Biological characteristics and biological fertility evaluation of soil in rubber plantation

【Objective】 This study aimed to investigate the differences in biological characteristics and biological ferti-lity levels of different parent material soils in rubber plantation， providing scientific basis for soil quality in rubber plantation and sustainable management of rubber forests. 【Method】 Typical parent materials （granite， basalt， metamorphic rock， sediment） of different fertility levels （high， medium， and low） in rubber plantation of Hainan were taken as the research objects. Soil samples at the layers of 0-20 cm and 20-40 cm were collected to determine physicochemical properties， microbial quantity， microbial mass， enzyme activity， and other indicators， and the correlations between soil physicochemical properties and biological characteristics were analyzed. Principal component analysis and membership function method were employed to determine biological fertility evaluation indicators of soil in rubber plantation to assess the soil biological fertility level. 【Result】 Marked differences in biological characteristics were found in soils from different parent materials in rubber plantation. Basalt soil had the highest fungal and actinomycete counts， the highest contents of microbial mass carbon （MBC） and microbial mass nitrogen （MBN）， and the highest phosphatase activity. Granite soil exhibited the highest microbial mass phosphorus （MBP） content. Metamorphic rock soil showed the lowest bacterial and actinomycete counts， the highest microbial mass carbon-nitrogen ratio （MBC/MBN）， and the highest urease and sucrase activities. Sediment soil had the highest bacterial count， the lowest microbial mass except MBP， and the highest catalase activity. Correlation analysis and redundancy analysis showed that： soil microorganism quantity， microbial mass， and enzyme activity were closely related to soil physicochemical properties； total nitrogen， organic matter， ammonium nitrogen， nitrate nitrogen， and available potassium in the soil were the main positive influencing factors of soil biological characteristics， while soil pH was the main negative influencing factor. Principal component analysis showed that， MBC， MBN， MBP， MBC/MBN， urease， catalase， phosphatase， and sucrase were determined as the key indicators for soil biological fertility evaluation of rubber plantation. Soil biological fertility index （BIF） calculation showed that： the BIF of rubber plantation soil ranged from 0.31 to 0.80； the fertility levels were mainly concentrated at grade two （38.46%） and grade three （43.08%）， while the grade one （4.62%） and grade four （13.85%） were less distributed； the ranking of the average BIF of soils from different parent materials in the rubber plantation was basalt （0.64） > granite （0.58） > metamorphic rock （0.56） > sediment （0.53）. 【Conclusion】 Obvious differences in biological characteristics are found in soils from different parental materials in rubber plantation， and biological indicators and physicochemical properties of soil are closely related. Microbial mass and enzyme activity are key indicators for assessing the biological fertility of soil in rubber plantation， and currently the soil biological fertility quality of rubber plantation is at a medium to high level.