Effects of Different Salinity Levels in Drip Irrigation with Brackish Water on Soil Water-Salt Transport and Yield of Protected Tomato (Solanum lycopersicum)

Abstract

The effective exploration and utilization of brackish water resources are crucial to alleviating the scarcity of freshwater in arid regions. This study focused on protected tomato plants and set up four irrigation salinity levels: T1 (2 g·L−1), T2 (4 g·L−1), T3 (6 g·L−1), and T4 (8 g·L−1), with freshwater irrigation as a control (CK). The aim was to investigate the effects of continuous brackish water irrigation on soil water-salt transport and tomato yield. The outcomes highlighted that the moisture content in different layers of soil exhibited a “high in the middle, low at both ends” pattern, with the primary accumulation of soil moisture occurring at the 40 cm depth. The range and moisture content of the soil wetted zone increased with elevated salinity levels. Under continuous brackish water irrigation, the range of the soil wetted zone expanded further for the autumn crops, and the moisture content significantly increased compared to the spring crops. The concentration of soil salt gradually decreased with increasing soil depth, exhibiting greater levels in the 0–20 cm layer compared to the 40–80 cm layer. The average salt concentration in the soil at the end of the growth period was significantly higher than before transplantation, and this phenomenon became more pronounced with increasing salinity levels. Initial irrigation with brackish water with a salinity level of 2–4 g·L−1 promoted the growth of the tomatoes planted in the spring and the plant height and stem diameter reached the peak values of 1.68 m and 1.08 mm for the T2 treatment, respectively, which were 7.1% and 9.2% higher than that of the CK treatment, ensuring efficient yield and water usage. However, continuous irrigation with brackish water with a salinity level of 2–4 g·L−1 inhibited the growth and yield of the tomatoes planted in autumn, while the T1 and T2 treatments only yielded 24,427.42 and 16,774.86 kg·hm−2, respectively, showing a decline of 32.2% and 46.1% compared to the yields of the spring season. Considering the soil water-salt and yield indicators, under the conditions of non-continuous brackish water irrigation, using water with a salinity level of 2–4 g·L−1 is recommended for drip irrigation of protected tomatoes.