COMMERCIAL FERTILISERS 395 



in ordinary soils than either potash or nitrogen; 

 and, furthermore, because the commercial supply 

 of phosphoric acid is apparently more limited than 

 that of the other two plant foods. In most cases 

 the supply of nitrogen may be maintained without 

 difficulty with barn manure and green-manuring. 

 Potash is found more in the straw than in the grain ; 

 the grain, which is rich in phosphoric acid, is 

 commonly shipped away from the farm while the 

 straw remains. From the point of view of the 

 future supply, then, phosphoric acid is the most 

 important of the three plant foods. 



From the point of view of the plant, however, 

 one food is as important as another. Plant foods 

 are often spoken of as though each one performed 

 certain definite functions ; as * * Potash makes fruit, ' ' 

 "Nitrogen makes stem and leaf growth," and 

 "Phosphoric acid fills out the grain." Undoubt- 

 edly each of the three plant foods does exert a 

 special influence in one of these several directions, 

 but all are essential to the well-being of the plant. 

 "Fertilising for fruit" or "fertilising for grain" or 

 "fertilising for growth" is apt to be one-sided and 

 unsatisfactory fertilising. The plant as a whole 

 is the unit; fertilise to make a symmetrical, well- 

 developed plant; not for an abnormal develop- 

 ment of any part. 



WHEN TO APPLY COMMERCIAL FERTILISERS 



This depends first of all upon the solubility of 

 the fertiliser. One would not apply nitrate of 

 soda, which dissolves almost immediately in soil 

 water, in the fall ; much of the nitrogen in it would 

 be leached from the soil by spring. But one might 

 apply raw bone meal in the fall, because this 



