Effect of rock fragments on unsaturated soil water flow

Abstract

Introduction: Rock fragments are commonly found in many soils as a consequence of natural processes or human activities. Stony soils represent a significant part of arable lands and are a component of this important land resource that is heavily modified comparable to SUITMA soils. Despite the significance of rock fragments, soil studies have tended to ignore them, and a rock fragment study is scarce. Soils containing rock fragments have a lesser capacity to hold water because rock fragments occupy space in place of mineral soil. There is now an increased interest to identify the relationship between rock fragments and soil properties. Eyrewell, a research area for this study, contains a lot of rock fragments, and soils are well-draining with high drought vulnerability. This research aims to identify the effects of rock fragments on in-situ soil water flow in Eyrewell. Material & Methods: A dye tracer was applied at a surface of experimental sites using a ponding method. Total volumes of 40 L of dye were applied in the field. The soils under the application plot were excavated vertically from soil pits, and exposed cross-sectional areas were photographed. The vertical excavation was conducted four times, in each case with exposures at 20 cm intervals. Results: Two significant influences of rock fragments on soil water flow were observed. When rock fragments were located in the way of heavy preferential flow, water detoured along a surface of rock fragments, remaining the soils underneath rock fragments remained undyed. This interrupted straightforward leaching of water and distributed water more broadly, which eventually increased water residence time in soil. On the other hand, rock fragments provided another flow pathways besides cracks in the profile. Horizontal cracks were common in the research area and most water rapidly flowed along the cracks without deep penetration. However, rock fragments located near cracks developed vertical water movements from the crack flow, which also broadened water distribution. Conclusions: Rock fragments can be beneficial to increase soil water efficiency by playing a significant role in water flow, distribution, and retention in soils. In many cases, this is contrary to the general assumption that rock fragments enhance free drainage.