Conserving Soil Moisture. 203 



crops but they materially lessen the evaporation of moisture 

 from the soil and thus help to secure a higher yield of 

 crops. *"The writer has observed that, when the rate of 

 evaporation at 20, 40, and 60 feet to the leeward of a 

 grove of black oak 15 to 20 feet high was 11.5 c. c., 11.6 

 c. c., and 11.9 c. c., respectively, from a wet surface of 

 27 square inches, it was 14.5, 14.2 and 14.7 c. c., at 280, 

 300 and 320 feet distant, or 24 per cent, greater at the 

 three outer stations than at the nearer ones. So, too, a 

 scanty hedge-row produced observed differences in the rate 

 of evaporation as follows, during an interval of one hour; 



At 20 feet from the hedge-row the evaporation was 10.3c.c. 



At 150 feet from the hedge-row the evaporation was 12. 5 c. c. 



At 300 feet from the hedge-row the evaporation was 13 . 4 c. c. 



Here the drying effect of the wind at 300 feet was 30 

 per cent, greater than at 20 feet, and 7 per cent, greater 

 than at 150 feet from the hedge. 



Then, too, when the air came across a clover field 780 

 feet wide the observed rates of evaporation were: 



At 20 feet from clover 9.3c, o. 



At 150 feet from clover 12. Ic. a 



At 800 feet from clover 13 c. c- 



Or 40 per cent greater at 300 feet away than at 20 feet, 

 and 7.4 per cent, greater than at 150 feet." 



* Irrigation and Drainage*, p. 169 



