A Technique to Estimate Nitrate–Nitrogen Loss by Runoff and Leaching for Agricultural Land, Lancaster County, Nebraska

Abstract

Nitrate-nitrogen (N) loss from agricultural land to natural water resources is an issue for both crop production and water quality. The objective of this study was to develop a technique to evaluate and map nitrate-N loss by surface runoff and subsurface leaching for agricultural land. The technique implemented water loss calculated by the National Resources Conservation Service (NRCS) runoff equation and a percolation model to predict nitrate-N loss for soils with different types of land cover. The technique was applied on agricultural land in Lancaster County, Nebraska, which covers 221,000 ha near the eastern edge of the Great Plains. The Soil Survey Report was used to identify 11 major soil series that comprise 83% of acreage in the county. Predicted nitrate runoff loss from soils ranged from 0.84 to 6.20 kg/ha/y for fallow, 0.83 to 5.97 kg/ha/y for cropland, and 0.80 to 5.29 kg/ha/y for grassland. For most soils nitrate loss by leaching was greater than that by runoff. The average loss predicted by leaching was 8.75, 7.01, and 3.73 kg/ha/y for fallow, cropland, and grassland, respectively. Nitrate concentration predicted in runoff water from three crop-covered soils exceeded the threshold of 10 mg/L, while most soils generated leaching water with nitrate exceeding 10 mg/L. The county-level average of nitrate predicted in runoff (6.55 mg/L) and leaching water (11.8 mg/L) emphasized a need of nutrient management plan to reduce N loss from cropland. The Geographical Information Systems (GIS) were applied to map water loss and nitrate risk potential (NRP) for surface and groundwater contamination in the county.