Tillage and Residue Management Effects on Soil Carbon and Nitrogen Under Irrigated Continuous Corn

Demand for corn (Zea mays L.) stover as forage or as a cellulosic biofuel has increased the importance of determining the effects of stover removal on biomass production and the soil resource. Our objectives were to evaluate grain yield, soil organic C (SOC), and total soil N (0-150 cm) in a 10-yr, irrigated, continuous corn study under conventional disk tillage (CT) and notill (NT) with variable corn stover removal rates (none, medium, and high). Natural abundance C isotope compositions (delta C-13) were used to determine C additions by corn (C-4-C) to the soil profile and to evaluate the retention of residual C-3-C. After 10 yr of management treatments, mean grain yields were 7.5 to 8.6% higher for NT when stover was removed compared with no stover removal, while grain yields were similar for CT in all stover removal treatments. Turnover of SOC occurred as C-3-C stocks were replaced by C-4-C in the 0- to 120-cm soil profile. Total SOC and N stocks changed mainly in surface soils (0-30 cm), with no detectable cumulative changes at 0 to 150 cm. Specifically, SOC declined after 10 yr under CT at 0 to 15 cm and was affected by residue management at 15 to 30 cm. Total soil N was greater when no stover was removed (P = 0.0073) compared with high stover removal at 0 to 15 cm. Long-term NT ameliorated medium stover removal effects by maintaining near-surface SOC levels. Results support the need to evaluate SOC cycling processes below near-surface soil layers.