Pore Size Distribution and Hydraulic Conductivity Affected by Tillage in Northwestern Canada

Abstract

AbstractTillage management can affect crop growth, in part by altering the pore structure and hydraulic properties of soil. We hypothesized that water retention, pore size distribution, and unsaturated hydraulic conductivity (k) differed under conventional tillage (CT) and no tillage (NT). We evaluated this hypothesis on a Donnelly silt loam (fine‐loamy, mixed, frigid Typic Cryoboralf) and a Donnelly sandy loam (coarseloamy, mixed, frigid Typic Cryoboralf) in northwestern Canada. Soil cores were collected from the 0‐ to 300‐mm depth in 75‐mm increments. Water retention was measured at 10 pressure levels from ‐2 to −400 kPa to calculate pore size distribution and k. Both soils retained 0.04 to 0.09 m3 m−3 more water under NT than under CT. The volume fraction of total porosity with pores <7.5 µm in diameter (effective pores for retaining plant‐available water) in the silt loam averaged 0.49 and 0.58 m3 m−3 under CT and NT, respectively, and in the sandy loam averaged 0.39 and 0.51 m3 m−3 under CT and NT, respectively. In contrast, the volume fraction of total porosity with pores >150 µm in diameter (pores draining freely with gravity) in the silt loam averaged 0.29 and 0.23 m3 m−3 under CT and NT, respectively, and in the sandy loam averaged 0.35 and 0.24 m3 m−3 under CT and NT, respectively. Conventional tillage appeared more likely to interrupt capillaries than NT, since large differences in k between tillage regimes were observed below a depth of 75 mm with increasing moisture deficit. Continuous NT management increased water storage of both silt loam and sandy loam soils in this cold, semiarid region.