Precise application of the N fertilizer rate is critical to achieve maximum yield. In major regions, empirical methods were used for determining N fertilizer requirement. These methods cannot take into account variation in management and environmental conditions on determining fertilizer requirement. Crop simulation models can provide an alternative means of determining the optimum crop N requirement under varied management and climatic conditions. In the present study for assessment of N fertilizing of wheat farms in Gorgan region, we conducted a survey on 95 wheat farms integrated with simulation experiment using CropSyst model. On-farm assessment showed that the amount of applied and recommended N fertilizer application varied between 45-175.5 and 67.5-146.3 kg ha-1, respectively. In addition, the amount of applied N fertilizer on 72 farms was more than recommended N values. Comparison of applied and recommended N fertilizer to optimum N fertilizer estimated by simulation model (171 kg ha-1) showed that the amount of applied N fertilizer on 93 farms and the amount of recommended N fertilizer on all farms were lower than optimum N fertilizer. This indicated that there was a gap between both applied and recommended fertilizer with optimum N fertilizer and this gap was more between recommended and optimum value. Therefore, it was concluded that the method of fertilizer recommendation on farms has not been effective and the current method of fertilizer recommendation should be revised for achieving the higher yield on farms.
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