Tilth and Tillage of the Soil 



1755 



been classified into groups and each division has been given a name. 

 The divisions most frequently used are as follows: 



TABLE 1. Textural Divisions of Soil Material 



X 



ame 



Stone 



Coarse gravel. . 

 Medium gravel 

 Fine gravel.. . . 

 Coarse sand . . . 

 Medium sand. . 



Fine sand 



Very fine sand. 



Silt 



Clay 



It will be noted that there are more divisions of the small particles 

 than of the large ones. The finer the particles are, the greater is their 

 effect on the properties of the soil in proportion to their volume. Sand 

 is gritty and does not stick together, especially when dry. Silt is flour- 

 like, but not gritty, and the particles have little tendency to stick together. 

 Clay is powdery, and when wet usually becomes very sticky. When dry 

 it hardens and bakes. The clodding of soil is evidence of the presence of 

 clay, although it does not necessarily mean pure clay. A loam soil worked 

 when wet may clod badly. 



On these textural groups are based many of the descriptive terms in 

 common use. (Fig. 89.) A sand soil is one made up essentially of sand 

 particles with so small an amount of silt and clay that the latter are 

 negligible. A clay soil is one in which clay particles prevail to such an 

 extent that the soil acts like pure clay. A silt soil contains so much 

 material of the size of silt that it acts essentially like pure silt. A loam 

 soil is one made up of such proportions of all grades of material that no 

 one of them is dominant. If soil is loamy but has one constituent 

 predominant, it may be termed accordingly a sandy loam, a silt loam, 

 a clay loam, or perhaps a silty clay loam. Thus, there may be a great 

 variety of combinations of these materials, giving rise to many classes 

 of soil based on their fineness. 



Because of the influence of texture on the properties of a soil and con- 

 sequently on its relation to plants, soils have sometimes been named 

 according to the kind of crops to which they are suited. For example, 

 wheat soils are generally of a clay-loam texture. The best grass soil is 

 usually a heavy clay. Corn does best on a loam or a sandy loam, and 

 early truck crops are grown on light sandy loam soil. 



