These words are popular names, and Its Principal Food for 

 are used for the convenience of the general Elements, 

 public. Nitrate of Soda contains an Nitrate, 33 



amount equivalent to about 15.65 per Phosphoric 

 cent, of Nitrogen, 313 pounds to the ton, Acid, Potash. 

 and cotton-seed meal, for example, about six per cent. More 

 than three pounds of cotton-seed meal are necessary to 

 furnish as much available Nitrogen as one pound of 

 Nitrate of Soda. We value the plant food on the amount 

 of Nitrate Nitrogen it contains, and on this account Nitrate 

 has become a standard name for this element of plant 

 food. In like manner, Phosphoric Acid and Potash are stan- 

 dards, hence the importance of farmers and planters in fa- 

 miliarizing themselves with these expressions. We always 

 should think of fertilizers and manures as just so much 

 Nitrate, Phosphoric Acid and Potash, as we can then at 

 once compare the usefulness of all fertilizer materials. 

 No doubt other substances are necessary for the proper devel- 

 opment of crops, but soils so generally supply these in ample 

 quantities that they may safely be neglected in a considera- 

 tion of soil needs and plant foods. The food of plants may 

 therefore be understood to mean simply Nitrate, Phosphoric 

 Acid and Potash. 



Farmyard manure acts in promoting 

 plant growth almost wholly because it con- ^ 



tains these three substances; green manur- yard Man 

 ing is valuable for the same reason and and Utner 

 largely for that only. Various refuse sub- d ucts 

 stances, such as bone, wood ashes, etc., a ua e ' 

 contain one or more of these plant food elements, and are 

 valuable to the farmer and planter on that account. 



The Quality of Manures and Fertilizers. 



While plant food is always plant food, 

 like all other things it possesses the limita- 

 tion of quality. Quality in plant food e-digesti 

 means the readiness with which plants can 

 make use of it. In a large sense, this is dependent upon the 

 solubility of the material containing the plant food not 

 merely solubility in water, but solubility in soil waters as well. 

 Fertilizer substances freely soluble in water are generally of 



