ADVANTAGES OF DRAINAGE 169 



Strange as it may seem, drainage increases the water 

 supply of the plant and reduces the injury that is likely 

 to be caused by drought. Roots do not readily penetrate 

 into the ground water. They are confined to the zone 

 above the water-table from which they absorb capillary 

 water. Free water is unavailable to them; A water-table 

 near the surface means, therefore, that the plant can absorb 

 water from only a limited area. In case of drought when 

 the water-table is likely to be lowered rapidly the plant 

 has but a shallow root system which is unable to endure 

 drought so well as a root system which extends well into the 

 soil and is able to take up moisture from a deep soil zone. 



Drainage allows the soil to become warm early in spring. 

 The high specific heat of water makes it slow to become 

 warm. This has great practical significance since a slow, 

 cold soil delays spring work and retards the development 

 of the young plant at a critical period in its life history. 



Roots require air for their normal functioning. If free 

 circulation of air through the soil is retarded by water- 

 logging, the plant does not get sufficient air for its best 

 growth. This condition reflects itself in the yield. Covered 

 drains promote the free movement of air through the soil; 

 this may help to account for the wonderful results that 

 follow drainage in cases where the water-table is not close 

 to the surface and alkali is not injurious. 



Going hand in hand with better aeration is the better 

 condition for the growth of desirable microorganisms. 

 Decay of vegetation in absence of sufficient air takes place 

 as putrefaction which results in products toxic to plant 

 growth. Nitrification, nitrogen-fixation, and normal plant 

 decay require air. If it is not present the organisms 

 promoting these beneficial processes will be replaced by 

 undesirable ones. 



