The Changing Nature of the Corn Yield Response to N: Role of Residual Soil N.

Current corn fertilizer N recommendations call for a somewhat greater rate for no-till corn relative to tilled corn. This distinction was based on a limited number of observations made in the early years of no-tillage research and bears review. The yield response to tillage (no-till versus tilled) and fertilizer N rates (0, 84, 168 and 336 kg N per ha) in a long term continuous corn with winter cereal cover crop trial was reexamined. In two production seasons, one droughty and one moist, the N rate plots were split in half and the appropriate N rate was either applied or not applied. This gave two corn yield production functions, yield versus residual N and yield versus residual plus added fertilizer N, in each tillage system for each of the two production seasons. The first 15 yr of yield response information confirms current recommendations, but the last 30 yr do not. No-till soils exhibited greater residual soil N in the moist season, but not in the droughty season when moisture limited the yield response to N. No-till soils caused greater crop resilience to drought, both without and with added fertilizer N. After 47 years of cropping, no-till soils maintain greater residual soil N levels and require similar to less fertilizer N than tilled soils when cropped to corn.