Effects of soil matrix potential regulation at various growth states on cotton growth and soil water and salt distribution

Water shortage and soil salinization are two main limiting factors for cotton production in southern Xinjiang. We examined the effects of soil matrix potential (SMP) regulation at various growth stages on cotton growth, soil water and salt distribution, to provide theoretical basis for water saving, salts control, and efficient production in cotton fields. The mulched drip irrigation experiments were conducted to monitor cotton growth, aboveground biomass, cotton yield, soil water and salt distribution and other indicators. Three SMP thresholds, i.e.,W1(-20 kPa), W2(-30 kPa) and W3(-40 kPa) were set at the seedling stage (A), seedling stage + budding stage (B), and seedling stage + budding stage + flowering stage (C), with SMP of -50 kPa at 20 cm soil depth below the emitter as the CK. The results showed that plant height, leaf area index (LAI) and aboveground biomass followed the order of WC>WB>WA>CK, when SMP were changed at various growth stages. Plant height, LAI and aboveground biomass increased with increasing SMP thresholds, with the values under W1C and W2C being significantly higher than the other treatments. The effective bolls per plant, single boll weight and lint percentage all increased with the increases of SMP thresholds. The yields of W1C and W2C were similar, which were significantly higher than those of other treatments. However, the water use efficiency of W2C was significantly higher than that of W1C. Controlling the SMP threshold at -20 or -30 kPa at different growth stages could improve soil moisture status of the primary cotton root zone. All treatments presented shallow salt accumulation (0-40 cm) at the harvest stage, with the bare land having greater salt accumulation than the inner film. The higher the SMP threshold was, the less salt was accumulated in the primary root zone (0-40 cm) under film. The salt accumulation (0-40 cm) under W1C and W2C were reduced by 24% compared with other treatments. Considering the efficient production of cotton, water saving and salt control, it was recommended to maintain the SMP threshold of -30 kPa during irrigation at various growth stages in cotton fields without leaching salts during the local off-crop period.