Effect Of Potassium Application Methods On Yield And Fiber Quality Of Cotton (Gossyium Hirsutum L.) And Its Physiological Basis

With application of modern cotton （Gossyium hirsutum L.） varieties including Bt（Bacillus thuringiensis） transgenic cotton, premature senescence caused by potassium （K）deficiency has become an important problem in cotton production in the Yellow River Valleyof China. The objectives of this research were to determine the effect of potassium applicationmethods on yield and fiber quality of cotton and its physiological basis. Field studies wereconducted in2009,2010and2011using the cotton cultivar, Lumianyan No.28. Potassiumrates of K2O0,100and150kg ha-1was applied as basal dressing and as12basal dressingand12top-dressing at the blossoming and boll forming stages. The main results are asfollows:1. Effect of potassium application methods on growth and development of cottonThe results show that there were no significant difference in leaf number per plant, leafarea per plant at seeding stage and the final plant height between potassium application andcontrol. Basal application of K₂O150kg ha-1produces significant higher inverse fourth leafarea, shoot dry weight at seeding stage and the final plant height and fruiting branch numbercompared with the untreated control, respectively. Split application of K₂O150kg ha-1produces significant higher the final fruit node number compared with the untreated control.When the K application rate is150kg ha^-1, the basal application of K produces significanthigher aerial part dry weight at seeding stage and the final plant height compared with thesplit application, respectively. Moreover, When the K application rate is150kg ha^-1, the splitapplication of K produces significant higher the final fruit node number compared with thebasal application. When the fertilizer K is basal applied, aerial part dry weight at seedingstage and the final plant height are significant increased with increases of the K applicationrate, respectively.2. Effect of potassium application methods on leaf physiological characteristics of cottonThe results show that the application of potassium increased chlorophyll content,maximum photochemical efficiency, potential photochemical efficiency, actualphotochemical efficiency, stomatal conductance, net photosynthetic rate, and reduced soluble sugar content and specific leaf weight, as compared with CK, respectively. In the same Kapplication methods, chlorophyll content, maximum photochemical efficiency, potentialphotochemical efficiency, actual photochemical efficiency, stomatal conductance, netphotosynthetic rate increased with increases of the K application rate, but soluble sugarcontent and specific leaf weight decreased with increases of the K application rate,respectively. At the same K application rate, effect of different potassium application methodson photosynthesis and assimilates transport in the former was different from that in the latterperiod. In the former, the photosynthesis and assimilates transport of basal application excelthat of split application. In the latter period, the photosynthesis and assimilates transport ofsplit application excel that of basal application.The application of potassium increased superoxide dismutase （SOD） and catalase （CAT）activities, soluble protein content and reduced peoxidase （POD） activity and the contents ofproline and malondialdehyde （MDA）, as compared with CK, respectively. In the same Kapplication methods, SOD and CAT activities and soluble protein content increased withincreases of the K application rate, but POD activity and the contents of proline and MDAdecreased with increases of the K application rate, respectively. At the same K applicationrate, split application increased antioxidant enzyme activities, decreased membrane lipidperoxidation and delayed the senescence of cotton leaves, respectively.The application of potassium increased the contents of nitrogen, phosphorus andpotassium of cotton leaves, as compared with CK, respectively. In the same K applicationmethods, the contents of nitrogen, phosphorus and potassium of cotton leaves increased withincreases of the K application rate, respectively. At the same K application rate, effect ofdifferent potassium application methods on the contents of nitrogen, phosphorus andpotassium of cotton leaves in the former was different from that in the latter period. In theformer, the contents of nitrogen, phosphorus and potassium of cotton leaves of basalapplication excel that of split application. In the latter period, the contents of nitrogen,phosphorus and potassium of cotton leaves of split application excel that of basal application.3. Effect of potassium application methods on PAR transmission parameters of cottoncanopyThe results show that the application of potassium increased leaf area index （LAI）, PARcapture ratio, PAR reflection ratio, and reduced PAR penetration ratio, as compared with CK,respectively. In the same K application methods, LAI, PAR capture ratio and PAR reflectionratio increased with increases of the K application rate, but PAR penetration ratio decreasedwith increases of the K application rate, respectively. At the same K application rate, split application increased LAI, PAR capture ratio, PAR reflection ratio, and reduced PARpenetration ratio, as compared with basal application, respectively.4. Effect of potassium application methods on soil nutrient contentThe results show that the application of potassium increased the contents of totalnitrogen, available nitrogen, available phosphorus and available potassium in0-40cm soil atdifferent stage of cotton compared with the untreated control, respectively. In the same Kapplication methods, the contents of total nitrogen, available nitrogen, available phosphorusand available potassium in0-40cm soil increased with increases of the K application rate,respectively. At the same K application rate, effect of different potassium application methodson nutrient content in0-40cm soil in the former was different from that in the latter period. Inthe former, nutrient content in0-40cm soil of basal application excel that of split application.In the latter period, nutrient content in0-40cm soil of split application excel that of basalapplication.5. Effect of potassium application methods on fiber quality of cotton at different fruitpositionsThe results show that the micronaire values in middle and upper fruit branches and innernodes under the K application are significant increased compared with the untreated control.Split application of K₂O150kg ha^-1produces significant higher fiber lengths, fiber strength inmiddle fruit branches and the outer nodes and fiber maturation in middle fruit branches andinner nodes compared with the untreated control, respectively. Moreover, in the same Kapplication methods, there were no effects on fiber length and fiber strength with the increaseof K application, respectively. At the same K application rate, there was no significantdifference in fiber strength between basal application and split application.6. Effect of potassium application methods on yield and yield components of cottonData collected in the two years indicate that the application of potassium producessignificant differences in seed cotton yield and lint yield compared with the untreated control,respectively. When the K application rate is150kg ha^-1, the split application of K producessignificant higher seed cotton yield and lint yield compared with the basal application,respectively. When the fertilizer K is1/2basal-applied and1/2top-dressed at the blossomingand boll forming stages, seed cotton yield and lint yield are significant increased withincreases of the K application rate, respectively, and the influence of K on the number of bollsper plant is the key reason for the increase.7. Effect of potassium application methods on potassium efficiencies of cottonWhen the K application rate is150kg ha^-1, the split application of K produces significant higher partial factor productivity from applied K （PFPK） and agronomic efficiency of appliedK （AEK） compared with the basal application, respectively. Moreover, in the same Kapplication methods, PFPKis significant decreased with increases of the K application rate,and this is consistent with the law of diminishing returns of fertilizer.