MODELING GRAIN-YIELD AND GRAIN-YIELD RESPONSE TO NITROGEN IN SPRING WHEAT CROPS IN THE ARGENTINEAN SOUTHERN PAMPA

Agronomic efficiency (kg grain yield kg(-1) N applied) is conditioned by environmental factors and nitrogen availability during the growing period. Hence, a fertilization model that considers environmental fact ors affecting wheat crop growth and effective N supply should be based on crop N demand. in this work, a simple model based on N balance dur ing the growing season is used as the frame to simulate both the deman d and the availability of N, and to determine grain yield. Fertilizati on experiments were conducted under different environments (50 sites, 8 y) of the Southern Pampa of Argentina. Nitrogen fertilization rates ranged between 25 and 125 kg N ha(-1). Soil initial conditions and wat er balance during the crop cycle were found to modify both N demand an d soil N supply. The amount of N taken up by crops, water balance duri ng the crop growth period and mean maximum temperature during grain fi lling, all affected grain yield components. The proposed model provide d a good agreement between observed independent data sets and simulate d values of grain yield (root mean square error = 9% of the mean value ). Model operation was performed for one site within the region using climatic records to estimate annual grain yield variability under thre e levels of N availability.