The effect of mineral (NPK) fertilization on the content of nitrogen fractions in timothy grass was assessed from the results of a three-year field experiment conducted at the Elizówka Experimental Farm near Lublin, on podzolic soil developed from loess. The experiment was included 27 fertilized treatments, i.e. nine nitrogen and potassium variants tested, each in four replications. against the background of three increasing phosphorus fertilization doses. Nitrogen was applied as ammonium nitrate at a dose of 120 kg N ha-1 (N1) and at two-fold (N2) and three-fold (N3) higher doses. Phosphorus was applied in the form of granular triple superphosphate at a dose of 34.9 kg P ha-1 (P1) and at two-fold (P2) and three-fold (P3) higher doses. Potassium was used as potassium salt (47.3%) at a dose of 83 kg K . ha-1 (K1) and at two-fold (K2) and three-fold (K3) higher doses. After grass harvest, plant material was sampled and the content of total, protein, ammonium and nitrate nitrogen(V) was determined in duplicate. It was found that the content of the nitrogen fractions analysed in timothy grass, i.e. total, protein, mineral, ammonium and nitrate(V) nitrogen, was significantly positively correlated with the mineral fertilization, in particular, with nitrogen and phosphorus and, to a lesser extent, with potassium. The mean share of protein nitrogen in total nitrogen was 53.8%; mineral, ammonium, and nitrate nitrogen fractions constituted 4.0, 2.5, and 1.5%, respectively. Timothy grass fertilized with increasing doses of nitrogen, phosphorus, and potassium fertilizers contained the largest share of protein nitrogen in total nitrogen, did not contain excessive amounts of nitrates(V) and proved to be valuable bulk feed.

20.1.2015