-

The genetically acidic, as well as the secondarily acidic soils in Bulgaria require our high awareness on wheat tolerance to increasing levels of exchangeable aluminum in soil. Under conditions of a vegetation experiment, the peculiarities of phosphorus uptake were investigated in 20 winter cereal genotypes: 18 T. aestivum L. cultivars, one T. durum Desf. Variety and the rye-wheat hybrid Triticale. The latter was used as a standard. The experiment was carried out against two backgrounds of soil fertilization: 1 – check variant with regard to the levels of exchangeable Al3+ ; 2 – mineral fertilization at N:P:K=1:1:1 from norms of 200 mg N, P2O5 and K2O/1000 g soil. The experiment was carried out on light grey forest soil (Stagnic Podzoluvicsols-FAO, 2002) with content of exchangeable Al3+ 0.5 meq/100 g soil (Ао). Furthermore, increasing levels of toxicity were created by addition of 2.5 meq Al3+/100 g (А1) and 5.0 meq Al3+ /100 g (А2). The independently applied increasing levels of exchangeable aluminum lead to lower amounts of phosphorus uptake in the organs of over ground bio mass and the roots of the tested cereals. Lowest amounts of phosphorus uptake were determined in the variants with additional introduction of 5.0 meq Al3+/100 g. At the end of the growing season, the phosphorus uptake in the total bio mass after additional introduction of 2.5 meq Al3+/100 g (А1) was 73.0 % from the phosphorus uptake in the check variant. The amount of P uptake in the roots decreased with 41.0 % and the uptake in grain yield – with 28.5 %. The balanced introduction of nitrogen, phosphorus and potassium in soil had a positive effect on P uptake in the tested cereals. The phosphorus uptake with the over ground bio mass increased at the end of the growing season with 82.8 % after treatment of the check variant, and with 40.4 % after treatment of the variants with introduction of 2.5 meq Al3+/100 g. The positive role of balanced mineral fertilization on phosphorus uptake in grain was very well expressed. The increase in the check variant was with 68.1 %, and in the variants with introduction of 2.5 meq Al3+/100 g – with 31.3%. A similar tendency was also observed for P uptake in the roots. The variation of phosphorus uptake on the level of the genotype was strongly expressed at all levels of exchangeable aluminum content in soil applied independently and in combination with balanced mineral fertilization. Triticale Vihren and cultivar Karat had higher phosphorus uptake in grain in comparison to the rest of the cultivars. The addition of high concentration of exchangeable aluminum in soil (5.0 meq Al3+/100 g) not only caused strong disturbance of phosphorus uptake in the tested winter cereals but also to perishing of common wheat varieties Pryaspa, Trakiya, Sadovo 1 and Kristal