EVALUATION OF CONTROLLED DRAINAGE EFFICIENCY IN LITHUANIA

Eight-year (2000-2007) field studies on the effectiveness of controlled drainage in loam sandy soil were carried out in the lowland of Middle Lithuania. The plot, which has existing subsurface water removal systems operating as conventional drainage, was readjusted for groundwater table management. Two separate systems - 4.9 ha free drainage (FD) and 5.4 ha controlled drainage (CD) - were arranged. A water level control structure with riser column and hand-operated rigid flap door was installed in the outlet of the drainage collector in the manhole at the junction of two collectors. The groundwater table level was allowed to rise to a maximum of 68 cm above the drains. Measurements to record groundwater table depth, crop yield, drain outflow quantity and quality were performed. It was determined that, in comparison with drainage operating in an ordinary regime, in the CD system annual drainage outflow duration was shorter by 40-62%, at the same time its amount was reduced by 25% and nitrate leaching was 20-28% lower. These quantities varied depending on weather conditions. Crop yield increases of 5.6-10% were obtained in CD treatment during years with a dry growing season. Groundwater table control in single-acting drainage systems is feasible and has a positive hydrological and environmental impact. Copyright (C) 2009 John Wiley & Sons, Ltd.