Different extractants, viz., water, dilute salt solutions, dilute organic acids, multinutrient extractants, mineral acids and various fractions of electro-ultrafiltration (EUF) were evaluated for their ability to extract the plant available K in smectitic soils using sorghum as a test crop. Mineral acids extracted higher amounts of K from soil, followed by dilute salt solutions, multinutrient extractants, organic acids and water. With the increase in voltage and temperature from 200V and 20°C to 400V and 80°C, respectively, there was almost two fold increase in K release in EUF fractions. Potassium released in 10 minutes by EUF was on par with the K release in water and organic acids. NH4Ac-K showed higher degree of correlation with sorghum shoot yield, root yield, relative yield, shoot K and flag leaf K compared to other forms of K. A critical K content was 240 mg kg−1 soil, and critical K content in flag leaf and in shoot of sorghum were 2.51 and 1.25 per cent, respectively.
Evaluation of different extractants, water, salt solutions, organic acids, multinutrient extractants, mineral acids, EUFfractions, sorghum response, critical levels, smectitic soils
