Effect of irrigation with salt water on yield and quality of grown-in-substrate tomatoes at the late fruiting stage in a greenhouse setting

To effectively use salt water to cultivate facility tomatoes, irrigation water with an electrical conductivity (EC) value at the 1.0 (as a control), 2.6, 4.2, 5.8 or 7.4 dS/m level was applied during the late fruiting stage. The effect of salt water at various salinity levels on plant growth, fruit yield and fruit quality was evaluated throughout the spring (January-May, 2021) and autumn (September, 2021-January, 2022) growing seasons. The results have demonstrated that salt water salinized at various levels did not significantly affect plant height, stem diameter, dry matter weight, single-fruit weight and fruit yield per tomato plant in either spring or autumn crop but increased the incidence of blossom end rot (BER) on the fourth fruit spikes in both spring and autumn crops with the highest disease incidence on plants irrigated with highly salinized water (EC value at 7.4 dS/m). The soluble solid content in the fruits of both spring and autumn crops irrigated with highly salinized water (EC value at 5.8 ~ 7.4 dS/m) was significantly greater than that in the fruits of plants with the control treatment in both crop seasons, except for that in the fruits of the third fruit spikes irrigated with salt water (EC value at 5.8 dS/m) in the autumn crop. The soluble sugar content in the fruits of the second fruit spike in both spring and autumn crops increased along with the increase in water salinity. The vitamin C (Vc) content in the fruits treated with salt water with an EC value at 2.6 ~ 7.4 dS/m in the spring and autumn crops, with the exception of the third fruit spike, was greater than that in the fruits of the corresponding spike with the control treatment in both seasons. The lycopene content in the fruits of the second fruit spikes under irrigation with salinized water (EC value at 2.6 ~ 7.4 dS/m) in the spring and autumn crops was greater than that in the fruits with the control treatment in both seasons. The soluble solid content in the fruits of all four fruit spikes in the spring crop was significantly greater than that in the fruits of all corresponding spikes in the autumn crop with the 1.0 ~ 7.4 dS/m salinized water treatments. In general, the fruit quality of the spring crop was greater than that of the autumn crop while the fresh water consumption in both seasons was reduced by 30.8%~47.5%. Therefore, we recommend that salt water with an EC value less than 5.8 dS/m be used for grown-in-substrate tomatoes in facilities at the late fruiting stage when the fruit size of the 4th fruit spikes reaches 3/5 of the expected fruit diameter to ensure both yield and quality.