巨桉人工林下土壤团聚体分形特征及碱解氮分布研究

Fractal Features of Soil Aggregates and Distribution of Alkaline Hydrolytic Nitrogen in Different Types of Eucalyptus grandis Plantations

了解川中丘陵区巨桉林土壤团聚体分形特征及碱解氮含量状况对于掌握该地区巨桉种植对土壤稳定性及土壤养分的影响十分必要。该研究以典型川中丘陵区3.5a生巨桉纯林、巨桉＋果树、巨桉＋粮食作物土壤为研究对象,以弃耕地土壤为对照,应用分形模型,分析了土壤团聚体分形特征及不同粒径团聚体对土壤碱解氮分布的影响。结果表明：土壤团聚体数量随着粒径的增大呈现出先减少再增加后减少的趋势,其中2~5mm粒径团聚体在土壤结构中占有重要地位;土壤分形维数排序为：弃耕地〉纯林〉林果〉林粮;土壤碱解氮含量排序为：弃耕地〉林粮〉林果〉纯林,巨桉林地较弃耕地土壤分形维数和碱解氮含量低,说明巨桉的栽培在有利于保持土壤水土流失的同时却造成了土壤养分流失和地力衰退;巨桉林地土壤碱解氮集中分布在〈0.25mm和0.25~0.5mm粒径的细砂和中砂砾中;相关分析表明,土壤碱解氮含量与0.25~0.5mm团聚体碱解氮含量呈负相关,与2~5mm团聚体碱解氮含量呈显著正相关。该研究结果科学评价了巨桉种植对土壤结构和养分的影响,为川中丘陵区土壤的水土保持和肥力维护工作提供了合理的经营模式。

Understanding the fractal characteristics of soil aggregates and alkaline hydrolytic nitrogen contents in Eucalyptus grandis plantations in the hilly region of Sichuan Basin was necessary to know the impact of Eucalyptus grandis plantations on soil stability and soil nutrient in this region. In this study, soils covered by 3.5-year pure Eucalyptus grandis, Eucalyptus grandis ＋ fruits and Eucalyptus grandis ＋ grain crops modes were selected as research examples, while abandoned farmland was taken as the control. Fractal theory was used as analytical method to investigate the fractal characteristics of soil aggregates and distribu tion of alkaline hydrolytic nitrogen content influenced by soil aggregates. Results showed that contents of soil aggregates presented the trend of increase first and decrease later with the decrease of soil aggregate sizes, the soil aggregates with 2~5 mm size played an important role in soil structure. Soil fractal dimension followed the sequence of abandoned farmland〉Eucalyptus grandis ＋ grain crops〉Eucalyptus grandis ＋ fruits〉pure Eucalyptus grandis, while alkaline hydrolytic nitrogen contents in soil aggregates followed the trend of abandoned farmland〉Eucalyptus grandis ＋ grain crops〉Eucalyptus grandis ＋ fruits〉pure Eucalyptus grandis. Both soil fractal value and the alkaline hydrolytic nitrogen content of Eucalyptus gran- dis plantations were lower compared with abandoned farmland, indicating that Eucalyptus grandis growth would contribute to control soil erosion and cause losses of soil nutrients and fertility. Content of alkaline hydrolytic nitrogen mainly concentrated in fine sand and gravel with diameters of 〈O. 25 mm and O. 25~0.5 mm. Correlation analysis indicated that soil alkaline hydrolytic nitrogen contents had a negative correlation with those soils aggregates with 0.25~0.5 mm size, significantly positively correlated with those with 2~5 mm size. The study scienti{ically evaluated the impact of Eucalyptus grandis plantations on soil structure and nutrients, providing a reasonable management model for soil and water conservation and fertility mainte- nance in the hilly region of Siehuan Basin.