NITROGEN FOR GARDEN CROPS. 151 



pounds each of potash and phosphoric acid; conse- 

 quently there would be an accumulation, during the 

 time stated, of over 7,000 to 9,000 pounds of potash, 

 and over 3,000 to 4,000 pounds of phosphoric acid 

 to each acre. The bulk of these substances is 

 probably distributed through the surface soil to the 

 depth of, say, eight or ten inches. Consequently 

 this whole surface layer is as rich in mineral plant 

 foods as the very best of ordinary compost. To 

 continue the annual dressings of the same kind of 

 manure would be like carrying coal to Newcastle, 

 or water to the sea. 



Such heavy dressings are expensive, no matter 

 whether we produce the manure on the place, or 

 have to purchase it. Every pound of potash in the 

 manure has a commercial value of more than four 

 cents, and every pound of phosphoric acid a value 

 of about six cents. The quantities already put into 

 the soil represent an investment of $600 or 

 more, and this gives no immediate returns of any 

 kind. Why should we invest more money in bonds 

 that bear no interest, and have a long time to run? 



But while the soil itself may have become richer 

 in mineral plant foods than even the barnyard 

 manure itself, no corresponding accumulation of 

 nitrogen has taken place. It can not be said that 

 the soil is destitute of that element. Most of the 

 crops which the market gardener pro- 

 Niteogen Needed, ^^^^s, consume nitrogen faster than 

 mineral plant foods; and besides 

 there is more or less loss of nitrates by leaching. 

 While there may be a considerable supply of nitro- 

 gen in the soil, there is at least no accumulation of 

 the available form of this element. 



The market gardener's success depends in a large 



