72 SOILS AND FERTILIZERS 



more soluble forms to aid in the first stages of growth. 

 In the following table the percentage amounts of 

 compounds soluble and insoluble in hydrochloric acid 

 are given : l6 



Wheat Heavy clay Grass and 



soil. soil. grain soil. 



Solu- Insolu- Solu- Insolu- Solu- Insolu- 

 ble in hie hie ble ble ble 



HCl residue in HC1 residue in HC1 residue 



Insoluble matter. 63.07 84.77 84.08 



Potash 0.54 2.18 0.21 3.46 0.30 1.45 



Soda 0.45 3.55 0.22 2.95 0.25 0.25 



Lime 2.44 0.36 0.48 0.16 0.51 0.35 



Magnesia 1.85 0.25 0.34 0.47 0.26 0.46 



Iron 4.18 0.78 3.76 0.72 2.56 1.07 



Alumina 7.89 5.54 6.26 5.44 2.99 9.72 



Phosphoric acid • 0.38 0.12 0.08 0.23 0.05 



Sulphuric acid- • . 0.11 0.24 0.09 0.25 0.08 0.02 



The insoluble matter after digestion with hydro- 

 chloric acid, was submitted to fusion analysis, and the 

 figures given under insoluble residue represent the 

 amounts of potash, soda, etc., insoluble in acids. In 

 the clay soil 96 percent, of the total potash is in forms 

 insoluble in hydrochloric acid. 



87. Soluble and Insoluble Potash and Phosphoric 

 Acid. — From the preceding table it is to be observed 

 that the larger portion of the potash in the soil is in- 

 soluble in hydrochloric acid. A soil may contain 

 from 2 to 3 per cent, of total potash, and 90 per cent, 

 or more may be in such firm chemical combination 

 with aluminum, silicon, and other elements, as to re- 

 sist the solvent action of plant roots. The larger 



