Modeling an irrigation management strategy for minimizing the leaching of atrazine

Possible contamination of water resources by applied pesticides (including insecticides and herbicides) is a problem currently confronting irrigated a gricultural production. Best management practices have to be adopted to min imize pesticide transport and leaching under irrigated conditions. A field capacity/mixing-cell model (IRRSCHM) and a model that uses Richard's equati on and the convection-dispersion equation to describe water and contaminant dynamics in soils (LEACHP) were used to assess the leaching of atrazine (a herbicide) under corn receiving different levels of early-season irrigatio n. The early-season irrigation levels were: 11.1, 16.8, 23.3, and 28.8 cm o ut of corresponding seasonal irrigation levels of 31.2, 39.6, 45.5, and 53. 1 cm. The objectives were to (a) use a modeling approach to evaluate water management effects on atrazine leaching, and (b) assess the feasibility of using IRRSCHM and LEACHP to guide irrigation for minimizing atrazine leachi ng. IRRSCHM and LEACHP simulations deviated from the measured atrazine profile, but both models predicted reasonably well the progression in atrazine leac hing with increasing water application. Additionally, atrazine pulses predi cted by IRRSCHM were ahead of those by LEACHP but lagged behind those obser ved under the different irrigation levels. Similarly, both models underesti mated atrazine leaching, with IRRSCHM leaching estimates being closer to th e observed than the LEACHP estimates. For trample, the atrazine profile's c enter of mass position at 143 days after application, ranged from 34.2 to 4 9.4 cm for IRRSCHM, 23.8 to 34.7 cm for LEACHP, and 40.6 to 60.9 cm for the measured atrazine profile under irrigation levels that ranged from 31.2 to 53.1 cm of water. Based on accurate predictions of the trends in atrazine leaching in relation to different irrigation levels, IRRSCHM and LEACHP cou ld be used for preliminary assessment of the likely amount of atrazine leac hing, resulting from targeted irrigation management strategies. (C) 2001 El sevier Science B.V. All rights reserved.