Assessment of Soybean Applied Water and Water Productivity (a case study: Tail End Region of Moghan Irrigation and Drainage Network, Ardabil Province, Iran)

Due to limitation of available water resources, improving agricultural water productivity has become an inevitable necessity. Therefore, it is important to have reliable estimates of the seasonal applied water and water productivity under current irrigation and farm management. In this paper, the seasonal applied water and physical and economic water productivity of soybean were studied through monitoring 29 farms under actual conditions located at the tail end region of Moghan irrigation and drainage network, Ardabil Province, Iran, during the growing season 2020-2021. The net water requirement estimates of soybean during the growing season 2020-2021 and its 10-year average ranged from 417-719 mm and 457-797 mm with a mean of 539 and 581 mm, respectively, over the studied farms. The total applied water (irrigation + effective precipitation, I + Pe) and the grain yield ranged from 3859-7105 m3 ha-1 and 1.30-2.80 ton ha-1, with a mean of 5664 m3 ha-1 and 2.35 ton ha-1, respectively. The lack of flexibility in water allocations led irrigation schedule to be not adapted with the crop water requirement. The limiting factors of soybean production in the study area caused the observed maximum grain yield to be significantly lower than the potential level of soybean yield in Moghan plain (4.00 ton ha-1). The soybean grain yield exhibited a quadratic correlation with I + Pe. Total water productivity (WPI+Pe) and economic water productivity (WP$) ranged from 0.33 to 0.47 kg m-3 and 21.18 ´ 103 to 48.29 ´ 103 Rials m-3 with a mean of 0.42 kg m-3 and 39.89 ´ 103 Rials m-3, respectively. The mean Israelsen's application efficiency (AE) over initial, development, and mid-season plant growth stages in the study fields were obtained 19, 95, and 100%, respectively.