Water Retention Characteristics of Some Shrink-Swell Soils as Influenced by Clay and Exchangeable Cations

In absence of detailed information on the depth-wise distribution of moisture retention properties as influenced by exchangeable cations in deep shrink-swell soils (Vertisols and Vertic intergrades), the present study was undertaken on twenty three shrink swell soils of Andhra Pradesh and Maharashtra. Results indicate significant positive correlations between smectitic clay and moisture constants. Highly significant positive correlations between moisture constants and exchangeable sodium (ES), exchangeable magnesium (EM) and with ES+EM indicate that both Na and Mg ions are responsible for more retention and less release of soil moisture in these clayey soils. This suggests that saturation of soils with magnesium ions also has the adverse effect even at ESP <5. On the contrary, significant negative correlations exist between exchangeable calcium and moisture constants. This suggests that saturation of soils with calcium ions can improve soil structure and release more amount of moisture for crop growth, whereas magnesium saturation of soils is not a favorable situation, though both Ca and Mg are grouped together by United States Salinity Laboratory (USSL) (Richards, 1954) as being beneficial cations in developing and maintaining soil structure. The effect of potassium on moisture constants is nonsignificant.