Investigation of Subsurface Drainage Water Quality in Paddy Fields Based on the Design Parameters

To prevent flooding and water logging condition and to provide cultivation condition for fall and winter seasons, installation of subsurface drainage is necessary in large areas of Northern Iran paddy fields. The correct design of depth and spacing of drainage systems causes minimum negative effects of drainage water on the environment. In this research, the effects of different drainage systems on the Sodium, Chloride and Sulfate of drainage water in 4.5 ha of paddy fields of Sari Agricultural Sciences and Natural Resources University (SANRU) during two successive growing seasons of rice and canola have been investigated. The experimental treatments were: Four subsurface drainage systems including drainage system with 0.9 m drain depth and 30 m drain spacing with mineral envelope (D0.9 L30), 0.65 m drain depth and 30 m drain spacing with mineral envelope (D0.65 L30), 0.65 m drain depth and 15 m drain spacing with mineral envelope (D0.65 L15S), and 0.65 m drain depth and 15 m drain spacing with Geotextile envelope (D0.65L15F) and a bi-level subsurface drainage system with 15 m drain spacing and drain depths of 0.65 and 0.9 m as alternate depths (Bi-level). During the study period, Na, Cl and SO4 of drainage water were measured. Based on the results, by increasing drain spacing from 15 m to 30 m, the average Na, Cl and SO4 of drainage water decreased. Also, the minimum Na, Cl and SO4 concentration and total dissolved drained were for D0.9L30 treatment. So, it can be concluded that this drainage system had less environmental effect with respect to other drainage systems, from drain water quality point of view.