Effects of controlled drainage on soil water regime and quality in Lithuania

Lithuania remains one of the most extensively drained of the Baltic and Nordic countries. The overall drained area (ditches plus tile drains) totalled 87% of the agricultural land area. Many nutrients from soil are leached through drainage resulting in polluting streams (drain flow receivers) water. Drain flow is treated as a major determinant of water quality. Therefore, the reduction of nutrients entering the drains is very important. Controlled drainage conception, when the outflow height is increased at the mouth, helps reduce drainage runoff and partially purify water. The aim of the research was to establish controlled drainage influence on the soil moisture regime, nitrogen and phosphorus leaching. Investigations were carried out in sandy loam and loam soils in the Middle Lithuanian Lowland. Based on studies, several tendencies were observed: when drainage outflow began, the amount of soil moisture in subsoil (50-80 cm layer of the soil) of controlled drainage plot was higher than in the conventional drainage plot, and higher moisture supplies stayed for a longer period of time. Controlled drainage had no direct impact on phosphorus and nitrogen concentrations but they were influenced by the leaching quantities of plant usable nutrients. The reason that in many cases lower nitrate nitrogen (54% of all measurements) and phosphorus concentrations (77% of all measurements) were found in the conventional system rather than in the controlled drainage might be connected to the fact that the latter area contained predominantly lighter textured soils (sandy loam) making it easier to wash away the nutrients unused by plantVytauto Didžiojo universitetasŽemės ūkio akademij