激光衍射法与湿筛-吸管法测定中国3种典型土壤粒径分布的差异分析

Comparison of Particle Size Distributions Measured by Laser Diffraction Method and Sieve-Pipette Method of Three Typical Soils in China

为探究激光衍射法(Laser Diffraction Method,LDM)与湿筛—吸管法(Sieve-Pipette Method,SPM)测定不同土壤粒径分布的差异,以中国3种典型土壤--黑土、褐土和紫色土为研究对象,采用LDM和SPM分别测定其250~2000μm,100~250μm,53~100μm,20~53μm,10~20μm,5~10μm,2~5μm和<2μm粒级的百分比含量,并对SPM所得各粒级土壤悬液进行了LDM测定。结果表明:LDM相比SPM显著高估了3种土壤10~20μm,5~10μm,2~5μm粒级含量,低估了<2μm粒级含量,且二者的绝对差异随粒级减小而增大;两种方法在>20μm各粒级的差异因土壤类型而异。LDM在SPM所得250~2000μm,100~250μm悬液中仅分别检出34.6%~70.1%和58.1%~70.6%的对应粒级颗粒。在SPM所得<100μm各粒级悬液中,LDM检出的对应粒级占比介于52.7%~98.4%;偏大颗粒主要分布在对应悬液的相邻粒级,且占比随悬液粒级减小呈增大趋势。LDM与SPM在土壤粒径分布测定方面的差异主要源自土壤颗粒尤其是细颗粒的不规则形状,二者之间的具体差异因土壤类型和粒级而异。

To investigate the differences of soil particle size distributions(PSD)measured by laser diffraction method(LDM)and the sieve-pipette method(SPM),eight size fractions of 250~2000μm,100~250μm,53~100μm,20~53μm,10~20μm,5~10μm,2~5μm and<2μm in three typical soils in China,i.e.,black,cinnamon and purple soils were analyzed using LDM and SPM,and the particle size distributions were systematically compared.The results showed that in contrast to SPM,LDM consistently overestimated the fractions of 10~20μm,5~10μm and 2~5μm and underestimated the clay fractions<2μm.Although the magnitude of either overestimation or underestimation varied among soil types,the absolute differences of particle fractions measured by LDM and SPM generally increased,as the particle size decreased.For the size fractions>20μm,by comparison,the proportions determined by LDM could be higher or lower than,or statistically similar with those by SPM,depending on soil types.In the sieved particles of 250~2000μm and 100~250μm obtained by SPM,LDM detected 34.6%~70.1%and 58.1%~70.6%of the corresponding size fractions,respectively,whereas,for those suspensions of the particles<100μm obtained by SPM,LDM detected 52.7%~98.4%of the corresponding size fractions.The larger particles determined by LDM mostly fell in their neighboring size fractions,and the corresponding percentages exhibited increasing trends as the particle size decreased.The disparate soil PSDs measured by LDM and SPM result from the non-spherical shapes of the soil particles,especially the fine ones,and the specific difference depends on variation among soil types and size fractions.