) and alternating corn-soybean (CS) were established in 1981. Soil samples were collected in each treatment after 14 y and analyzed for bulk density, pH, delta C-13 values and SOC. Marked interactive effects of tillage and crop sequence on SOC occurred. Treatments with MP or SS decreased SOC from an estimated 187 Mg C per ha to an average of 135 Mg per ha (0 to 45 cm depth), an annual loss of 3.7 Mg C per ha, while CP treatments with corn (CC and CS) and NT with CC averaged 164 Mg per ha, an annual loss of 1.6 Mg C per ha. Crop sequence effects on SOC (0 to 45 cm) only occurred when tillage was reduced, with CP and NT averaging 15% greater SOC in CC than SS. Tillage effects on SOC were greatest in CC where CP had 26% and NT 20% more SOC than MP. Continuous soybean was the only crop sequence where tillage had no influence on SOC as C inputs from SS were 55% of CC and SOC decomposition rates were accelerated. A large proportion of the greater SOC under CC for CP and NT, as compared to MP, occurred below tillage operating depths (30 to 45 cm). Despite reduced tillage and high-yielding annual crops, substantial losses in SOC occurred over a 14 y period. We concluded that the combination of low C decay rates, high C inputs and a large proportion of labile soil C may not be achievable with conservation tillage in cropping systems with either corn or soybean.