[Objective] The soil aggregate stability and differences in organic carbon distribution for Bayanbulak alpine grassland

Xinjiang Wei Autonomous Region under different land utilization methods were analyzed in order to provide a theoretical basis for the evaluation of soil aggregate organic carbon and other ecological functions in this region. [Methods] Three land utilization methods for an alpine grassland in Bayinbuluk were evaluated: reclamation

abandoning farming to grazing

and grazing. Soil aggregates were screened by dry screening and wet screening

mean weight diameter (MWD)

geometric mean diameter (GMD)

percentage of aggregate destruction (PDA)

and soil organic carbon (SOC) contents of soil aggregates were measured and calculated to quantify differences in soil aggregate stability and organic carbon in an alpine grassland under different land utilization methods. [Results] ① Under the three land utilization methods

soil aggregates in an alpine grassland were primarily large aggregates (≥0.25 mm). In the subsurface (10—20 cm) soil

the PDA for the treatment of abandoning farming to grazing was significantly lower than that of the grazing treatment (p＜0.05)

and was not significantly different from the PDA for the reclamation treatment (p＞0.05). In addition

the soil PDA values of the remaining soil layers in the treatment of abandoning farming to grazing were significantly greater than those observed for the reclamation treatment and the grazing treatment (p＜0.05). In the surface layer (0—10 cm)

there was no significant difference in PDA between the reclamation treatment and the grazing treatment (p＞0.05). The PDA values of the other soil layers in the reclamation treatment were significantly greater than in the grazing treatment. ② The SOC content

soil aggregate organic carbon content

and the contribution rate of soil aggregates in the treatment of abandoning farming to grazing were significantly less than those in the other treatments (p＜0.05). In the 0—10 cm soil layer

organic carbon content and its contribution rate of aggregates with particle size greater than 5 mm in the grazing treatment were greater than those in the reclamation treatment (27.89 g/kg

6.34%) and the treatment of abandoning farming to grazing (36.96 g/kg

14.3%). In the subsurface layer (10—20 cm)

lower layer (20—30 cm)

and deep layer (30—40 cm)

the organic carbon content and contribution rate of soil aggregates with a particle size of ≥5 mm in the treatment of abandoning farming to grazing were significantly less than those in the reclamation treatment and the grazing treatment (p＜0.05). ③ The mass percentage of soil aggregates and their stability were significantly correlated with SOC content (p＜0.05). The mass percentage of soil aggregates ≥2 mm

MWD and GMD of soil aggregates were significantly positively correlated with SOC content (p＜0.05)

of which soil aggregates ≥5 mm showed a very significant positive correlation (p＜0.01) with SOC content. The mass percentage of soil aggregates less than 2 mm and the stability of soil aggregates were significantly negatively correlated with SOC content (p＜0.05)

of which soil aggregates ＜1 mm were extremely significantly negatively correlated with SOC content (p＜0.01). [Conclusion] Grassland reclamation activities reduced the stability of soil aggregates and their SOC contents. Soil aggregate stability and SOC content were the lowest in the treatment of abandoning farming to grazing. It is recommended that grassland should be moderately restored (fertilized

sown

etc.) after abandonment for grazing and utilization.