Tillage effects on near-surface soil hydraulic properties

The processes for the formation of porosity are thought to differ between tilled and non-tilled cropping systems. The pores are created primarily by the tillage tool in the tilled systems and by biological processes in non-tilled systems. Because of the different methods of pore formation, the pore size distribution, pore continuity and hydraulic conductivity functions would be expected to differ among tillage systems. The objective of this study was to determine effects of three tillage systems — mold-board plow (MP), chisel plow (CP), and no-till (NT) — on hydraulic properties of soils from eight long-term tillage and rotation experiments. Tillage effects on saturated and unsaturated hydraulic conductivity, pore size distribution, and moisture retention characteristics were more apparent for soils with a continuous corn (CC) rotation than for either a corn-soybean (CS) rotation or a corn-oats-alfalfa (COA) rotation. Pore size distributions were similar among tillage systems for each soil except for three soils with a CC rotation. The MP system increased volume of pores >150 μm radius by 23% to 91% compared with the NT system on two of the soils, but the NT system increased the volume of the same radius pore by 50% on one other soil. The NT system had 30 to 180% greater saturated hydraulic conductivity than either the CP or MP systems. The NT system with a CC rotation showed a greater slope of the log unsaturated hydraulic conductivity; log volumetric water content relationship on two of the soils indicating greater water movement through a few relatively large pores for this system than for either the CP or MP systems.