MODELING APPROACH TO NITROGEN UPTAKE BY FIELD-GROWN CORN

Although the plant root system is one of the most important plant para meters affecting nutrient uptake by plants, root studies in field expe riments are rarely conducted in plant nutrition and fertility studies. Since collection of root samples and measurements are difficult and t ime consuming, they are not considered as a routine plant parameter. T herefore, the effect and importance of the corn root system on plant n itrogen (N) uptake and grain yield was studied under field conditions in Adana, Turkey. Nitrogen was applied at rates of 200, 250, 300, and 350 kg N ha(-1) as urea in a randomized complete block design experime nt-with three replications. During course of the experiment, soil, pla nt, root, and grain samples were collected and prepared for chemical a nalysis. Nitrogen uptake by plants was predicted using a COMP8 mathema tical computer model and compared to actual plant uptake. Grain yield and leaf N content increased with increasing N rates, but root length did not change statistically, Predicted N uptake increased with added N, but was much smaller than observed N uptake under field conditions. Consequently, additional soil and plant parameters should be consider ed in nutrient uptake models to make the prediction more sensitive.