ABSTRACT: Diverse cropping systems can have significant impacts on nutrient losses through tile drain systems and to surface water bodies (rivers and streams). Increased transport
of nitrogen to water bodies can reduce dissolved oxygen and enrich the supply of nutrients, resulting in hypoxic zones. With the objective of reducing the transport of nutrients from agricultural watersheds, long term studies (1990 to 1998) were conducted in Iowa to investigate the impact of tillage, crop rotation, and N-management practices on NO3-N leaching Iosses
to tile drain water. Results of these studies indicated that continuous corn production systems required higher input of nitrogen fertilizers and resulted in significantly higher NO3-N leaching losses compared to rotated corn in plots either fertilized with manure or urea ammonium nitrate. Also, rotated corn gave higher corn yields, 8 megagrams per hectare (Mg/ha) versus 6 Mgfha, than continuous corn. The higher N application
rates resulted in increased NO3-N concentrations in tile water. A strip cropping system with alfalfa lowered NO3-N concentrations
in tile water to less than 10 mg/l. These studies indicated that better land use practices can reduce NO3-N leaching losses to surface and ground water systems and will help in mitigating
environmental concerns of the production agriculture.