Implications of Observed and Simulated Soil Carbon Sequestration for Management Options in Corn‐based Rotations

Managing cropping systems to sequester soil organic C (SOC) improves soil health and resilience to changing climate. Perennial crops, no‐till planting, manure, and cover crops can add SOC; however, their impacts have not been well documented in the northeastern United States. Our objectives were (i) to monitor SOC from a bioenergy cropping study in Pennsylvania that included a corn ( Zea mays L.)–soybean [ Glycine max (L.) Merr.]–alfalfa ( Medicago sativa L.) rotation, switchgrass ( Panicum virgatum L.), and reed canarygrass ( Phalaris arundinacea L.); (ii) to use the CQESTR model to predict SOC sequestration in the bioenergy crops (with and without projected climate change); and (iii) to use CQESTR to simulate influence of tillage, manure, cover cropping, and corn stover removal in typical dairy forage (silage corn–alfalfa) or grain corn–soybean rotations. Over 8 yr, measured SOC increased 0.4, 1.1, and 0.8 Mg C ha −1 yr −1 in the bioenergy rotation, reed canarygrass, and switchgrass, respectively. Simulated and measured data were significantly correlated ( p < 0.001) at all depths. Predicted sequestration (8–14 Mg C ha −1 over 40 yr) in dairy forage rotations was much larger than with corn–soybean rotations (−4.0–0.6 Mg C ha −1 over 40 yr), due to multiple years of perennial alfalfa. No‐till increased sequestration in the simulated dairy forage rotation and prevented a net loss of C in corn–soybean rotations. Simulations indicated limited impact of cover crops and manure on long‐term SOC sequestration. The low solids content of liquid dairy manure is the likely reason for the less‐than‐expected impact of manure. Overall, simulations suggest that inclusion of alfalfa provides the greatest potential for SOC sequestration with a typical Pennsylvania crop rotation. Core Ideas Bioenergy crops sequestered significant quantities of SOC. CQESTR accurately predicted SOC levels at the site. Inclusion of alfalfa in rotation was predicted to significantly increase SOC. No‐till was predicted to increase SOC in both dairy forage and corn–soybean rotations. Cover crops and manure had limited impact on simulated long‐term SOC accumulation.