Water infiltration and saturated hydraulic conductivity in an agricultural watershed with pedogenetic discontinuity

Abstract

Understanding soil hydrology is crucial for effective watershed management, particularly in landscapes characterized by pedogenetic discontinuities and gravelly soils. This study investigates soil hydraulic properties within a tobacco-cultivated watershed, focusing on granulometry, bulk density, water retention (from saturation to permanent wilting point), steady-state infiltration rate (Is), and saturated hydraulic conductivity (Ksat and Keff) across different hillslopes, slope positions, and soil layers. Results show a wide range of Ksat (0 to 387 mm h−1), with the highest conductivity consistently found in surface layers, attributed to intense tillage from ridge construction in tobacco farming. Variability was also high in Is (4 to 402 mm h−1) and Keff (0 to 224 mm h−1). Acrisols exhibited some low infiltration values, while midslope positions generally showed higher Is across soil types. A linear relationship between Keff and Is (r² = 0.67) was observed, though the Ksat of surface soil was not related to Is. More permeable soils (higher Ksat) had lower bulk density and reduced water retention under wet or dry conditions. In surface layers, Ksat correlated positively with water retention near field capacity, Keff related directly to Is and gravel content but inversely to retention at permanent wilting point, and Is correlated positively with fine sand and saturation water retention and negatively with bulk density. This spatial heterogeneity reflects the influence of texture, compaction, land use, and microtopography in sloped terrains. Pedogenetic discontinuities shape soil horizon development and hydrological response, especially under saturation, highlighting the importance of incorporating these factors into hydrological models and watershed management to mitigate subsurface erosion risks. Enhanced understanding of these soil layers aids prediction of infiltration, runoff, and chemical transport, improving land and soil management in similar environments.