Soil hydraulic properties such as soil infiltration rate and hydraulic conductivity are closely linked to runoff generation and infiltration processes but little is known about them on karst hillslopes. The objectives of this paper were to investigate the change in soil stable infiltration rate (q s) and near-saturated hydraulic conductivity (K ns) in different slope positions and to understand their relationship with rock fragment content and soil texture within the topsoil in subtropical karst regions of southwest China. Tension infiltrometers (20 cm in diameter) were used to measure q s and K ns at pressure head of −20 mm on hillslopes 1 (a disintegrated landslide failure) and 2 (an avalanche slope). The change of q s and K ns was great and they mostly had a moderate variability with coefficient of variations (CV) between 0.1 and 1.0 in the different slope positions. On average, q s ranged from 0.43 to 4.25 mm/min and K ns varied from 0.75 to 11.00 mm/min. These rates exceed those of most natural rainfall events, confirming that overland flow is rare on karst hillslopes. From bottom to top, q s and K ns had a decrease–increase–decrease trend due to the presence of large rock outcrops (2 m in height) on hillslope 1 but had an increasing trend on hillslope 2 with less complex landform. They tended to increase with increase in total rock fragment content (5–250 mm) within the topsoil as well as slope gradient on both hillslopes. Pearson correlation analysis suggested that higher coarse pebble (20–75 mm), cobble (75–250 mm), and sand (2–0.05 mm) contents as well as total rock fragment content could significantly facilitate water infiltration into soils, but higher clay (0.002 mm) content could restrict water movement. This result indicated that rock fragment, sand, and clay contents may remarkably affect water flow in the topsoil layers, and should be considered in hydrological modeling on karst hillslopes in subtropical regions.
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机译：土壤水力特性（例如土壤入渗率和水力传导率）与径流的产生和入渗过程密切相关，但在喀斯特山坡上对其了解甚少。本文的目的是研究不同边坡土壤稳定入渗率（q s ）和近饱和导水率（K ns ）的变化，并了解它们与西南亚热带喀斯特地区表层土壤中岩石碎片含量和土壤质地的关系。张力渗透仪（直径20厘米）用于在山坡1（崩解的崩塌破坏）和2（雪崩坡度）。 q s 和K ns 的变化很大，并且在不同的坡度位置，它们的变化系数（CV）在0.1和1.0之间的变化很大。平均而言，q s 的范围为0.43至4.25mm / min，K ns 的范围为0.75至11.00mm / min。这些速率超过了大多数自然降雨事件的速率，这证明在喀斯特山坡上很少有陆上水流。自下而上，由于山坡1上存在大的岩石露头（高度> 2 m），q s 和K ns 呈下降-上升-下降趋势。但山坡2的地势呈上升趋势，地形复杂度较低。随着表层土壤中总岩石碎片含量（5-250 mm）的增加以及两个山坡的坡度梯度的增加，它们往往会增加。皮尔逊相关分析表明，较高的粗卵石（20-75mm），卵石（75-250mm）和沙子（2-0.05mm）含量以及总碎石含量可以显着促进水分渗入土壤，但粘土含量较高（<0.002 mm）的含量可能会限制水的流动。该结果表明，岩石碎片，沙子和粘土含量可能会显着影响表土层的水流，因此在亚热带地区喀斯特山坡的水文模拟中应考虑这些因素。
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