28 AGRICULTURE FOR COMMON SCHOOLS 



By so doing they could draw upon the moisture in the lower 

 layers and would not have to depend upon capillarity bring- 

 ing the water so far. When we know that a corn plant com- 

 ing into tassel uses nearly three pounds of water daily we see 

 the importance of having moisture convenient for the plant 

 roots. Not only does drainage give the roots a larger amount 

 of soil from which to get moisture, but at the same time the 

 roots draw plant food from a larger amount of soil. Because 

 drainage gives access to more soil, we say that it deepens the 

 soil. 



Drainage has the effect of warming the soil. The evap- 

 orating of water is a cooling process. When there are no 

 drains much of the surface water has to evaporate. This 

 takes a good deal of time and keeps the land cold and wet. 

 There is usually a difference of five to ten degrees between 

 the temperature of drained and undrained soil in the same 

 field. This makes a decided difference in the germination 

 of seeds and the growth of the plants. It may be noticed in 

 fields that corn comes up quicker and grows faster in the 

 drier parts of the field. This is not entirely because the soil 

 is looser and richer, but because it is warmer. Then, too, 

 the summer rains soak quickly into a drained soil and are 

 more fully used by the growing crops. 



Several other results can be mentioned briefly. In drained 

 soil bacteria are more active, making more plant food 

 available. The bacteria cause the decay of the manure or 

 other organic matter in soil, so that we get more good from 

 the manure applied to the land. As the water finds its way 

 through the soil to the tiles it leaves small passage-ways. 

 This permits the air to come into the soil. We have seen in 

 another chapter that this is desirable. Furthermore, when 



