Characteristics and Simulations of Soil Infiltration in Agroforestry on Karst Mountains

  Objective  Characteristics of soil infiltration in agroforestry on karst mountains were studied, and their infiltration patterns fitted to simulation models.

  Method  Through experiments in the field, the soil infiltration characteristics and factors affecting agroforestry of forest+medicinal herb, forest+grain crop, and forest+grass types were analyzed by comparing with a monocultural economic forest setting. The infiltration patterns were entered in 4 commonly applied mathematical models for best fitting.

  Result  ① The initial, stable and average infiltration rates as well as the total infiltration amounts of the 3 agroforestry types were higher than those of the monocultural forestry. They decreased in the soil layers of increasing depth. The infiltration curves showed 3 distinctive stages with varied durations (t), i.e., rapid reduction phase (t≤10 min), slow reduction phase (10 min<t≤40 min), and stabilization phase (t＞40 min). ② The forest+medicinal herb type agroforestry had the highest comprehensive performance score of 0.405 with the greatest infiltration capacity among all. It was followed by forest+grass with a score of 0.357, and forest+grain of 0.209. Since forest+grain scored higher than control (0.175) but not significantly, only the other two cultivation types were considered more effective on water-retention and soil-fixation. ③ A significant inverse correlation on the infiltration performance was observed with the soil bulk density (P＜0.01), an extremely significant correlation with the total porosity (P＜0.01), and a significant correlation with the non-capillary porosity (P＜0.05). ④ The mean R² was 0.783 with the Philip model, 0.942 with the Kostiakov model, whereas 0.977 with the Horton model, and 0.976 with the general empirical model, indicating the later two models fitting the infiltration characteristics of all agroforesrty types better.

  Conclusion  All 3 tested agroforestry types improved the soil infiltration to varying extents by affecting the soil porosity and bulk density on karst mountains. The agroforestry of forest+medicinal herb type appeared to provide the greatest impact on soil infiltration, followed by forest+grass, and the infiltration pattern could best be described by the Horton or the general empirical model.