442 
Journal of Agricultural Research 
Vol. VII, No, io 
Fortier (5) shows, in the measurement of losses from water surfaces 
kept at different temperature, that reducing the temperature from 88° 
to 80.4° F. lessened evaporation 20 per cent; reducing it to 73.5 0 de¬ 
creased evaporation 40 per cent; to 61.3 0 decreased it to 67 per cent; and 
to 53.4 0 reduced it to 85 per cent. 
Shade, which is a great protection from heat, aids in preventing 
evaporation. Seelhorst (16) shows that a loam soil shaded by dry rye 
plants evaporated 13.9 per cent less of the rainfall than the same kind of 
soil unshaded. 
Widtsoe’s (20) work on the influence of shade on evaporation gives a 
loss of 22 pounds to the square foot as against 32 pounds for the un¬ 
shaded portion; that is, there was 29 per dbnt greater loss in sunshine 
than in shade. 
Fortier (6) shows that in actual experiments on Mount Whitney evapo¬ 
ration decreased with altitude. The decrease was rather regular, except 
at the summit (14,502 feet), where greater evaporation took place than 
at either 10,000 or 12,000 feet. 
According to Carpenter (4), diminished barometric pressure tends to 
increase evaporation to the extent of 14 per cent at 9,000 feet and 18 
per cent at 10,000 feet over that at 5,000 feet. 
Mulching the surface of the soil a few inches by stirring it is the most 
common practice in use for the preservation of moisture under field 
conditions. Ridgaway (15) shows that stirring the surface to depths 
of 2, 4, and 6 inches in different tanks once a week, with the water level 
kept 22 inches below the surface of the soil, lessened evaporation by 19, 
23, and 45 per cent, respectively, of the amount lost from unstirred 
soil. His work also shows that where water is maintained at 6, 12, 18, 
and 22 inches below the surface, the losses were 95, 70, 45, and 35 per cent 
of evaporation from a free-water surface. This bears out Wollny’s (21) 
statement that “if there is water underneath the soil the evaporation 
decreases as the distance between the surface of this water and that of 
the soil increases.” 
Fortier (7) sums up the results when dry soil coverings were substi¬ 
tuted for stirred surfaces, as shown in Table II. 
Table; II .—Losses by evaporation from soil surfaces variously treated 
Locality. 
Loss from 
unmulched 
soil. 
Loss from 
3-inch 
mulch on 
soil. 
Loss from 
6 -inch 
mulch on 
soil. 
Loss from 
9-inch 
mulch on 
soil. 
Number 
of days 
run. 
• 
Per cent. 
Per cent. 
Per cent . 
Per cent. 
Davis, Cal.. 
35 -oo 
14. 71 
5 - 94 
O. 78 
32 
Wenatchee, Wash.. 
14- 33 
3 - 9 8 
2. 10 
I. 06 
21 
Reno, Nev.. 
20. 39 
8. 26 
2. 74 
1. 96 
21 
Average. 
23. 24 
8. 98 
3 - 59 
I. 27 
24 . 7 
