CHAPTKK XXV 



SOIL ORGANISMS 



THE soil contains large numbers of organisms, both plants and 

 animals of various kinds, that act upon botli the organic and min- 

 eral constituents of the soil. They produce changes, many of which 

 are highly beneficial, while others are detrimental. For convenience 

 they may be divided into macro-organisms, such as rodents and in- 

 sects, and micro-organisms, those of microscopic sixe, such as furgi 

 and bacteria. 



MACRO-ORGANISMS 



1. Rodents. Large numbers of rodents, such as squirrels, rats, 

 mice, prairie dogs and gophers, have the habit of burrowing in the 

 soil, thus facilitating the action of certain agencies. These carry 

 soil upward and a more thorough mixing of the surface and sub- 

 soil is thus brought about. Later these openings are iilled with 

 surface soil. Much vegetable matter also is carried into these 

 burrows, which helps in decomposition of the minerals with which 

 it comes in contact. Aeration and percolation are aided by the work 

 of these animals. It is interesting to note that very few burrowing 

 rodents are found in regions of tight clav subsoils. 



2. Insects. A great many insects live in the earth during their 

 larval state or even the whole of their lives. The larval stage of in- 

 sects, is their most active period. They are constantly working 

 their way through the soil and in this way aid aeration and drainage. 

 Seventeen-year locusts are very abundant in soils in some local 

 areas. Over r>00 e\uvi;e. or cast-oil" shells, of these insects were 

 counted upon a hawthorn bush not over three feet high. Ants 

 work up their hills, tilling them with vegetable matter, and when 

 they are abandoned form very rich spots of soil. 



3. Worms. Earthworms are most common organisms and 

 are found in medium and heavy soils of humid areas that are well 



'supplied with organic matter. They do not seem to be so abundant 

 in acid soils, evidently preferring those containing some limestone. 

 They do not live in sands, light sandy loams, arid or semi-arid 

 soils. They aid in aeration and their burrows improve drainage. 

 They pass large quantities of soil through their bodies. The min- 



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