Comparison of Drainage Water Quality and Soil Salinity in Irrigated Areas with Surface and Subsurface Drainage Systems

Drainage should be practiced in conjunction with irrigation to ensure maximum production and for environmental protection in all irrigation projects. An efficient drainage system removes salts added to the soil brought in by irrigation water. Various problems such as the increase in soil salinity, waterlogging, and water table rise into the crop root zone may be encountered when an efficient drainage system has not been provided in an irrigated area. Surface drainage removes excess water accumulated in the cropped area, and excess water and harmful salt solutions in the soil profile are removed by subsurface drainage. In this study, an area of 6,120 ha in the Erzincan irrigation area and where drainage waters are used for irrigation, was chosen for the study. Monthly water samples were taken from two points on surface drainage canals and again two points on drainage outlet of subsurface drainage system during irrigation season. In order to determine the rate of salt removed from soil by surface and subsurface drainage canals, salinity values of drainage waters were determined. In addition, in order to determine the effect of irrigation water on drainage water, water samples were taken from the same points on irrigation canals bringing water to the mentioned areas each month. Although water samples from surface and subsurface canals had high salinity, no water sample from irrigation canals with high salinity was encountered. Two pilot areas of 10 ha under the influence of surface and subsurface drainages were selected and soil samples were taken to determine soil salinity at the end of the irrigation season. In order to compare data taken from two pilot areas, t test was performed using SPSSWIN program. High salinity levels were found in the areas where subsurface drains do not exist, compared to the deeper parts of the same soil profile. Lack of proper drainage system leads to salinity and sodicity in soil. Therefore, to avoid environmental problems, it is very important to ensure proper drainage conditions.