THE SOIL PAETICLE 



79 



Table XIV 



COMPOSITION OF SOIL SEPARATES (hALL) 



Separate 



SiO, 



AI.O3 

 1.6 



Fe^Os 



CaO 



.4 



MgO 

 .5 



K.O 



.8 



PaOs 



Coarse Sand (1 — .2 mm.) 



93.9 



1.2 



.05 



Pine Sand (.2— .04 mm.) 



94.0 



2.0 



1.2 



.5 



.1 



1.5 



.1 



Silt (.04 .01 mm.) 



89 4 



5.1 



1.5 



.8 



.3 



2.3 



.1 



Fine Silt (.01 .002 mm.) 



74.2 



13.2 



5.1 



1.6 



.3 



4.2 



.2 



Clay (Below .002 mm.) 



53.2 



21.5 



13.2 



1.6 



10 



4.9 



.4 



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 

 tcf 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— liow 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. MeGeorge, W. T., Composition 

 of Eawaiicm Soil Particles; Haw. Agr. Exp. 8ta., Bui. 42, Jan. 1917.' 



