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) quotient, a ratio between strongly held and easily desorbable EUF fractions of K to measure K‐buffering capacity of illite‐dominant soils under intensive 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 after the cropping. As a result of cropping, the mean K‐ replenishment rate 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 significant positive correlation with dry matter yield (r = 0.78*) and K uptake (r = 0.79*) in the first harvest of crop and in the subsequent harvests it maintained correlations of lower order. While other EUK‐K fractions, i.e. EUF 20°C, EUF 80°C, and EUF 35 min increased or maintained the same extent of correlation with conventional soil test methods after cropping, EUF‐K quotient failed to have significant correlation with those soil test methods after cropping. The current study brought out that exhaustive cropping differentially depleted the EUF fractions leading to an increase in the estimated buffering capacity (EUF‐Q) which failed to show satisfactory relationship with K removal by the crop. [ABSTRACT FROM PUBLISHER]