[8 



1522 



The Cornell Reading-Courses 



I. The first effect of drainage is to remove the excess of water from 

 the pores in the soil and to replace it with air. This means better soil ven- 



tilation. Ventilation is 

 as essential for the 

 roots of most plants as 

 it is for animals. Cut 

 off their air supply by 

 submersion or other 

 means, and the roots of 

 plants soon die. Inter- 

 mittent wetness does 

 this. There is a re- 

 peated pruning of the 

 small roots as the soil 



Fig. 45. — Sectionalview of soil ayidrock formation, shoiinngthe changes from a dry to 

 underground tnovement of water and the position of result- 



ing wet areas on the surface. In addition to the springy ^ prolonged wet COn- 

 places, the soil is kept wet by the seepage of water along dition. By produc- 

 the top of the compact subsoil. This figure also illustrates . . ' 



the reason for locating a cross drain above the springy l^g deeper aramage 

 area in order to effect drainage. This method cuts off the and better ventila- 

 water supply . .^ . , - . 



tion, artificial dram- 

 age promotes deeper penetration of the roots of plants. 



2. The tilth of the soil is improved, and less cultivation is required 

 in order to get the soil in condition for a crop. Drainage is the first 

 requisite for good tilth and the efficient use of tillage implements. Not 

 only can the land be worked sooner after each rain, but it can be worked 

 more days in the year. Consequently a smaller equipment of tools, teams, 

 and men is required in order to handle a given area of well-drained land 

 than for .that which is wet-. The waste of energy and returns is especially 

 large where there are wet spots. All the soil is never in condition to 

 work at the same time, and the crop does not ripen evenly. These con- 

 ditions entail increased cost and reduced returns. 



3. Drainage does not remove any water that would be beneficial if it 

 remained. It removes the standing water. On the other hand, the 

 improvement of the tilth of the soil and the deeper penetration of plant 

 roots make a larger amount of film water available to the crop. On 

 drained land, crops usually stand dry weather better than those on inter- 

 mittently wet land. If a person goes into a cornfield in August after 

 a dry spell, it will be possible to pick out the wet spots in the soil by the 

 curled leaves on the plants. 



Near the surface of the soil the fluctuation in the moisture content 

 is greatest. Deep in the soil the supply is more uniform. Consequently, 

 the deeper the roots of a crop can maintain themselves, the more uniform 

 is their water supply likely to be. 



