NITROGEN, VARIETY AND GROWING SEASON EFFECTS ON GRAIN YIELD AND PROTEIN CONTENT IN WINTER WHEAT

Four domestic winter wheat varieties (Superzitarka, Zitarka, Monika and Srpanjka) were grown under field conditions (Osijek hydromeliorated hypoglay) in the period 2001-2004. Presowing N (PS-N) was applied in four rates (40, 70, 100 and 130 kg N ha(-1)). Top-dressing N (TD-N) was applied in the amounts (kg N ha(-1)) 0 (without TD), 40 (TD in tillering), 95 (tittering + stem elongation) and 120 (tittering + stem elongation + before shutting). Differences of yields among the years were in the ranges from 7.50 to 8.40 t ha(-1) and proteins from 13.4% to 14.2%. Yield differences among the varieties (4-year means) were in the range from 5.57 t ha(-1) to 9.40 t ha(-1). Srpanjka had significantly the highest yield for all four tested years (mean 9.40 t ha(-1)), while yield of the last-ranged Monika was for 41% lower (mean 5.57 t ha(-1)). However, the highest yield of Srpanjka had significant lowest grain protein (means 13.4% and 13.8%, for Srpanjka and remaining three varieties). PS-N resulted by non-significant yield differences among the treatments (4-year means in range from 7.91 to 7.99 t ha(-1)). Also, wheat yields were independent on TD-N fertilization (4-year means 7.97 and 8.00 t ha(-1)). We presume that high fertility of the soil could be responsible for low response of wheat to N. However, for two growing seasons (2001 and 2002) application of the highest PS-N rate influenced significantly on increase of grain protein compared to the lowest N rate. Especially high influences were found for 2001 (13.1 % and 13.9% protein, for 40 and 130 kg N ha(-1), respectively). TD-N influenced also on protein contents (13.5 and 14.0%, for 0 and 120 kg N ha(-1), respectively).