Effect of nitrogen fertilization on yield and nitrogen and water use efficiencies of winter wheat (durum and bread) varieties grown under conditions found in Central Anatolia

In order to evaluate the influence of different N rates on percent N derived from fertilizer (%Ndff) at different growth stages, on yields and the percent N use efficiency (%NUE) values of two winter wheat varieties (durum and bread), field experiments on fallow were carried out at four different locations in Central Anatolia, in the 1991–1992 and 1992–1993 growing seasons. At each site the rates of N (0, 40, 80 and 120 kg N/ha) were applied as ammonium sulphate [(NH4)2SO4] using a Latin Square experimental design with four replicates. The total amounts of N fertilizer were applied once after seedling emergence at all experimental sites. Labelled (15NH4)2SO4 fertilizer was applied to sub-plots from which %Ndff values were determined at tillering, booting, grain filling, and harvest stages. Yield sub-plots received unlabelled (NH4)2SO4 from which total dry matter (seed and straw) and N yields were determined. Also the %NUE values were calculated by the 15N and "difference" methods at the harvest stage. Stored soil moisture at 0–90 cm depth, evapotranspiration and water use efficiency values were calculated as well. The results obtained showed that (1) Gerek-79 variety used both the applied N fertilizer and the available soil moisture more efficiently, (2) the percent NUE values obtained overall were generally less than 20 for both varieties and (3) with the 15N method, less variable %NUE values were obtained in comparison to the difference method.