490 NATURE AND PROPERTIES OF SOILS 



In spite of the intangible nature of the question, certain gen- 

 eral rules seem to govern the compounding and use of fertiliz- 

 ers. In the first place, the ratio of the nutrients removed by 

 the average crop bears no relation to the composition of the 

 fertilizer usually added. This is to be expected because of 

 the complex changes that the fertilizer undergoes in the soil 

 and because the different nutrients influence the plant di- 

 versely. 



Table XCIX 



Constituents 



Ammonia 



Phosphoric acid 

 Potash 



Ratio of the 



oonstituents 



AS They CJccue 



in the aveeage 



Crop 



Ratio op the 



Constituents 



Caeried by the 



Average 



Fertilizer 



0-2 

 16-8 



It is immediately noticeable that the ratios of the ammonia 

 and potash in fertilizers are low. The ammonia ratio is low 

 because of the ready response of plants to nitrogen and the 

 ease with which this constituent is lost from the soil. The 

 potash ratio is likewise small because potassium is a rather 

 expensive constituent and it is generally better if possible to 

 render available by suitable means that which is already in 

 the soil than to buy it commercially. The phosphoric acid 

 is high in comparison with the ammonia and potash because 

 of its complex reversion in the soil and the tendency of much 

 of it to remain unavailable for long periods due to the high 

 absorptive power of the soil. 



The following data may now be presented. These for- 

 mulae are tentative and suggestive only, being a modification 

 and curtailment of certain analyses standardized for the use 

 of fertilizer manufacturers in the United States. 



