REGULATING THE WATER SUPPLY 157 



DRAINAGE 



111. Corn requires a thoroughly drained soil, both be- 

 cause it flourishes in a " warm " soil, and because it re- 

 quires large amounts of available nitrates when making its 

 rapid summer growth. On poorly drained land, even 

 when such land is rich bottom soil, the corn plant will 

 often have a yellow color indicating a need of nitrogen. 



/S^: 



Fia. 40. — Plan of ridging land for surface drainage. Two rows on each 



ridge. 



The water-logged soils interfere with bacterial activity 

 and the normal nitrifying processes are prevented. Sur- 

 face drainage for corn on very flat lands is often provided 

 by plowing in narrow beds, 8 feet wide, and planting two 

 rows of corn 4 feet apart on each bed. 



Underdrainage is so thoroughly discussed in several 

 soil texts that it is not necessary to take up the subject 

 here. 



