Near-saturated hydraulic properties in the surface layer of a sandy loam soil under conventional and reduced tillage
Information on the quantitative tillage effects on pore space and near-saturated hydraulic characteristics is important to improve decision support systems for soil and environmental management. The purpose of this study was to determine the effect of conventional (CT) and reduced tillage (RT) on water retention and infiltration properties of an Agrudalf sandy loam surface soil under long-term winter wheat (Triticum aestivum L.) cropping. Using tension disk infiltrometry, with supply pressure heads (h) from –15 to –120 mm, the steady-state infiltration rate [i(h)] and hydraulic conductivity [K(h)] were highest shortly after tillage in October, followed by a steep decrease to minimum values in winter and a recovery to intermediate values during spring and early summer. The range in the temporal variation in saturated K was about 65 to 5 and 52 to 8 mm h–1 under CT and RT, respectively. Compared with CT, K(h) under RT was slightly lower shortly after tillage, similar during winter, and considerably higher during early summer. Changes in K were accompanied by temporal variations in pore space characteristics, indicating structural collapse during late autumn and early winter followed by structural recovery with aggregation during spring and summer. The air-entry pressure head was highest under RT. The effective porosities were found to be smaller, by two to three orders of magnitude, than the equivalent fractional pore volumes estimated from the water retention curves determined on soil cores in the laboratory. Wheel traffic was found to obliterate any differences in hydraulic properties between the tillage treatments. Therefore, compared with CT, RT is likely to improve water availability and soil resilience but offers no comparative advantage for controlling wheel-traffic-induced topsoil compaction.