The Effect of Returning Stalk to Field on Photosynthetic Rate and Chlorophyll Fluorescence of Long-Term Continuous Cropping of Cotton

Cotton micro-experiment was adopted to study the effect of returning stalk to field on cotton photosynthesis and chlorophyll fluorescence parameters under long-term continuous cropping of cotton.The results show that:with the time of continuous cropping, SPAD value and photosynthetic rate declined.Photosynthetic rate declined considerably after 20-year continuous cropping.The treatment of returning stalk to field increased the values by 11.9%,I.8%and 3.6%,in 5,10 and 15 years of continuous cropping,respectively, indicating that the continuous cropping obstacle had an obvious impact on cotton growth in short term and after 20 years.Returning stalks to field helped to a certain degree ease the continuous cropping obstacles.In 5-10 years continuous cropping,the maximum photochemical efficiency of PS II(Fv/Fm) and PSII potential activity(Fv/Fo) decreased first,followed by increase,photo-synthetically activities were only temporarily inhibited,and photosynthetic organs had not been damaged,indicating that continuous cropping slowed down univalent photosynthetic rate(Pn) by decreasing maximum photochemical efficiency of PS II(Fv/Fm) and photochemical quenching coefficient(qP),and finally affected the cotton plant physiology growth.