EFFECTS OF LIMING AND THE APPLICATION OF VARIOUS PHOSPHOROUS FERTILIZERS ON POTATO YIELD IN PSEUDOGLAY TYPE SOIL IN THE DRAGACEVO REGION

During the period between 1993 and 1995, an investigation of the fertilizing effect on the potato yield was conducted on the extremely acidulous pseudoglay (pH in KC1 3.25) in Guča. NJIVAL was applied as a lime source in the quantity of 8 t.ha-1, and LIFOS (origin Lisina, near Bosilegrad, containing 15% P2Os and 22% CaO) in the quantity of 1.2 and 3 t.ha-1. On the basis of different applied lime quantities, the effect of fertilizing with standard nitrogen and potassium was established. Unfavorable soil chemical properties (pH, content of P 2O5, Al, and % V) were considerably improved by the application of a NJIVAL and LIFOS combination, compared to an application of NJIVAL alone. Chemical characteristics of the soil were also corrected to a certain point, first of all, P2O5 with the application of LIFOS in the combination with nitrogen and potassium fertilizers. Potato yields in all variants with NJIVAL and LIFOS applications were statistically quite significantly higher in regard to the control variant and to the variant with NPK fertilizers. The average potato yield of 13.414 kg.ha-1 achieved by the application of LIFOS (3 t.ha-1) and NJIVAL (8 t.ha -1), in combination with nitrogen and potassium fertilizers, represented a yield increase of 44 % apropos to the control variant.