Fertilizer nitrogen budgets of two doses of Na15NO3 dressings split-applied to winter wheat in microplots on a loam soil

In a field experiment performed in microplots, winter wheat was fertilized at two different total N dressings (135 and 180 kg ha^–1) split-applied as Na¹⁵NO₃ in three equal applications at tillering, stem elongation, and flag leaf.No significant differences were found in the percentage recovery values for the entire plant at the three split applications between the two N dressings. The total percentage recovery of fertilizer N by the plant was high and practically equal at both fertilization levels (76.65% and 75.84% for 135 and 180 kg N ha^–1, respectively); crop yields were also similar. In contrast, gaseous losses calculated after drawing up the balance sheet were, in absolute values, higher for the tillering and stem elongation split applications when using the 180 kg N ha^–1 dressing (7.67 and 4.84 kg N ha^–1, respectively) than for the 135 kg N ha^–1 dressing (3.45 and 1.26 kg N ha^–1, respectively). They were found to be zero at flag leaf at both fertilization levels. The amount of applied fertilizer N did not influence the amount of N taken up from the soil which was about 143 kg ha^–1.