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SOIL PHYSICS

Hydraulic Conductivity as Influenced by Stoniness in Degraded Drylands of Chile

^a Dep. of Soil Management, Ghent University, Coupure links 653, 9000 Ghent Belgium
^b Centro del Agua para Zonas Áridas y, Semiáridas de América Latina y el Caribe, Benavente 980, La Serena, Chile
^c Centro de Estudios en Zonas Áridas, Universidad de Chile, Campo Experimental Agronómico Las Cardas, Ruta 43, km 45, Coquimbo, Chile

^* Corresponding author (Koen.Verbist{at}UGent.be).

Infiltration measurements in arid, stony soils are notoriously variable in visually homogeneous areas, and have been reported to be influenced by embedded stone fragments. This study aimed to identify the influence of rock fragment contents, orientation, and position within a small arid watershed on hydraulic conductivity in northern Chile. Two different measurement techniques were used, a single-ring infiltrometer with constant ponding head and a tension infiltrometer, which were applied at both an undisturbed field site (44 locations along three transects) and on the disturbed <2-mm soil fraction from the same locations. Variations in saturated and unsaturated hydraulic conductivities were observed when using different calculation methods, adding to the observed variability. For saturated conditions, only small differences in conductivities were observed between two calculation methods, whereas unsaturated hydraulic conductivities calculated by five different methods showed more important variations. Stone fragment content correlated significantly with both saturated and unsaturated conductivities, probably due to a positive correlation between stone content and coarse lacunar pore space. Slope orientations with higher amounts of stone fragments gave higher infiltration rates, as well as transects with steeper slopes and more, but smaller, rock fragments. When evaluating differences in infiltration rates observed along three transects in the watershed, variability could be mainly attributed to stone fragment content influences.

Abbreviations: ME, mean error • MWD, mean weight diameter