Irrigated corn yield and nitrogen accumulation response in a comparison of no-till and conventional till: Tillage and surface-residue variables

Comparisons between no-till and conventional-till management are often confounded by variation in both tillage and residue placement. The objective of this research was to separate the tillage variable from the surface-residue variable associated with no-till and conventional-fill management comparisons in irrigated continuous corn (Zea mays L.) production. Two Nebraska locations (Mead and Clay Center) with differences in soil types and climate were selected. Four tillage-residue treatments [NT-NR (no-till, residue removed), NT-R (no-till, surface residue), T-NR (till, residue removed), T-R (conventional till, surface residue)] were fertilized by either broadcasting at planting or sidedressing at the 6-leaf stage with rates of 0, 56, 112, and 168 kg N ha^-1. At Clay Center, grain yields and total N accumulation were similar for all tillage-residue treatment combinations in all years when the highest fertilizer N rate was used. In 2 of 3 yr at Mead, grain yields and total N accumulation were less for no-till than conventional-till treatments, but in 1 yr the yields and total N accumulations were greater in no-fill than conventional-till treatments. At Mead, surface residue resulted in lower grain yields and total N accumulation compared with bare soil at lower N rates, but not at greater N rates, in 2 of 3 yr. Sidedressing fertilizer N was generally a more efficient N placement than broadcasting. Differences between tillage and residue effects at Clay Center and residue effects at Mead were overcome with higher rates of fertilizer N. Tillage effects at Mead did not appear to be N-related. The data suggest that tillage may be necessary to maintain optimum production levels on finer-textured soils when spring soil temperatures are cool and slow to warm. When spring soil temperatures are warm, no-till strategies can be used for optimum production levels on these soils.