108 



THE SOIL AND ITS IMPROVEMENT 



68. Number and Grade of Drains. In heavy clay soils 

 more drains are needed than in soils where there is an 

 admixture of sand, because in the latter natural drain- 

 age is better. In clay bottom it is a good plan to place 

 the "side drains about sixty feet apart, while in lighter soil 

 one hundred feet or more is the proper distance. The 

 grade or fall of the main ditch should be at least an inch 



to eighty feet, and the 

 fall of the side drains 

 should be an inch to 

 twenty feet. 



69. Does Drainage 

 Pay ? The drainage of 

 water-soaked lands 

 yields a large income on 

 the investment. Pro- 

 fessor Waid describes 

 some experiments made 

 by the Massachusetts 

 Experiment Station. 

 Ordinary land was used 

 for the test. Before 

 drainage it had pro- 

 duced a rotation of corn, 

 potatoes, rye, and clo- 

 ver. The same rotation was followed for four years after 

 drainage. The second four years gave an increased yield 

 of twenty-five per cent, on the average, over the average 

 yield of the four years before drainage. Professor Waid 

 shows that this increase, at market prices, amounted to a 

 profit of forty-one per cent on the cost of drainage. 



70. Irrigation is used, as drainage is, to secure the proper 

 amount of soil water; but it is used under conditions just 

 the opposite to those that make drainage profitable. Irri- 



PART OF AN IRRIGATION DAM. 



