Halvorson, Ardell (USDA-ARS, Fort Collins, CO2150 Centre Ave, Bldg. D, Ste 100Fort, Collins, CO, 80526; Phone: 970-492-7230; Fax: 970-492-7213; Email: ardell.halvorson@ars.usda.gov)

Tillage and Nitrogen Effects on Soil Carbon and Greenhouse Gas Emissions Under Irrigated Continuous Corn

A.D.Halvorson *, A.R.Mosier, C.A.Reule, X.J.Liu

Tillage system and N fertilization effects on soil organic C (SOC) sequestration and greenhouse gas emissions in irrigated continuous corn production are not well documented. A study was initiated in 1999 to investigate the potential of no-till (NT) management to sequester SOC while maintaining continuous corn yields at levels similar to conventional-till (CT) practices. In April 2002, measurement of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes from three of the N rates (0, 134, and 224 kg N/ha) were initiated in the NT and CT systems. Fluxes of CO₂, CH₄, and N₂>O were measured, using vented chambers, one to three times per week, year round, from April 2002 through October 2004. CH₄> fluxes were small and did not differ between tillage treatments, but varied with year. CO₂ efflux was higher in CT compared to NT in 2002, but was not different by tillage treatment in 2003 and 2004. N₂O fluxes increased linearly with increasing N-fertilizer rate each year with emission rates varying with year but not by tillage treatment. Trends were for SOC to be increasing in the NT system but remaining fairly constant in the CT system. Grain yields and crop residue increased with increasing N rate in both tillage systems, but grain yields were slightly higher in CT than in NT system. NT soils were greater net sinks for global warming potential when adequate fertilizer was added to maintain crop production than CT soils. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer