FIELD STUDIES ON CONTROLLED DRAINAGE AND RECYCLING IRRIGATION DRAINAGE FOR REDUCTION OF NUTRIENT LOADING FROM ARABLE LAND

Three on-farm trials were established to evaluate the suitability of w ater table management for Finnish growing conditions. The sites differ ed in soil texture, topography and cultivation. Drainage control was m anaged through specific wells in collector pipes. In recycling, a rese rvoir stored drainage water discharging from the fields. This water wa s used for subirrigation through conventional drainage or a dual level irrigation-drainage system. Hydro-meteorological variables were monit ored continuously and real time transfer of the data was carried out v ia radiolink and microcomputers. Quality of surface and subsurface wat ers was surveyed by manual sampling from the weirs, piezometers and re servoirs. Physical soil properties and mineral nitrogen (N) from sever al soil profiles were determined. Furthermore, above ground biomass, a nd N content and yield of crop were observed. In fine sand/loamy sand, subinigation and controlled drainage raised groundwater table on aver age 80 cm compared to the reference areas. N concentration in the rese rvoirs declined significantly during May-August. Nitrogen in the piezo meters and soil showed considerable spatial and temporal variation wit hin a single field. Evidence of the relationship between groundwater l evel and N concentration was observed. However, no unique correlation from the existing data could be detected. N yield of cereals was 10-50 % higher in the controlled drainage and subinigation areas compared to the reference areas. Most of this extra N was allocated to grains and removed from the fields reducing N load into the environment. Copyrig ht (C) 1996 IAWQ.