Estimation of Yield Gap and the Potential of Rainfed Barley Production Increase in Iran

Barley (Hordeum vulgare. L) is well adapted to drought and saline conditions as the most important limiting factors for crop production in Iran. This consistency, as well as widespread application in animal feeding, are the reasons for cultivating approximately 1.77 million hectares of barley, in which, 1.04 million hectares was attributed to rainfed barley. The previous studies demonstrated that there was a significant difference between the actual and potential yield of crops due to farm management condition. According to the calculated yield loss, the optimized crop field management is necessary to increase agricultural production. This study was aimed to estimate the yield and production gap of barley under rainfed condition as the first step in the terms of the schematization of stable increase in Iran.

This study is conducted based on the Global Yield Gap Atlas (GYGA) Protocol. As the first step in the implementation of present study, the main rainfed barley harvested areas were determined using GYGA climate zones and the distribution of rainfed barley harvested area maps and the country's meteorological station points layer. After defining the designated climate zones (DCZs) and the reference weather stations (RWSs), the collected data (2000-2014) of agronomic management, meteorological and soil characteristics in each region were employed to estimate the potential yield at the RWSs of rainfed barley as one of components of the yield gap calculation. Estimating barley potential yield under water-limited condition (Yw) was carried out by SSM-iCrop2 during 15 growing seasons. Moreover, the actual yield (Ya) data of rainfed barley was collected at the RWS level as another constituent for yield gap calculation. In the end, the estimated rainfed barley yield gap (Yg) in the RWSs was aggregated to DCZs and finally country-level.

In the current study, 38 RWSs within 17 DCZs of rainfed barley harvested areas were identified. The results showed that the average Yw was estimated 2723 kg. ha-1 and the range varied from 1072 to 4002 kg. ha-1. Ya range in the zones were calculated between 390 and 1510 with average of 1009 kg. ha-1. The results illustrated that there was a significant correlation between mean rainfall and maximum temperature during anthesis to harvest maturity period and Yw within 17 DCZs. Hence, with simultaneous increase in rainfall and decrease in average maximum temperature during this phenological period, concomitantly, the Yw value has been amplified. Yg values was estimated between 615 to 3125 kg. ha-1 (equivalent to 53 to 82% of yield gap (%)) with an average of 1714 kg ha-1. Improving the current management conditions to advance toward the attainable yield (Ya) (equivalent to 80% of Yw) in farmers' lands, can increase the average yield of rainfed barley from 1009 to 2178 kg ha-1. Based on the results, the country's production will grow from 1.05 million tons to 2.26 million tons in rainfed conditions through increasing yield to the level of attainable yield (80% of potential yield). The rate of barley import from other countries will decrease due to improvement in the production.

Our results showed 85 percent of rainfed barley production had been attributed to 17 designated climate zones. Due to the presence of 63% yield gap in rainfed barley fields, by considering 80% of this value as exploitable yield gap, the production can be increased to about 1.22 million tons which is appreciable for the economical and food security issues in Iran. It is not feasible to achieve the potential yield at the farmer level owing to existing constraints, but approaching the attainable yield by improving field management conditions can be accessible in the current situation.