激光衍射法和吸管法分析黏性富铁土颗粒粒径分布的比较

COMPARISON BETWEEN LASER DIFFRACTION AND PIPETTE METHODS IN ANALYSES OF PSD OF CLAYEY FERRISOL

激光衍射技术(Laser diffraction technique,简称LD法)近年来被认为是一种有效的分析土壤颗粒粒径分布(Particle size distribution,PSD)的手段。为检验LD法在黏粒含量高的富铁土上应用的可行性,用LD法和传统的吸管法实测了6个黏性富铁土剖面(黏粒含量>40%)不同层次土样的PSD数据,比较发现:LD法能够提供更多颗粒粒径级别,尤其是黏粒部分(<2μm)的PSD信息,且分析耗时短,效率高。但是LD法与吸管法测定的不同粒级土壤颗粒的含量存在一定的差异。两种方法相比,激光衍射法"低估"黏粒和"高估"粉粒,或者沉降法"高估"了黏粒和"低估"了粉粒。虽然在黏性富铁土的黏粒部分未发现两种方法的线性关系,但粉粒和砂粒分别存在显著的线性相关。供试土壤黏粒含量高且分布范围窄是导致上述差异的主要原因。经过模型转换后,LD法和吸管法PSD实测数据之间的误差明显降低,这说明LD法可以用于黏性土壤的PSD分析。但是LD法PSD测定结果尚不能直接用于目前基于沉降法的土壤质地三角图,需要一定的数据转换。应该尽快通过对各类代表性土壤进行系统化和规范化的对比研究,提高LD技术的可靠性和实用性,建立起基于LD技术的新的土壤质地三角图,以便进一步深化其在土壤科学上的应用。

The laser diffraction technique （LD method） has been regarded as an effective means of measuring soil particle size distribution （PSD） in recent years. To assess feasibility of applying the LD method to red soil high in clay fraction, soil samples collected from various layers of 6 forestry ferrisol profiles （clay fraction 〉 40% ） were analyzed using the LD and traditional pipette methods for comparison. It was found that the LD method is more efficient and effective and capable of providing PSD information of more particle size fractions, particularly of the clay fraction （ 〈 2μm）, but it might ＂underrate＂ clay fraction while ＂overrate＂ silt fraction. Significant liner-relationship was found between the two methods in measured data of silt fraction and sand fraction, but not of clay fraction, because it is. high in content but narrow in distribution. Modification of their models has significantly narrowed the difference between the two methods in measurement, which means the LD method can be used-for PSD analysis of clayey ferrisol. However, its measurements or PSD dada are not yet ready to be used directly＇ in the current sedimentation-based triangular texture diagram to define soil texture before certain data transformation. It is an inevitable trend for LD technique to be used widely in analyzing soil PSD in the future, thus, it is urgent and significant to conduct systematical and standardized comparison studies of various typical soils, so as to improve the reliability and practicability of the LD technique, and build up a new LD-based triangular texture diagram, which will further application of the LD technique in soil science.