Effects of controlled-release potassium fertilizer on available potassium, photosynthetic performance, and yield of cotton

Potassium (K) is one of the major mineral elements required for normal growth of cotton. However, understanding the effect of controlled-release K fertilizer on leaf photosynthesis and K use efficiency (KUE) of cotton is currently limited. A two-year pot experiment was consecutively conducted in 2014 and 2015 with three kinds of K fertilizer including K2SO4, KCl, and polymer-coated KCl (CRK), each at four application rates (0.00, 0.86, 1.73, and 2.59 g K plant(-1), respectively). For each type of K fertilizer, the yield and K uptake of cotton increased but the KUE decreased with higher K fertilizer application. The release characteristics of K from CRK corresponded well to the K requirements during cotton growth. Plant-available soil K, as well as leaf SPAD values, net photosynthetic rate (P-n), maximal photochemical efficiency (Fv/Fm), and effective quantum yield of photosystem II (phi PSII) in CRK treatments were increased after full bloom stage compared to conventional K fertilizers under the same potassium application rate. Consequently, the CRK treatments significantly increased lint cotton yields by 8.1-32.7% and 3.7-20.8%, while the KUE increased by 15.5-54.8% and 14.5-45.4% compared to KCl and K2SO4 treatments, respectively. The results indicate that the application of CRK is intensively recommended to replace conventional potassium fertilizers for gaining greater yields and higher KUE of cotton.