A Soil‐Water‐Nitrogen Model for Irrigated Corn on Sandy Soils

Abstract A model was developed which describes the net changes of nitrogen amounts due to transformations and the movement, uptake, and loss of nitrogen from the root system of irrigated corn ( Zea mays L.) grown on sandy soils. A potential nitrogen uptake function developed from field data is used to determine the maximum uptake for nonlimiting soil water and nitrogen availability. Actual uptake is calculated as less than potential when soil water content and/or mineral nitrogen concentration and distribution limit convective and diffusive movement of nitrate to the root system. Separate calculations are made for uptake resulting from each of these two mechanisms. Seasonal nitrogen uptake was computed within ± 15% of measured uptake on field plots where uptake by above ground plant material ranged from 105 to 218 kg/ha. Computed nitrate leaching losses compared favorably with losses estimated by multiplying percolation loss determined from a weekly water balance, by measured nitrate concentration at 150 cm depth. Field leaching losses estimated by the water balance‐concentration method ranged from 37 to 154 kg/ha.