Characteristics of soil moisture infiltration in shrub land and terraces dryland in Karst peaks hillslopes

Abstract: Vulnerable ecosystems in Karst area are sensitive to external environmental changes, and human activities have affected the vegetation environment and hydrological water cycle to some extent. It is of great significance to formulate soil and water conservation measures and groundwater management measures, predict soil erosion, and explore the impacts of human activities and disturbance levels on the soil infiltration in the fragile ecology in the Karst area. Peak cluster sloping field in Karst area is a typical landform in the southwest in China; due to natural, historical and artificial reasons, the economic benefits of agriculture are relatively backward, and the ecosystem has seriously deteriorated to the fragile state due to the impact of rocky desertification. In order to expand the benefit of agricultural production, the villagers spontaneously carried out the behaviors of changing slope cropland into terraces, and converting farmland to slope cropland. Therefore, a unique landscape pattern has also been formed, which produces good ecological benefits. In this paper, the infiltration process of different soil layers in shrub land and terraced field was determined by ring method, and the influencing factors of soil infiltration were analyzed by measuring the soil properties. In addition, the infiltration process was fitted by different mathematical models. The results showed that: 1) Shrub land has better infiltration performance than terraces, and the average infiltration coefficient (0.84) of natural slopes is 1.3 times that of terraced fields (0.66). The average initial infiltration rate and average stable infiltration rate of terraces at 30-60 cm are only 4.3% and 4.4% of the shrub land respectively. There is distinct infiltration barrier at 30-60 cm soil layer in the terraced field, and the reason is mainly as follows: Firstly, terraces land itself has enough soil clay content; secondly, artificial tillage will make the upper and lower soil mixed, so the finer particles migrate easily down; lastly, under the action of gravity, the soil is transported or migrated to the underground space along the path of the dissolving channel that develops on the surface of the bedrock. 2) The infiltration properties of shrub land and terraced fields are significantly correlated with soil properties. The contents of sand and organic matter in the shrub land were significantly higher than those in the terraced fields. The differences of soil properties between different soil layers in shrub land are not distinct, while the soil properties at 0-30 and 30-60 cm soil layers in terraced farmland are obviously different, which means the soil bulk density of the lower layer is very large and the soil porosity is small. 3) The fitting effect of Horton model on shrub land and terraced farmland is better, and the general accuracy for the upper layer is better than that for the lower layer, while the Kostiakov model and Philip model are poor in fitting effect. Infiltration models can better reflect the different infiltration processes. This research can provide a theoretical basis for further study on the soil moisture management and hydrological models in Karst sloping fields, and promote understanding of the relationship between soil infiltration and human activities.