Effects of forestland and grassland restoration process on soil infiltration characteristics in loess hilly region

Vegetation restoration can improve the soil infiltration capacity, the way and process of the vegetation restoration affect the soil properties in soil hydrological characteristics, and it will determine the distribution of vegetation restoration. In this paper, sites with different restoration types (secondary acacia forestland, secondary grassland) and the forestland and grassland whose vegetation restoration years were 9, 15 and 25 located in Guanshan Forest Farm in the west of loess hilly region were chosen as research objects. We aimed to illustrate the effects of vegetation restoration types and years on the hydraulic conductivity, the wetting front penetration time of 60 cm column and analyze the factors affecting the infiltration characteristics in soil layer of 0-60 cm using the constant head infiltration of undisturbed soil columns in May 2014. The results showed that: 1) the stable infiltration rate, mean infiltration rate, accumulative infiltration amount in 120 minutes and the wetting front penetration time of 60 cm column in the site of 25 years vegetation restoration forestland were 1.86, 2.60 mm/min, 387.82 mm, 23.00 min, respectively; in the 15 years vegetation restoration forestland, they were 1.38, 1.90 mm/min, 288.88 mm, 35.33 min; in the 9 years vegetation restoration forestland, they were 0.35, 1.03 mm/min, 194.50 mm, 40.00 min. Comparatively, these values were 3.17, 3.17 mm/min, 386.43 mm, 24.00 min in 25 years vegetation restoration grassland; 1.86, 2.60 mm/min, 387.82 mm, 34.33 min in the 15 years vegetation restoration grassland, and 1.86, 2.60 mm/min, 387.82 mm, 38.33 min in 9 years vegetation restoration grassland. 2) Additionally, the universal empirical model was fitted to the undisturbed soil columns infiltration process of all the six experimental area. 3) The soil infiltration rate was positively correlated with the organic matter content and the >0.25 mm water-stable aggregates content, while was negatively correlated with the bulk density. In conclusion, soil infiltration capacity was enhanced with the restoration years increased; at the same restoration year, soil infiltration capacity of the grassland performed better than that of the forestland, so it is recommended to increase the secondary grassland to improve the soil rainfall infiltration rate on the loess hilly region area, where the water resource is limited.