These words are popular names, T . t>_;_,.;_ a t 5? od * for 

 , i j. .1 P .1 Its Principal Plants 



and are used tor the convenience ot the Elements, 



general public. Nitrate of Soda con- Nitrate, 29 



tains an amount equivalent to about Phosphoric 

 15 per cent, of Nitrogen, 300 pounds Acid Potash, 

 to the ton, 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, phos- 

 phoric acid and potash are standards, hence the im- 

 portance of farmers and planters familiarizing them- 

 selves 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 

 development 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 promot- 

 ing plant growth almost wholly because Why Farm- 

 it contains these three substances; yard Manure 

 green manuring is valuable for the SbdudiMtt* 

 same reason and largely for that only. Valuable. 

 Various 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, like all other things it possesses 

 the limitation of quality. Quality in 

 plant food means the readiness with 

 which plants can make use of it. In a large sense, this 

 is dependent upon the solubility of the material contain- 



