ACID-INSOLUBLE MATTER OF SOILS 



/ 2.3. 



Total /nsolub/e Matter- 



Fig. 17. Graphic composition of 200 soils, 

 i. Nitrogen. 2. Potash. 3. Phosphoric acid. 



many fertile soils the sum of the nitrogen, phosphoric 

 acid, potash, lime, magnesia, and sulphuric and car- 

 bonic anhydrides is less than 1.50 per cent. This 

 means that in every 100 pounds of soil there are only 

 from 1.5 to 3.5 pounds of matter which can take any 

 active part in the support of a crop, and 96 to 98.5 

 pounds are present simply as so much inert material. 

 Not all of the plant food soluble in hydrochloric acid 

 is equally valuable. In fact, the acid represents more 

 than the limit of the crop's feeding power, when there 

 is not enough of more soluble forms to aid in the first 

 stages of growth. 



89. Acid-Insoluble Matter of Soils. This class in- 

 cludes all of those compounds of the soil which re- 

 quire the joint action of the highest heat and the 

 strongest chemicals in order to decompose them. The 



