Surface soil hydraulic properties in four soil series under different land uses and their temporal changes

The concepts of "genoform" and "phenoform" distinguish the genetically-defined soil series and the variation of soil properties resulted from different land uses and management practices. With the repeated field measurements over time, we attempted to understand the difference of soil hydraulic properties among different land uses for a given soil series, and their temporal dynamics. Four soil series (Glenelg, Hagerstown, Joanna, and Morrison) in Pennsylvania with contrasting textures, structures, and parent materials were investigated. Within each soil series, four common land uses (woodland, cropland, pasture, and urban) were examined. At each site of soil series-land use combination, field-saturated and near-saturated hydraulic conductivities, K(ψ), were measured at the soil surface using standard tension infiltrometers at water supply potentials (ψ) of - 0.12, - .06, - 0.03, - 0.02, - 0.01, and 0 m. Surface infiltration measurements were repeated at each site in May and October from 2004 to 2006. The analysis of variance indicated that the measurement time (May or October) had the greatest impact on all measured hydraulic conductivities (p < 0.001), followed by the land use (p < 0.05 for K_{ψ = 0} and K_{ψ = - 0.06}) and soil series (p < 0.06 for K_{ψ = - 0.01} to K_{ψ = - 0.03}). The interactions between the time and land use and between the soil series and land use were statistically significant for K_{ψ = 0} and K_{ψ = - 0.01.} When separated by the measurement time, land use showed greater impacts in October than in May, while soil series had greater impacts in May than in October. Among the four land uses, woodland showed less obvious temporal change compared to the other three land uses because of less human-induced impacts and more consistent ground cover. Other three land uses generally showed a higher hydraulic conductivity in May than in October due to the drier initial soil moisture condition and related management practices in the spring that gave rise to more significant macropore flow. The results suggested that the initial soil moisture is an important variable that drives the temporal variation of the surface soil hydraulic properties.