5i8 



REPORT OF THE COMMISSIONERS OF 



As another class of data applying to the problem in hand we may refer to the 

 results obtained in experiments relative to the quantity of water required by different 

 classes of forest trees and by the principal cereals and other farm crops as well as 

 various grasses, vineyards and potatoes, by E. Risler, who carried on an exceedingly 

 interesting study on these points at his farm near Nyon, Switzerland, a number of 

 years ago. Risler's results may be found cited by Ronna in his Manual, Les 

 Irrigations; also Risler's paper, Recherches sur I'Evaporation du Sol et des Plantes, 

 etc., and in other places. The following from Risler gives the best available 

 information as to the daily consumption of water by various crops and two classes of 

 forest trees, the water being supplied in such quantity as to produce the best result in 

 the growing plants. 



Meadow grass requires from 

 Oats 



Indian corn " " 



Clover " " 



Vineyards '• " 



Wheat " " 



Rye '■ " 



Oak trees '• " 



Potatoes " " 



Fir trees " " 



C.I 34 to 0.267 inches 



0.140 to 0.193 '" 



0.1 10 to 0.1 57 " 



0.140 to " 



0.035 to 0.031 



0.106 to 0.1 10 " 



0.091 to •' 



0.038 to 0.035 " 



0.038 to 0.055 '' 



0.020 to 0.043 



Applying these figures, we learn that ordinary farm crops may take up from twelve 

 to fifteen inches of water over the whole area cropped during the growing period. 

 Forests in the same way may take up in their growing period from April to August, 

 inclusive, from four to five inches, while cleared areas which are unculti\'ated 

 probably absorb from seven to eight inches. F"orests then not only use less water than 

 cultivated areas, but they further tend to increase the summer flow of streams by 

 holding back the water in accumulations of leaves, mosses, and forest litter until it can 

 be gradually absorbed into the soil. If we examine in detail the figures as to run-off 

 of the Hudson River in comparison with those of the Genesee and other deforested 

 drainage areas, we learn that a forest area may yield more than double the flow during 

 the growing season than will be obtained from a deforested area. Again, on culti- 

 vated areas the quality of the leading crop will materially influence the run-off. Thus 

 streams issuing from an Illinois prairie where Indian corn may occupy from 50 to 60 

 per cent, of the total area will give a very different summer flow from streams 

 similarly situated but issuing from areas with crops demanding less moisture than 

 Indian corn. 



