Spatial Specificity Of Cotton Yield Formation Directly-sown In Summer

In order to cope with the high production cost of the traditional cotton planting mode,the summer direct-seeding and lighting cotton planting mode characterized by“late sowing,high density,low nitrogen and one-time fertilization at the first flowering stage”has been progressively practiced in Yangtze River Valley cotton growing regions.For optimize further the management technology and improve the yield and planting efficiency,it is necessary for us to understand the spatial specificity of cotton yield formation direct-sown in summer.Selecting 5 cotton cultivars（of which CRI 619 and CRI 425 are popularized in the north,JHM 116,HM 3097 and ZD 2040 are popularized in Hubei Province）,a two-year（2019-2020）field experiment was conducted with a completely randomized block design to discuss the spatial distribution characteristics of cotton yield formation under short season cultivation by explore cotton bolls spatial distribution,biomass spatial accumulation with stem nodes characteristics,and their relationship with yield to clarify the impact of biomass in different stem segments on cotton bolls spatial distribution.The main results are as follow:1.The summer direct-seeding cotton average lint yield in 2019 was 973.6 kg hm^-2,10.4%higher than that of Hubei Province（National Bureau of Statistics,2021）.The average lint yield of summer direct-seeding cotton yield decreased by 27.9%in 2020 because the precipitation was 285.6%more than that in 2019.Cluster analysis showed that the middle branches provided 70.5%-91.4%of cotton yield in 2019 and the bottomt branches provided83.7%-96.5%in 2020.2.The mass accumulation of biomass and nutrients in the bottom 2/3 stem nodes（1-14 stem nodes）was conducive to summer direct-seeding cotton yield formation.The reproductive organs biomass rapid accumulation stem segment initial node of HM 3097with the highest yield was 20.8%lower than the average value of other cultivars,but the average accumulation rate and maximum biomass were 28.1%and 31.9%higher than the average value of others,respectively;Similarly,the initial nodes of N,P and K rapid accumulation stem segments of HM 3097 were 30.4%,21.1%and 23.5%lower than the average values of others,respectively,and the average accumulation rate and maximum biomass were higher than the average values of others.3.Summer direct-seeding cotton yield was positively correlated with plant width,stem diameter and ratio of height to nodes,negatively correlated with the first fruit branch node.For the bottom 1-5 branches,the shorter the branch length,the larger the proportion of the first fruit node in the length of the branch,and the larger the angle between the branch and the stem,the higher the yield;For the 7^th and above branches,the longer the branch length and the smaller the proportion of the first fruit node in the length of the branch,the higher the yield.The cotton plant configuration with higher overall light transmittance of canopy has higher cotton yield.4.Among the meteorological factors in cotton growth period,the daily temperature range was positively correlated with yield,while precipitation and humidity were on the contrary;The higher effective accumulated temperature of flowering and boll setting period was beneficial to improve the middle branches yield.The results suggest that the key to improve the summer direct-seeding cotton yield is to increase the middle and bottom branches biomass.Therefore,at the beginning of fast growth of reproductive organs,it is beneficial to meet the needs of cotton for nutrients and light to the greatest extent,which will increase the accumulation of photosynthetic products,and finally,obtain higher yield.