Methods of Use of Fertilizers 207 



than if the expensive element, nitrogen, were included ; and 

 a greater economy in the use of nitrogen is accomplished if 

 it is added in small amounts when required. Besides, in 

 the improvement of soils, the liberal application of the min- 

 erals is conducive to an abundant growth of the legumes, 

 which are able to acquire their nitrogen from the air, thus 

 reducing to some extent the outlay for this expensive ele- 

 ment. This system is strongly recommended where cheap 

 phosphatic and potassic materials are readily accessible, as 

 is the case in those countries where it is successfully used. 



A system based on the needs of the plants for the different 

 elements as shown by chemical analysis. 



Another system of fertilization is based upon the theory 

 that the different plants should be provided with the essen- 

 tial elements in the proportions in which they exist in the 

 plants, as shown by chemical analysis. Different formulas 

 are, therefore, recommended for each crop, the constituents 

 of which are so proportioned as to meet its full needs. 

 This method, if care is taken to supply an abundance of 

 all the necessary constituents, may result in a complete 

 though perhaps not an economical feeding of the plant, 

 since it assumes that a plant which contains a larger amount 

 of one constituent than of another requires more of that 

 constituent in the fertilizer than of the others. It does 

 not take into consideration the fact that the plant which 

 contains a larger amount of one element than another 

 may possess a greater power of acquiring it than one which 

 contains a smaller amount. 



Neither does this system take into consideration, as al- 

 ready pointed out (p. 199), that the period or time of growth 

 of the plant also exercises a considerable influence in indi- 

 cating the capability of the plant to acquire its necessary 



