Food fou Plants, 25 



the importance of farmers and planters familiarizing 

 themselves with these expressions. We ahvays shonld 

 think of fertilizers and manures as just so much Nitrate, 

 phosphoric acid and potash, as we can then at once com- 

 pare the usefulness of all fertilizer materials. No doubt, 

 other substances are necessary for the proper develop- 

 ment of crops, but soils so generally supply these in 

 ample quantities that they may safely be neglected in a 

 consideration 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 

 Why Farm- plant growth almost wholly because it 



yard Manure contains these three substances ; green 



and Other manuring is valuable for the same rea- 



Products Are son and largely for that only. Various 



Valuable. refuse substances, such as bone, wood 



ashes, etc., 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, 

 Nitrate like all other things it possesses the limi- 



Pre-digested tation of quality. Quality in plant food 



Nitrog-en. means the readiness with which plants 



can make use of it. In a large sense, 

 this is dependent upon the solubility of the material con- 

 taining the plant food — not merely solubility in water, 

 but solubility in soil waters as well. Fertilizer sub- 

 stances freely soluble in water are generally of the high- 

 est quality, yet there are differences even in this. For 

 example. Nitrate of Soda is freely soluble in soil liquids 

 and water, and is the highest grade of plant food Nitro- 

 gen; sulphate of ammonia is also soluble in water, but 

 of distinctly lower quality because plants always use 

 Nitrogen in the Nitrate form, and the Nitrogen in sul- 

 phate of ammonia must be nitrated before plants can 



