The Method To Measure Soil Texture By Laser Diffractoin And Its Application On Soil Structure

Laser diffraction method has been regarded as an effective mean of analyzing the soilparticle size distribution in recent years. To improve the accuracy of method measuring soilparticle size distribution,20soil samples collected from15provinces were determined byLaser method and Pipette method.Results show that the clay and sand content using the laser diffraction method wereobviously lower than that using the sieve pipette method, while the silt content using theformer was higher than that using the latter. The mean values of clay and sand contentdetermined by LD method are lower than them by pipette method for about73.4g/kg and59.6g/kg. The mean content of silt is higher than that measured by pipette method （131.2g/kg）. However, significant relationships were found between the clay sand contentsdetermined by the two different methods （r>0.92, p<0.01）. For it has a very significantcorrelation between the two methods for the clay and sand, the linear model can beestablished between the LD method and the pipette method, where clay: y₁=1.84x₁-84.5（r=0.98, P<0.01, n=20）, sand: y₂=1.10x₂+24.2（r=0.96, P<0.01, n=20） and y₃=1000-（y₁+y₂）,（x₁, x₂and x₃mean the content of clay, sand and silt by LD method, g/kg; y₁, y₂and y₃meanthe content of clay, sand and silt by pipette method, g/kg）. The findings demonstrate that datafrom the laser diffraction method can be directly used to classify soil texture. A newalternative model between two methods is found by studying the cumulative particle sizedistribution. If the function fitted by particle size cumulative distribution by laser method of asoil is y=1000x/（b+x）, then the function by pipette method is y=1000x/（1.32b-1.01+x）. Thecontent of clay is not right obtained by the function.To calculate the soil particle weight fractal dimension and volume fractal dimensionusing Yang Peiling method,we can find that the soil volume fractal dimension measured byLD method had a highly significant positive correlation with weight fractal dimensionmeasured by the pipette method. A function can be established between volume fractaldimension and the weight fractal dimension: D_v=0.9357D_m+0.0406（r=0.85, p<0.001）, which,D_vis the volume fractal dimension, D_m is the weight fractal dimension. All sample volumefractal dimension is less than the quality of the fractal dimension. D_vwas lower4.92percentthan D_m. Soil weight particles fractal dimension measured had a very significant positive correlation with the content of clay and sand.（r=0.92and0.62）; Soil volumn particles fractaldimension measured had a significant positive correlation with the content of clay, silt andsand.（r=0.92,0.47and0.62）.Values of D_m of clay, silt and clay were2.77,2.65and2.51, which of D_vwere2.64,2.51and2.47. D_m were greater than D_v. Mean value converted from D_vby the formula D_v=0.9357D_m+0.0406was only lower2.3percent for the value of D_m. In a word, the LD methodis meaningful to the study for soil structure.By measuring13kinds of soil microaggregates using laser diffraction method, the resultsshow, micro-aggregates in2⁵3μm grade had the largest share （691.6g/kg）; and that in250²000μm grade had the smallest（18.5g/kg）. Values of soil microaggregate fractaldimension distributed from2.36to2.68. Soil aggregates fractal dimension had a verysignificant positive correlation （r=0.93）,with the content of the aggregate under2μm.