Identification of nitrogen leaching based on water chemistry studies in agricultural drainage systems in the Kałuszyn Upland

The paper presents the water chemistry from subsurface drainage systems located in an agricultural area. Studies have shown a significant degree of transformation of chemical composition, observed in a hydrochemical multi-ionic type, in which nitrates play the main role. This is the predominant form of mineral nitrogen in the water and accounts for an average of 95%, which corresponds to a concentration range of 11.07 to 47.82 mg/dm3. Field studies were the basis for determining the reliability of the theoretical model for the distribution ofnitrogen loading leached from soils. Loading was computed on the basis of statistical data concerned average annual fertilizer usage expressed as a pure component, and data from own research on the estimation of nitrogen leaching rate. Nitrogen loadings in the range of 1.54-13.17 kgN/ha-year was converted to the expected nitrate concentrations in infiltration waters through the vadose zone, taking into account the average infiltration recharge. The expected nitrate concentration range of 1.69 to 120.00 mg/dm3 (with the concentrations above 50 mg/dm3 observed in 18.4% of the area) may be the basis for designing the most vulnerable areas (OSN) for nitrogen leaching to surface water and groundwater