Transpiration as a Factor in Crop Production. 
87 
THE RELATION OF CLIMATE TO TRANSPIRATION. 1 
HOURLY TRANSPIRATION AND EVAPORATION IN RELATION TO CLIMATIC 
FACTORS. 
Records have been secured during two years, 1910 and 1914, 
relative to the amount of water transpired by a corn plant and 
the amount evaporated from a free water surface during consec- 
utive hours of the day in a cornfield. A record of the accom- 
panying climatic factors was taken by means of self-recording 
instruments in the cornfield. The facilities and methods for 
obtaining these records are shown in Figure 5, p. 47. 
The United States Weather Bureau has installed at the Ne- 
braska Experiment Station a Marvin pyrheliometer and a 
Callendar recording pyrheliometer, so that beginning with 1915 
solar radiation records will be available for correlation with tran 
spiration and evaporation in addition to those weather records 
taken heretofore. 
The transpiration data were secured from plants standing 
undisturbed on platform scales thruout the tests. The scales 
were read at the end of each hour between 7 a. m. and 8 p. m., 
and the hourly transpiration was determined by loss in weight. 
Only the total transpiration and evaporation were determined 
for the night, but the weather factors were being taken continually. 
The test was made after the plants had acquired their maximum 
leaf-area. In 1910 the soil contained 60 per cent and in 1914 ,70 
per cent of its water-holding capacity. 
In 1910 the evaporation data were secured by averaging the 
losses from five Livingston porous clay cups at an elevation 
midway between the base and tip of the plant. In 1914 a shallow 
free water surface was used, 1.5 inches deep and of 36 square- 
inch surface area, in which the water was restored by weight to 
the jar each day to one-half inch below the top. A shallow body 
of water has been found to respond more readily to changing 
conditions than a deeper body. The data are given in Tables 
23 and 24, and in Charts VIII and IX. 
The 1914 data are an average for 30 days between July 14 and 
August 22 (weighings were not made on rainy days), while the 
1910 data are the average for only nine days. The former, 
therefore, are more representative because of a greater duration. 
1 References concerning the relation of transpiration to climatic factors: 
Briggs and Shantz (1913, 1914), Fittbogen (1873), Hasselbring (1914), Hell- 
riegel (1883), Heinrich (1894), Kiesselbach and Montgomery (1911), Kiessel- 
bach (1910), King (1905), Leather (1910, 1911), Montgomery and Kiesselbach 
(1912), Pfeiffer et al. (1912), Seelhorst and Miither (1905), Sorauer (1880), 
and Wollny (1877). 
