Estimation of Volume of Applied Water and Water Productivity for Onion in Some Provinces of Iran

This project was implemented with the aim of measuring water applied to onion under farmers’ management in 190 selected sites at the production hubs of onion in Iran including Azarbaijan Sharghi, Isfahan, Khusestan, Zanjan, Kerman, Fars, Khorasan Razavi, Khorasan Shomali, and Hormozgan provinces. According to the results, differences between the average volumes of irrigation water in those provinces, different irrigation methods, various sources and salinities of irrigation water and soil, and different onion varieties were significant (p<1%), during the growing season of 2020-2021. The average amount of applied water by farmers in those provinces was 9502, 13273, 9740, 16588, 9618, 13880, 11998, 8438 and 7057 m3/ha, respectively, with the weighted average of 10823 m3/ha. The onion yield in selected sites, varied from 20000 to 90000 kg/ha, with an average of 49980 kg/ha. The measured values were compared with the net irrigation water requirement estimated by the FAO Penman-Monteith method and with the National Water Document values. The results showed that the differences between average volumes of applied water by farmers, yield and irrigation water productivity, and irrigation water plus effective rainfall productivity in the selected sites were significant at 5% probability level. Irrigation water productivity varied from 3.13 to 6.30 kg/m3 and its average was 4.93 kg/m3. The average irrigation water plus effective rainfall productivity for onion in Iran was 4.50 kg/m3. The average net irrigation water requirement in the study areas by the Penman-Monteith method and the National Water Document were 8834 and 6972 m3/ha, respectively. These results showed that the average applied water in surface, sprinkler, and drip irrigation methods were 11453, 12740 and 10317 m3/ha, respectively, with significant (p<5%) difference. These results showed that in drip irrigation method, applied water was 10% lesser while irrigation water plus effective rainfall productivity was 35% higher. Transplanting seedling compared to direct seeding caused 14.7% reduction in applied water and 16.7% increase in water productivity. According to the results of this study, drip irrigation and transplanting method for onion fields is recommended.