Evaluating chemical extractants to estimate available potassium for pinto beans (Phaseolus vulgaris) in some calcareous soils

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-diethylenetriamine 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.