Estimation of potential yield and the effect of water requirement satisfaction index on the regional yield of rainfed wheat (Case study: East of Lake Urmia basin)

In the present study, in order to evaluate the effect of stress periods on wheat yield gap in rainfed lands of Bostanabad, Tabriz, Sarab, Maragheh and Harris regions located in the east of Urmia Lake basin, in periods of 11 to 20 years, the water requirement satisfaction index has been used. The linear production function, which was provided by FAO, was also implemented to estimate the potential yield. According to the obtained results, in terms of water supply percentage of rainfed wheat or evapotranspiration ratio in rainfed to standard conditions, Harris with 42% has the best situation and Sarab with 23% has the worst situation. On average, the actual yield of rainfed wheat in the east of Urmia Lake basin is 976 kg/ha. The potential yield was estimated at 4216 kg/ha, indicating a significant gap between potential and actual yield in the study area. The highest regional yield coefficient equal to 0.41 was related to Harris and the lowest value was equal to 0.21 related to the Maragheh region, respectively. The results obtained from the water requirement satisfaction index indicate the existence of suitable conditions for the production of rainfed wheat in the region. However, the actual yield in the east of Lake Urmia basin is on average about 27.2% of the potential yield. This shows that the condition of rainfed lands in the east of Lake Urmia basin is not favorable in terms of the development of the production system and it is necessary to reduce the yield gap. Additionally, the evaluation of the results showed that the correlation of the water requirement satisfaction index with the regional yield coefficient is higher compared to the actual yield and this index can be used to evaluate the yield gap.