Filling the yield gap caused by some agronomic factors in some of the major climatic zones of irrigated barley in Iran using modelling approach

Background and objectives: Following wheat, barley is the second most important cereal grain in Iran and plays an important role in livestock and poultry nutrition. To feed the growing population, cereal production should be increased noticeably in the coming years. One of the ways to increase production is to reduce the existing yield gap. Considering the average yield of about 3 t ha-1 in the country and the existence of a large gap compared to the exploitable yield, this study was conducted to identify and quantify some of the factors affecting irrigated barley yield in the major barley-growing areas of Iran.



Materials and methods: In this study, the APSIM model was employed to simulate exploitable, water-limited, sowing date-limited, and cultivar-limited yields. The data required for running the model included the long-term weather data (from 1989 to 2019 for 30 years) of the studied areas obtained from the Iran Meteorological Organization, the soil data which were extracted from the HC27 soil database, and management data obtained from some questionnaires filled out by farmers of the study areas. The main zones of irrigated barley cultivation in the country and the farmer's actual yield in these areas were determined using the statistics of the Ministry of Agriculture. Finally, by calculating the types of yield gaps at different production levels, the impact of limitation in water, sowing date, and cultivar on yield gap was determined.



Results: The results showed that the exploitable yield gap in the studied zones was an average of 4.4 t ha-1, equivalent to 56.4% of the exploitable yield. The average of water-limited, sowing date-limited, and cultivar-limited yield gaps were estimated as 1.4, 0.5, and 0.16 t ha-1 in the studied zones, respectively. The other agronomic yield gap with 2.3 t of yield reduction had the largest share of the exploitable yield gap. The highest increase in yield due to the change of sowing date was observed in Kabudarahang (8%) and the lowest one was simulated in Sabzevar (3%). The simulation results showed that three times more irrigation in Arak, Kabudarahang, and Hamedan and two times more in other studied zones is necessary to fill the water-limited yield gap. Cultivar-limited yield gap was observed only in three locations of Shiraz, Marvdasht, and Sabzevar (on average, 3.6% of exploitable yield gap). This type of yield gap could be compensated by replacing the Bahman cultivar with Reyhan.



Conclusion: Our results approved that the exploitable yield gap in the studied areas varied from 3.9 to 5 t ha-1. About 32% of the exploitable yield gap in the studied zones was due to the water-limited yield gap and around 11% of the yield gap was owing to the sowing date-limited yield gap. Cultivar-limited yield gap also had the lowest share of the exploitable yield gap with 3.6 %. The greater proportion of the exploitable yield gap (around 53%) was owing to other limiting and reducing factors such as pests, diseases, weeds, soil salinity, soil compaction, improper nutrition, unfavorable density, and other socio-economic factors. The results of this study showed that with a slight change in the sowing date, increasing the number of irrigation and improving irrigation management, and using appropriate cultivars, a significant increase in barley yield is achievable in the studied locations and close the yield gap to the self-sufficiency level in barley production in Iran.