DETERMINATION OF YIELD GAP OF WINTER WHEAT IN WATER AND NITROGEN LIMIT CONDITIONS USING CERES-WHEAT MODEL IN SHIRVAN REGION, IRANAhamad Ghanbari, Baratali Fakheri and Abolfazl TavassoliAbstract One of the most important problems in crops production is difference between actual yield with attainable yield and potential yield (yield gap). So recognition of limited factors of yield and determining yield gap is very important. For reaching to this goal a study was carried out as survey (in 20 farms selected in region) and field experiments in Shirvan region at years of 2009/10 and 2010/11 on winter wheat (cv. Sayonz). In this experiment the most important decreased and limited factors of yield were water, nitrogen and management factors. For simulation of wheat potential yield was used from climatic and soil data of region. And wheat potential yield was simulated using CERES-Wheat model. The results of research showed that potential yield (yield simulated by model in optimum condition), available yield (yield obtained in field experiments in management optimum condition) and actual yield (yield average obtained by region farmers) was equal to 10755, 6647 and 5025 kg/ha respectively. Between limited and decreased factors under study was determined that irrigation is the most important limited factor of wheat yield in region. So that water and nitrogen limited led to 72.84% decrease of wheat yield relation to potential yield. The thrice reduced factor of yield was management factors, which led to decrease of 27.16% wheat yield relation to potential yield. At the last can to recognizing effective factors in yield gap and optimizing them, wheat yield would increase exceedingly in region.
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