Effects Of Wheat-cotton Cropping Systems On Cotton Yield Formation And Soil Properities

Wheat-cotton double cropping practiced at a large scale in the Yellow River valley and the Yangtze River valley in China,since wheat-cotton double cropping can increase multiple-crop index,and alleviate the competition for arable land between food crops and cotton.Little information was available on the productivity and soil use efficiencies of wheat-cotton double cropping.Field experiments involved four cropping systems,namely monoculture cotton(MC),wheat/intercropped cotton(W/IC),wheat/transplanted cotton(W/TC)and wheat/direct-seeded cotton(W/DC)and two cotton cultivars(Siza 3,mid-later maturing;CCRI 50,early maturing)were conducted in 2012/2013 and 2013/2014 growing seasons at the the cotton experimental station of Nanjing Agricultural University(33°20′N,120°46′E),Dafeng City,Jiangsu Province,China.The objectives of this study were to explore the physiological mechnism of cotton yiled formation in double-cropped wheat-cotton though investaging cotton growth and development,and to elucidate the effects of cropping system on soil physical and chemical properities in wheat-cotton double cropping system,and provide the valuable reference for scientific fertilization.The main results were as follows:1.Effects of wheat-cotton cropping systems on cotton yield formationThe lint yield of cotton in double cropping systems was markedly lower than that of monoculture cotton.Analysis of the yield components revealed that fewer bolls per unit area,particular the upper fruit branches,was largely contributed to the reduction in cotton yield followed by the decreased boll weight.Cotton in double cropping systems showed a pronounced delay in reproductive development and reproductive growth period,which was caused by wheat shading for W/IC system,and delayed sowing for W/TC and W/DC systems.The later formation of fruits thus results in a reduction in fruit sites and boll number and also in a reduction in boll weight and pro-frost lint yield,limiting their growth and the sink capacity of the plant as a whole.The main determinant of cotton yield in W/IC and W/TC systems was the diminished source capacity,whereas the reduced sink capacity is the main determinant of cotton yield in W/DC systems.Early maturing cotton cultivar is at an advantage in wheat-cotton double cropping systems.Cropping system had significantly effect on cotton biomass and its distribution.The findings suggest that the key factor that limitied cotton yields in W/IC and W/TC systems was inadequate production of biomass,while the key determinant limiting the yield in W/DC system was the inadequate biomass and reduced partitioning to reproductive organs.2.Effects of wheat-cotton cropping systems on soil physical and chemical prosperitiesSignificant differences were observed in the soil temperature,the contents of soil organic matter,total N,available N,P,and K under different cropping systems.On the other hand,soil bulk density was less affected by the cropping systems,indicating lager effects of cropping systems on soil chemical properties than soil physical properties.The effects were higher on soil chemical properties than on soil physical properties.The content of soil organic matter and total N increased with the growing process of cotton.There were no significant differences in soil total P content and pH value.Temporal and spatial heterogeneity of available N,P,and K contents in soil was observed in diverse cropping system cotton farm.The findings in this study with cotton-wheat double cropping system showed that soil available N,P,K in double-cropped cotton field had the similar changing trends to those in mono-cultured cotton field,but the values were significantly higher in double-cropped than in mono-cultured cotton at late growth stages of cotton,especially for DC.The main reasons for this were the straw-returning of wheat and cotton,the high rate application of nitrogen fertilizers,and the fewer uptakes of double crops.The results indicated that W/TC and W/DC should be extended in the Yangtze River Valley and that there is the potential for further enhancement in resource productivity and yield through the use of scientific agricultural practices.The early maturing cultivar appeared to be superior to the late maturing cultivar in the double cropping system.This finding has important instruct for crop management,as it suggests that there are several ways for further enhancement in double cropped cotton yield through the use of scientific agricultural practices.