Effects of rock fragments on the water infiltration and hydraulic conductivity in the soils of the desert steppes of Inner Mongolia, China

Soils that contain rock fragments (particles > 2 mm in diameter) are distributed all over the world. The presence of these small rock fragments can have a great impact on soil water retention properties, as well as on the soil-water infiltration and vegetation restoration in semi-arid regions. To quantitatively describe the transport of water in stony soils, repacked soil cores were used to determine the infiltration rates for different rock fragment contents (0%, 10%, 20%, 30%, and 40%) and rock fragment sizes (2-5, 5-8, 8-11, and 2-11 mm). The results showed that both the content and size of the rock fragments and their interaction significantly affected the infiltration process. The infiltration rates over time and the saturated hydraulic conductivity (Ks) decreased with an increasing rock fragment content to an observed minimum value for a 40% rock fragment content. The soil-water infiltration processes were accurately described by the Kostiakov model. The measured and calculated Ks values decreased with an increasing rock fragment content, which was in accordance with the published data and in accordance with the Ks obtained by five empirical methods. The variations in the measured Ks were likely due to the variations in the soil properties caused by the soil sample repacking. The results of this study may improve the understanding of the effects of the rock fragment content and size on the infiltration processes in arid and semi-arid desert steppes.