Abstract
Soil architecture exerts an important control on soil hydraulic properties and hydrological responses. However, the knowledge of hydraulic properties related to soil architecture is limited. The objective of this study was to investigate the influences of soil architecture on soil physical and hydraulic properties and explore their implications for runoff generation in a small agricultural watershed in the Three Gorges Reservoir Area (TGRA) of southern China. Six types of soil architecture were selected, including shallow loam sandy soil in grassland (SLSG) and shallow loam sandy soil in cropland (SLSC) on the shoulder; shallow sandy loam in grassland (SSLG) and shallow sandy loam in cropland (SSLC) on the backslope; and deep sandy loam in grassland (DSLG) and deep sandy loam in cropland (DSLC) on the footslope. The results showed that saturated hydraulic conductivity (Ksat) was significantly higher in shallow loamy sand soil under grasslands (8.57 cm h−1) than under croplands (7.39 cm h−1) at the topsoil layer. Total porosity was highest for DSLC and lowest for SSLG, averaged across all depths. The proportion of macropores under SLSG was increased by 60% compared with under DSLC, which potentially enhanced water infiltration and decreased surface runoff. The landscape location effect showed that at the shoulder, Ksat values were 20% and 47% higher than values at the backslope and footslope, respectively. It was inferred by comparing Ksat values with 30 min maximum rainfall intensity at the watershed, that surface runoff would be generated in SSLC, DSLG, and DSLC sites by storms, but that no overland flow is generated in both sites at the shoulder and SSLG. The significantly higher Ksat under grasslands in comparison to croplands at the backslope indicated that planting grasses would increase infiltration capacity and mitigate runoff generation during storm events. The findings demonstrated that croplands in footslope positions might be hydrologically sensitive areas in this small agricultural watershed.
Highlights
The knowledge of soil hydraulic properties, including hydraulic conductivity and water retention, is of great importance for understanding hydrological responses such as water infiltration, surface runoff, and water storage
The results showed that soil architecture and landscape position had significant effects on bulk density at the topsoil
The study assessed the effects of six different soil architectures (SLSG, SLSC, shallow sandy loam in grassland (SSLG), shallow sandy loam in cropland (SSLC), deep sandy loam in grassland (DSLG), and deep sandy loam in cropland (DSLC)) on bulk density, saturated hydraulic conductivity (Ksat ), soil water retention characteristics, and pore size distributions at different landscape positions in a small agricultural watershed
Summary
The knowledge of soil hydraulic properties, including hydraulic conductivity and water retention, is of great importance for understanding hydrological responses such as water infiltration, surface runoff, and water storage. Soil architecture refers to the organization of soil from the microscopic to the megascopic scales and encompasses three interlinked components (solid components, pore space, and their interfaces) at each scale [1,2]. It is commonly recognized by two general categories: (1) soil architecture within a soil profile, such as mineral structure, aggregates, soil horizons, and pedons; and (2) soil architecture in the landscape including soil catena, soilscape, soil sequence, and pedosphere. Soil architecture within a soil profile is often different due to the heterogeneity of soil horizonation, texture, rock fragments, and macropores, which results in different hydraulic properties [6,7]. Schwen et al (2014) compared the vertical variations of soil hydraulic properties between silty-loam Chernozem and forested sandy Cambisol profiles and revealed that variations of saturated hydraulic conductivity (Ksat ) were largest within the plowed
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