106 THE SOIL AND ITS IMPROVEMENT 



districts that could not otherwise be farmed at all; and on 

 old farm lands it corrects the three evils named above due 

 to too much free water. That is, it admits air and bac- 

 teria to more soil, and so gives the plant roots more soil to 

 feed in. It makes it easier for the sun to warm the soil. 

 It lengthens the growing time upon certain lands. 



Artificial drainage is not needed in an open, porous soil, 

 such as we find in sandy or gravelly regions. It is the 

 hard, compact, clayey soils which hinder the escape of the 

 surplus water and which need to be drained by the farmer. 

 There are two methods of effecting drainage, the open 

 method and the closed method. 



66. Open drainage means the use of open ditches or sur- 

 face drains as water carriers. These ditches are expected 

 only to remove the surplus water in times of flooding. 

 Their size and cost depend entirely on local conditions. 

 The greater the territory to be drained, the greater must 

 be the capacity of the ditches. In the Central West 

 many miles of these surface drains, extending through 

 many farms, have been constructed by farmers working 

 together. Side or lateral drains run into the mains. The 

 main ditch may be perhaps eight feet deep and twenty 

 feet wide. Large dredging machines are used in digging 

 these large ditches. 



The first cost of open ditches is less than that of closed 

 drains ; but they take up a good deal of the farm area, 

 cut up the farm inconveniently, and cost much labor and 

 trouble to maintain. 



67. Closed Drainage. The second method of effecting 

 drainage is by closed drains underground. This method 

 has certain advantages over the former. No valuable sur- 

 face land is used ; the farm is not disfigured and cut up ; 

 and if the drains are properly made, they last a life time. 



The most simple kind of closed drain is made by plow- 



