PURCHASE AND USE OF FERTILIZERS 337 



hum, sugar cane, turnips, and Swedes. Potash is the ruling 

 ingredient for peas, beans, clover, vetch, flax, and potatoes. If 

 the soil is fertile, the dominant element would be supplied to 

 force a maximum growth of the crop, in such quantity as might 

 be found necessary. If the soil is not fertile, moderate applica- 

 tions of the other plant foods are made, supplemented with more 

 liberal additions of the dominant element. 



2. System Based on Necessity of an Abundant Supply of the 

 Minerals. This system is based upon the fact that potash and 

 phosphoric acid are cheap and not easily washed from the soil, 

 while nitrogen is expensive and easily lost. According to the 

 needs of the soil, a reasonable excess of phosphoric acid and 

 potash is applied, sufficient to satisfy more than the maximum 

 needs of any crop, and then the nitrogen is applied in active 

 forms, such as nitrate of soda or sulphate of ammonia, and at 

 such times as will insure the minimum loss of nitrogen and 

 the maximum development of the plant. The phosphoric acid 

 may be drawn from the cheaper mineral substances, such as 

 ground bone, tankage, and ground phosphate rock. 



This system is useful in building up a very poor soil when ac- 

 companied by a rotation which involves the use of legumes and 

 manure. 



3. A System Based on the Amount of Plant Food Taken up by 

 the Crop. According to this system, different plants are fertilized 

 with phosphoric acid, nitrogen, and potash in the proportions in 

 which chemical analysis shows them to exist in the plants. If 

 care is taken to supply an abundance of plant food, this method 

 may result in complete, though not economical, feeding of the 

 plant, and may be profitable for crops of high value per acre, but 

 for ordinary farm crops, it is likely to be unprofitable. 



This system does not take into consideration the fact that one 

 plant may have much greater power of taking up an element than 

 another. Neither does it consider that the period or season of 

 growth exercises some effect on the capability of a plant to ac- 

 quire plant food from the soil. It may, however, be taken as a 

 general rule that an application of easily available plant food 



