THE SOIL PARTICLE 



79 



Table XIV 



COMPOSITION OF SOIL SEPARATES (HALL) 



43. Value of a mechanical analysis. — It is evident that a 

 proper interpretation of a mechanical analysis will throw con- 

 siderable light on the probable condition of a soil, especially 

 physically. To the trained observer the preponderance of 

 sand, clay, or silt signifies the probable presence of certain 

 physical properties, which may affect the plant not only me- 

 chanically but physiologically as well, through air, water, and 

 nutrient movement. 



The chemical and mineralogical phases of such interpreta- 

 tion are also worthy of consideration, as the proportion of the 

 various separates determines whether the essential nutrient 

 will be present in sufficient quantities to permit normal crop 

 growth. Thus a mechanical analysis not only enlightens as 

 to the general properties of a given soil, but when correlated 

 with other factors is to some extent a criterion of agricultural 

 value and crop adaptation. Some authors maintain that in 

 the investigation of any soil a mechanical analysis should first 

 be made, as it throws much light on many properties of a soil. 



44. Soil class — how soils are named. — As a soil is not 

 composed of particles of uniform size and shape, a blanket 

 term is needed, which will not only give some idea of the 

 textural character of the mixture, for every soil is a mixture, 



that he found the lime and magnesia higher in the coarser particles and 

 the silica higher in the finer separates. McGeorge, W. T., Composition 

 of Eawaiicm Soil Particles; Haw. Agr. Exp. £>ta., Bui. 42, Jan. 1917.' 



