Effects of irrigation with brackish water and biogas slurry on dry matter accumulation, yield and quality of greenhouse tomatoes

【Objective】 Brackish water has been used as a complementary resource for irrigation in regions that are scarce of freshwater. This paper investigates the effect of irrigation using combined brackish water and biogas slurry on dry matter accumulation, fruit yield and quality of greenhouse tomatoes. 【Method】 The two-year experiment was conducted from 2022 to 2023. It consisted of three treatments by controlling salt concentration of the irrigation water at 2, 3 5 g/L and 5 g/L respectively. The crop was irrigated using different combinations of these saline waters and biogas slurry at seedling, flowering and fruit development, and fruit ripening stage, respectively. The control was irrigation with freshwater. In each treatment, we measured dry matter accumulation, yield and quality of the fruits, irrigation water use efficiency, and fruit ion contents. The comprehensive fruit quality benefits to tomato production were evaluated using the principal component analysis method and the combination evaluation method. 【Result】 Irrigation using saline water with salt concentration of 5 g/L and biogas slurry at seedling, flowering and fruit development stages reduced dry matter accumulation in all tomato organs. Regardless of salt concentration of the irrigation water, irrigation using brackish water and biogas slurry reduced the ultimate fruit yield due to the decreased individual fruit quality rather than because of the number of fruit sets per plant. However, it improved fruit quality, contents of soluble sugar, titrable acid, soluble solid matter, vitamin C and soluble protein, and reduced the ratio of sugar to acid. Comprehensive quality parameter evaluation gave the highest score when salt content of the irrigating water did not exceed 2 g/L at the seedling stage, 3 g/L at the flowering and fruit development stage, and 5 g/L at the fruit ripening stage. All treatments reduced the accumulation of Na+ and Ca2+ in the fruits, although the reduction varied with salt concentration of the irrigation water. 【Conclusion】 In regions where freshwater resources are scarce and brackish water resources are abundant, brackish water and biogas slurry can be used as a complementary irrigation resource. For irrigating greenhouse tomatoes, the best irrigation schedule is to control salt content of the irrigation water not to exceed 2 g/L at the seedling stage, 3 g/L at the flowering and fruiting development stage, and 5 g/L at the fruit ripening stage.