Yield Gap Analysis: quantifying the gap between actual yield and potential yields of wheat in Gorgan

Food security is a main subject in the world. Many international and governmental organizations to ensure the nutritional needs of human are being explored. According to the restrictions on agricultural lands, an increase in production per area unit is a way to improve food security. Despite high yielding varieties, these varieties do not reach their potential yield due to lack of access to favorable environmental conditions. Therefore, yield gap will be created between potential yield and actual yield. Before any progress in the agronomic operations of crop, it is necessary to identify the crop’s potential yield and to calculate the gap between potential and actual yield. Therefore, the aim of this study was to evaluate the historical trend in different yield gaps and to calculate different mean yield gaps in the studied region.

Potential and conventional yields were simulated using CropSyst model over 1981-2008 period and researchers’ potential yields over 1994-2008 period, maximum achievable yield over 1989-2008 period and actual yield over 1981-2008 period were collected from Agricultural Research Center, and Agriculture Organization. In this study, four types of yield gap were calculated as the difference between simulated potential yield and actual yield (yield gap 1), the difference between researchers’ potential yield and actual yield (yield gap 2), the difference between maximum achievable yield and actual yield (yield gap 3) and the difference between the simulated conventional yield and actual yield (yield gap 4).

The trend of changes in actual yield compared with both simulated potential and conventional yields over 1981-2008 period showed the gap between simulated potential and conventional yields with actual yield were decreasing. The decrease in the yield gaps was due to decrease in the trend of changes in simulated potential and conventional yields and increase in the trend of changes in actual yield over the studied period. According to the results, to increase the simulated potential yield, the varieties should be selected which have high radiation use efficiency. While for reducing the yield gap between simulated conventional yield and actual yield, the varieties with high radiation use efficiency should be cultivated under unlimited water and nitrogen condition. The trend of changes in yield gap between researchers’ potential yield and the actual yield was fixed yields over the period of 1994-2008 which was due to unchanged trend of both yields over this period. The trend of changes of the gap between actual yield and maximum achievable yield was increasing over 1989-2008. This was indicated the better management operations of prior farmers to achieve maximum yield, while other farmers did not work hardly to enhance the yield over the studied years. The simulated mean potential and conventional yield, the researchers’ potential yield, the maximum achievable yield and the actual yield were 6.35, 6.6, 6.0, 4.42 and 3.4 t ha-1, respectively, over 1994-2008 period. The differences between these yield levels with the actual yield were about 3.0, 1.0, 3.2 and 2.6 t ha-1.

It can be concluded that the difference between the management operations performed for achieving actual yield and the other yield levels can be created a yield gap and the more management differences, the higher yield gap.