Combined application of polymer coated potassium chloride and urea improved fertilizer use efficiencies, yield and leaf photosynthesis of cotton on saline soil

Conventional potassium fertilizers had been used widely, but few studies paid attention to controlled-release potassium fertilizer. The objective of this study was to explore the effects of polymer coated potassium chloride (PCPC) -an innovation product, especially the interaction application of PCPC and polymer coated urea (PCU) on cotton yield, fiber quality, leaf photosynthesis and fertilizer use efficiencies under salinity stressed conditions. A two-year experiment was conducted in two nearby fields with the similar fertility but varying salinity, using a split-plot design in the Yellow River Delta area of China. The main plots were assigned to the types of K fertilizers (K1-180 kg ha-1 K from potassium sulfate, K2-90 kg ha-1 K from potassium sulfate + 90 kg ha-1 K from PCPC, K3-54 kg ha-1 K from potassium sulfate + 126 kg ha-1 K from PCPC, hereafter referred to as 0, 50% and 70% PCPC), while the types of N fertilizers (N1-220 kg ha-1 N from urea, N2-110 kg ha-1 N from urea + 110 kg ha-1 N from PCU, N3-66 kg ha−1 N from urea + 154 kg ha-1 N from PCU, hereafter referred to as 0, 50% and 70% PCU) were assigned to the subplots. The results indicated that the lint yield, number of bolls, boll weight, lint percentage, fiber qualities, leaf photosynthesis and fertilizer use efficiencies were significantly affected by the types of K, N fertilizers and their interaction. The K and N release characteristics of PCPC and PCU under field condition were closely matched to the nutrients requirements of cotton growth. The contents of soil available K and inorganic N were significantly augmented from the first bloom stage to the initial boll-opening stage by using PCPC and PCU compared to potassium sulfate and urea treatments. Meanwhile, PCPC and PCU interaction increased lint yields by 11.16-26.44% and 14.17-32.11% in comparison with potassium sulfate and urea in 2014 and 2015, respectively, and the maximum lint yield was achieved by the combination of 70% PCPC and 50% PCU. Besides, the boll number and boll weight were improved 5.2-18.2% and 4.75-10.29% by the PCPC and PCU treatments compared to both potassium sulfate and urea treatments, respectively. The potassium recovery efficiency (KRE) and nitrogen recovery efficiency (NRE) of PCPC and PCU treatments were significantly raised by 24.34-33.77% and 19.68-36.25%, respectively, compared with potassium sulfate and urea treatments in 2014 and 2015. PCPC owned the great potential to alter the current application of potassium fertilizer due to its ubiquitous traits. The interaction of PCPC and PCU at optimal dose was significant on cotton growth in saline soil. Consequently, the application of 70% PCPC in combination with 50% PCU is recommended to increase cotton yield and fertilizer use efficiency, and to improve the fiber quality and leaf photosynthesis properties in the Yellow River Delta area of China.