Abstract: To optimize water-saving irrigation regimes for late-maturing winter wheat region in North China, we conducted a field experiment in consecutive seasons of 2018-2020 to investigate the population development, post anthesis dry matter accumulation in wheat and starch accumulation in grains under different irrigation treatments. In the first year, there were eight treatments, including non-irrigation as control (CK), irrigation at overwintering stage (W), jointing stage (J) and booting stage (B), irrigation at overwintering and jointing stages (WJ), irrigation at overwintering and booting stages (WB), irrigation at jointing and booting stages (JB), and irrigation at overwintering, jointing and booting stages (WJB). The latter is the common practice in the local region. According to the results of the first season, four treatments were chosen in the second year, including CK, W, B, and WB. Treatment W had stronger positive effects on the stem number of winter wheat population. Compared with CK, irrigation treatments significantly improved dry matter accumulation at the stages of fore and post-anthesis. Irrigation at early stage (e.g. W) was beneficial to increase the transportation of pre-anthesis storage assimilates to grains, while irrigation at late stage (e.g. treatment B) was beneficial to increase the allocation of post-anthesis accumulated assimilates into grains. The contribution rates of pre-anthesis stored assimilates and post-anthesis accumulated assimilates to grains varied with precipitation of fallow summer period. With increasing irrigation frequency and amount, the contribution rate of post-anthesis assimilates to grains increased significantly. Dry matter content and proportion in different organs of winter wheat at the maturity was in the order of grain (about 50%)>stem sheath+leaf (about 33%)>glume+spike-stalk (about 17%). Irrigation increased the contents of starch and its components, but decreased the ratio of amylose to amylopectin. Total starch amount and its components were higher in treatments W and B, but the ratio of amylose/amylopectin was lower. With increasing irrigation frequency and total amount, total starch amount and its components increased first and then decreased, while the ratio of amylose/amylopectin decreased. The contents of total starch and amylose in grains were in the order of JB>WJB>WB>WJ>W>B>J>CK and without significant differences between the treatments with two and three irrigation times. Synthetically considering the factors including the population development and post-anthesis dry matter accumulation in plants and starch in grains of winter wheat, and water save, irrigation at overwintering and booting stages (WB) had the best performance. Our results could provide theoretical basis for water conservation and achieving stable yield in winter wheat production in the study area.

Key words: irrigation, winter wheat, dry matter, starch, accumulation.