170 PRACTICAL DRAINAGE 



Water-logged land has a tendency to heave in freezing. 

 This results in the winter-killing of such crops as alfalfa, 

 clover, and fall grains. Where the soil is not covered with 

 a protective layer of snow, winter-killing may be one of 

 the most serious handicaps to farming. Anything that 

 reduces it will add greatly to the farmer's profits. 



The tilth, or structure, of the soil is benefited by drain- 

 age. An undrained soil puddles readily, whereas one that 

 is drained tends to form the crumb-like structure which 

 is sought by the farmer. 



Determining the Need of Drainage. As with all other 

 expenses, that required for drainage should be investigated 

 before it is incurred. It would of course be folly to spend 

 15 or 20 dollars an acre draining land that would not be 

 benefited thereby. Drainage is usually carried on to re- 

 move either excess water or excess alkali. In spite of 

 secondary benefits, it is doubtful if it would pay to drain 

 in most cases unless one of these undesirable conditions 

 existed. 



An excess of water can easily be determined by boring 

 test holes with a soil auger. The surface indications are 

 not an absolutely reliable guide. In many soils having a 

 dry, baked crust at the surface, borings will reveal free 

 water 2 or 3 feet below the surface. The color and thrift 

 of the vegetation are valuable aids in determining the need 

 of drainage, but the final test should be made by the 

 use of an auger. 



Excessive quantities of alkali can readily be determined 

 by a chemical analysis. Water extracts of the soil can 

 easily be tested for chlorides, sulphates, carbonates, and 

 nitrates. With information of this sort available it is 

 possible to say whether or not some of the salts should be 

 removed. The electrolytic bridge is very useful in this 



