200 SOILS AND FERTILIZERS 



In nitrates and ammonium salts. These are generally 

 present in nitrate of soda and sulfate of ammonia. Their 

 availability has already been discussed (see § 218). 



Water-soluble organic nitrogen. This is probably not 

 so readily available as the two former kinds, but differs little 

 from them in this respect. 



Active water-insoluble organic nitrogen. Although not 

 directly available this becomes so quickly enough for the 

 crop to which it is applied to obtain part of it. 



Inactive water-insoluble organic nitrogen is that part of 

 the organic nitrogen that is of little value for immediate 

 plant growth. 



Percentage of phosphoric acid in the following forms : 



Water-soluble phosphoric acid, which is readily available 

 (see § 227). 



Reverted phosphoric acid. Not so readily available 

 (see § 227). 



Available phosphoric acid. This usually consists of the 

 sum of the two forms mentioned above. Sometimes when 

 this term is used no distinction is made between the water- 

 soluble and the reverted, but this is not so satisfactory. 



Insoluble phosphoric acid. This is slowly available, but 

 in animal products, such as bone, tankage and other slaughter 

 house waste, it becomes available more quickly than if present 

 in rock phosphate. However, the analysis does not distin- 

 guish between the organic and inorganic carriers. 



Percentage of potash in the following forms : 



Soluble in water. 



Present as chloride. 



255. Trade values of fertilizer ingredients. — In the 

 states having fertilizer inspection laws, it is customary for 

 the officers in charge of the inspection to adopt each year a 

 schedule of trade values for nitrogen, phosphoric acid and 

 potash in each of the carriers ordinarily found in fertilizers. 



