Effects of Using Agricultural Drainage Water on Chemical, Biological, and Physical Properties of Soil and Yield of Tomato in Moghan Plain, Iran

This study assesses the use of drainage water in agriculture by mixing irrigation water and agricultural drainage water to examine the effects of the mixture on soil properties and the yield of tomatoes in Moghan Plain, Iran. The experimental design was completely random, conducted with three irrigation treatments and four replications for two years. The treatments were the control treatment (only irrigation water) (T0), 50% drainage water +50% irrigation water treatment (T1), and only agricultural drainage water treatment (T2). The results showed the treatments had significant differences (p≤0.05) in terms of the microbial population, basal respiration, and substrate-induced respiration. There were also significant differences among the treatments in terms of soil pH and EC (p≤0.01). However, the soil organic matter, yield, bulk density, and chlorophyll content of tomatoes showed no significant differences among the treatments. The treatments did not differ significantly in terms of the saturated hydraulic conductivity (Ks</sub>) in the first year, whereas the Ks</sub> for the drainage water treatment differed significantly (p≤0.05) in the second year. No significant differences were observed in the parameters of van Genuchten (θs</sub>, θr</sub>, and α) among the treatments. Whereas the statistical results showed that there was a significant difference (p≤0.01) in the parameters of van Genuchten (n</em>) between T0 with T1 and T2 treatments, there was no significant difference between T1 and T2 treatments. It can be concluded that the use of drainage water negatively affected soil pH, salinity, and biological properties; but it did not decrease the plant yield.