DRAINAGE 105 



64. Free water shuts out the air from the soil. Bacteria 

 must have air ; and so free water hinders the growth of soil 

 bacteria. More heat is necessary to warm a quantity of 

 water than to warm the same bulk of earth; and so free 

 water makes the soil cold. Frequent rains in spring some- 

 times flood fertile parts of a farm and delay seeding 

 enough to shorten the growing season seriously or even 

 fatally to the year's crop. 



In these three ways, then, free water on the soil is harm- 

 ful to farming. It is capillary water upon which nearly 

 all farm plants depend. But the supply of capillary water 

 is kept up from the free water. A chief problem for many 

 farmers, therefore, is to keep up the proper supply of 

 capillary water by securing enough free water at all times 

 without having too much of it at any one time. 



If the water from the clouds would fall in every place at 

 the desirable time in quantities just sufficient to supply the 

 capillary water needed by the crops, there would be no 

 free-water problem. But rains are not always dependable; 

 and some land needs more water than other land close by 

 that gets the same rainfall. So the farmer must often 

 drain lands which are too wet, or irrigate lands which are 

 too dry. 



65. Drainage. There are nearly 75,000,000 acres in the 

 United States which are unproductive because they are too 

 wet and marshy. " Bottom lands " and swamp lands are 

 common in almost every state. In many districts, entire 

 cultivated fields, or parts of fields, are drowned during 

 parts of the year. Some of this wet land cannot be 

 drained, because there is no lower place near it to which 

 the water can be carried, but much of it can be drained. 



Drainage carries away the useless or harmful water. It 

 lowers the " water table," or the level at which free water 

 stands in the ground. Thus it opens to cultivation many 



