Evaluation of the nutrient status in soil is important for
nutritional, environmental, and economical aspects. The objective of this study was to determine
potassium (K) available to Pinto beans (Phaseolus vulgaris) in 15 soils from the Charmahal Va
Bakhtyari province. The treatments included two K levels [0 and 200 mg K/kg as potassium sulfate
(K2SO4)] and 15 soils in a factorial experiment in a randomized block design with three
replications. The results indicated that in some soils K application increased yield, K
concentration and K uptake by bean. The 9 extracting solutions used in this study were classified
in 4 groups on the basis of the mechanism of the extraction. The first group of extractants were
acidic extractants, boiling 1 mol/L HNO3, 0.1 mol/L HNO3, 0.1 mol/L HCl, and Mehlich 1. The
second group includes 0.1 mol/L BaCl2, and 0.01 mol/L CaCl2. The third group includes 1 mol/L
NH4OAc (ammonium acetate), and AB-DTPA (ammonium bicarbonate-diethylenetriA amine
pentaaceticacid), and finally distilled water. The correlation studies showed that NH4OAc, AB-
DTPA, 0.1 mol/L BaCl2, 0.1 mol/L HCl, and boiling 1 mol/L HNO3 could not be used as available K
extractants. But the correlation of other extractants with relative yield, plant response,
concentration K, and K uptake were significant. Therefore, these extracting solutions can be used
as available K extractants. Potassium critical levels by extractants were also determined by
Cate-Nelson method. Potassium critical levels for 90% of relative yield were 22, 190, 28, and 50
mg/kg for distilled water, 0.1 mol/L HNO3, Mehlich 1, and 0.01 mol/L CaCl2, respectively.