Currently, agriculture is one of the leading contributors to the nitrate (NO3-N) contamination of both surface and ground waters. Site-specific management zones combined with variable rate N application have been shown to increase N use efficiency, and therefore may have the potential to reduce NO3-N leaching. The objectives of this study were (i) to establish N balances for three N management strategies and (ii) to compare the potential for NO3-N leaching across strategies. This study was conducted over 4 site-years on irrigated continuous corn (Zea mays L.) fields in northeastern Colorado. Fields were classified into low, medium, and high site-specific management zones based on three data layers: (i) bare soil imagery, (ii) field topography, and (iii) farmer's past experience with crop and soil management. The N management strategies used were a control, a variable yield goal N rate based on the productivity potential of each zone, and a uniform N rate based on a constant yield goal across the field. Soil sample cores were randomly collected to a maximum depth of 3.05 m from geo-referenced locations before planting and after harvest from each N management strategy within each management zone. Soil samples were analyzed for total NO3-N content. Particle-size analysis was performed on one soil sample from each zone. Aboveground biomass samples were collected from geo-referenced locations at crop physiological maturity and were analyzed for total N content. Irrigation water from each site was collected and analyzed for NO3-N. Results for 2 site-years of data will be presented.
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