杨树低效林下土壤粒径分布与分形特征

Distribution of Soil Size and Fractal Characteristics Under Low-Efficiency Poplar Forests

[目的]研究鄂尔多斯地区杨树低效林下土壤粒径分布与分形特征,为该地区杨树低效林的成因分析及改造提供基础依据,并为杨树人工林的科学管理提供参考与决策支持。[方法]使用Mastersizer3000激光衍射粒度分析仪测量土壤粒径,采用土壤颗粒体积分形维数模型计算分形维数D值,并测定土壤养分。[结果]①鄂尔多斯地区杨树低效林下土壤颗粒组成主要以细砂粒(42.33%)、极细砂粒(15.72%)、中砂粒(19.77%)为主;主要土壤质地类型为砂土;土壤颗粒的分形维数D值在1.222 5~2.204 5范围内,处于较低水平。②土壤颗粒分形维数D值与粉粒、极细砂粒、细砂粒含量呈显著正相关关系,与中砂粒、粗砂粒、极粗砂粒呈显著负相关关系。③随着土层加深,粒径<250μm的土壤颗粒含量增加,粒径>250μm的土壤颗粒含量减少;土壤颗粒分形维数D值随土层加深而增大,增大幅度不大。④土壤颗粒分形维数D值与土壤有机质、全氮、速效氮、速效磷含量的关系均未达到显著水平,土壤各养分含量的变化对分形维数D值没有显著影响。[结论]鄂尔多斯地区杨树低效林下土壤颗粒组成以砂粒为主,土壤分形维数较低,土壤结构极不均匀,这样的土壤结构对杨树的正常生长发育极为不利,不良的土壤结构也在一定程度上导致了低效林的形成,因此在对杨树低效林进行预防和改造时也要改善林下土壤结构。

[Objective] The particle size distribution and fractal characteristics of soil under low-efficiency poplar forests in Ordos region were studied to provide a basis for the cause analysis and transformation of low-efficiency poplar forests in this region, and to provide a reference and decision-making support for the scientific management of poplar plantations. [Methods] We used a Mastersizer 3000 laser diffraction particle size analyzer to measure soil particle size, and a fractal dimension model of soil particle volume to calculate the fractal dimension D, and measured soil nutrients. [Results] ① The main components of soil particles in the low-efficiency poplar forests were fine sand(42.33%), ultra-fine sand(15.72%), and medium sand(19.77%). The main soil texture type was sand and the fractal dimension D of the soil particles was in the range of 1.222 5~2.204 5, which was at a low level. ② The fractal dimension D of soil particles was positively correlated with the silt, ultra-fine sand, and fine sand content, but was negatively correlated with the medium sand, coarse sand, and ultra-coarse sand content. ③ With an increase of the soil layer, the soil particle content with particle size <250 microns increased, whereas the soil particle content with particle size >250 microns decreased. The fractal dimension D value of soil particles increased with an increase of the soil layer;however, the increase was not significant. ④ The relationship among the fractal dimension D of soil particles and the soil organic matter, total nitrogen, available nitrogen, and available phosphorus content was not significant, and the change of soil nutrient content had no significant effect on fractal dimension D. [Conclusion] Sand is the main component of soil particles in low-efficiency poplar forests in the Ordos area. The fractal dimension of the soil is low and the soil structure is very uneven. This type of soil structure is very harmful to the normal growth and development of poplar. This poor soil structure leads to the formation of low-efficiency poplar forests to a certain extent. The soil structure under the forest could be improved by prevention and transformation.