Nitrogen movement in tile-drained clay and sandy agricultural watersheds

One of the primary objectives of the PLUARG Task C Detailed Watershed studies was to examine probable sources of nutrient pollution to the Great Lakes. Agricultural activities were suggested as major sources of nitrogen loads to the Great Lakes. As a result, the study presented here was initiated to examine some of the nitrogen transformation and transport processes on agricultural land in order to quantify and suggest remedial measures to help control nitrogen pollution to ground and surface waters. Two small agricultural watersheds were selected and nitrogen additions under different cropping and fertilizing practices were monitored. Also, at the mouth of the respective watersheds, N loss rates were monitored over time. The study was initiated with the following objectives in mind: 1. To monitor seasonal changes in nitrogen losses under various cropping and fertilizer practices. 2. To develop, where possible, nitrogen balance and simulation models to predict nitrogen levels entering groundwater supplies from various cropping and fertilizer practices by: (a) Utilization of soil nitrogen characterization data as an aid in quantifying nitrogen transformations (Kowalenko, 1977). (b) Utilization of field data defining soil water transport and storage properties (Topp, 1978). 3. To relate where possible, the collected information to groundwater nitrogen concentrations (Gillham et al., 1978) and nitrogen losses from the two watersheds studied. 4. To suggest remedial measures or alternative practices that might aid in the reduction of nitrogen loads from agriculture to surface and groundwater supplies.