Effects of Soil Properties and Illumination Intensities on Matric Suction of Vegetated Soil

Qi Liu,Lijun Su,Hai Xiao,Zhenyao Xia,Daxiang Liu,Wennian Xu

doi:10.3390/su11226475

Abstract

Matric suction induced by evapotranspiration is an important parameter for determining the hydraulic mechanisms of vegetation on slope stability. Despite evapotranspiration closely associated with atmospheric parameters and soil conditions, the influence of soil properties and illumination intensities on matric suction of vegetated soil has so far received the least research attention. In this paper, three kinds of soil, namely, fine sandy loam, sandy silt, and silty clay, were selected as experimental soils, and Indigofera amblyantha was chosen as the test plant. The test conditions were controlled, such as the use of homogeneous soil and uniform plant growth conditions. Each specimen was exposed to identical atmospheric conditions controlled in a laboratory for monitoring matric suction responses over 10 days. The results showed that illumination intensities play an important role in evapotranspiration, and the thermal energy from lighting had a direct impact on plant transpiration, whereas the lighting only affected plant photosynthesis. Plant roots in vegetated soil can effectively improve the air intake value of soil, and matric suction induced by plant transpiration in vegetated soil was 1.5–2.0 times that of un-evapotranspirated soil. There is a correlation between matric suction and the silt and clay contents, and the matric suction of silty clay was sensitive to changes in the soil moisture content. Compared to fine sandy loam, the water retention of sandy silt and silty clay was high, and a high level of matric suction was maintained in the corresponding time. The results for predicting soil water evapotranspiration based on matric suction have theoretical and practical significance for preventing soil erosion and shallow landslides. In addition, these results have great guiding significance for agricultural production, such as irrigation.

Highlights

Matric suction is one independent variable that controls the stress-strain characteristics of unsaturated soil [1,2], variations of which change soil properties, such as permeability and shear strength [3,4,5]
Comparison of Plant Transpiration and Soil Evaporation. In this test, based on the viewpoint that plant roots occupy soil particle gaps and reduce soil porosity, the void ratio of vegetated soil was deduced via the three-phase diagram of soil [25]
For a given decrement of matric suction, the response time of vegetated soil was high; in other words, the matric suction can be maintained during the corresponding period, which is a great significance to enhance the stability of shallow slope

Summary

Introduction

Matric suction is one independent variable that controls the stress-strain characteristics of unsaturated soil [1,2], variations of which change soil properties, such as permeability and shear strength [3,4,5]. The analysis of hydrological and mechanical factors influencing vegetated slope stability based on numerical simulation shows that hydraulic reinforcement is prior to that of mechanical effects [13]. Matric suction induced by plant transpiration (hydraulic reinforcement) in vegetated soil can reduce soil permeability [19,20] and increase soil shear strength [4,19,21]. It has been recognized that plant transpiration induces matric suction and is an important mechanism in the stability analysis of soil slopes and riverbanks covered with vegetation [9,16,17,22,23,24,25]. Plant roots can change soil hydraulic properties, arguably by altering the soil structure due to root occupancy of the soil pore-spaces [15,17]

Objectives

Methods

Results

Conclusion