Balances of N, P and K of agricultural soils of Southern Bulgaria and risk of soils contamination with nitrates and phosphates

Political and economic changes in Bulgaria led to essential changes in soil management. The balances of N, P and K in soils of Southern Bulgaria were established, as well as possibilities of contamination of river waters with nitrates. The reduced application of mineral fertilizers and manure decreased positive nitrogen balance of soils from 76.6 to 34.5 kg N /ha for the period of 1986 - 1996. The P balance dropped from 54.7 kg P2O5 /ha (1986) to 2.7 kg P2O5 /ha (1996). The potassium balance decreased its positive values during the study period from 30.0 to 5.6 kg K2O/ha. The K balance was positive for the regions Sofia-district and Plovdiv and negative for the regions Bourgas and Haskovo. The total amount of NO3 - N removed by rivers to Aegean Sea was 10836 t/ year. About 75 % of nitrates removed to this sea were with waters of river Maritza (Evros).