Spatial variation of soil functions affected by land use type and slope position in agricultural small watershed.

• 1. Soil functions changed greatly with land use type and slope position. • 2. Soil functions were dominantly controlled by CEC, AN, Ur, SSI, I, TN, SOM and AKP. • 3. Soil functions of cropland were seriously damaged due to long-term intensive utilization and erosion. • 4. Conservation practices are urgently needed to promote soil functions of eroded cropland in the black soil region. Soil function assessment is critical to mitigate soil degradation and achieve the sustainable use of soil resources. The changes in soil properties induced by land use type and slope position likely affect soil function considerably. Few studies have been carried out to investigate the spatial variation of soil function with land use type and slope position in small watershed impacted by intensive agricultural activities. Hence, eight typical land use types and five slope positions were selected in one agricultural small watershed to quantify the spatial variations of soil functions and their influencing factors in the Chinese black soil region. The five soil functions, e.g., primary productivity (PP), water purification and regulation (WPR), climate regulation and carbon sequestration (CRCS), provision of habitat for biodiversity (PHB), and nutrient cycling and provision (NCP) were computed from 22 measured soil properties. The results showed that all measured soil properties exhibited significant variations with land use type and slope position (p < 0.05). Significant variation was found in soil functions between different land use types and slope positions (p < 0.05). The lower soil functions were detected in road and cropland, especially at the middle slope position of cropland. The redundancy analysis revealed that soil cation exchange capacity, available nitrogen, urease, structure stability index, invertase, total nitrogen, soil organic matter and alkaline phosphatase were the dominant factors attributed to the spatial variation of soil functions. The corresponding contributions were 13.9 %, 11.4 %, 8.9 %, 7.6 %, 7.0 %, 6.1 %, 5.7 % and 5.50 %. Combined with the results of structural equation model, soil erosion was the dominant process to reduce soils by altering soil properties. The measures promoting nutrient accumulation and controlling soil erosion should be implemented to enhance soil functions of degraded cropland in the black soil region. The findings of this study are helpful to design the measures of soil and water conservation in agricultural small watershed to promote its ecological service. [ABSTRACT FROM AUTHOR]