Temporal changes in soil hydraulic conductivity in saturated and unsaturated fields

Abstract

Soil hydraulic conductivity ($K$) is an important soil property that exhibits relatively large uncertainty. The temporal variability of $K$ is often ignored when calculating water movement in soil. Various factors such as tillage, rain, temperature, wetting/drying, soil surface crusting, solution concentration, and biological activity can influence field $K$. We investigated soil $K$ in a central Iowa field as a function of time and tillage by using tension infiltrometer measurements with pressure head tension settings of 0 cm and − 3 cm. No clear relationship was found between bulk density ($\rho_{\text{b}}$) and $K$. Path analysis was conducted to assess the contribution ratios and causal relationships between factors affecting $K$. The $K$ values were influenced by physical impacts such as tillage, precipitation, and surface crusting with contributions of 24%, − 32%, and 49%, respectively, and with error of 60%. Soil surface crusting had a particularly large impact on saturated $K$. The maximum volume fraction influenced $K$. Earthworm activity that impacted the soil pore structure was also noticed in the field. Owing to this biological mechanism, no relationship was observed between $\rho_{\text{b}}$ and $K$. It is important to recognize the multiple combined effects of soil physical processes and biological activities when documenting $K$ in field soils.