Effect of water-salt regulation drip irrigation with saline water on tomato quality in an arid region

Saline water irrigation can alleviate the deficiency of agricultural freshwater resources, especially in arid regions. However, saline water may lead to soil salinization and affect crop quality. A water-salt regulation (WSR) irrigation method has been developed to avoid soil salinization. To investigate the effect of saline water irrigation on crop quality while maintaining soil salinity balance, we conducted a field experiment on tomatoes under the WSR method in the arid region of northwest China from 2018 to 2019. Five treatments with electrical conductivity (ECi) of 0.5 dS/m, 3.1 dS/m, 4.7 dS/m, 6.2 dS/m, and 7.8 dS/m were designed, where ECi indicates salinities of irrigation water. We applied the WSR method for all five treatments to maintain the soil matric potential (SMP) above 20 kPa at a depth of 20 cm below drip emitters. The results from three aspects (quality, yield, and soil salinity) are as follows: (i) Saline water irrigation can improve tomato quality, as evidenced by increasing the content of soluble solids, reducing sugar, organic acid, and vitamin C. When ECi ranged from 4.7 dS/m to 7.8 dS/m, the sugar-acid ratio was in the appropriate scope (7.4-9.8). (ii) The commercial yield and total yield declined by 4.8% and 4.4% as the ECi increased 1 dS/m. (iii) the soil salinity can be kept balanced under the WSR method after a 2-year experiment when the ECi of saline water did not exceed 4.7 dS/m. Therefore, in similar arid areas with a lack of freshwater resources, saline water of 4.7 dS/m under the WSR method can be used to irrigate field grown tomatoes, compensating for the reduced yield by improving quality.