The amount of 'available K' was estimated by the following methods:

(1) 0.002 M SrCI z, with a soil-solution ratio of 1:10 and an equilibration time of 30 min.

(2) 0.1 M HC1, with a soil-solution ratio of 1 : 10 and an equilibration time of 30 in.

(3) 1 M NH4OAc, with a soil-solution ratio of 1:10 and an equilibration time of 15min (Knudsen et al., 1982).

(4) 0.2 M CH3COOH + 0.25 M NHnNO 3 + 0.015 M NHaF + 0.013 M HNO 3 + 0.001 M EDTA, with a soil-solution ratio of 1 : 10 and an extraction time of 5 min (Mehlich, 1984).

(5) Boiling 1 M HNO3, with a soil-solution ratio of 1:2.5 and boiling time of 10 rain (Knudsen et al., 1982).

(6) Electro-ultrafiltration (EUF) in three fractions (i) 10 min at 50 V and 20°C (EUF-I), (ii) two sequential desorptions of 10 min at 200 V and 20°C (EUF-II), and (iii) five sequential desorptions of 5 min at 400 V and 80°C. The first desorption at 80°C will be referred to as EUF-III and the total amount of K desorbed between 30 and 55 min as EUF-80. The sum of the amounts of K in the extractions at 20°C will be referred to in the text as EUF-20. The soil-to-solution ratio was 4:60 (4 g of soil in 60 mL of water) for all soils except soil 29, a calcareous soil, for which the ratio was 1:60 in order to maintain a constant voltage at 400V and low electrical current (

Thanks Saheb for giving details of various methods. If you can share the results of these methods used, we can get sonme idea about their relative efficiency.

Following

Following