Yield Formation Characteristics Of Late Sowing Wheat And The Effect Of Variety And Density

Affected by the change of climate and production mode,in recent years,the annual double cropping production of winter wheat and summer corn in the Huang-Huai-Hai Plain has faced many problems,such as frequent climate disasters,shortage of water resources and low utilization efficiency,and it is difficult for summer corn to harvest seeds mechanically and directly.The previous research of this research group shows that optimizing the winter wheat and summer corn double cropping system,delaying the wheat sowing date(mid and late November)and prolonging the summer corn harvest period is one of the important ways to realize the direct grain harvest of summer corn and reduce the water consumption in winter wheat season.The selection of suitable variety types and reasonable planting density are the key to maintain the high yield of very late sowing wheat.However,at present,the regulation mechanism of variety and density interaction on the yield formation of very late sowing wheat and its response mechanism to different meteorological conditions are not clear.Therefore,the split zone design was adopted in this study.The main area was the sowing date,the sub area was the density,and the sub sub area was the variety.The effects of delayed sowing on the yield formation of winter wheat was studied,and the regulation effect of variety and density on the yield formation of delayed sowing winter wheat was clarified.The results show that:(1)With the delay of sowing date,the sowing seedling emergence days were extended from 6d to 50d,the emergence maturity days were significantly reduced from 229d to 120d,the whole growth period days were significantly shortened from 235d to 178d,the maximum tiller amount,the total panicle number and the maximum leaf area index in harvest period were significantly decreased,resulting in a significant decrease in biomass and yield,and the yield was delayed with the sowing date,The yield reduction range was 15.78 kg·hm-2 and the yield reduction rate was 0.17%·d-1.(2)Delayed sowing resulted in the decrease of accumulated temperature,radiation and rainfall.There was a significant positive correlation between accumulated temperature and yield.There was a high negative correlation between effective accumulated temperature and yield from sowing to emergence;At tillering-jointing stage,dry matter quality had a very significant positive correlation with effective accumulated temperature.The delay of sowing date and the decrease of effective accumulated temperature resulted in the decrease of dry matter quality and effective panicle number;At heading maturity stage,the radiation amount was the largest at SD4 sowing date,and the daily average temperature increased,the grain weight decreased under high temperature stress.(3)Suitable varieties and increasing planting density can reduce the yield loss caused by delayed late sowing.Under the condition of low density(D1,2.25 million basic seedlings hm-2),the yield of different types of varieties decreased gradually with the delay of sowing date;Under the density of medium(D2,4.5 million basic seedlings hm-2),the yield of Jimai 22(JM22)decreased significantly with the delay of sowing date,the yield difference between sdl and SD3 sowing dates of Zhongmai 66(ZM66)and Zhengmai 618(ZM618)was not significant,and Zhengmai 101(ZM101)was the highest at SD2 sowing date;Under the high density(D3,6750000 basic seedlings hm-2),the yield of ZM66 and JM22 decreased gradually with the delay of sowing date,and the yield of ZM101 increased gradually.Under the condition of very late sowing(SD4,12/5),the yield difference between D2 and D3 densities was not significant(except ZM66 in 2019),but it was significantly higher than that of D1 density(except zm66 and ZM618 in 2019).The yield of JM22 decreased the least with the delay of sowing date,especially under very late sowing(SD4)and high density(D3),the number of panicles and grain weight increased,and the yield reached 8.87-9.44×l03·kg·hm-2,significantly higher than other varieties.In conclusion,the yield of winter wheat decreased with the delay of sowing date.The yield loss of late sowing winter wheat can be reduced to a certain extent through the optimal combination of different types of varieties and density;The low temperature at seedling stage and high temperature after anthesis caused by delayed sowing are the main climatic factors leading to the reduction of yield of very late sowing wheat.Under the condition of very late sowing and high density planting,JM22 has more ears and 1000 grains,the yield decreases the least with the delay of sowing date,and the yield is significantly higher than that of other varieties.Therefore,JM22 can be selected under very late sowing of winter wheat,with a planting density of 6.75 million basic seedlings hm-2 to ensure stable yield.