CHAPTExv -Kl V 

 THE 80IL SOLUTION 



The soil is a heterogeneous mixture of solids, gases, and a 

 liquid. The mineral constituents come from the debris of 

 rock, the organic matter is derived from plant and animal 

 tissue, while through and around these complex materials the 

 water and gases of the soil circulate in ever-changing propor- 

 tions. Minute organisms are also present in great numbers, 

 aiding, through their enzymic activities, the intricate trans- 

 formations. As a result of the reactory inter-relations of the 

 soil components, a solution is generated which tends to come 

 into equilibrium with the solids and gases with which it is 

 in contact. As it is from this source that plants obtain their 

 mineral nutrients, the soil solution and its control demand 

 especial attention. 



The fundamental error of many soil conceptions has been 

 to regard the soil as a static system. Chemical, physical, and 

 biological activities are admitted, but they have been regarded 

 as of little importance in influencing the soil mass as a whole. 

 Such a conception is in error as every constituent of the soil 

 is dynamic. The presence of large amounts of material in 

 a colloidal state makes the constancy of any particular con- 

 dition impossible over any extended period. 



In studying the soil solution, especially as to its composi- 

 tion and concentration, the phenomenon of absorption can 

 not be ignored. The tendency of certain portions of the soil 

 to go into solution, while other parts are absorbing both the 

 solvent and the solute, must be reckoned with. Moreover, 

 the losses of nutrients to the plant and through leaching are 



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