Regulation effects of fulvic acid on tomato yield and quality under saline water irrigation

In view of the problem that lack of freshwater resources restricts crop growth in saline-alkali areas around Bohai Sea, the regulation effect of fulvic acid on the yield and quality of tomato under saline water irrigation was studied based on regional salt water resource endowment. In this study, the integrated water and fertilizer test method for substrate cultivation was adopted, and three fulvic acid concentrations: 0 mg·L⁻¹, 450 mg·L⁻¹, and 900 mg·L⁻¹; and five salt water concentrations: 1 g·L⁻¹, 3 g·L⁻¹, 5 g·L⁻¹,7 g·L⁻¹, and 9 g·L⁻¹, making a total of 15 treatments, were used for the experiment. The results showed that compared with no fulvic acid addition, fulvic acid addition had significant yield-increasing effects on tomatoes under different saline water concentrations. The yields of tomatoes under 450 and 900 mg·L⁻¹ fulvic acid increased by 6.14%−21.08% and 12.83%−34.63%, respectively. With the increase in salt water concentration, tomato fruit weight, fruits number per plant, water consumption, yield, water use efficiency, vitamin C content, and lycopene content decreased significantly and fruit reducing sugar content increased first and then decreased. Under saline water irrigation, the applications of 450 and 900 mg·L⁻¹ fulvic acid increased tomato single fruit weight, fruits number per plant, water consumption, yield, water use efficiency, vitamin C content, lycopene content, reducing sugar content. With the increase in fulvic acid concentration, proline content and K⁺/Na⁺ in tomato leaves increased significantly, whereas malondialdehyde and Na⁺ contents decreased significantly. The yield and water consumption per plant positively correlated with K⁺/Na⁺ and negatively correlated with contents of proline, malondialdehyde, and Na⁺; vitamin C and lycopene contents in tomato fruit significantly positively correlated with K⁺/Na⁺ and negatively correlated with malondialdehyde and Na⁺ contents. A significant negative correlation was observed between reducing sugar content and malondialdehyde and Na⁺ contents. The above results showed that fulvic acid could alleviate the inhibition effect of salt water irrigation on tomato yield and also promote the yield, water use efficiency, and vitamin C, lycopene, and reducing sugar contents. Fulvic acid alleviated salt stress mainly by promoting the accumulation of organic osmotic adjustment substance proline, increasing K⁺/Na⁺, and reducing the production of the membrane lipid peroxidation product — malondialdehyde.