Effects Of Straw Returned To Soil On Cotton Biomass, Nutrition Accumulation And Distribution From Wheat-cotton Double Cropping Model

The stationary field experiments,including different rate of straw mulching and K fertilizer,were conducted in Experimental Station of Jiangsu Academy of Agricultural Sciences in Nanjing(32 ° 20 ' N and 118 ° 52 ' E),and Dafeng Basic Seed Farm in Dafeng(33 ° 24 ' N and 120 ° 34 ' E)from 2011 to 2013,using insect-resistant cotton under wheat-cotton double cropping system.In production,the yield of wheat straw and cotton residue is 9000 and 7500 kg ha-1 in Yangtze River Valley,respectively.Therefore,application rates of wheat straw in cotton season were designated as 0,4500 and 9000 kg ha-1(W0,W4500,W9000),and those of cotton residue in wheat season were designated as 0,3750 and 7500 kg ha-1(C0,C3750,C7500).Finally,there were nine crop residue incorporation treatments without organic K fertilizer applied in the wheat-cotton rotation system,by the processes of independent assortment of wheat straw and cotton residue.Additionally,two independent K fertilizer treatments without crop residue incorporation were designated as 150 and 300 kg K2O ha-1(K150 and K300),with potassium sulfate(50%K2O)applied as basal fertilizer in cotton season,and they were not applied in wheat season.The subject is to investigate the different effects of consecutive crop residue incorporation on biomass,nutrition and lint yield.The research should not only provided a theoretical basis for cotton yield,but also improved straw utilization,having a great significance in futuristic insect-resistant cotton cultivation.The main results were as follows:1 Effects of Straw Returned to Soil on Cotton Yield and Yield Components from Wheat-cotton Double Cropping ModelStraw mulching significantly increased boll number,boll weight and lint yield of cotton and had no effect on lint percentage,but the yield-increasing effect was less than K fertilizer.Yield-increasing effect was much promoted at Nanjing site than that at Dafeng site.Lint yield was effected by different wheat straw mulching rate but not different cotton straw mulching rate.Lint yield and boll number were promoted among years,and they were effected by soil type,year and straw mulching.Boll number on middle fruiting branch and upper fruiting branch was promoted by straw mulching and K fertilizer at boll opening stage.2 Effects of Straw Returned to Soil on Biomass Accumulation and Distribution of Cotton from Wheat-cotton Double Cropping ModelFriuing branch,fruiting sites and bolls were enhanced as the rate of wheat straw mulching raised and abscission rate was reduced.The difference were not significant among cotton straw mulching at both sites.Compared to control,plant height was much promoted by K fertilizer at Nanjing site,but not at Dafeng site.Root activity was increased by straw mulching at Nanjing site and the difference was significant between half straw mulching and total straw mulching in 2013.Period of rapid growth days of biomass accumulation was prolonged and theoretical maximum of biomass accumulation was increased.The difference was obviously two years after straw returning at Nanjing site,but it was three years at Dafeng site.3 Effects of Straw Returned to Soil on Nutrients Uptake and Utilization of Cotton from Wheat-cotton Double Cropping ModelThe general pattern of cotton nutrients followed a logistic curve with the progress of growth.The eigenvalues of the dynamic accumulation model of nutrients accumulation was affected significantly by the straw mulching and K application.Nutrients absorption at different growth stages were significantly improved by straw mulching and K application,especially in the boll opening stage,and the senescence of vegetative organs was delayed.K absorption was further promoted than N and P,and the K-increasing effect was larger at Nanjing site than that at Dafeng site.Compared with control,K uptake per 100 kg lint was increased by straw mulching and K fertilizer.The treatment of total wheat straw returning much promoted nutrients uptake and delaying premature senescence than the treatment of half wheat straw returning,while significantly less than K fertilizer.The lint yield in the treatment with consecutive crop residue incorporation and K application had a highly significant simple linear correlation with potassium concentration of cotton plant,which was more closely at Nanjing site than that at Dafeng site.