EXPERIMENT STATION BULLETINS. 467 



DRAINAGE. 



Special Bulletin No. 56. 



Need for drainage is indicated when water stands at or near the sur- 

 face of the soil sufficiently long (I) to interfere with farm operations in 

 the way of tillage, planting or harvesting or (2) to render the soils soggy 

 or compact. 



Three things are essential to the growing of good crops, so far as the 

 jthysical condition of the soil is concerned, viz.: 



The right condition of temperature. 



The right condition of moisture. 



Sufficient ventilation. 



The seed of our ordinary crops will germinate most rapidly when the 

 temperature ranges from 75 to 95 degrees F., depending upon the crop. 

 They will not germinate vigorously at a temperature below 60 degrees, 

 nor much above 100 degrees. 



The vigor of the growth of the future plant will be modified quite ma- 

 terially by the rate of germination. 



In a soil with a surface temperature as low as GO degrees the rate of 

 plant feeding will be low, as will also be the rate of nitrification and free 

 nitrogen fixing. 



It requires much more heat to warm an ovei^wet soil than it does to 

 warm the same soil with the best amount of moisture for the growing 

 of crops. 



If a soil is kept over wet because of improper or insufficient drainage 

 much of this moisture will disappear into the air by evaporation. 



From a soil in proper moisture condition as much as ten tons per 

 acre may evaporate into the air in twenty-four hours in ordinary weather. 

 In very windy weather this amount may be increased. With the soil 

 over wet as much as thirty tons have been known to evaporate from an 

 acre in twenty-four hours in early spring weather. 



In the evaporation of a single pound of water as much heat is used 

 as would raise 966 pounds of water one degree in temperature, and in 

 the evaporation of a ton of water from our fields an amount of heat is 

 used sufficient to heat the soil on an acre one foot deep, including twenty 

 per cent of moisture (which is not far from the average optimum 

 amount of moisture for the growing of crops,) over one and one-quarter 

 degrees. If, in one of these over-wet fields, the excess of evaporation 

 amounted to only ten tons per day enough heat is used to heat the soil 

 as indicated above over twelve degrees, so that the waste of sunshine 

 that should be used in warming the soil is very great indeed. 



Soil must be ventilated for the same reasons that our houses must 

 be ventilated; namely, to keep up a proper supply of oxygen in the soil 

 and to remove from the soil undesirable gases which are deposited in the 

 soil by the germination of seeds, the growth of roots, etc., etc., and in 



