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 water table management for Finnish growing conditions. The sites differed in soil texture, topography and cultivation. Drainage control was managed through specific wells in collector pipes. In recycling, a reservoir stored drainage water discharging from the fields. This water was used for subirrigation through conventional drainage or a dual level irrigation-drainage system. Hydro-meteorological variables were monitored continuously and real time transfer of the data was carried out via radiolink and microcomputers. Quality of surface and subsurface waters was surveyed by manual sampling from the weirs, piezometers and reservoirs. Physical soil properties and mineral nitrogen (N) from several soil profiles were determined. Furthermore, above ground biomass, and N content and yield of crop were observed. In fine sand/loamy sand, subirrigation and controlled drainage raised groundwater table on average 80 cm compared to the reference areas. N concentration in the reservoirs declined significantly during May-August. Nitrogen in the piezometers and soil showed considerable spatial and temporal variation within a single field. Evidence of the relationship between groundwater level 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 subirrigation 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.