Potassium Release in Relation to Miner~ogy of Silt and Clays

Total amount of K released from silt and clay fractions by successive boiling with normal nitric acid of three alluvial soils, S1 (Udic Ustochrept), S2 (Ustifluvent) and S3 (Typic Ustochrept) was more but per cent release (18.9 to 65%) of total K cuntent was less than that of a mixed red and black soil, S4 (Vertic Ustochrept) and a laterite soil, S5(Typic Haplustalf) which. ranged from 50.5 to 92.4 per cent. While the first extract from S1, S2 and S3 samples contributed 44 to 71 per cent of total release. it was 15.7 to 54.7 in case of S4 and S5 samples. Calculated values of rate constants (first order) decreased sharply from 0.040 to 0.002 min⁻¹ after three extractions and thereafter remained constant in case of S1, S2 and S3 samples, but varied with alternate decrease, and increase in case of S4 and S5 samples. This differential behavior of K release between two groups of samples (S1, S2, S3) and (S4, S5) has been explained in terms of the amount and nature of micaceous minerals present in them. Effect of particle size on K release was not prominent and did not follow any general trend.