Soil texture and layering effects on water and salt dynamics in the presence of a water table: a review

Abstract

Soil texture and its vertical spatial heterogeneity may greatly influence soil hydraulic properties and the distribution of water and solutes in the soil profile; therefore, they are of great importance for agricultural, environmental, and geo-engineering applications such as land reclamation and landfill construction. This paper reviews the following aspects on water and salt dynamics in the presence of a water table: (i) the effect of soil texture on the extent of upward movement of groundwater in homogenous soils and (ii) the impact of soil textural layering on water and salt dynamics. For a homogenous soil, the maximum height of capillary rise (hmax) or the evaporation characteristic length (ECL) is closely related to the soil texture. When the water table is deeper than hmax, water will evaporate at some depth below surface and salts will be retained below the evaporation front, causing the separation of water and salt. For layered soils, flow barriers (capillary and hydraulic barriers) can make the soil hold more water than a nonlayered one. A capillary barrier may work when a fine-textured layer overlies a coarse-textured layer during infiltration or a coarse-textured layer overlies a fine-textured layer during evaporation, and a hydraulic barrier may occur when a poorly permeable layer exists in the soil profile. The extra water held by flow barriers may improve water availability to plants and may at the same time increase salinization and other environmental risks. Under special conditions, such as in seasonally frozen soils with a shallow water table, there is an additional soil salinization incentive caused by freeze–thaw cycles. Above all, further research is needed to understand the complex effects of soil texture and layering on water and salt dynamics, especially in artificial soils such as reclaimed soils with contrasting properties.