The optimal irrigation water salinity and salt component for high-yield and good-quality of tomato in Ningxia

Although saline water can be used as an alternative of freshwater resources for agricultural irrigation, especially in arid and semiarid areas, however, unsuitable saline water quality and unreasonable irrigation technology may result in the detrimental effects on plant growth, yield and quality of products. Thus, a three-year open field experiment was conducted in Ningxia to investigate the influence of three irrigation water salinity levels (1, 2 and 3 g/L) and five molar concentration ratios (MCR) of Na:Ca (1, 3, 5, 7 and 9) on processing tomato planting, in terms of crop water consumption, tomato yield traits and fruit quality characteristics. The results are as follow: (i) The water consumption decreased significantly with the increasing irrigation water salinity and MCR of Na:Ca. (ii) With the increase of irrigation water MCR of Na:Ca, both the average fruit weight, marketable yield and total yield decreased linearly, as well, the ratio of marketable yield to total yield decreased. Additionally, irrigation water with higher salinity (2 g/L and 3 g/L) and lower MCR of Na:Ca (1 and 3) was more conducive to root water uptake and average fruit weight accumulation, than that with lower salinity and higher MCR of Na:Ca. (iii) With irrigation water salinity of 1 g/L and 2 g/L, both the vitamin C, lycopene, fructose, sucrose and starch content of tomato fruit have quadratic function relationship with the irrigation water MCR of Na:Ca. Moreover, the threshold of irrigation water MCR of Na:Ca for soluble solids, lycopene and starch accumulation was 7, while the content of total soluble sugar, fructose and sucrose achieved the maximum value as the MCR of Na:Ca arrived 5. (iv) With irrigation water salinity of 3 g/L, the total soluble sugar and glucose of fruit decreased with the increase of irrigation water MCR of Na:Ca, especially, the fruit fructose, sucrose and starch concentration decreased linearly, furthermore, the threshold of irrigation water MCR of Na:Ca for vitamin C and soluble solids accumulation was 5. Synthetically, saline water with salt content of 2 g/L and MCR of Na:Ca at 5 was optimal in the present study for mulched drip irrigation on tomato cultivation in the northern Yinchuan plain of Ningxia, obtaining the relatively high-yield (9.72 ×104 kg/hm2) and good-quality of tomato.