Land Covers to Conserve Moisture. 49 
potato culture; but while these lands are giving fair 
yields of potatoes of good quality, they are in many 
places suffering great injury from the destructive 
effects of winds. On these lands, wherever broad, 
open fields lie unprotected by wind-breaks of any 
sort, the clearing west and northwest winds after 
storms often sweep entirely away crops of grain after 
they are 4 inches high, uncovering the roots by the 
removal of from 1 to 3 inches of the surface soil. 
It has been observed, however, that such slight bar- 
riers as fences and even fields of grass afford a 
marked protection against drifting for several hun- 
dred feet to the leeward of them. 
“In the case of groves, hedge-rows and fields of 
grass, their protection results partly through their 
tendency to render the air which passes across them 
eooler and more moist, and partly by diminishing 
the surface velocity of the wind. 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 cc., 11.6 cc., and 
11.9 ec., respectively, from a wet surface of 27 
square inches, it was 14.5, 14.2 and 14.7 at 280, 
300 and 320 feet distance, or 24 per cent greater 
at the three outer stations than at the nearer ones. 
So, too, a scanty hedge-row produced observed dif- 
ferences in the rate of evaporation, as follows, dur- 
ing an interval of one hour: 
“At 20 feet from the hedgerow the evaporation was 10.3 cc. 
“«“ 450 «§ “ce “cc “ac cb “ce ee 42.5 
“300 « “cr 6“ 6c ‘c “ sé 13.4 “ 
E 
