Effects of consecutive overturning of green manure on soil physical and biological characteristics in tobacco-planting fields

【Objectives】Soil biological characteristic can be used as evaluation indexes for soil eco-environment quality, and soil physical characteristic can regulate soil water, fertilizer, gas and heat. Green manure has rich nutrients as a high-quality biological fertilizer, the variety of green manure, application ratio of green manure with chemical fertilizer will affect soil microbial population quantity and soil enzyme activity, which would affect soil physical, chemical and biological properties and soil productivity. In this study, an inter-annual variation of soil microbial population quantity, microbial biomass carbon and soil enzyme were investigated after consecutive overturning of green manure, and the effect of long-term overturning of green manure on soil granular structure and soil compaction was also studied to offer theoretical basis for soil amelioration and featured tobacco exploitation.【Methods】A consecutive 3-year field experiment was conducted to study effect of incorporating green manure on soil physical and biological characteristics. The fresh soil samples were sieved (less than 2 mm), and used for analysis on the quantity of bacteria, fungi and actinomycetes, and the content of microbial biomass carbon after consecutive overturning of green manure by dilution-plate method and chloroform fumigation culture method. Samples of air-dried soil were sieved (less than 1 mm) and subjected to analyze the activities of soil urease, acid phosphatase and catalase. Soil compaction was measured in situ by CP 40Ⅱ digital soil compactness instrument. Soil aggregate structure was analyzed by Xaviers method, collective undisturbed soil were graded by dry sieve method. The content of different aggregate, mean weight diameter and geometric mean were calculated.【Results】The results showed that the consecutive overturn of green manure could remarkably reduces soil compactness in 10 cm soil layer, and the soil compactness in inputting high quantity of green manure treatment (GMH, 30000 kg/ha green manures+85% fertilizers) is the lowest. Compared with the conventional fertilization treatment (F) and no fertilization treatment (CK), the soil compactness in GMH treament is increased by 25.4% and 29.9%, respectively. The overturn of green manure could increase the content of more than 7 mm soil mechanical-stable aggregates and reduce the content of less than 1 mm soil mechanical-stable aggregates. With the increase of the returning age, the numbers of bacteria, fungi and actinomyces and the content of microbial biomass carbon are increased in incorporation green manure treatment. Compared with F treatment, the numbers of bacteria, fungi and actinomyces and the content of microbial biomass carbon in GMH treatment are respectively increased by 49.0%, 47.8%, 35.4% and 40.7% after 3-year consecutive overturn of green manure. The activities of soil urease, catalase and acid phosphatase in GMH treatment are increased year by year with the increase of the returning age. Compared with F treatment, the activities of urease and catalase are reduced in inputting low quantity of green manure treatment (GML, 15000 kg/ha green manures+85% fertilizers), but GMH treatment could restore and improve the activities of these enzymes.【Conclusions】The consecutive overturn of green manure could reduce soil compactness, and increase the numbers of bacteria, fungi and actinomyces and the content of microbial biomass carbon, and enhance stability of soil aggregate structure. It is benefit for improving activities of soil urease, acid phosphatase and catalase to input high quantity of green manure.