CHAPTER VI 



THE SOIL: ORGANIC MATTER 



That portion of the earth's crust which can support 

 vegetation, or can raise crops, is what the farmer terms the 

 soil. That loose mass of particles derived from rock dis- 

 integration and decay, and which covers most of the land 

 portion of the globe is the way the geologist defines the soil. 

 These definitions for the most part describe the same mate- 

 rial but geological soil is not always agricultural soil, for 

 not all loose rock particles will raise crops, and hence to the 

 farmer are not soil. 



115. Composition of Soil. — Soil agriculturally is composed 

 of fine and coarse particles of rock in all stages of decompo- 

 sition, of organic matter derived from decayed or decaying 

 plants and animals, of water, of bacteria, fungi, and other 

 forms of life, and of gases. 



116. Function of the Soil. — Soil serves not only as an 

 anchorage for plants, where they can spread out their roots 

 and maintain a position which will enable them to absorb 

 the sun's rays to the best advantage, but also serves as the 

 source of most of those elements which are essential to the 

 plant's growth. A perfect soil is one which maintains a 

 reserve supply of insoluble food material that cannot be 

 washed away; which produces enough soluble material to 

 feed the growing crop; which is so constructed that it can 

 supply sufficient water to the crop; which is capable of main- 

 taining the right temperature or of warming up quickly in 

 the spring; and which has a structure that permits of proper 

 root movement. 



117. Soil Study. — The study of the movements of water 

 in the soil, of its holding capacity for water, of the arrange- 

 ment of soil clusters, of the size of ultimate particles, of the 

 relations of soils to heat, and of the various methods of 



