MANURING AND FERTII.IZING 39 



It almost invariably occurs that potatoes grown with- 

 out any manure mature earlier and contain more dry 

 matter, with a correspondingly reduced yield,' than 

 those grown on land manured with barn manures or 

 a complete fertilizer. The vigorous growth induced 

 under the latter conditions cannot be matured in the 

 same time, hence for an early crop it is unwise to 

 stimulate too vigorous growth. 



The Function of Fertilizers. — The prevailing 

 opinion in purchasing fertilizers is that they contain 

 a certain amount of plant-food — usually nitrogen, phos- 

 phoric acid, or potash — in a more or less available 

 form, and that the benefits received from their appli- 

 cation is due to the addition of this plant-food to the 

 soil. So deeply seated is this theory that all fertilizers 

 are bought and sold on this basis, and laws controlling 

 the business have been formulated upon it. The in- 

 gredients — nitrogen, phosphoric acid, and potash, with 

 others — are necessary for the growth of all crops, but 

 the amounts of the essential ingredients, other than 

 the above mentioned, are believed to be present in the 

 soil in suflScient quantities to meet all the requirements 

 of the crops grown. 



A 300-bushel crop of potatoes has been found to con- 

 tain 81 pounds of nitrogen, 30.6 pounds of phosphoric 

 acid, and 79 pounds of potash. Taking 49 New York 

 soils, the chemist found that the surface eight inches 

 contained, per acre : * 



Nitrogen . . . 3,053 pounds, enough for 38 crops 

 Phosphoric acid, 4,219 " " " 137 " 



Potash .... 16,317 " " " 207 " 



1 Va. Bui. 92, p. 107. * (N. Y.) Cornell Bui. 130, p. 157. 



