1 8 SOILS AND FERTILIZERS 



The form and arrangement of the particles are im- 

 portant factors to consider in dealing with the water 

 content of soils. In the wheat lands of the Red River 

 Valley of the North, the particles are small and spher- 

 ical, being formed largely from limestone rock, while 

 the subsoil of the western prairie regions is composed 

 largely of angular silt particles, intermingled with clay, 

 forming a mass containing only a minimum of inter-soil 

 spaces. The silt particles being angular and embedded 

 in the clay, the soil has more the character of clay than 

 of silt. While these two soils are unlike in physical 

 composition, the form and arrangement of the particles 

 give each nearly the same water-holding power. Two 

 soils may have a somewhat similar mechanical composi- 

 tion and yet possess materially different physical proper- 

 ties because of a difference in the form and arrangement 

 of the soil particles. In some soils 10 per cent of clay 

 is of more agricultural value than in other soils. Ten 

 per cent of clay associated with 60 or 70 per cent of 

 silt makes a good grain soil, while 10 per cent of clay 

 associated largely with sand makes a soil poorly suited 

 to grain culture. 



The classification of the soil particles into clay, silt, 

 and fine, medium, and coarse sand is purely an arbitrary 

 one. Various authors use these terms in different ways, 

 and when comparing the mechanical composition of soils 

 reported in different works, one may avoid confusion 

 by omitting the names and noting only the sizes of the 

 particles. 



