Drain Discharge and Salt Load in Response to Subsurface Drain Depth and Spacing in Paddy Fields

Drainage continues to be a vital and necessary component of agricultural production systems in consolidated paddy fields in northern Iran. Agricultural and environmental sustainability in these fields requires more attention to the water quality impact of drainage water disposal. This study aimed to quantify the influence of different drain spacings and depths on the salinity of drainage water. Data on drainage flows and salinity were collected from 4.5 ha of paddy fields of Sari Agricultural Sciences and Natural Resources University, Iran, during four successive rice-canola-rice-canola growing seasons (July 2011 to May 2013). By increasing drain spacing, the electrical conductivity (EC) and volume of drainage water and total salt load decreased. On the other hand, decrease in drain spacing in relation to increase in drain depth had greater environmental effects from salinity point of view. So, where a new drainage system is to be installed, there is the opportunity to design a drainage system that provides adequate salinity and waterlogging control while minimizing salt loads.