Different forms of soil potassium and its correlation with qualitative and quantitative characteristics of tobacco in soils of tobacco cultivated areas in northern Iran

Potassium content in tobacco leaves is highly affected the quality of tobacco and considered the important indicator for determining the tobacco leaf quality. The objective of this study was to investigate the relationship between different soil K forms (soluble, exchangeable, non-exchangeable, mineral and extracted with aqua-regia extractable) with quantitative and qualitative characteristics of tobacco. Nineteen surface soil samples were collected from tobacco cultivated areas of Golestan, Mazandaran and Guilan provinces. Physical, chemical properties and different forms of potassium in the soils were measured. A pot experiment in a completely randomized with three replications for the soils without application of potassium fertilizer was design to study the potassium uptake by tobacco. The results showed the lowest amountsall potassium forms in Guilan soils (except exchangeable potassium) and the highest amountsin Mazandaran soils. The effect of soil type on all the morphological and chemical characteristics of tobacco was significantat P<0.01. Soluble and exchangeable potassium were highly correlated with morphological and chemical characteristics of tobacco. The amount andalso the ratio of solubleto total potassium in percent)at P<0.01and exchangeable potassium at P<0.05had the relatively strong correlation with the tobacco potassium percentage. Also, because the amount of different forms of potassium did not explainedthe reasonof potassium changes in the tobacco plant. Therefore,it is suggested to use the ratio of soluble and exchangeable potassium to total potassium (in percent) formore precise potassium fertilizer recommendation.