564 IOWA DEPARTMENT OF AGRICULTURE 



Drainage removes surplus water from under the surface. There is a 

 body of stagnant water helow the surface of the ground, as those who 

 have w^orlved clayey soil have observed. .This body of water saturates 

 the soil and excludes the air, to the detriment of the plants. 



Drainage lengthens the seasons. 



By drainage of the fall rains before they become stagnant by draining 

 off all extra moisture between the drain and frozen surface during the fall 

 and winter and then in the springtime by draining off all the moisture 

 from the surface as it finds its way into the soil. 



Drainage deepens the soil. 



By lowering the line of standing water and by making the subsoil ac- 

 cessible to the roots of plants. 



Drainage warms the under soil. 



As the rain falls through the air it acquires the temperature of the 

 atmosphere. If this be higher than the surface soil, the latter is warmed 

 by it; and if the rains be copious and sink easily into the subsoil they 

 will carry this warmth with them to the depth of the drains. Thus the 

 undersoil in well drained land is not only warmer, because of the* evapo- 

 ration is less, but because the rains in the summer season actually bring 

 down warmth from the heavens to add to their natural heat. 



The reason why drained land gains heat, and water bogged land 

 is always cold, consists in the well-known fact that heat cannot be trans- 

 mitted downward through water. , 



Drainage equalizes the temperature of the soil during the season of 

 growth. 



Water discharged from drains is always several degrees above freez- 

 ing point. Heat naturally tends upwards, so that the soil is warmed 

 from below during the germinating season of the seeds, and not infre- 

 quently the soil is during the month of April much warmer than the air 

 is at night, although colder than the air during the day; therefore the soil 

 of a drained field is free from the extremes of the temperature of day and 

 night air. 



Drainage carries down soluble substances to the roots of plants. 



When rain falls upon heavy, undrained lands, or upon any land into 

 which it does not readily sink, it runs over the surface, dissolves any 

 soluble substance it may meet with, and carries it to the nearest ditch 

 or creek. Rain robs such land of its fertility. 



Drainage improves the quantity and quality of crop. It is the opinion 

 of all who have observed closely that the plants and fruits grown upon 

 under-drained soil are more fully developed and of much better quality 

 than those grown on undrained soil. 



Drainage increases the effects of manures. On undrained lands the 

 rains dissolve the essential portions of the manures and carry them off, 

 or, if lands are more than ordinarily wet, it prevents the rotting of the 

 manure. 



Drainage facilitates pulverization. 



One object of plowing land is to pulverize it, and every one knows 

 that a wet soil can never be pulverized, and plowing a clayey or loamy 



