IRRIGATION AND DRAINAGE 



111 



DRAI2v^AGE 



Too much water in the soil at any time during the growing 

 season is as bad as, or worse than, too little water, but the 

 removal of surplus water is not the sole purpose of drainage. 

 If water stands too close to the surface during wet seasons, 

 drainage will help the soil in the following ways : 



(1) By removing surplus water at those times. 



(2) By deepening the feeding area for plant roots (Fig. 

 63). 



(3) By admitting air and' aiding the ventilation of the 

 soil and roots. 



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Fig. 63. — Underdrains encourage roots to feed deeper. A shows water just 

 under the roots in wet weather. B shows the roots fa,r above the water during 

 drouth. C shows the roots and the water as deep as the tile drain. 



(4) By allowing the roots to grow deeper and reduce, the 

 suffering at time of drouth. 



(5) By raising the temperature of the soil. 



(6) By increasing the chemical action. 



(7) By aiding tillage. 



When water is carried to greater depths by drainage, air 

 and warmth follow. These are important factors in making 

 plant-food soluble and increasing' the grovrth of plants. If 

 the school garden is not properly drained, a good lesson in soil 

 drainage should be taught. A practical demonstration can 

 be made by the installation of the drains, under the obser- 

 vation and perhaps by the aid of the pupils present. 



Kinds of Drainage. — Most fields are fairly well drained 



