38 FERTILIZERS 



COST OF COMBINATIONS 



59. Based on the foregoing, a tankage containing 

 5.5% nitrogen and 13% phosphoric acid would have 

 value as follows : 



5.5% (units) nitrogen @ $4.20 per unit $23.10 



13% phosphoric acid @ $1.24 16.12 



$39.22 



The nitrogen and phosphoric acid are in much the 

 same form as found respectively in blood and 

 steamed bone. 



A guano containing 5% nitrogen, 10% phosphoric 

 acid and 2% potash, would have a value as follows : 



5% (units) nitrogen, @ $4.20 (21c. per Ib. )$ 21.00 

 10% " phosphoric acid @ $1.24 12.40 



2% " potash $1.20 2.40 



$35.80 



MOST ECONOMICAL FORM OF FERTILIZERS. 



60. If the price of nitrogen is the same in nitrates, 

 and bone and blood, the cheapest is that which 

 becomes available just as fast as the crop requires it, 

 neither faster nor slower. Is nitrate too quickly 

 soluble for the crop to use all of it before a part of it 

 is carried away by wasted water ? Is ground bone 

 too slowly available or blood and bone just right? 

 are questions to be answered by crop and con- 

 ditions. 



If a form of plant food becomes available too 

 rapidly, the moisture holding it in solution rises and 

 evaporates, leaving this soluble, valuable food on 

 the top of the ground, whence it is partly lost by 

 escaping surface waters and part carried back into 

 the soil by penetrating moisture. That is why slow- 

 running water gives the most profitable irrigation. 



