Effect of Drainage System Design and Operation on Nitrate Transport

ABSTRACT THE computer simulation model, DRAINMOD, was modified to predict nitrate movement from artificial-ly drained soils with high water tables. Nitrate concentra-tions in surface runoff, subsurface drainage and seepage waters were assumed to be constant and independent of the drainage system design for a corn-soybean rotation on these high water table soils. Total annual nitrate outflow was determined for alternative drainage system designs and operational procedures. The results showed that trafficability and crop protection requirements can be satisfied by several different drainage system designs. For the poorly drained soil considered in this study, there was a three-fold difference in NO3-N outflow among systems that satisfied drainage objectives. The amount of nitrate that leaves the field through drainage waters can be reduced by using controlled drainage during the winter months and during the growing season. However if the controlled drainage systems are not used properly an overall increase in nitrate outflow may result.