CHAPTER XV 



THE REMOVAL OF NUTRIENTS FROM THE SOIL BY 

 CROPPING AND LEACHING 



The soil solution, because of its dynamic character, offers 

 two sources of loss for nutrient materials, one of which should 

 be economically encouraged, while the other should be reduced 

 by suitable control to as low a point as is consistent with good 

 soil management. These two sources of exhaustion are (1) 

 cropping and (2) leaching or drainage. One is a legitimate 

 expenditure ; the other is a waste, which within certain limits 

 in a humid region is unavoidable. 1 



152. Intake of water by plants — osmosis. — Plants ob- 

 tain their raw materials from the air and the soil, the former 

 furnishing the carbon and the oxygen, most of the water and 

 the nutrients proper coming from the soil. Although many 

 constituents, some necessary and some incidental, pass into 

 the plant from the soil, for convenience of discussion two 

 groups may be established: (1) water, and (2) nutrients prop- 

 er. It must be kept in mind, however, that water, while per- 

 forming certain mechanical functions, has a nutrient relation- 

 ship also. 



The most important mechanical principle governing the ab- 

 sorption of water by the plant is osmosis. 2 The abstract phe- 

 nomenon should be clearly in mind before its plant relation- 

 ships are considered. A bag of collodion (pig's bladder or 

 parchment paper will do as well) is filled with a strong solu- 



1 Gases, such as carbon dioxide, nitrogen and possibly ammonia, may 

 be lost from the soil also. 



3 Water may also be taken up by colloidal absorption which is called 

 imbibition. This is common in seeds. 



