Tomato performance and changes in soil chemistry in response to salinity and Na/Ca ratio of irrigation water

Although unconventional water can be applied as an alternative for agricultural production, inappropriate irrigation water quality may adversely affect the soil crop system. Thus, field experiments under mulched drip irrigation were performed over three years (2017–2019) to investigate the impacts of three salinity (1, 2 and 3 g·L−1) with five Na:Ca molar ratios (1, 3, 5, 7 and 9) of irrigation water on tomato plant growth, fruit development, soil salt accumulation and soil sodium adsorption ratio. The results showed that, with irrigation water salinity of 1 g·L−1, the critical value of irrigation water Na:Ca molar ratio for the high yield and dry matter accumulation was 3 and 5, respectively, while the threshold for high concentration of vitamin C and lycopene was 7. With the irrigation water salinity of 2 g·L−1 and 3 g·L−1, the Na:Ca molar ratio threshold for a high concentration of soluble solids, vitamin C and lycopene was 5. Moreover, considering the increase of plant nitrogen and phosphorus accumulation, the decrease of sodium adsorption ratio at 40–100 cm soil layer inside the film, and the diminution of soil salt accumulation at 0–100 cm layer, irrigation water with higher salinity and lower Na:Ca molar ratio was more proper than that with lower salinity and higher Na:Ca molar ratio. Based on the multi-objective optimization with entropy-weight TOPSIS method, irrigation water with a salinity level at 2 g·L−1 and the Na:Ca molar ratio at 5 was suggested for tomato planting in the Yinbei Yellow River Irrigation District, China.