IMPROVEMENT OF THE SOIL 81 



pounds of phosphoric acicl, and 100 pounds of potash. 

 If we assume a value of 15 cents per pound for the 

 nitrogen, and 5 cents for each of the other ingre- 

 dients, we will have a value as follows : — 



80 pounds of nitrogen at 15 cents = $12 



160 pounds of soluble phosphoric acid at 5 cents = 8 



100 pounds of potash at 5 cents = 5 



Total value per ton = $25 



It will readily be seen that such a fertilizer would 

 really be cheaper at $25 than one with 3 per cent of 

 nitrogen, 6 per cent of phosphoric acid, and 4 per 

 cent of potash would be at '$20, for the real value 

 of the latter would only figure out $19. It is usu- 

 ally a mistake to buy cheap, low-grade fertilizers, 

 for even if bought at their real value, there is a 

 larger proportion of inert matter or " filler " on 

 which to pay freight and to handle in the field. 



The valuable ingredients of fertilizers are ob- 

 tained from many different sources. The nitrogen 

 may be of either animal, vegetable, or mineral origin. 

 Nitrate of soda, or, as it is sometimes called, Chile 

 saltpeter, is found in large deposits in some of the 

 drier parts of South America. It is used as a fer- 

 tilizer in great quantities, either alone or combined 

 with other substances. Being very soluble, and in 

 a form to be immediately taken up and utilized by 

 the plant, it acts very quickly, giving almost im- 

 mediate results, the leaves taking on a darker color, 

 and the plant showing increased vigor of growth 

 within a very few days after its application. On 

 account of its solubility, however, it is easily washed 

 and leached away by the rain, and as it is expensive 



