KINDS OF SOIL 1ST 



be classified on the basis of physical composition or of 

 chemical composition. It is not the place here to discuss 

 soil types and characteristics in detail, but it may be of some 

 help to briefly discuss general soil classifications, using as a 

 basis merely the common terms which are familiar to every 

 farmer, and not trying to adhere rigidly to some technical 

 basis which is of value only to the soil expert. The chemical 

 properties of soils in every case will form the basis of the 

 discussion. They can be discussed as: (a) Arid and humid 

 soils, which will distinguish in a general way those soils 

 which are located, on the one hand, where very little rain 

 falls, and on the other hand, where sufficient rain falls; 

 (b) sand, clay, loam, muck, and peat, names which are 

 very commonly used and which depend on physical and 

 chemical characteristics; (c) soil and subsoil, terms suffi- 

 ciently plain; (7/) alkali soils or special soils that are very 

 important in certain arid regions of the United States 

 particularly — an extreme type of arid soil. 



(a) Arid and Humid Soils. — The principal chemical dif- 

 ferences between soils in an arid or dry region and those in 

 a humid or moist region is in the amount of available or 

 soluble plant food. In a humid climate the soil is continu- 

 ally subject to leaching and fixation of soluble compounds. 

 Decomposition takes place as indicated in Section 135. 

 In a region of little rain, the plant food made soluble by 

 decomposition remains in the soil for the most part as such. 

 Decomposition of rocks takes place largely by the action 

 of sudden extremes of heat and cold, and not to a very 

 great extent by the solvent action of soil moisture. As a 

 result arid soils are not only pulverulent and sandy in 

 texture, but the soluble compounds which are formed remain 

 in the soil. Little clay is formed from feldspars, because of 

 lack of water for hydration. This means a coarse textured 

 soil, as mentioned above. In other words kaolinization 

 is not marked in arid regions. Since there is little leaching, 

 calcium carbonate derived from limestone, or from silicate 

 rocks by slow decomposition, is not removed from the soil 

 and exerts its flocculent effect on what little clay is formed. 

 Arid soils are more fertile as a rule than humid soils if water 



