76 SOILS AND FERTILIZERS 



silicate, in which case the soil may be deficient in ac- 

 tive lime compounds. 



In the case of phosphoric acid, a soil which gives 

 an alkaline or neutral reaction, contains 0.15 per 

 cent, of phosphorus pentoxide and is well supplied with 

 organic matter and lime, is amply provided with phos- 

 phoric acid, and under such conditions the extensive 

 use of phosphate fertilizers is not required, except pos- 

 sibly for special crops. Hilgard states that should 

 the per cent, of phosphoric acid be as low as 0.05, 

 there is, in all probability, a poverty of this element. 

 It frequently happens that in acid soils the phosphoric 

 acid is unavailable until a lime fertilizer is used to 

 neutralize the acid. 



Soils containing less than 0.07 per cent, of total 

 nitrogen are usually deficient. A soil containing as 

 high as 0.15 or 0.2 per cent, of nitrogen may fail to re- 

 spond to crop production. Such cases are generally 

 due to some abnormal condition of the soil, as a lack 

 of alkaline compounds which are necessary for nitri- 

 fication. The appearance of the crop is the best indi- 

 cation as to a deficiency of nitrogen. 



A soil which contains less than o.io percent, of pot- 

 ash soluble in hydrochloric acid is quite apt to be de- 

 ficient in this element. Soils which contain 0.5 per 

 cent, or more of lime carbonate will produce good 

 crops on a smaller working supply of potash than soils 

 which are proverty-stricken in lime. As a rule the 

 best agricultural soils contain from 0.3 to 0.6 per cent, 

 of potash. Sandy soils of good depth may contain 



