Soil quality evaluation of various microtopography types at different restoration modes in the loess area of Northern Shaanxi

Various forms of microtopography are widely distributed and exist in the loess area of northern Shaanxi. Microtopography is also an important consideration for near-natural vegetation restoration models. The soil quality under the different microtopography types affects which near-natural vegetation configuration and restoration mode should be applied. Therefore, this paper took the microtopography of the Hegou watershed, which was restored by the natural exclosure method, and that of the Chaigou watershed, which was restored by artificial afforestation, in the loess region of northern Shaanxi as the research objects. A comprehensive evaluation of the soil quality in the study area was carried out by assessing 22 soil indicators and performing sensitivity analysis and principal component analysis. The results showed the following: (1) Soil available phosphorus, total nitrogen, organic matter, sucrase activity, urease activity, maximum water-holding capacity, field capacity, capillary water-holding capacity, noncapillary porosity, natural water content, available nitrogen, available potassium, cation exchange capacity, total phosphorus, total potassium, alkaline phosphatase and catalase constituted a sensitive-indicator data set for soil quality evaluation in the study area. (2) There was a significant linear fit between the sensitive-indicator data set and the all-indicator data set (y = 1.032x 0.027, R-2 = 0.96 (P < 0.05)). (3) The microtopography types under natural restoration were ranked by soil quality as follows: collapse (0.672) > platform (0.565) > shallow gully (0.529) > gully (0.515) > undisturbed slope (0.422) > scarp (0.351). The microtopography types under artificial afforestation were ranked by soil quality as follows: gully (0.731) > platform (0.66) > undisturbed slope (0.431) > shallow gully (0.411) > scarp (0.395) > collapse (0.221).