Development and evaluation of a macropore flow component for LEACHM

LEACHM (Leaching Estimation And Chemistry Model) and a modified LEACHM were used to predict NO₃-N and atrazine transport in two Kansas soils. NO₃-N and atrazine concentration data obtained from two monolith weighing lysimeters containing two different Kansas soils were used to calibrate and validate the nitrogen and pesticide versions of LEACHM. Since LEACHM (ver. 3.0) does not include any means to deal with macropore flow, the macropore flow subroutine from RZWQM (Root Zone Water Quality Model) was incorporated into LEACHM. Measured concentrations of NO₃-N and atrazine were compared with those predicted by LEACHM with and without the macropore flow subroutine. In general, concentrations predicted by both models tend to follow the trend of measured concentrations. Addition of the macropore flow subroutine improved the predictions a little, especially for atrazine transport in silty clay loam soil. However, no such improvement was observed in sandy loam soil. Overall, the results of this study showed that addition of the macropore flow component had potential for improving prediction capability of LEACHM in silty clay loam soils. The use of more site specific macroporosity data is likely to improve the model predictions.