196 



SOILS AND FERTILIZERS 



224. Soil Solution. Soil water obtained by leaching 

 .soils is an exceedingly dilute solution of various mineral 

 salts and organic compounds. Through rock disinte- 

 gration, mineral matter is rendered soluble, but the pro- 

 cess of fixation prevents accumulation in the soil solution 



FIG. 40. Plants grown in Sand and watered with Leachings (Soil Solu- 

 tion) from Soil as used in Fig. 39. 



of compounds of such elements as potassium and phos- 

 phorus. As a result of disintegration and fixation, 

 numerous chemical changes take place in the soil, and 

 the soil solution is an important factor in bringing about 

 these changes. Many of the phenomena which have 

 been studied in connection with solutions in physical 

 chemistry take place in the soil. Diffusion, absorption, 

 osmotic pressure, and ionization, 88 disassociation of the 

 molecule in solution, all occur in soils and are due 



