Modeling Nitrate Movement and Dissipation in Fertilized Soils 1

It is important to know the fate of nitrogen (N) fertilizers to ensure crop production and avoid pollution, but frequent measurement of soil N is difficult. Therefore, we developed a digital model to calculate the occurrence, movement, and dissipation of nitrate-nitrogen (NO₃-N) within the soil profile of fertilized agricultural lands. Daily NO₃-N amounts and distributions within a 1.8-m soil profile were calculated by representing the major processes influencing NO₃-N for the entire year. Daily soil moisture amounts and movement were predicted by a previously developed soil moisture-evapotranspiration model. Profiles of NO₃-N measured periodically on two research watersheds in western Iowa, one normally fertilized (168 kg/ha per year) and the other excessively fertilized (448 kg/ha per year) with N were used for model verification. The daily calculations for the fertilized cornfields (Zea mays L.) with moderately permeable soils included NO₃-N movement, dissipation, and profile leaching. The predicted NO₃-N profiles closely represented those measured.