Effect of irrigation regime on yield, harvest index and water productivity of soybean grown under different precipitation conditions in a temperate environment

In temperate climatic regions, agricultural production depends on precipitation amount and its distribution during the growing season. A 3-year field study was conducted to investigate the effects of different irrigation regimes on yield parameters and water productivity of sprinkler-irrigated soybean [Glycine max (L.) Merr.], grown under wet, semi-dry and dry conditions in a temperate environment. Four irrigation levels were applied: full irrigation (I100), 65% and 40% of full irrigation (I65 and I40) and non-irrigated control (I0). On average, the I0 treatment resulted in the highest harvest index (HI) and I100 produced the lowest HI. A significant quadratic correlation between seed yield and crop water use was observed in dry and semi-dry year. The irrigation regime significantly influenced seed yield and water use. I65 treatment produced the highest seed yield (3.69 t ha-1) and showed the highest water productivity (WP) (0.90 kg m-3) and irrigation WP (1.08 kg m-3). The present study indicated that irrigation is necessary for soybean cultivation in semi-dry and dry years i.e., when seasonal precipitation is lower than about 300 mm. In wet years, with a favourable amount and distribution of precipitation during the growing season, yields are similar to those achieved with irrigation and high ET values of soybean are attributable to increased evaporation.