6o 



Nature-Study Agriculture 



Alkali 



Drainage 



by 



ditching 



and by 



tiling 



compared 



In some parts of the West where irrigation is prac- 

 ticed, drainage serves to carry away an excess of alkali 

 (Fig. 41 and Exp. 6). 



U. S. D. A. 



FIG. 42. Cross section of soil, showing tile in place. The soil is 

 drained and roots can grow above the "ground-water curve." 



Open ditches may be used to carry off surplus water, 

 but they are very inconvenient and take space where 

 crop plants might grow. Underground drains, on the 

 contrary, leave the surface of the field as it was. They 

 are made by laying short lengths of tile end to end 

 several feet underground. The water gets in where 

 the ends of the tiles are loosely joined to one another. 

 The water table cannot stand much higher than the 

 bottom of the drain (Fig. 42) , for any free water will run 

 into the drain and be carried away. 



Experiments and Observations 



i. Pulverize a little sugar with a table knife. Heap the pow- 

 dered sugar upon a lump of loaf sugar and set the lump into a 

 shallow dish of water. How far does the water go up? What 

 does this experiment suggest as to the effect of a mulch ? (Fig. 30.) 



