CHAPTER IX 

 SOIL TEXTURIE, STRUCTURE, AIN'D COMPOSITION 



The problem of maintaining a fertile soil and at the same 

 time harvesting from it large crops is founded on principles sim- 

 ilar to the maintaining of a savings account. A sound bank 

 account is founded on the following principles: (i) The insti- 

 tution must be maintained on sound principles. It must be able 

 to keep the money safe and refund it v^hen called for. (2) The 

 amount which is in the bank to one's credit may be money in- 

 herited or that obtained by one's own effort. (3) The speed with 

 which the money can be withdrawn depends upon the contract en- 

 tered into with the bank. The duration of the account will de- 

 pend upon the quantity on deposit and the speed with which it is 

 withdrawn. 



Now, in soil fertility we have three similar fundamental prin- 

 ciples: (i) The texture and structure of the soil. Is it of such 

 a nature that it will hold our capital, the fertility, and yield it to 

 us as desired in the form of large crops? (2) The elements 

 of plant food which it contains constitutes our bank account of 

 fertility. The quantity of this is measured by the native fer- 

 tility which the soil contains plus the plant-food added to it from 

 time to time. (3) The biological factor, the tiny microbes, 

 which correspond to the contract determinins* the speed with 

 which the capital can be withdrawn. In the banking business all 

 recognize the fact that they can draw out only that which is 

 placed to one's account. In fertility the same principle holds. 

 One cannot obtain something from nothing. 



SOIL TEXTURE AND STRUCTURE 



Soil Classes. — ^Soils may be classified as to origin as: 



(i) Residual Soils — ^These are formed in place through the 

 decomposition and disintegration of the native rock. By dig- 



