EVALUATION OF EUF-POTASSIUM QUOTIENT AS A MEASURE OF POTASSIUM BUFFERING CAPACITY OF ILLITE-DOMINANT SOILS UNDER INTENSIVE CROPPING

Suitability of the electro-ultrafiltration (EUF)-potassium (K) quotien t, a ratio between strongly held and easily desorbable EUF fractions o f K to measure K-buffering capacity of illite-dominant soils under int ensive cropping, was studied. EUF-K quotients which ranged from 0.333 to 0.580 before cropping increased to the range of 0.405 to 0.710 afte r the cropping. As a result of cropping, the mean K- replenishment rat e decreased from 6.98 kg/ha/day to 0.2 kg/ha/day, whereas the mean EUF -K quotient increased from 0.43 to 0.53. EUF-K quotient showed signifi cant positive correlation with dry matter yield (r = 0.78) and K upta ke (r = 0.79) in the first harvest of crop and in the subsequent harv ests it maintained correlations of lower order. While other EUK-K frac tions, i.e. EUF 20 degrees C, EUF 80 degrees C, and EUF 35 min increas ed or maintained the same extent of correlation with conventional soil test methods after cropping, EUF-K quotient failed to have significan t correlation with those soil test methods after cropping. The current study brought out that exhaustive cropping differentially depleted th e EUF fractions leading to an increase in the estimated buffering capa city (EUF-Q) which failed to show satisfactory relationship with K rem oval by the crop.