Determining the critical level of potassium in the soils of tobacco farms of Golestan and Mazandaran Provinces

K is a nutrient that has a significant role in increasing quantitative and qualitative tobacco yield. The aim of this study is to explore K status and to determine its critical level in the soils of tobacco farms of Golestan and Mazandaran Provinces. 48 soil samples were collected from 0-30 cm depth and 20 samples were selected on the bases contents of clay, OC and K extracted by Ammonium acetate for subsequent studies. The experiment was carried out as a factorial in the form of completely randomized design with three replications in the 20 kg plastic pots. First factor contained 20 tobacco cultivated soils and second factor included two levels of 0 and 150 kg K2O from K2SO4 source. A Healthy similar tobacco seedling, K326 cultivar, was transplanted in each pot. Mature leaves were harvested in 6 cuts during growing period and then their fresh and dry weights were measured. Morphological characteristics such as length and width of leaves, shoot diameter and leaf chlorophyll and chemical properties such as K, sugar and nicotine contents were determined. Fresh leaves were evaluated after processing and finally gross income was also calculated. Results showed that K content significantly affects length and chlorophyll of leaf, fresh and dry matter weights, and nicotine and K contents at α=1% probably level and on shoot diameter and on gross income at α=5% probably level. The critical level of soil K was obtained 240 mg/kg, through graphical Cate and Nelson method on the basis of tobacco relative yield of fresh weight and relative concentration of K using a ratio of 1:20 soil: ammonium acetate (1 N) extractant.