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TECHNICAL REPORT
Vadose Zone Processes and Chemical Transport

Fate of Nitrate and Bromide in an Unsaturated Zone of a Sandy Soil under Citrus Production

^a Center for Marine, Environmental Sciences, and Biotechnology Research, P.O. Box 20600, Savannah State University, Savannah, GA 30404
^b USDA-ARS, Vegetable and Forage Crops Research Unit, 24106 N. Bunn Road, Prosser, WA 99350
^c University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850
^d CMESBR, Savannah State University Savannah, GA 30404

* Corresponding author (siva{at}savstate.edu)

Received for publication October 10, 2000. Understanding water and nutrient transport through the soil profile is important for efficient irrigation and nutrient management to minimize excess nutrient leaching below the rootzone. We applied four rates of N (28, 56, 84, and 112 kg N ha^-1; equivalent to one-fourth of annual N rates being evaluated in this study for bearing citrus trees), and 80 kg Br^- ha^-1 to a sandy Entisol with >25-yr-old citrus trees to (i) determine the temporal changes in NO₃–N and Br^- distribution down the soil profile (2.4 m), and (ii) evaluate the measured concentrations of NO₃–N and Br^- at various depths with those predicted by the Leaching Estimation and Chemistry Model (LEACHM). Nitrate N and Br^- concentrations approached the background levels by 42 and 214 d, respectively. Model-predicted volumetric water content and concentrations of NO₃–N and Br^- at various depths within the entire soil profile were very close to measured values. The LEACHM data showed that 21 to 36% of applied fertilizer N leached below the root zone, while tree uptake accounted for 40 to 53%. Results of this study enhance our understanding of N dynamics in these sandy soils, and provide better evaluation of N and irrigation management to improve uptake efficiency, reduce N losses, and minimize the risk of ground water nitrate contamination from soils highly vulnerable to nutrient leaching.

Abbreviations: ET_P, potential evapotranspiration • LEACHM, Leaching Estimation and Chemistry Model • LEACHN, one-dimensional water flow and nitrogen transport model