Nitrogen management impacts on yield and nitrate leaching in inbred maize systems

Little information is available regarding N management of inbred maize (Zea mays L.), which exports less N than hybrid maize. Nitrate contamination of the groundwater has been a concern in St Joseph County in southwest Michig an where >20 000 ha of seed maize are grown on sand and sandy loam soils. O ver application of N fertilizer potentially reduces profits of the local gr owers and poses a threat to the environment. A field experiment was conduct ed from 1990 to 1994 to estimate N fertilizer requirements of three differe nt inbred varieties for maximizing yields while minimizing ground water pol lution. Yield and N content of grain and stover were analyzed at the end of each growing season. Nitrate leaching was monitored throughout the 5 yr of study by collecting and analyzing drainage flows out of five large field l ysimeters. Grain yield was the least responsive to N fertilization, compare d with stover biomass, and grain and stover N concentrations. Analyses of y ield, NO3-N leaching and soil N balance indicated that the appropriate fert ilization of the P38 mid-season inbred approximated 108 kg N ha(-1). Nitrat e leaching out of unfertilized plots reached a threshold of 12 to 15 kg N h a(-1) yr(-1), during the last 2 gr of treatment. Application of 101 and 202 kg N ha(-1) generated an average annual loss of 26 and 60 kg N ha(-1), res pectively, during the last 2 gr of treatment.