Tillage effects on hydraulic properties and macroporosity in silty and sandy soils

In agricultural soils, macroporosity and hydraulic properties are influenced by tillage practices. The objective of this study was to characterize macroporosity and surface soil hydraulic properties in two soils of different texture (Lietzen: sandy loam-Humic Dystrudept; Adenstedt: silt loam; Typic Hapludoll) under conventional (CT) and conservational (RT) tillage systems. Soil hydraulic conductivity was assessed in situ by ponded infiltration with single rings (n = 70) and tension infiltration by means of a closed-top hood infiltrometer (HIF; n = 48). Macroporosity (pore diameters > 1 mm) was estimated from differences in infiltration at saturation and at -3 cm H2O soil matric potential. Mean saturated hydraulic conductivity (K-s) for Lietzen was 3.1 x 10(-5) m s(-1) and for Adenstedt was 4.3 x 10(-5) m s(-1). These values are by one order of magnitude higher than values estimated from soil texture. This implies that soil structure has a dominant influence on hydraulic conductivity. Mean values of macroporosity were 0.005% for Lietzen and 0.018% for Adenstedt (using the method of Watson and Luxmoore). The respective values were 0.0008 and 0.0013% when the method of Bodhinayake et al. was used. For Adenstedt, RT showed higher macroporosity than CT (not significant at P < 0.05 for n = 12). Such treatment-induced differences were less developed for Lietzen. The K-s values measured with the ponded ring infiltrometer (RIF) at the sandy Lietzen site were higher than the corresponding values measured with the tension infiltrometer. These differences may be caused by subcritical soil water repellency (i.e., contact angles of the soil-water-air interface below 90), although further factors could also be important (e.g., air entrapment, differences in water saturation, geometry of infiltration devices).