Leaf and Air Temperature under Hawaii Conditions 
T. L. Noffsinger 1 
Air temperature may give a poor indication 
of the actual temperature experienced by a plant 
leaf under various meteorological conditions. 
Leaf temperature is dependent upon the type 
and condition of the plant as well as on a num- 
ber of meteorological elements including wind, 
humidity, cloud cover, solar radiation, and air 
temperature. 
MATERIALS AND METHODS 
During the period from March 9 through 
April 15, I960, leaf and air temperatures were 
measured using a 12 -channel single-input ther- 
mister-type thermometer. Leaf temperatures of 
pineapple and papaya plants were measured 
using a 2 2 -gauge hypodermic probe. Air tem- 
perature was measured with the thermister air 
temperature probe and checked with a standard 
mercury-in-glass thermometer. The wet-bulb 
temperature was determined by a standard psy- 
chrometer and solar radiation was measured by 
a recording bimetallic actinograph (pyrheli- 
ometer) . 
Soil temperature was measured from a 
mercury-in-glass thermometer implanted 4 in. 
in the soil. 
In measuring leaf temperatures the needle was 
carefully inserted from the underside of the leaf, 
parallel to the leaf veins, to approximately Vi 
in.; i.e., at least V 2 in. of the probe was enclosed 
within the leaf tissue. All temperatures were 
read to the nearest 0.1° C. The average tempera- 
ture of the plant was taken as the mean value 
obtained from one leaf exposed to solar radia- 
tion and one in shade. 
RESULTS 
Data were collected at 0800, 1200, and 1600 
hr. during the period of March 9 through April 
15. In addition, a continuous hourly collection 
was made over a 24-hr. period from 0800, April 
11, through 0700, April 12. 
1 Climatologist, Land Study Bureau, University of 
Hawaii. Manuscript received May 19, I960. 
During the daylight hours pineapple leaf tem- 
perature was consistently higher than the air 
temperature measured in an instrument shelter 
at the same elevation as the plants. The values 
usually ranged from 1.5° to 3.5° C. above the 
air temperature but occasionally a leaf exposed 
to direct sunlight had a temperature as much as 
7.6° C. higher than the air temperature. 
The corresponding average temperature of 
the papaya leaf was consistently lower than the 
air temperature. Temperature of leaves exposed 
to direct solar radiation and temperature of 
leaves on the same plant but shaded by higher 
leaves are given in Table 1 together with the 
average air temperature, average leaf tempera- 
ture, soil temperature, and solar radiation values. 
Table 2 gives air temperature, leaf tempera- 
ture, insolation values, soil temperature, cloud 
cover, and wind speed at 4-hr. intervals for a 
24-hr. period April 11 through April 12. Maxi- 
mum air temperature (27.0° C. ) occurred at 
1300; maximum soil temperature for the pine- 
apple (28.0° C. ) occurred at 1400; maximum 
soil temperature for the papaya (30.5° C.) oc- 
curred at 1500 and 1600. Maximum average leaf 
TABLE 1 
Leaf and Air Temperature and 
Related Meteorological Data for 
March 9-April 15, I960 
TIME 
0800 
1200 
1600 
Air temperature °C. 
21.5 
26.7 
26.4 
Leaf temperature °C. 
Pineapple 
average 
23.2 
29.1 
26.6 
in sun 
24.7 
31.0 
28.0 
in shade 
21.7 
27.2 
25.2 
Papaya 
average 
21.3 
25.4 
24.5 
in sun 
21.7 
25.9 
24.9 
in shade 
20.9 
24.9 
24.1 
Insolation Langleys /min.. 
0.21 
0.99 
0.74 
Soil temperature 
Pineapple 
19.5 
26.4 
26.3 
Papaya 
19-5 
27.1 
29.8 
304 
