Long-term tillage and residue removal effects on soil carbon, nitrogen, and grain yield in irrigated corn

Corn (Zea mays L.) stover demand as a forage or for an emerging bioeconomy has increased the importance of determining the long-term effects of stover removal on grain yield and soil properties. Study objectives were to evaluate grain yield, soil organic carbon (SOC), and total soil N (0-150 cm) in a 20-year, irrigated, continuous corn study, located in eastern Nebraska, under conventional tillage (CT) and no-till (NT) with variable corn stover removal rates (none, medium, and high). After 20 years, grain yield was up to 6.0% greater under NT with stover removal compared with NT and no stover removal, while yield was similar for CT in all stover removal treatments. Grain yield was similar between NT with stover removal and CT in all stover removal treatments. High stover removal rates resulted in greater SOC loss at the surface soil layers (0-15 cm and 0-30 cm) after 20 years compared with no or medium stover removal. Corn stover retention under NT resulted in the same cumulative SOC stock loss as CT or stover removal. All management practices resulted in cumulative (0-120 cm) SOC stock loss (8% decrease) that occurred in the last 10 years of the study. Total soil nitrogen stocks were maintained or increased after 20 years at the surface soil layers (0-15 cm and 0-30 cm) and were similar between NT and CT. In an irrigated continuous corn system, neither NT nor stover retention was able to maintain cumulative SOC stocks over time. Corn yield increased under no-till with stover removal but not under conventional tillage. Corn yield was similar in conventional tillage under no, medium, and high stover removal rates. High residue removal rates decreased SOC stocks at the soil surface (0-30 cm) under both no-till and conventional tillage. All management practices resulted in a net loss of cumulative SOC stocks.