Selection of a Suitable Extractant for Sequential Leaching of Soil to Evaluate Medium-Term Potassium Availability to Plants

The study aimed to select an extractant for assessing medium-term potassium (K) availability in Indian soils under controlled environment.

Potassium was extracted from five different Indian soils (alkaline alluvial, acidic alluvial, calcareous alluvial, red, and black) with ten successive leachings (18 h of incubation in each) using twelve 0.1 N solutions (acetic acid, hydrochloric acid, acetates, and chlorides of ammonium, sodium, magnesium, calcium and barium). A pot experiment was also conducted taking five crops of sorghum-Sudan grass hybrid. Kinetic equations were fitted to the cumulative K-released by different extractants. Path analysis was performed to comprehend the effect of soil parameters on initial and overall K-release constants, obtained from the best fitted kinetic model. Stepwise multiple-regression was performed to quantify medium-term K-availability based on important soil parameters.

Total K-leached by barium chloride (BaCl₂) showed highest correlation (r² = 0.76; P < 0.01) with the cumulative K-uptake of 5 crops. The K-release by BaCl₂ was best explained by the parabolic diffusion equation. Initial K-release constant (a_pd) was directly influenced by the water soluble-K and cation exchange capacity; while, overall K-release coefficient (b_pd) was directly governed by both water soluble-K and exchangeable-K.

0.1 N BaCl₂ emerged as the best among the twelve extractants for the assessment of medium-term plant K availability through sequential leaching in five major soils of India. The soil properties and K fractions had different influence on initial and overall rate constants of K release from the soils.