Comparative Study On The Determination Of Soil Particle Composition By Laser Particle Size Analyzer And Wet Sieve-sedimentation Method

The main purpose of determining the composition of soil particles is to determine the soil texture,which is a combination of soils according to the relative proportion of different grain size in the soil.The traditional method for determining soil particle composition is wet sieve-sedimentation method,and the obtained soil particle composition is the percentage of mass.Laser particle size analyzer is used to measure the volume percentage of soil particles.In order to determine soil texture by laser particle size analyzer,soil science has always established a conversion model between the results of soil particle composition measured by wet sieve-sedimentation method and the volume percentage of soil particle composition converted to the mass percentage by using the conversion model to determine soil texture.The particle size of soil measured by laser particle size analyzer has a range of particle size.With the improvement of the instrument,the range of particle size measured by laser particle size analyzer is getting larger and larger,and the precision is getting higher and higher.In this study,two types of soils developed from basaltic volcanic detritus and loess parent material were selected to establish the conversion models of the results of soil particle composition determination by new laser particle size analyzer and wet sieve-sedimentation method respectively.The accuracy of soil texture determined by the conversion model calculation data was discussed in order to provide the feasibility of using laser particle size analyzer MS3000 in soil texture determination.Scientific basis.The results show that:The proportion of basaltic volcanic clastic soils varies widely,ranging from 2.56 to 2.95 g cm-3.The higher the degree of soil development,the greater the specific gravity of soil.The influence degree of soil specific gravity on the content of soil granules was as follows: sand < silt < clay.In the conversion model of wet sieve-sedimentation method and laser particle size analyzer method for basaltic volcanic detritus developed soil,the sand and silt particle size were significantly correlated(p <0.01,n = 42),but the clay particle size was not correlated;and the conversion model established under the measured specific gravity was better than that established under the commonly used specific gravity(2.65 g cm-3).By using laser particle size analyzer,the accuracy of judging large types of soil texture(sandy soil,loam,clay)is 59.52%,and the accuracy of judging precise soil texture is only 30.95%.In the conversion model of wet sieve-sedimentation method and laser particle sizer method,the sand and clay particle size were significantly correlated(p < 0.001,n = 65),and the powder particle size was significantly correlated(p < 0.05,n = 65).Using laser particle size analyzer,the accuracy rate of judging large types of soil texture(sandy soil,loam,clay)is 70.77%,and the accuracy rate of judging precise soil texture is only 32.31%.Compared with the wet sieve-sedimentation method,the laser particle size analyzer method hasunderestimated the clay content,overestimated the silt content,and the sand content is high or low in both the basaltic volcanic detritus developed soil and the loess parent material developed soil.Because the shape of soil particles is difficult to meet the precondition of applying Stokes' law,and the proportion of soils developed by different parent materials is also different,it is not an accurate result to determine the composition of soil particles by wet sieve-sedimentation method.The measurement range of particle size is the main factor affecting the results of laser particle size analyzer,but for agricultural soils,loam and coarser soils,the content of soil particles less than 0.01 m,and the results of laser particle size analyzer MS3000 may be more realistic than those of wet sieve-sedimentation method.Therefore,this study suggests that the volume percentage determined by laser particle size analyzer MS3000 should be popularized to determine soil texture without establishing the conversion model between laser particle size analyzer and wet sieve-sedimentation method.