Variation Characteristics Of Soil Quality In Eucalyptus Plantations

In this study, soil quality evolvement with different planting generations and forest ages in Eucalyptus plantations was systematically researched, contents including 4 aspects: characteristics of soil and water conservation, nutrient characteristics and biological characteristics (Including enzyme activities, microbial diversity, microbial biomass carbon, microbial biomass nitrogen, microbial biomass phosphorus), soil activity organic carbon and stable organic carbon, and comprehensive evaluations was did. The results as follows:(1) Functions on soil and water conservation decreased as forest ages increased, successive planting of Eucalyptus may cause soil hardening below 20 cm. The process of soil infiltration fit Kostiakov model, R2=0.7942-0.9842, process of soil particles disintegration fit exponential function y=alnx+b,R2=0.8512-0.9945, microbial biomass nitrogen, urease activity and hydrolysable nitrogen has obvious effects on soil and water conservation.(2) Soil fertility changes mainly in 0-20 cm, increased as plantations ages increase, successive planting has the tendency of soil fertility decline, soil fertility in July was lowest, October or April was highest, available phosphorus were below 1 mg·kg-1, available boron between 0.15-0.28 mg·kg-1.(3) Successive planting lead to the activities of invertase, catalase and acid phosphatase increased, polyphenoloxidase activity decreased. Microbial biomass increased as planting ages and generations increase, the maximum appeared in July, the minimum appeared in October; microbial diversity richness and evenness decreased as planting history change, common microbes has no significantly change.(4) Soil organic carbon(SOC) decreased as power exponent with soil depth increased, the differences mainly in 0-5 cm, SOC storage between 56.18-71.55 t·hm-2,64.87±5.70 t·hm-2 in average. Readily oxidation carbon(ROC) changed greatly in 0-20 cm, ROC could be increased under acid environment; the ratio of stable organic carbon/SOC increased as soil depth increase, Eucalyptus plantations has powerful utilization ability in using stable organic carbon which was cannot be oxidized by Na2 S2O8.(5) Sustainable indexes, grey relation degree, multiple-indicators comprehensive evaluation are excellent methods on evaluating soil quality of research area, the evaluation results as below: 0.3 a<1a<4 a<2 a<6 a<18 a(first generation),4 a>7 a (second generation), compared by average score, first generation>second generation.