Effects of polymer-coated potassium chloride on cotton yield, leaf senescence and soil potassium

Potassium (K) is one of the most important nutrients influencing plants, including cotton growth and metabolism. Because of toxicity from chloride ions, potassium sulfate (K2SO4) usually is used instead as a potassium fertilizer, especially for cotton, although it is lower in K2O content and dearer than potassium chloride (KCl). The objective of this study was to investigate the effects of polymer-coated potassium chloride (PCPC) fertilization on cotton yields, yield components, fiber qualities, potassium use efficiencies and leaf senescence under saline conditions. A 2-yr field experiment was conducted in the Yellow River Delta of China with a high-yielding cotton cultivar ('Guoxin 99-1'). The experiment had the following six treatments with varying potassium fertilization: 70% PCPC mixed with 30% K2SO4 applied once before planting; PCPC applied once before planting; K2SO4 (KCl) applied twice with one application (40%) before planting and second application (60%) during first bloom stage; K2SO4 (KCl) applied once before planting; and fertilization none potassium as the control. The release rate of PCPC appeared to be slow before the squaring stage, but accelerated between the first bloom and boll-setting stages, and then decreased during the late stage including harvest. The number of cotton bolls was 8.99-19.71% higher and seed yields 4.39-28.10% higher, in 70% PCPC mixed with 30% K2SO4 treatment than in the other potassium fertilizer treatments. Also, the potassium recovery efficiency and net profits were increased by 3.38-40.90% and 5.77-137.26%, respectively, in the 70% PCPC mixed with 30% K2SO4 compared with the other potassium fertilizer treatments. Available soil potassium contents, fiber qualities and leaf photosynthetic indices were all significantly improved by using PCPC instead of the more standard potassium fertilizers. Hence, combining PCPC with K2SO4 at a 7:3 potassium ratio can delay leaf senescence, increase yields and fiber qualities, and improve potassium use efficiencies and economic benefits in cotton.