激光粒度仪与沉降吸管法测定喀斯特地区土壤机械组成的对比研究

Comparative Study on Determining Soil Particle Size Distribution Measured by Laser Diffraction and the Sieve-Pipette Method in Karst Regions

与传统的沉降吸管法相比,激光粒度仪在测定土壤机械组成时具有效率高、操作误差低的优势,但其粘粒含量的测试结果通常偏低。本文在桂西北喀斯特地区选取具有代表性的棕色石灰土和砂页岩红壤土,包括表土和剖面样品共70个,对比分析激光粒度分析仪和沉降吸管法的测定结果,并建立不同粒级二者之间的相互转换关系。结果表明:按照美国制分类标准,与沉降吸管法相比,激光粒度仪测试的粘粒(<0.002 mm)体积含量均偏低,粉粒(0.002 mm-0.05 mm)含量均偏高,粘粒和粉粒的相对误差均随吸管法粘粒含量的增大而增加,砂粒含量(0.05 mm-2 mm)则互有高低且平均相对误差最小。两种方法测定的粘粒及砂粒间具有极显著的相关关系,粉粒相关性不显著,但<0.02 mm粒级呈极显著线性相关。激光粒度仪和传统吸管法的测试结果可通过<0.002 mm、<0.02 mm、0.02 mm-0.05 mm及>0.05 mm四个粒级的回归方程建立转换关系。

Compared with the traditional sieve-pipette method, the laser diffraction method is a new technology for determination of soil particle size distribution, which has obvious advantages in measurement efficiency and operation error reducing. However, the laser diffraction method always underestimates the clay content. In order to set up the conversion models, 70 soil samples selected from karst areas of Northwest Guangxi were measured by Mastersize2000 laser diffraction and the sieve-pipette method. The results showed that based on the classification criteria of USDA （United States Department of Agriculture）, the clay volume content （〈 0.002 mm） using the laser diffraction method was lower than that using the sieve-pipette method, while the silt volume content （0.002 mm - 0.05 ram） was higher. The relative errors of the clay and silt contents increased with the increase of clay content measured by sieve-pipette. The sand content was sometimes higher and sometimes lower with the lowest relative error. Significant relationships were found between the clay and sand contents determined by the two methods, but not between the silt content. However, the 〈 0.02 mm content measured by the two methods was significantly correlated. The laser diffraction measured results of soil particle size distribution could be converted by the linear regression equation of the following four particles grades including 〈 0.002 mm, 〈 0.02 mm, 0.02 mm- 0.05 mm and 〉 0.05 mm.