THE PROPERTIES OF SOILS 61 



on his particular land ; also to modify the land in some cases by 

 manuring, liming, or special systems of culture, in order to fit it 

 better for the crops to which it is not naturally adapted. Agri- 

 cultural soils are usually loams or sandy loams, and most of our 

 important farm crops can be made to grow well on such soils. 



63. Soil structure. The term soil structure refers to the 

 manner in which the particles are arranged in the soil. A soil 

 with its fine particles gathered together in granules is said to 



FIG. 32. A badly cracked soil 



A heavy soil badly cracked as the result of drying after having been saturated 

 for a leng time 



have a granular, or crumb, structure, and is loose and friable. 

 Such a soil is frequently said to have a good physical condition, 

 or good tilth (Fig. 31). On the other hand, the small particles 

 may be compacted together in such a way that these granules 

 are broken down. In this case the soil is compact and is said 

 to have a poor physical condition, or a poor tilth. The way in 

 which a soil works when it is turned by the plow that is, 

 whether it crumbles or breaks up into clods is determined 

 by its structure and condition. 



