Objective The southern grassy hills and slopes have a humid climate and suitable temperature for high forage production with ecological value. Therefore, it is important to investigate the soil nutrient characteristics of the southern grassy hills and slopes under different land use for sustainable development and utilization.

Methods Changyang County, Hubei Province, has the most representative natural grassy hills and slopes (WL), artificial pastures (GL), and cropland (CL) in southern China. We collected soil samples (0−10, 10−20 and 20−30 cm layer) from the three land use patterns in Huoshaoping Town as a pilot area and measured the physicochemical properties. Further, each land use type’s soil quality level was evaluated using principal component analysis, one-way ANOVA and multiple comparison methods.

Results 1) The organic C and total N in the three soil layers of WL were (P<0.05) higher than GL and CL. The total K, available N, were (P<0.05) lower than CL and GL. However, pH did not differ across the treatments. The nutrient content in WL decreased with the increasing soil depth. In contrast, the nutrient in GL and CL did not change within 0−30 cm layer. 2) WL had higher peroxidase activity than CL and GL, which decreased with soil depth. CL had higher urease activity than WL and GL, and urease activity did not vary across 0−30 cm soil depth. Protease activity was less affected by land use patterns and soil depths. The converting enzyme showed the highest activity among the four enzymes, decreasing with soil depth in WL and GL. 3) CL had higher N-fixing bacteria than WL and GL. However, the number of denitrifying and cellulolytic bacteria in the 10−20 cm soil layer was higher than in WL and GL. N-fixing, nitrifying, and cellulolytic bacteria did not differ (P>0.05) across soil layers in the three land types. 4) From the principal component analysis, soil nutrients, microorganisms, and enzyme activities contributed 39.8%, 30.8%, and 10% to the total soil quality score. The total soil quality score follows the order of natural grassy hill and slope (WL)>artificial grassland (GL)>farmland (CL).

Conclusions Following the transformation of the natural grassy hill slopes into artificial grassland and farmland in southern China, soil total carbon, organic carbon, and total nitrogen declined. In contrast, the total and available phosphorus and potassium in the natural grassy hill slopes were lower than in artificial grassland and farmland due to the absence of chemical fertilizers. The organic matter and total nitrogen decreased with soil depth in natural grassy hills and slopes, with no change in 0−30 cm depth in artificial grassland and farmlands. The topsoil of the natural grassy hills and slopes had higher enzyme activities, while artificial grassland and farmlands had a higher microbial population. Total soil fertility comprised 39.8% nutrient content, 30.8% microbial population, and 10% enzyme activities. The fertility order was natural grassy hill and slope>artificial grassland>farmland.