Different forms of soil potassium in tobacco cultivated areas of northern Iran

Potassium (K) is one of the major essential nutrients for growth of tobacco. Tobacco leaf K content is highly correlated with tobacco leaf quality and is an important index reflecting tobacco leaf quality. The forms of soil Κ in the order of their availability for plants are soil soluble, exchangeable, non-exchangeable and structural potassium. This study aimed to investigate the forms of soil potassium (soluble, exchangeable, non-exchangeable and structural) and aqua-regia extractable potassium in tobacco cultivated areas of Golestan, Mazandaran and Gilan provinces.
Three soil profiles were described and sampled in each tobacco cultivated areas of Golestan, Mazandaran and Gilan provinces. All soil profiles were described and classifid according to Keys to Soil Taxonomy. The soluble, exchangeable, non-exchangeable, structural and aqua-regia extractable potassium were measured and their relationships with each other and soil physical and chemical characteristics were investigated.
Mean concentrations of soluble, exchangeable, non-exchangeable, aqua-regia extractable, structural and total potassium in studied soils were 0 to 38.24, 7 to 513, 44 to 1933, 70 to 4267, 4114 to 15607 and 4166 to 16157 mg kg-1, and the percentage of mean concentarions of soluble, exchangeable, non-exchangeable, aqua-regia and structural potassium to total potassium varied from 0 to 0.32, 0.12 to 4.41, 0.83 to 11.96, 1.21 to 33.72 and 85.60 to 98.96 %, respectively. The lowest concentrations of all potassium forms were measured in the studied soils of Gilan Province. The highest concentrations of soluble, exchangeable, non-exchangeable and aqua-regia extractable K occurred in the studied soils of Mazandaran Province, and structural and total potassium in the studied soils of Golestan Province. The correlation analyses indicated the positive significant correlation (P
Plant available potassium (soluble, exchangeable and non-exchangeable potassium) in Mazandaran province tobacco cultivated areas was more than that in Golestan and Gilan provinces. Therefore, potassium fertilizer management should be different in these areas. Aqua-regia potassium had a good correlation with other forms of potassium. Since contains soluble, exchangeable, non-exchangeable and part of the structural potassium, could show the soil potassium ability for plants during the growing season to be considered, greenhouse and field experiments that need to be examined.