A study on the Suitable Sowing Dateof Winter Wheat with limited water supply under the background of climate change

Since the industrial revolution climate change has intensified, leading to changes in the growth conditions of winter wheat and summer maize in the central and northern parts of North China Plain. It is of great significance to adjust the sowing date of winter wheat to implement the "two early - two late" technology in this area. Based on the interannual variation of meteorological factors in the growing season of winter wheat from 1984 to 2023 at Luancheng Agro-Ecosystem Experimental Station of Chinese Academy of Sciences, this experiment studied the suitable sowing date of winter wheat under the background of climate change. Using the field measured data of two cultivars of winter wheat for 7 growing seasons from 2016-2023 with 4 sowing dates under limited irrigation from 2016 to 2023, the suitable sowing date and necessary heat conditions of winter wheat were determined for achieving stable yield. The four sowing dates were the normal (date 1), and extended 5- 7 days each for delayed sowing dates as date 2, date 3 and date 4. The results showed that yield of winter wheat decreased after date 2 and the yield for date 4 was significantly lower as compared with the yield of other three sowing dates (p < 0.01). Under the current climate conditions, the suitable sowing date was from 12^th Oct. to 24^th Oct., the thermal time before winter and the total thermal time during the growth period should reach 350 d °C and 2010 d °C, respectively. Different sowing dates affected duration of different stages of winter wheat through thermal time. Wth the delay of sowing date, the duration of different growth stages (sowing-winter dormancy, winter dormancy-jointing, jointing-anthesis, and anthesis-maturity) was shortened, prolonged, prolonged, and shortened, respectively, and the response to sowing date of different cultivars was different. Late sowing winter wheat was not be capable of sufficient tillering before winter and formed the largest population at the jointing stage. The lag of development process had negative effects on spikes number, shrank the duration of reproductive growth, resulting in crop yield reduction eventually. Before anthesis rate of biomass production of late sowing winter wheat with different sowing dates was synchronized with the dynamic changes of community. If high temperature was encountered in late winter and early spring, the gap caused by the slow growth process in the early stage could be narrowed. The effects of sowing date on the three elements of yield were as follows: spikes number decreased, kernels per spike increased and there was no statistically significant difference in 1000-kernels per spike. The harvest index of late sowing winter wheat was higher than that of early sowing. The grain quality decreased with the delay of sowing date, but there were differences among different cultivars. The conclusion of this study that the suitable sowing date is postponed under the background of climate change provides theoretical support for the decision to implement the "two early - two late" technology in the central and northern parts of North China Plain, and reduces the pressure on agricultural development to adapt to climate change.