Research studies on cotton potassium fertilization in the last years at the Cotton and Durum Wheat Research Institute – Chirpan, Bulgaria have been reviewed. The soil Eutric vertisols was well supplied with available potassium (31-43 mg/100 g soil). The effect of K application was not clearly established. At K the seed-cotton yield increased with 6.4 % compared to the unfertilized. K O use efficiency was 0.18-0.61 kg of seed-cotton. For 100 kg seed-cotton yield it 160 2 was necessary to apply 3.36-4.94 kg K O. Production of dry matter was 5.0 % higher at 160 kg K O/ha. The concentration in the seeds was considerably higher 2 2 (1.3-1.4 %) in comparison with the lint (0.5-0.98 %). The total annual potassium uptake was 55-115 kg/ha. The changes of quality indexes were not essential. The difference between KNO , KCL and NaKNO with respect to yield and quality was insignificant. The optimum balance was created at applied 70 kg K O/ha.
G. Panayotova, N. Valkova