Exploring the current status of barley yield and production gap of Iran

Barley (Hordeum vulgare. L) is adapted to drought and salinity as the most critical constrained factors in Iran's crop production. Hence, the grain barley's importance is exhibited via 1.75 million hectares of harvested areas and 3.2 million tons of production in the country with arid and semi-arid climate conditions. However, the current production status meets only about 50% of Iran's barley's grain demands and is globally recognized as one of the largest barley importers in recent years. This study aimed to estimate the potential and yield gap and the potential barley grain production increase under the irrigated and rainfed conditions as the first step in schematizing the promotion of barley production. The impact of determinant climate factors on barley yields was also investigated at dominant barley productions regions over Iran. The present study approach is implemented based on the Global Yield Gap Atlas (GYGA). Accordingly, 12 and 17 designated climatic zones (DCZ), are distinguished as the dominant areas of the irrigated and rainfed barley production in the country, respectively. Afterwards, 48 and 38 reference weather stations (RWSs) within the DCZs were distributed to irrigated and rainfed barley harvested areas, respectively. The SSM-iCrop2 crop model was employed to simulate potential yield in irrigated (Yp) and rainfed (Yw) conditions by utilization of required data in each RWS through 15 barley growing seasons (2000-2014). The yield gap (the difference between simulated potential yield (Yp or Yw) and actual yield (Ya)) were calculated based on the bottom-up approach of GYGA in RWSs, DCZs and national-scale, respectively. Based on the results, the estimated potential yield varies between 5283 and 8286 kg/ha (with an average of 7090 kg/ha) in irrigated condition, and in the case of rainfed barley ranged between 1072 and 4002 kg/ha (with an average of 2723 kg/ha). In contrast, the actual yield in the DCZs was reported in the range of 1406 and 3723 kg/ha (with an average of 3009 kg/ha) for irrigated barley and ranged around 390-1510 kg/ha in rainfed conditions (with an average of 1009 kg/ha). According to the results, the DCZs that are confronted with higher temperatures and shorter growth length periods due to less total received daily solar radiation have low yields in irrigated conditions. In rainfed barley harvested areas, a significant correlation between rainfall distribution, high temperature and Yw has existed during the reproductive phase within 17 DCZs. Ultimately, the results indicated that the calculated yield gap varies between 3237 and 4697 kg/ha (50-76%) with an average of 4081 kg/ha (58%), and also between 615 and 3125 kg/ha (53-82%) with an average of 1714 kg/ha (63%) in the DCZs of irrigated and rainfed barley harvested areas, respectively. Consequently, it has been concluded that by achieving attainable yield (80% of potential yield) via improving production management, irrigated barley yield production can be increased to 5672 kg/ha and 4.17 million tons, respectively, provided that water resources are available. It can also be exploitable to increase rainfed barley's current yield and production from 1009 to 2178 kg/ha and 1.05-2.26 million tons, respectively. Finally, it makes sense to be inspired by increasing total national barley production from 3.26 to 6.43 million tons per year and bring the country closer to obtain full selfsufficiency in supplying the required barley grain.