Effects of conventional and conservation tillage on soil hydraulic properties of a silty-loamy soil

Infiltration into soils is strongly correlated with macroporosity. Under agricultural land use, the properties of the macropore network are governed by the applied management and tillage system. On an experimental site with a silt loam soil partly under conventional and conservation tillage, the methods of visual inventarization of stained and unstained macropores and infiltration measurements with an infiltrometer were applied to the macropore system. Dye tracer experiments with methylene blue as tracer agent yielded a penetration depth of 120 cm on the conservation tillage plot while a penetration depth of only 50 cm was recorded on the conventionally tilled plot. For both tillage treatments, infiltration rates were lower in the topsoil than in soil depths >30 cm. The conservation tillage plot showed higher infiltration rates at 50 and 90 cm soil depth than the conventional tilled plot. For both tillage systems, the visual recording of stained and unstained macropores (d greater than or equal to mm) resulted in macropore densities ranging between 100 and 1,000 macropores/m(2), with the highest numbers in the topsoil and a gradual decrease with soil depth. At the conservation tillage plot, below 20 cm soil depth, macropore density was greater than at the conventionally tilled plot. Macroporosity obtained from the visual registering varied between 0.09% and 0.83% for the conventional tillage plot and between 0.08% and 0.6% for the conservation tillage plot. Macroporosity derived from tension infiltrometry, assuming a minimum macropore radius of 0.5 mm, range between 0.02% and 0.1%, about one order of magnitude lower than the figure obtained from visual inventarization. The results indicate a greater continuity and connectivity of the macropore system for silty soils with conservation tillage systems. Therefore, conservation tillage could possibly offer a means to reduce surface runoff and flood generation in agricultural landscapes dominated by silty-loamy soils. (C) 2004 Elsevier Ltd. All rights reserved.