Characterizing soil water-conducting macro- and mesoporosity as influenced by tillage using tension infiltrometry

Abstract

Knowledge of soil water conductive porosity is of paramount importance for understanding the water and solute movement in soil. The objective of this study was to describe and evaluate an alternative pore index, i.e., the representative mean pore radius for two consecutive soil water tensions (lambda(Delta psi)), for characterizing the water-transmitting macro- and mesoporosity of soil. The hydraulic conductivity (K) and related hydraulic parameters were measured using a tension disk infiltrometer at -14, -4, -1, and 0 cm water pressure heads at a soil depth of 2 cm on a long-term conservation tillage experiment (after 9 yr of trial) under conventional tillage (CT), reduced tillage (RT), and no-tillage (NT) treatments. The soil was loam (Xerollic Calciorthid). The measurements were performed within the first half of a 16- to 18-mo-long fallow period. Unlike the model based on the classical capillary rise theory, which assumes no differences between measurement sites (e.g., tillage treatments) for the corresponding equivalent pore radius (CD) for macro- and mesopores, significant differences in lambda(Delta psi) values for macro- and mesopores were found between the three tillage systems tested. The number of water-transmitting macro- and mesopores per unit area estimated by means of the capillary rise approach was significantly greater than that calculated using the lambda(Delta psi) pore index. Although significantly higher values of lambda(Delta psi) for both macro- and mesopores were observed under NT a significantly lower near-saturation K was found under NT than CT and RT treatments due to the lower density of water-transmitting macro- and mesopores.