Effect of Residual Profile Nitrate on Corn Response to Applied Nitrogen

Residual profile NO₃ significantly affects crop N fertilizer requirements in semiarid regions, but little information is available on the influence of profile NO₃ on crop response to applied N in humid climates. Experiments were conducted on three well-drained silt loam soils to investigate profile NO₃ accumulation and retention and to determine the effect of profile NO₃-N on corn (Zea mays L.) response to applied N under humid climatic conditions. In 1983, spring preplant N (0, 134, 268, or 402 kg N ha⁻¹) was applied to corn at each location. Fall 1983 profile NO₃-N to 90 or 120 cm was linearly related to 1983 N rate and ranged from 52 to 644 kg N ha⁻¹. Overwinter retention of fall profile NO₃-N varied from 45 to 66% among locations in a year with above normal fall to spring precipitation. Original plots at all locations were split in 1984, and preplant N rates of 0, 78, 156 or 234 kg N ha⁻¹ were superimposed on each 1983 N treatment. Corn yields in the absence of applied N and yield response to added N were significantly affected by spring profile NO₃-N content. With no applied N, profile NO₃-N to 90 cm accounted for 84% of the variation in yield at the most responsive site. Grain yields were maximized (8.5 to 9.5 Mg ha⁻¹) in the absence of applied N where profile NO₃-N to 90 cm was >150 kg N ha⁻¹. Similarly, yields were not increased by applied N where profile NO₃-N exceeded 150 kg N ha⁻¹. These results indicate that profile NO₃-N significantly affects corn response to applied N on some Wisconsin soils. Adjustment of N recommendations for profile NO₃-N should allow more accurate prediction of corn N fertilizer requirements on these soils when substantial overwinter carryover of profile NO₃-N occurs. Research supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin-Madison through project 2764.