302 



THE PRINCIPLES OF SOIL MANAGEMENT 



167. Absorption as related to drainage. The drainage 

 water from cultivated fields in the humid region, and 

 to a less extent in the semi-arid and arid region, except 

 where irrigation is practiced, carries off very consider- 

 able amounts of plant-food material. The loss of this 

 material is due to the operation of the various natural 

 disintegrating agents upon the soil mass, and to the 



Fig. 101. Wasting manure by leaching. 



application of fertilizing materials in a soluble form. 

 The various absorptive properties stand between the 

 natural solubility of the soil and the tendency to loss in 

 drainage, and hold these materials that would otherwise 

 be lost, in a condition in which they may readily be used 

 by the plant. 



168. Substances usually carried in drainage water. 

 However, some material is always lost in drainage 

 water, of which, among the bases of the soil those most 



