Effect of long-term potassium fertilization on the chemical composition of Oriental tobacco Влияние на системното калиево торене върху химичния състав на ориенталски тютюн

The effects of the different potassium rates (0, 75 and 450 kg K2O ha -1 ) on nutrient concentrations in the above-ground biomass and chemical characteristics of sun-cured tobacco have been studied in a stationary field trial. Annual fertilization with 75 kg K2O ha -1 was adequate to maintain soil K concentration near the initial value. It was found that yield of cured leaves was not significantly affected by rate of K application when oriental tobacco was grown on soils with high available soil K. With the increase of K fertilization rate the content of the potassium in leaves increased from 0.65 to 4.49%. The concentration of Ca and Mg in the leaves ranged from 2.03 to 5.23% and from 0.52 to 0.71%, respectively and decreased with increases in added potassium. No effect of K rates on nicotine and protein content was noted. Only the reducing sugars’ content tended to increase to 11.42% at the highest K rate. Fertilization with moderate potassium rates (75 kg K2O ha -1 ) on soils high in available K is necessary to maintain the good potassium reserves. When oriental tobacco was grown on alkaline soils with high available K and Ca, potassium fertilization improves K nutrition and therefore may favorably affect burning properties of tobacco.