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TECHNICAL REPORTS

Vadose Zone Processes and Chemical Transport

Soil Nitrogen Balance under Wastewater Management: Field Measurements and Simulation Results

^a Kansas Geological Survey, University of Kansas, 1930 Constant Ave., Lawrence, KS 66047
^b Servi-Tech Laboratories, Agri/Environmental Consulting, 1816 East Wyatt Earp, P.O. Box 1397, Dodge City, KS 67801
^c USDA-ARS-NPA-ASRU, 2150 Centre Ave., Bldg D, Ste 200, Fort Collins, CO 80526

^* Corresponding author (marios{at}kgs.ku.edu).

Received for publication July 10, 2008. The use of treated wastewater for irrigation of crops could result in high nitrate-nitrogen (NO₃–N) concentrations in the vadose zone and ground water. The goal of this 2-yr field-monitoring study in the deep silty clay loam soils south of Dodge City, Kansas, was to assess how and under what circumstances N from the secondary-treated, wastewater-irrigated corn reached the deep (20–45 m) water table of the underlying High Plains aquifer and what could be done to minimize this problem. We collected 15.2-m-deep soil cores for characterization of physical and chemical properties; installed neutron probe access tubes to measure soil-water content and suction lysimeters to sample soil water periodically; sampled monitoring, irrigation, and domestic wells in the area; and obtained climatic, crop, irrigation, and N application rate records for two wastewater-irrigated study sites. These data and additional information were used to run the Root Zone Water Quality Model to identify key parameters and processes that influence N losses in the study area. We demonstrated that NO₃–N transport processes result in significant accumulations of N in the vadose zone and that NO₃–N in the underlying ground water is increasing with time. Root Zone Water Quality Model simulations for two wastewater-irrigated study sites indicated that reducing levels of corn N fertilization by more than half to 170 kg ha^–1 substantially increases N-use efficiency and achieves near-maximum crop yield. Combining such measures with a crop rotation that includes alfalfa should further reduce the accumulation and downward movement of NO₃–N in the soil profile.

Abbreviations: DSSAT, Decision Support for Agrometeorology Transfer • EC, electrical conductivity • NUE, nitrogen-use efficiency • RZWQM, Root Zone Water Quality Model • SAR, sodium adsorption ratio