WATER AND AGRICULTURE 83 



land by irrigation alone. There is much land in the 

 United States which is rendered unfit for agriculture not 

 by too little water, but by too much water. Such land is 

 reclaimed by drainage. We have more than one hundred 

 million acres of swamp-land, most of which by drainage 

 can be made fit for farms. The soil is very fertile, once the 

 excess of water is removed. In Florida thousands of acres 

 have been reclaimed by drainage, and smaller drainage 

 projects are found practically all over the United States. 



Drainage. We note then that though water is neces- 

 sary to plants, there may be "too much of a good thing." 

 So scientific farming involves, among many other things, 

 the effort to secure for crop plants the optimum (best) wa- 

 ter-supply. It is for this reason that good farmers lay tile- 

 drains in their fields where there is need for them. Let 

 us note, however, that such drains benefit the plants in 

 other ways than merely by carrying off the excess of water. 

 In the excess of water they carry off excretions from the 

 roots of previous crops which, if not removed, make the 

 soil less fertile. They also indirectly permit more air 

 to get into the soil, which is important to plants. The 

 increase in the porosity of the soil caused by draining off 

 the excess of water also permits heat to penetrate it more 

 rapidly; the wanning up of the soil in spring is especially 

 important in connection with the germination of seeds. 

 These incidental benefits of drainage are so important that 

 it has been found desirable to provide artificial drainage 

 even for irrigated farms. 



Water in the Soil. The amount of water which is held 

 by soil depends on what kind of soil it is. More specifically, 



