CHAPTER V 

 THE SOIL AND SOIL FORMATION 



The soil is that part of the earth's surface into which 

 the roots of plants penetrate. We often speak, in a nar- 

 rower sense, of the soil as that part of the earth which 

 we handle with tillage implements. The term " furrow- 

 slice " refers to that rather definite zone of soil which is 

 inverted by the moldboard, disk plow or the gar- 

 den spade in preparing the surface of the land for cul- 

 tivation. " Subsoil " refers to that part of the soil 

 below the furrow-slice. The terms " dust blanket " and 

 " dirt mulch " are often used to indicate that upper por- 

 tion of the furrow-slice which is kept open and mellow, 

 as by intercultural tillage, that the soil moisture may not 

 readily rise quite to the surface by capillary action, but 

 be stopped before it reaches the surface where it would 

 be readily evaporated. The term " furrow pan " is 

 sometimes used to designate a layer at the top of the 

 subsoil, made by the compacting of the horses' feet and 

 the plowshare on the bottom of the furrow. 



The soil is usually made up of a framework of 

 more or less finely divided mineral particles, of partially 

 decayed inorganic particles, of water, of air, of small 

 quantities of soluble substances, and of bacteria and 

 other low forms of life. In some cases, as peaty soils, 

 the body of the soil solids is decaying organic matter, 

 and in rare cases soils are mainly water. Most plants 

 prefer to live in soils composed mainly of stony par- 

 ticles, with only sufficient water to partially fill the 

 interstices, giving room for considerable air. Some 

 plants prefer a soil so saturated with water that 

 the air is excluded. Still other plants like best to have 



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