Comparison of Performance of Subsurface Drains with Mineral and Geotextile Envelopes in Paddy Fields

Due to newly-installation of drainage systems in the northern Iran paddy fields and special conditions of soils in these areas, performance evaluation of different drainage envelopes has a great importance. In this study, effect of two types of drain envelopes (mineral and geotextile) on the quantity and quality of drainage water of subsurface drains and water table depth was studied in the consolidated paddy fields of Sari Agricultural Sciences and Natural Resources University. During four successive growing successive seasons of rice and canola, from July 2011 to May 2013, discharge and water table depth in midway between of drain lines and the concentration of EC, pH, Na and Cl of drainage water were measured. Average of drain discharge volume with mineral and geotextile envelopes per day was 2381 lit and 2961 lit, respectively. Comparison of amounts of SEW30 (Sum of Excessive Water) in two growing canola seasons showed that geotextile envelope was more effective in lowering of water table depth than mineral envelope. Also, the minimum and maximum of EC were 1280 and 2190 for drains with mineral envelope and 1190 μs/m and 2026 μs/m for drains with geotextile envelope, respectively. Assessment of amounts of SEI (Salt Export Indicator) of soil showed the leaching during growing seasons. According to the results, geotextile envelope was more effective than mineral envelope in draining surplus water and controlling water table in the study area.