Assessment of Rapeseed Water Use and Water Productivity across Moghan Plain, Ardabil Province, Iran

In this work, the seasonal applied water and physical water productivity of rapeseed (Brassica napus L.) were evaluated through monitoring 26 farmer fields (including 18, five, and three farmer fields with furrow, center-pivot, solid-set irrigation systems, respectively) over Moghan Plain, Ardabil Province, Iran, during the growing season 2019-2020. The rapeseed seasonal water use (irrigation + effective precipitation) and the grain yield value ranged from 2921-6762 m3 ha-1 and 1.00-3.70 ton ha-1, respectively (with a mean of 4798 m3 ha-1 and 2.64 ton ha-1, respectively). The net rapeseed water requirement during the growing season 2019-2020 and its 10-year mean value ranged from 285-399 mm and 282-354 mm, respectively (with a mean of 325 and 304 mm, respectively). The mean seasonal applied water at farmer fields with furrow irrigation (4328 m3 ha-1) was significantly (p < 0.01) higher compared to the farmer fields with center pivot and solid set sprinkler irrigation (2154 and 2633 m3 ha-1, respectively). Total water productivity (WPI+Pe) and irrigation water productivity (WPI) ranged from 0.28 to 0.95 kg m-3 and 0.41 to 1.45 kg m-3, respectively (with a mean of 0.58 and 0.77 kg m-3, respectively). Based on the results of multivariate linear regression analysis, the factors, including irrigation water salinity, sowing date, seeding rate, date of the first irrigation, growth period length, strong winds near harvest time, the latitude of farmer fields, flowrate of delivered water, mean irrigation interval, and rapeseed grain moisture content and impurity rate were recognized as the most important factors affecting the grain yield and the physical water productivity indices.