Effects of different treatment and utilization types after land leaving unused on soil microbial properties in Karst region

Abstract: Soil microbial properties are the reserve for soil nutrients, while soil nutrients would in reverse influence soil microbial activities. Therefore, gaining some knowledge of the interaction between them is urgent to help with land utilization and management. Depression between Karst hills is a typical landscape, which is located in the slope of the Karst region in southwest China, with a small environmental capacity resulting in a low ability in recovery. However, the related research studies under different land use types in the depression between Karst hills are rare. Based on the dynamic monitoring and investigation of six common land use types (i.e., burning, cutting, cutting plus with root removal, enclosure, maize plantation, and pasture of Guimu No. 1 (Pennisetum purpureum cv. Guimu-1) plantation) on a slope in a Karst region, this paper analyzed soil microbial properties, as well as the interactions between microbial properties and soil nutrients. The results showed that the status of soil nutrients differed among six land use types, and contents of soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and available nitrogen (AN) reduced along the conversion from enclosure, burning, cutting, cutting plus with root removal, pasture plantation, to maize plantation. Soil microbial biomass varied in the six land use types, microbial biomass carbon (MBC) ranging from 244.98 to 1 246.89 mg/kg, microbial biomass nitrogen (MBN) from 35.44 to 274.69 mg/kg, and microbial biomass phosphorus (MBP) from 30.88 to 64.72 mg/kg. Among them, soil microbial biomass was lowest under maize plantation and when it was indicated that the soil was in a severe degradation status. Soil microbial population and composition varied in the six land use types: bacterium were predominant under planting maize and pasture of Guimu No. 1, which may be due to fertilization making some improvement in soil physical properties and microbial zone; actinomycetes were predominant under burning, cutting, cutting plus with root removal, and enclosure, which suggests that under these four land use types, actinomycetes had stronger fertility, competition, and consumption over soil nutrients other than microbial populations; while fungi accounted for a small proportion in all the six land use types. The interaction between soil microorganisms and soil nutrients diversified in the different land use types. The interactions between soil TP and MBP, total potassium (TK) and MBC, TN and actinomycetes under burning, TN and MBC under cutting, available phosphorus (AP) and MBN under cutting plus with root removal, pH values and actinomycetes under pasture plantation were positively strongest. While the interaction between pH values and MBC and fungus under enclosure, TN, TK, and MBP under maize plantation, pH values and fungi under planting pasture of Guimu No.1 were negatively strongest. The six land use types in the Karst region could be clustered into four categories, and enclosure and burning were best. This would provide some basis for land utilization and management in the depression between Karst hills and even for the whole Karst region in the southwest of China.