RZWQM SIMULATIONS OF WATER AND NITRATE MOVEMENT IN A MANURED TALL FESCUE FIELD

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Abstract
Disposal of animal waste on agricultural lands has been a widely used practice. The mechanisms and processes controlling the fate of manure in agricultural systems have not been fully understood, however. In this study, the Root Zone Water Quality Model (RZWQM) was used to simulate water and nitrate movement in a tall fescue (Festuca arundinacea L.) field after broiler litter applications. The simulations were evaluated against experimental results from a well established tall fescue field in Fayetteville, Arkansas, which had not received any fertilizer or manure for several years before the experiment. Broiler litter was applied at 8.96 Mg/ha twice a year in the Spring and Fall. Tall fescue yield, soil nitrate-N, soil temperature, soil water content, and soil water pressure head were measured during the 2-year period. Generally, the model provided adequate predictions of soil temperature, soil water content, and soil water pressure head at various soil depths. It also predicted adequately the responses of soil profile (90 cm) nitrate-N to broiler litter applications. However, the model overpredicted nitrate concentration in water samples collected at 200-cm soil depth with suction lysimeters. This trend could be attributed to the effects of a fragipan at 80 to 114-cm soil depth on preferential transport of water and nitrate that was not considered in the model. It is also plausible that water samples from suction lysimeters did not represent preferential transport of nitrate in the field.