78 



Elementary Principles of Agriculture 



available soil and add the substances to the soil. This is 

 called fertilizing the soil. Fig. 43 illustrates the effect 

 of applying different fertilizing substances to a sandy 

 soil taken from a field in Eastern Texas. Fig. 44 shows 

 the effect of adding nitrogen, potassium and phosphorus 

 to pot-cultures of alfalfa made at the Oklahoma Agri- 

 cultural and Mechanical College. 



Fig. 43. Orangeburg fine sandy loam. An application of phosphoric acid is 

 denoted by P; potash by K; nitrogen by N. 



111. The Quantity of Fertilizing Substances added to 

 the soil is but a small fraction of the increased weight of 

 the crop which it produces. Minerals are absorbed by 

 the plants in exceedingly small amounts, for they form 

 only about one part in two hundred of the fresh, living 

 plant, and rarely more than five per cent of the dry 

 substance. They are necessary as food substance; they 

 become a part of the living plant substance. Exceedingly 

 small amounts suffice in the case of iron, sulphur, chlo- 



