Assessing plant-available potassium in soil using cation exchange membrane burial

We assessed a method for extraction of plant-available potassium using a cation exchange membrane (CEM) burial technique. The study compared the amounts of K extracted by CEM burial with three reference chemical-based extractants for 19 soil samples representing a wide range of soil types in Saskatchewan, Canada and the People's Republic of China. The three reference extractants were (1) 1 M NH4OAc, (2) a mixed solution of 0.01 M EDTA, 0.25 M NaHCO3 and 0.01 M NH4F and (3) 1 M HNO3. Potassium extractable by 1 M NH4OAc ranged from 37 mg kg(-1) to 1889 mg kg(-1) among the 19 soils. The K availability as predicted by CEM was significantly correlated with the reference methods with the strongest relationship (r(2) = 0.94, P < 0.001) with the EDTA-NH4F test. To evaluate the relative ability of CEM and the conventional tests to predict K availability to plants, canola and wheat were grown on the 19 soils in the growth chamber and plant K uptake was compared with test-predicted K availability. All test methods revealed a similar ability to predict K availability with good correlation (r(2) approximate to 0.70, P < 0.001) with plant uptake. However, the CEM method showed its advantages in predicting plant availability in a variety of soil types with large coefficients of determination in both acidic and neutral to alkaline soil groupings. The CEM burial technique could be readily adopted in soil K availability analysis because of low cost and simplicity as well as its consistency over a wide range of soil types.