Stone Content Influence on Soil Water Retention.

A century of research focused primarily on agricultural soils has largely ignored stony soils, which are poorly understood in terms of their water retention functions. Motivated by this knowledge gap, we quantified the influence of soil-containing stone fragments on bulk soil hydraulic properties by determining soil- and stone-soil-mixture-water retention curves (WRC) for different volume fractions of stone content. The measured WRC for seven different stone types showed maximum and minimum saturated water contents of 0.55 m³ m^-3 in Pumice and 0.025 m³ m^-3 in fine sandstone, respectively. The stony soil water retention function was measured for two contrasting scenarios considering the mixture having stone fragments with lower- and fine soil with higher- porosities and vice versa, using the evaporation experiment. An averaging scheme to describe the WRC of stony soil was developed based on individual water retention properties of stone fragments and fine soil and validated against the set of laboratory measurements. The stony soil water retention function obtained from the experiment was in accordance with the proposed averaging scheme. The HYDRUS-3D simulation of an evaporation process in a stony soil was also demonstrated with significant contribution of stone fragments in total volumetric water content of the stony soil. In summary, both stone content and stone porosity can alter soil hydraulic properties, generally the result is to reduce soil-stone mixture saturated water content however, reverse is the case when the stones are of higher porosity than of the fine soil.