Changes in soil water content with ambient relative humidity in relation to the organic matter and clay

Abstract

Changes in soil water content with increasing ambient relative humidity was examined using model soils prepared by mixing silica sand with different types of organic matter and different types and con tents of clays. In this study, we used commercially available hydrophobic and hydrophilic organic mat ter, and kaolinite and montmorillonite under four levels of relative humidities. Soil water content of all the soils increased with increasing relative humidity. Hydrophilic organic matter, which is reported to decrease the wettability of soils, was found to increase the absorption of water into soils in the vapor form. In model soils without clay, hydrophobic organic matter, which is reported to impede water entry in liquid form (water repellent), was found to have little or no effect on water vapor absorption. In con trast, when the model soils containing 1–2% clays, hydrophobic organic matter slightly decreased the water vapor absorption. Montmorillonite containing samples showed higher water vapor absorption, and therefore, higher water contents compared with those containing kaolinite. The difference in water content between samples containing montmorillonite and kaolinite increased with increasing clay con tent. Increase in clays with high water absorption capacity was found to make the clay effects on water vapor absorption prominent and to hinder the effects of hydrophobic or hydrophilic organic matter on water vapor absorption. The absorption of water into soils in vapor form was found not to be compara