THE FORMS OF SOIL WATER 



239 



of such a method of attack lies not only in the fact that 

 a large area of undisturbed soil is considered, but also 

 in the opportunity to study practical field treatments 

 in relation to the movement and composition of drainage 

 water. 



165. The lysimeter method of studying gravitational 

 water. — The lysimeter method, however, has been the 

 usual mode of attacking these problems. In this method 

 a small block of soil is used, being entirely isolated by 

 appropriate means from the soil surrounding it. Effective 

 and thorough drainage is provided. The advantages of 

 this method are that the variations found in a large field 

 are avoided, the work of carrying on the study is not so 

 great as in a large field, and the experiment is more easily 

 controlled. One of the best-known sets of lysimeters 

 was that established at the Rothamsted Experiment 



G>rac/e 



Fig. 38. — Cross section of a lysimeter at the Rothamsted Experiment 

 Station, England, in'), soil column under study; (p), outlet for 

 collected drainage water. 



