THE DRAINAGE OF FARM SOILS 199 



soil. Most of the time the tiles carry air, as well 

 as water. When the surface air is much warmer 

 than the soil air, as on a warm day in early spring, 

 a system of tile drains may supply a slight bottom 

 heat, or at least be the means of equalising tem- 

 perature. Thus a good system of under-drainage 

 aerates the soil both from above and from below. 



Practical Results from Draining Land. The 

 practical result of the better aeration and increased 

 warmth secured by draining land is that the soil 

 becomes richer and more productive. Not only 

 does more plant food in the soil itself become 

 available, but also the manures or fertilisers that 

 may be applied are more effective, since they too 

 must first be treated with Nature's chemicals before 

 the plants can use them. The beneficial bacteria 

 of the soil, which thrive only in warmth and mois- 

 ture not wetness are encouraged to multiply. 

 The season is lengthened at both ends; the soil 

 can be worked earlier and later, so crops have the 

 use of it longer. 



If a poorly drained field is sloping there may be a 

 considerable loss of fertility by surface washing. 

 After this field is drained, rains sink into the soil 

 more readily, as it is looser and dryer, and so a large 

 part of the surface washing is checked. The cost of 

 growing a crop is reduced, especially in preparing 

 the seed bed, for a mellow, well-drained soil is easier 

 to handle and can be brought into the right shape 

 quicker than cloddy, poorly drained soil. Seeds 

 germinate better, because the soil is warm and dry 

 instead of cold and wet. 



The quality as well as the yield of the crop 

 is often improved. This is particularly true 

 of grass or hay; that which grows in well- 

 drained meadows or pastures is of much higher 



