NITROGEN AND PHOSPHORUS FERTILIZATION IMPACTS ON WHEAT NUTRITIONAL STATUS

The winter wheat (Triticum aestivum L. cultivar KG-56) was grown on degraded Vertisol of Central Serbia over the 2000-2005 periods. Acid reaction (pH in In KCl: <4.5), moderate supplies with total N (<0.15% N), low in AL-soluble P and adequate in AL-soluble K (5.0 mg P2O5 and >15.0 mg K2O 100 g(-1) respectively) are main characteristics of the soil. Four steps of N fertilization (0, 60, 120 and 250 kg N ha(-1)) from two surces (CAN = calcium ammonium nitrate 27% N and Urea 46% N) on the constant P (80 kg P2O5 from two sources: MAP monoammonium phosphate 11% N and 52% P2O5 and SP = superphosphate 17% P2O5) and K (60 kg K2O in form of KCl containing 60% K2O) fertilization were used in the experiment. Annual yields in 2005 were for 28% (grain) and 19% (straw) lower than in 2001. Depended on year, mean concentrations were in the ranges from 1.72% N to 2.40% N and from 0.25% to 0.33% P (grain), from 0.41% N to 0.55% N and from 0.032% to 0.056% P (straw). Grain N and P were considerably higher in 2005 (2.40% N and 0.33% P) compared to remaining four tested years (means: 1.96% N and 0.26% P). The analogous values for straw were 0.55% N and 0.056% P (2005), 0.42% N and 0.042% P (means 2001-2004). The highest grain and straw yields for 2001 were accompanied with the lowest grain and straw N and P concentrations. N rates considerably influenced wheat nutritional status and yields. For example, yield increases of N fertilization (means three N rates) were for 65% (grain) and 35% (straw) compared to unfertilized plot (t ha(-1): 2.22 and 3.65 for grain; 3.20 and 4.33 for straw). With that regard, the optimal N rate was 120 kg N ha(-1). N fertilization considerably increased grain and straw N, while P status was similar on three rates of applied N. In general, sources of N and P were less influencing factors of wheat nutritional status and yields and mainly resulted by non-significant differences of tested properties.