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 Michigan where >20000 ha of seed maize are grown on sand and sandy loam soils. Over application of N fertilizer potentially reduces profits of the local growers and poses a threat to the environment. A field experiment was conducted from 1990 to 1994 to estimate N fertilizer requirements of three different inbred varieties for maximizing yields while minimizing ground water pollution. 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 lysimeters. Grain yield was the least responsive to N fertilization, compared with stover biomass, and grain and stover N concentrations. Analyses of yield, NO₃-N leaching and soil N balance indicated that the appropriate fertilization of the P38 mid-season inbred approximated 108 kg N ha^-1. Nitrate leaching out of unfertilized plots reached a threshold of 12 to 15 kg N ha^-1 yr^-1, during the last 2 yr of treatment. Application of 101 and 202 kg N ha^-1 generated an average annual loss of 26 and 60 kg N ha^-1, respectively, during the last 2 yr of treatment.