Effects of irrigation amount on water-use efficiency, flag leaf senescence, and grain yield of winter wheat

Objectives We studied the wheat yield formation, water-use efficiency and characteristics of flag leaves of winter wheat under different irrigation amounts to provide a basis for water-saving and efficient cultivation techniques for wheat production in Shandong Province.

Methods A winter wheat field experiment was conducted in Jining, Shandong Province from 2016 to 2018. The irrigation treatments included no irrigation during the whole growth period (W₁), and irrigating the soil moisture in 0−40 cm layer to 70% (W₂) and 90% (W₃) of field water capacity at the jointing and anthesis stages of wheat. The daily water consumption, water consumption model coefficient (WSMC) and flag leaf senescence index were analyzed, and the grain yield were investigated at harvest.

Results Compared with W₁, W₂ treatment had 23.95%, 23.92%, and 13.61% higher water consumption, daily water consumption, and WSMC, while W₃ had 25.15%, 25.17%, 4.58% higher values, respectively. There was no significant difference between W₂ and W₃ treatments in daily and periodical water consumption, but W₂ treatment had significantly higher WSMC than W₃. W₂ and W₃ treatments had similar superoxide dismutase activity and soluble protein content in flag leaves, which were significantly higher than those of W₁ treatment. Compared with W₁, W₂ and W₃ treatments had 21.68% and 5.94% higher ¹³C assimilates translocated from vegetative organs to grains after anthesis. The grain auxin content in W₂ was significantly higher than that in W₃, and that in W₃ was significantly higher than that in W₁. The grain abscisic acid contents of W₂ and W₃ treatments were significantly lower than that of W₁ treatment, but W₂ treatment was significantly higher than that of W₃ treatment. The grain zeatin nucleoside contents of W₂ and W₃ treatments were similar and both were significantly higher than that of W₁. W₂ treatment significantly improved grain yield by increasing the number of grains per ear and 1000-grain weight. In 2016−2017 and 2017−2018, W₂ treatment increased wheat grain yield by 29.72% and 6.14%, compared with W₁ and W₃ treatments, respectively. In 2016−2017 and 2017−2018, W₂ treatment increased water-use efficiency by 18.88% and 16.47%, compared with W₁ and W₃ treatments, respectively.

Conclusions At the jointing and anthesis stages of wheat, irrigating soil moisture to 70% of the field water capacity (W₂) in 0−40 cm soil layer could delay leaf senescence, promote the transport of ¹³C assimilates from vegetative organs to grains, regulate the balance of endogenous hormones in grains, increase the number of grains per spike and 1000 grain weight, and consequently enhance water use efficiency and grain yield. It is an effective way of water management for wheat production in the region