Effects of negative pressure irrigation with saline water on tomato yield and soil salt

Abstract: This research wass to test the effect of salt water irrigation on tomato growth and development, water use, and soil salty accumulation situation in a greenhouse. In the treatments, the negative pressure irrigation facilities were applied to irrigate tomatoes at different growth stages (whole growth period, blooming and fruit period, fruit enlargement period, and harvest period), using different concentrations of salt water (fresh, 3, 5, 7, 9g/L) and soil matric potential (0, -40, -80hpa) to research the effect of salt water irrigation of the tomato production, root weight, water consumption, water use efficiency, and soil salinity. The results indicate that there are remarkable differences of salt-tolerance capacity at different growth periods of tomatoes. That means the blooming and earlier fruit periods are more sensitive to soil matric potential and salt stress than other stages. The most adapted one to salt stress is the harvest period. The data shows that the salinity of salt water irrigation should be less than the 3g/L at both the whole growth period and the blooming and the fruit period, and less than 5g/L at the fruit enlargement period. Relatively, high concentration salt water irrigation of 7g/l-9g/l can be used at the harvest period. The result is a difference between the relationship of yield at different growing periods and the soil matric potential, based on the concentration of salt. The conicoid relationship was found in the tomatoes yield and the concentration of salt, the soil matric potential at the whole growth period and the blooming and the fruit period, and the effect on the yield was significant. However, only the concentration of salt has significant effects on the yield at the fruit enlargement period, and there is a parabolic relation between the concentration of salt and the tomatoes' yield. The two factors at the harvest period have no effects on the tomatoes' yield. The relationship between the concentration of salt, the soil matric potential, and the root weight could be expressed by a conicoid relationship. The concentration salt at whole growth period has significant effects on the root weight, and there is a significant interaction between the concentration salt and the soil matric potential. Only the concentration of salt has significant effects on the root weight at the blooming period, and there is a parabolic relation between the concentration of salt and the tomatoes' root weight. The effect of the tomatoes' root weight is not significant at the fruit enlargement period and the harvest period. The positive linear relationship is shown between the soil salinity and the concentration of salt, the soil matric potential in all growth stages. The salt content would be increased 50% -400% by using the brackish water resources with a mineral concentration between 3~9 g/L to irrigate. Salt water irrigation will result in soil salt accumulation in green house production systems. The water consumption of irrigating tomatoes is positively correlated with the soil matric potential at every growth period, however, it is negatively correlated with the concentration of salt. Hence, the effect of salt water irrigation on plant growth appeared in the "from control to promotion" regulating trends when a moderate amount is chosen, which will help reduce water consumption and improve tomato yield and WUE. As a result, based on the characteristics of salt tolerance of tomatoes at different growth periods, the use of a certain concentration of salt water irrigation can not only replace fresh water, but also improve WUE.