| The appropriate application of nitrogen(N),phosphorus(P),and potassium(K)is a necessary practice to promote the growth and development of cotton,improve the physiological activities of cotton plants,and increase cotton yield.Inadequate supply and inappropriate ratio of N,P,and K tend to reduce cotton plant physiological activity,decrease the activities of antioxidant enzymes(superoxide dismutase,catalase and peroxidase),imbalance cell turgor pressure and water potential,and decrease biomass transport from cotton leaves to bolls.Compared with the studies on phosphorus and potassium,the effects of nitrogen fertilizer on Bt transgenic cotton were more widely studied.It has been widely accepted that insufficient nitrogen would result in insufficient nitrogen nutrition for cotton plants,reduced photosynthesis and dry matter accumulation,and inhibited boll growth and fiber development.Excessive nitrogen application,however,tend to decrease the utilization efficiency of nitrogen and increased the emission of nitrogen oxides,resulting in the environmental pollution of groundwater caused by NO3-.At the same time,the efficiency of over application of nitrogen fertilizer on yield increase is also significantly reduced.In recent years,due to the increased cost of nitrogen fertilizer and the increasing concern about greenhouse gas emission,more and more attention has been paid to increasing the utilization efficiency of nitrogen.Meanwhile,the application of phosphate and potassium is receiving increasing recognition from both cotton scientists and cotton producers.Therefore,it is of great practical significance to study how to properly apply N,P,and K at appropriate ratios to improve cotton growth,increase physiological activities,and increase cotton yield.In the present study,a field experiment was done on the Experimental Farm of Yangzhou University,Yangzhou,China(32.9 0N,119.41 0E)in the two cotton growing seasons of 2016 and 2017 to determine the effects of the ratios of N,P,and K(N:P2O5:K2O=1:0:0,1:0.3:0.6,1:0.6:0.9,and 1:0.9:1.2)on the physiological parameters of boll subtending leaves and the characteristics of boll development of two different genotypes of Bacillus thuringiensis(Bt)cotton(cultivars Siza 1 and its parent Sikang 1).The field experiment was arranged in a complete block design with two factors(genotype and ratio of N,P,and K).For all the treatments,300 kg ha-1]nitrogen was applied twice at the equal rate before seeding and at initial flowering stage during both experimental years.The main results are the following.1.As compared with the treatment without P and K application(1:0:0),combined application of N,P,and K significantly increased chlorophyll a content by 5.7%and 14.6%,chlorophyll b content by 22.6%and 3.8%,carotenoid content by 14.7%and 9.9%,soluble protein content by 0.1%and 0.6%as well as soluble sugar content by 16.8%and 7.9%in the boll subtending leaves in the two growing seasons.Similarly,the activity of catalase was enhanced by 12.2%and 10.0%,the activity of peroxidase(POD)by 25.9%and 47.5%,the activity of superoxide dismutase(SOD)by 4.9%and 10.8%,fresh stem weight by 22.0%while dry stem weight by 19.0%,and seed cotton yield by 29.2%and 18.7%,respectively.The combine application was better at enhancing the physiological activity of bollsubtending leaves and seed cotton yield and the ratio of 1:0.6:0.9 considerably performed best for Sikang 1 cultivar amongst all the treatments.2.As compared with the treatment without P and K application(1:0:0),combined application of N,P and K significantly increased boll length by 5.8%and 2.3%,fresh boll weight by 12.2%and 3.2%,dry lint weight by 15.2%and 1.7%,number of seeds boll-1 by 15.2%and 2.5%as well as dry boll shell weight by 11.0%and 4.9%in both experimental years.Furthermore,the activity of superoxide dismutase was improved by 2.3%and 15.6%and soluble protein content by 5.1%and 14.1%as compared to control,respectively,in both experimental years.The ratio of 1:0.6:0.9 considerably performed best amongst all treatments during two growing seasons.Taken together,the ratio of nitrogen,phosphorus,and potassium at 1:0.6:0.9 performed best across two years in which all the treatments and increased the content of chl a and b,carotenoid,soluble protein,and the activity of superoxide dismutase,catalase,and peroxidase.Sikang 1 showed remarkably higher activity of SOD,POD,boll length,boll width,fresh boll weight,dry lint weight,number of seeds boll-1,dry boll shell weight,boll volume and seed weight during the two growing seasons(2016 and 2017)and showed best results as compared with Siza 1.In conclusion,combined application of N,P,and K at appropriate ratios enhanced the physiological activities of boll subtending leaves,promoted boll development,and increase seed cotton yield and the ratio of 1:0.6:0.9 with 300 kg ha-1 N considerably performed best amongst all the treatments for Sikang 1 during the two growing seasons. |
PDF Full Text Request