Effects Of Boron Application On Cotton Growth,Yield And Fiber Quality

Cotton is one of the important cash crops in China,which is sensitive to boron（B）.B deficiency in cotton will lead to less blossom,abnormal boll development,while excess B will cause poisoning of cotton plant,wasting of B fertilizer and pollution in environmental,both led to reduction in seed cotton yield and fiber quality.Yangtze river basin cotton area,one of the three major cotton areas in China,is a serious B deficiency area.The soil available B content of this area is between 0.08-1.12 mg kg^-1,with an average of 0.34 mg kg^-1,which is far from sufficient for cotton growth.B application rate of cotton production in this region is not only higher but also has the greatest variation.In order to improve seed cotton yield and fiber quality,save growing cost and prevent environmental pollution,B application rate should be precise and reasonable.Thus,we set up B application experiments in 2020.Cotton cultivars CCRI 425 and Siza 3 were used,3 B application rates(0,2.0 and 3.5 kg B ha^-1)in the field experiment at Nanjing,7 B application rates(0,1.0,1.5,2.0,2.5,3.0 and 3.5 kg B ha^-1)in the column at Nanjing and in field experiment at Dafeng and Xinghua were conducted,respectively,to investigate B effects on cotton agronomic traits,biomass and nutrient accumulation and distribution,seed cotton yield,and fiber quality.The main results are as follows:1.Effect of B application on leaf area,agronomic traits,biomass accumulation and distribution of cottonB application significantly affected the leaf area,agronomic traits,and biomass accumulation and distribution of cotton.With the increase of B application,the leaf area,number of fruiting branches,fruiting nodes,boll number of cotton increased and then decreased,peaked at 2.0 kg B ha^-1 both in column and field experiments.With the increase of B application,the boll shattering rate of cotton decreased and then increased,bottomed at 2.5,2.0 kg B ha^-1 in the column and field experiments,respectively.With the increase of B application,the root,shoot and total biomass accumulation of cotton in the column increased and then decreased,and peaked at 2.0,2.5 and 2.5 kg B ha^-1,respectively.The biomass accumulation of cotton in the field increased with the increase of B application.B application had a significant effect on biomass distribution in Dafeng and Xinghua,but the trend were irregularly;biomass distribution in Nanjing was not significant affected by B application.B application significantly increased leaf area and reproductive organ distribution of the middle and lower fruiting branches but had no significant effect on upper fruiting branches.The value of leaf area and reproductive organ distribution in middle and lower fruiting branches peaked at 2.0 kg B ha^-1.2.Effect of B application on seed cotton yield,yield com BOSition,and fiber qualityB application had no significant effects on fiber quality.Seed cotton yield significantly increased and then decreased with B application increasing,peaked at 2.5,2.0 kg B ha^-1in column and field,respectively,in Nanjing,at 2.5 kg B ha^-1 in Dafeng,and at 1.5,2.5 kg B ha^-1,respectively,for the cultivar CCRI 425 and Siza in Xinghua.Trends of cotton yield components changes with B application rates were irregularly.The seed cotton yield in the upper,middle and lower fruiting branches were peaked at 2.5,2.5 and 1.5 kg B ha^-1,which increased by 14.6%,17.3%and 21.5%,respectively.Besides,seed cotton yield in middle and lower fruiting branches was more sensitive to B application than in upper fruiting branches.Based on fitting curve of seed cotton yield and B application,The seed cotton yield of CCRI 425 were peaked at 2.0,1.8 and 1.9 kg B ha^-1 in Nanjing,Dafeng and Xinghua,respectively;the seed cotton yield of Siza 3 were peaked at 1.4 and 1.9 kg B ha^-1 in Dafeng and Xinghua,respectively.3.Effect of B application on contents and accumulation of cotton plant nutrients and B agronomic utilization rate（BAE）Cotton plant N content was not significantly affected by B,while P and K content significantly increased and then decreased as B application rate increasing,peaked at 2.0kg B ha^-1.Cotton plant B content and N,P,K,B accumulation significantly increased by B application.Besides,BAE was biggist at 2.0 kg B ha^-1 in Nanjing;at 2.0,1.5 kg B ha^-1,respectively,for the cultivar CCRI 425 and Siza 3 in Xinghua,and at 1.0 kg B ha^-1 in Dafeng.4.Relationship between cotton plant B contents and seed cotton yieldSeed cotton yield and cotton plant B content showed the parabolic trend.The optimum B content of the cotton plant for CCRI 425 and Siza 3 were 42.9,36.9 mg kg^-1,respectively,corresponding to B application of 1.7、1.8 kg B hm^-2.To sum up,B application rate of 1.5-2.0 kg B ha^-1 is optimum to seed cotton yield formation in the Yangtze river basin cotton area.