120 Nebraska Agricultural Exp. Station, Research Bui. 6. 
of the atmosphere, should transpire relatively less water than an 
isolated plant in an exposed place. This self-protection in mass 
makes it possible to grow a larger amount of vegetation on a 
given amount of soil moisture than would be possible if the 
plants were freely exposed. 
In all tests the evaporation at the surface of the ground bore a 
rather constant proportion to the evaporation from the highest 
jar. These ratios were: Corn, 1912, 0.31; corn, 1913, 0.36; 
corn, 1914, 0.31; spring wheat, 1912, 0.36; oats, 1913, 0.39. 
From these figures it may be concluded that, as a general prin- 
ciple, the water-dissipating influences are approximately three 
times as effective just above the growing crop as at the ground. 
The relationship may be expected to vary with the stage of 
development and character of the crop. In an open, bare field, 
the evaporation rates would not be identical above the ground 
and at the surface, but rather increase with elevation. However, 
we can assume that the above reduction in evaporation rate 
represents in large measure the degree of protection afforded by 
the crop. This has an important effect on reducing the loss of 
Table 44. — Weekly summary of evaporation from free water sur- 
faces 36 square inches in area at six elevations in a cornfield. 
1912. 
Av. daily 
evaporat'n 
Elevation of evaporating surface above ground 
Average 
for week 
of six 
ending 
6 in. 
2 ft. 
3.5 ft. 
5 ft. 
8 ft. 
10 ft. 
elevations 
Grams 
Grams 
Grams 
Grams 
Grams 
Grams 
Grams 
(1) 
(2) 
(3) 
(4) 
(5) 
(6) 
(7) 
(8) 
June 5 . . 
" 12 1 . 
203 
354 
366 
401 
450 
452 
371 
" 19.. 
120 
211 
202 
218 
224 
236 
202 
" 26.. 
179 
302 
308 
333 
343 
359 
304 
July 3 . . 
141 
299 
331 
369 
370 
364 
312 
" 10.. 
203 
378 
436 
543 
529 
519 
435 
" 17.. 
149 
244 
346 
380 
444 
434 
333 
" 27.. 
86 
126 
164 
226 
377 
337 
219 
Aug. 3 . . 
85 
130 
153 
165 
313 
332 
196 
" 10.. 
30 
55 
70 
86 
188 
189 
103 
" 17.. 
55 
113 
139 
163 
321 
344 
189 
" 24.. 
56 
108 
122 
150 
265 
278 
163 
" 31.. 
98 
173 
190 
223 
413 
440 
256 
Sept. 7. . 
95 
185 
192 
241 
451 
453 
270 
" 14.. 
69 
124 
136 
173 
285 
296 
181 
Daily av. 
112 
200 
225 
262 
355 
360 
252 
1 Satisfactory data could not be obtained this week because of heavy rains. 
