Oct. 25, 1915 
Soil Temperatures 
177 
Plot A maintained the highest maximum temperature during the 
spring and summer and until quite cold weather in the fall, when plot C 
registered the highest maximum temperature. This lasted for a month 
or so during the coldest weather, and as soon as it began to moderate 
in late winter plot A warmed up rapidly, with D next. 
The greatest variation between plots occurred during the summer 
months. In the spring and fall there is a transition period in which the 
temperature differences are less. During the summer of 1913 plot A 
registered a maximum temperature of 80.5° the week of July 7, when 
plot D was 78.5°, and plot C was 71 0 F. However, plot C later, the week 
of August 18, registered a maximum temperature of 72 0 F. During the 
week of July 13, the following summer, plot A registered a maximum 
of 8o°; plot D, 77 0 , the week of July 24; and plot C, 70° F., the week of 
August 3. 
Figures 1 to 4 are reproductions of typical seasonal charts of soil tem¬ 
peratures prevailing under the three cultural systems. These give an idea 
of the diurnal variations. During the winter the temperatures are quite 
constant from day to day, with very little variation between plots 
(fig. 1). In the spring the diurnal range is considerable in the plot under 
tillage with cover crop and the grass land, but varies little under the straw 
mulch, which exhibits a very gradual warming up (fig. 2). During the 
summer season, fluctuations become quite pronounced under tillage and 
grass, but the straw mulch still maintains its uniformity (fig. 3, C). 
During the season of greatest daily range the maximum and minimum 
temperatures occur about 10 p. m. and 10 a. m., respectively (fig. 3, 
A and D). In the fall the temperatures and ranges are not radically 
different from those of spring, except that the general trend of tempera- 
atures is reversed (fig. 4). « 
In conclusion, it may be said that a system of clean cultivation with 
a winter cover crop is characterized by extreme diurnal and annual 
fluctuations in soil temperature; that a straw mulch equalized these 
fluctuations to a marked extent, as does also a grass crop, though in 
less degree. 
