WHAT WE FIND IN SOILS 25 



that they can be classified into various groups, as follows : 

 fine gravel, coarse sand, medium sand, fine sand, 

 very fine sand, silt, fine silt and clay. To these 

 components let us add humus, moisture, the sol- 

 uble plant food elements, and we shall have the 

 soils of our fields. 



The size of these particles and their mechanical ar- 

 rangement have much to do in way of influencing soil 

 productivity, of influencing heat, moisture, and plant 

 food factors, of governing the type of soil that each crop 

 fancies. Thus it is that a sand soil where the coarser 

 particles predominate is a most favorable medium when 

 reenforced with humus, in which certain crops, like the 

 vegetables, are most at home. On the other hand, you 

 will find the opposite extreme where the finest soil 

 grains predominate most favorable to wheat and grass. 

 In the first case the sand type water is freely received 

 and as freely given to the subsoil, while with the clay 

 type water enters with difficulty but remains longer with 

 its host. Between these extremes we find all sorts 

 of modified types : light sand loams, sand loams, 

 loams, clay loams, and heavy clay loams. We 

 should add, also, humus to these combinations, for 

 it must be understood that humus is positively a 

 necessity for remunerative crops, regardless of type 

 or of ancestry. 



What mechanical analysis shows. To illustrate this 

 point, let us take the mechanical analysis of barren sand 

 soils : examples of the sand type that are found in many 

 sections of the country along the seashore, in the sand 

 hills of the arid West, and throughout the desert regions. 



Using the plan now generally approved by soil investi- 

 gators, we get the following the average of 11 barren 

 sand soils : 



