EVALUATION OF LEACHM .1. SIMULATION OF DRAINAGE, BROMIDE LEACHING, AND CORN BROMIDE UPTAKE

Use of mathematical models to predict solute transport in soils, for research purposes, is increasing, the simpler management-oriented models are needed that require less field-specific data. Evaluation is needed to know which type of model is appropriate. The input-intensive research and simpler management options of the pesticide and tracer version of LEACHM (LEACHMP) were evaluated to predict drainage in zero-tension pan lysimeters, bromide (Br-) leaching, and corn (Zea mays L.) Br- uptake from a 3-yr leaching experiment. Eighteen pan lysimeters (0.465 m2) were installed 1.2 m below the soil surface to collect gravitational water samples. In May 1988, a one-time application of KBr was broadcast to all plots at 100 kg Br- ha-1. Corn Br- uptake was evaluated by taking whole-plant samples at 2-wk intervals in 1988 and 1989. The research model adequately predicted drainage. Significant differences between predicted and observed drainage were not found, and the correlations were significant (0.73 to 0.83). The management model, however, significantly underestimated cumulative drainage. The research model overestimated Br- leaching, because the convection-dispersion equation and used in LEACHMP cannot model dual-pore water flow and solute diffusion found in this soil. The model generally under-predicted corn Br- uptake, which probably contributed to the overpredicted Br- leaching. The research version of LEACHMP adequately modeled drainage, but a more sophisticated approach to solute transport and corn Br- uptake is needed to adequately model Br- movement in this soil-plant-water system. Management model results were generally less accurate than the research model.