The Research On Soil Fertility Quality Assessment Of Multi-Generation Eucalyptus Plantations

Eucalyptus is one of the three fast-growing tree species in our country.It can be planted in that year,cut in three or four years and has good wood quality,straight trunks and strong ability of germination and regeneration.Only 2%of the national forest land contributes 25%of the national timber output.However,the successive planting and high-intensity predatory management mode of plantation have a strong impact on soil quality.Eucalyptus plantation in South China has a strong impact on soil quality.High-intensity continuous cropping has attracted widespread attention in society.In this paper,five kinds of soil forests of Eucalyptus plantation and adjacent evergreen broad-leaved forest in Daguishan Forest Farm of Guangxi were divided into study objects.Each stand was divided into three random blocks.Four layers of soil samples of 0-20,20-40,40-60 and 60-80 cm were collected in each block.Based on 32 soil physical and chemical properties,the principal component analysis,Pearson correlation analysis and redundancy analysis were used to calculate and screen Norm values.The minimum data set of soil fertility quality evaluation for Eucalyptus plantation was determined.Soil fertility quality was evaluated by soil quality index method,grey relational degree,Nemerow index method and factor analysis method.It was intended to provide theoretical basis for soil nutrient management and efficient cultivation of Eucalyptus plantation and realize sustainable utilization of Eucalyptus plantation.The main conclusions are as follows:(1)The maximum water holding capacity,minimum water holding capacity and capillary water holding capacity of soil physical properties of multi-generation Eucalyptus plantation and evergreen broad-leaved forest are consistent with the changes of soil total porosity and capillary porosity,showing a trend of increasing first and then decreasing,and soil bulk density shows a trend of decreasing first and then increasing.In the course of multi-generation continuous planting,the significant differences of physical indexes are mainly in the 0-20 cm and 20-40 cm soil layers(p<0.05).The four-generation continuous planting of Eucalyptus makes the soil compact,water-holding capacity decreased,porosity decreased,and compaction may occur.(2)The soil chemical indexes of multi-generation Eucalyptus plantation and evergreen broad-leaved forest showed significant differences in 0-20 cm soil layer except pH and available magnesium(p<0.05),and the correlation of each chemical index was close.Soil organic matter,cation exchange capacity,nitrate nitrogen,ammonia nitrogen,total potassium,available phosphorus,available potassium and available copper in the second generation of Eucalyptus plantation were significantly higher than those in other Eucalyptus plantations,and decreased significantly from successive planting to the third generation.Total nitrogen and available iron decreased significantly from the fourth generation.(3)Among the seven soil biological indicators,soil enzyme activity and microbial biomass had significant difference between multi-generation Eucalyptus forest and evergreen broad-leaved forest(p<0.05).The content of surface soil was significantly higher than that of the following three layers.Except acid phosphatase,the other indicators showed a trend of increasing first and then decreasing.Soil sucrase,catalase,microbial biomass carbon,microbial biomass nitrogen and microbial biomass nitrogen reached the maximum from the second generation,and then gradually showed a downward trend.Soil urease decreased significantly from the fourth generation,while soil acid phosphatase increased with the planting algebra.(4)There was a significant correlation between soil properties of multi-generation Eucalyptus plantation and evergreen broad-leaved forest(p<0.05).The highest correlation between soil organic matter and nitrate nitrogen was 0.922,followed by available iron,total nitrogen,total potassium,available potassium,available phosphorus,available copper,available zinc and cation exchange capacity.Most soil nutrients were positively correlated with biological properties.Soil organic matter,nitrate nitrogen,ammonia nitrogen,cation exchange capacity,available iron,available boron and available zinc were strongly correlated with biological indicators.(5)Soil bulk density,organic matter,available phosphorus,available potassium,available iron,microbial biomass carbon,invertase and catalase were finally determined as the minimum data set of soil fertility quality of Eucalyptus plantation.Stepwise discriminant analysis was used to verify the results,and the accuracy rate was as high as 82.5%.Therefore,the minimum data set selected in this paper is more reliable.(6)There were significant differences in soil fertility quality between multi-generation Eucalyptus plantation and evergreen broad-leaved forest(p<0.05).The results of soil quality index,Nemerow index,grey correlation analysis and factor analysis are slightly different,but the overall trend is the same,which is as follows:evergreen broad-leaved forest>second generation>first generation>third generation>Fourth generation.The results of soil fertility quality evaluation using 8 indicators of the minimum data set and the total indicators are basically consistent and highly correlated.The fitting degree between the evaluation results and tree height is high,and the correlation coefficient reaches 0,705,which indicates that the evaluation results have biological significance.The soil fertility of evergreen broad-leaved forest is significantly higher than that of Eucalyptus plantation.The soil fertility quality of Eucalyptus plantation reaches its maximum in the second generation with the increase of algebra,and decreases gradually from the third generation.