DRAWAGE 239 



tially in the direct removal of the gravitational water 

 from the root zone of the soil by affording free passages 

 for its percolation and flow. In general, the soil condi- 

 tions requiring drainage may be divided into two groups, 

 which are fairly distinct in the problems which they 

 present. These are: (1) Those lands which are satu- 

 rated with water throughout the year. (2) Those lands 

 which are saturated with water for only brief periods. 

 Into the first group are placed all those lands of an 

 acknowledged swamp character, which not only retain 

 a large part of the water which falls upon their own sur- 

 face, but may receive the water which flows from other 

 lands. Into the second group is put all those wet lands 

 which are saturated for a sufficient period to interfere 

 with the best condition of the soil, or the proper develop- 

 ment of the crop. It represents a very mild or incipient 

 stage of the conditions included in the first group. 



In the manipulation of soil for the staple upland 

 crops, the establishment of effective drainage is at the 

 foundation of all the other practices which must be 

 employed. If it does not exist, the other farm practices, 

 such as tillage, fertilization etc., can not be applied 

 effectively. 



An excess of water in the soil has many and far-reach- 

 ing effects upon the soil as a medium for plant growth, 

 especially if this condition is intermittent. The manage- 

 ment of the latter condition is even more crucial than 

 the former. 



109. Effects of drainage. Twelve of the most 

 important effects of drainage are as follows: (1) Firms 

 the soil. (2) Improves the granulation. (3) Increases 



