112 LAND DRAINAGE AND IRRIGATION 



helpful soil organisms, and the growth of more and deeper roots 

 are results of pioper diainage, which, in turn, become important 

 factors in making available the plant-food elements. Thus a 

 well-drained soil can peiform its functions in relation to plant 

 growth much better than if it were too wet, or water-logged. 



6. Good Drainage Favors Better Farm Management. — ^When 

 all the fields on a farm are well drained, the farm can be managed 

 more profitably — cultivation is made easier, square fields are made 

 possible, fields can be laid out to best advantage, seeds can be 

 planted better, crops can be planted earlier and hence are given 

 a longer growing period, fall frosts are delayed, bigger crops can 

 be produced, and farm work in general is not hampered unneces- 

 sarily because of wet fields. 



Why Lands are Wet.— Some depressions on uplands are wet 

 because of lack of surface drainage, coupled with impervious 

 subsoils which prevent the water from soaking away. Some level 

 and fine textiKed uplands having ^ ^ tight '^^ subsoils are wet largely 

 because the surface water runs away very slowly. Seepage accounts 

 for many wet areas, both on uplands and lowlands. Many low- 

 lands and uplands are periodically wet because of flood water. 

 Some lowlands are wet because they are so nearly on the same level 

 with streams or bodies of water that the escape of free water 

 is impossible. 



Much Land Needs Drainage. — There are in the United States 

 a total of about 122,000 sections (squax^e miles) of land unfit for 

 cultivation because of too much moisture, but which could be 

 profitably drained. This is equal to the combined areas of Iowa, 

 Wisconsin, Massachusetts, Connecticut and Rhode Island. 



How Drainage is Accomplished. — ^Wet lands can be made dry 

 in different ways, depending largely upon the nature or source of 

 the damaging water. 



1. Surface Drainage.-Getting rid of surface water is called 

 surface drainage. When the offending water is that which stands 

 on the surface after rains, drainage may be effected by giving it 

 a chance to flow away through furrows or shallow ditches. If the 

 damaging water is that which flows from uplands to lower, and 

 across lower areas, during flood flow, drainage may be accom- 

 plished by controUing the course of the water through the use of 

 surface-runs and shallow ditches. 



2 A ''tight" soil or subsoil is one through which water cannot pass except 

 very slowly. 



