INVESTIGATION OF PHOSPHORUS CHANGE IN A SANDY LOAM ASSOCIATED WITH CONTROLLED DRAINAGE

Most of the soil chemical matters are soluble in the water; therefore changes in hydrological regime of ecosystem are closely related to the changes of nutrient leaching. Excess phosphorus causes eutrophication in surface waters. The aim of the research was to establish controlled drainage influence on the soil moisture regime, on the amount of mobile phosphorus in the soil and its leaching. Investigations were carried out in sandy loam and loam soils in the Middle Lithuanian Lowland from June 2014 to June 2015. During the study period precipitation was 93 % of the climate normals, the average temperature was 1.4 ° C higher than the climate normals. Based on preliminary studies, several tendencies were observed, that 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. Also the fluctuation (variation’s coefficient 24 %) of mobile P2O5. was higher. The Ptotal and PO4-P concentrations were lower in the controlled drainage than in the conventional drainage during winter – spring flood period, when water pressure was the highest (70 cm) in the outlet of drainage and water flowed through flap of the riser column