Maize Production Impacts on Groundwater Quality

The cumulative effects of management practices on nitrate-nitrogen (NO3-N) leaching and ground water quality are frequently difficult to document because of the time required for expression and the diversity of interacting process involved. This work reports results of a N and water management program initiated by the Central Platte Natural Resource District (CPNRD) in Nebraska. Cultural pratices recommended by the (CPNRD) in Nebraska. Cultural practices recommended by the CPNRD and reported by producers for the 1988 growing season, representing approximately 3900 fields covering 84 210 ha of irrigated corn (Zea mays L.) indicated NO3-N contamination of groundwater was influenced by yield goals and fertilizer N application rates. Groundwater NO2-N concentrations were positively correlated with residual N in the surface 0.9 m of soil prior to the growing season, reflecting the effects of past N and water management practices. Yield goals in 1988 averaged 9% higher than the average 10.0 Mg ha-1 corn yield attained, which accounts for an average of about 20 kg N ha-1 in excess of the average N recommendation. By comparison, in a 1980 to 1984 study from an area within the CPNRD, yield goals in 1988 accounted for 42% of the average excess N application rate of 48 kg ha-1 (based on University of Nebraska recommendations). A large portion of average excess N application is attributed to producers in 14% of the area who applied \u3e100 kg N ha-1 more than the recommended rates. Fertilizer N applied showed little relationship to fertilizer N recommended. Better education and more stringent measures may be required to address the select group of producers who fail to follow CPNRD recommendations