Catchment and drainage field nitrogen balances and nitrogen loss in three agriculturally influenced Latvian watersheds

Agriculture is one of the major sources of nitrogen that contributes to the eutrophication of the inland waters and the Baltic Sea. The results of a 6-year study of three small agricultural catchments (Vienziemite, Berze and Mellupite) and three drainage fields in these catchments indicated that the most important factors of agricultural pollution are acreage of arable crops, farming practices, and nutrient management. In particular, attention was focused on the land use as well as on the effects of the soil nutrient balance. Large variations in N losses (Ntot= 2–27 kg ha−1 per year) could be demonstrated. The losses appeared to be smaller than the results under similar cropping systems and soils in the Nordic countries where the measured losses were 20–50 kg ha−1 per year. The most significant increase of nitrogen loss was associated with the large share of arable land and increased fertiliser application in Berze small catchment during the last 2–3 years. The negligible increase of nitrogen leakage in Vienziemite catchment had resulted from the low input agriculture with a negative N balance. The results indicate that the N balance as well as the land use play an important role in the leakage of nutrients from drainage and small catchments.