38 
THIRTEENTH REPORT. 
The fundamentals to crop production so far as the soil is concerned 
are: 
Proper temperature 
Proper moisture 
Proper ventilation. 
In this soil investigation work the Soils Department is attempting to 
c ike a study of 
Temperature 
As modified by other conditions \ Physical 
( Etc. 
As a modifier of other conditions 
f Phvsical 
\ Etc. 
As an index of other 
/ conditions ( Physical 
< ^ Etc. 
\ activities, ^ 
(The relations other than physical are to be studied co-operatively) 
Some of the questions presenting themselves are: 
I. What is the normal temperature for the different types of Mich- 
igan soils, (under normal conditions) ? 
II. How far does any individual of a type, as the soil numbered 2, 
fall below normal? 
III. How far may jrnoper farm practice raise the temperature toward 
normal or above normal, which may be desirable, — is desirable in most 
cases? 
IV. How far may such rise in soil temperature affect crop produc- 
tion? 
A good deal has been discovered and written already concerning soil 
temperatures and it may be questioned whether this data already found 
might not be used in this experiment. 
It is a fact which is coming more and more to be appreciated that 
the facts apparently controlling the temperature in one soil may not be 
effective in the same direction and to the same degree in another soil. 
It is true also that much of the data already found may have been im- 
properly interpreted and even improperly presented in our Agricul- 
tural literature. 
It is commonly set forth that the application of manures to the soil 
has the effect of raising the temperature and this rise of temperature is 
credited quite largely by some writers to the fermentations taking place 
in the manure thus added. Experiments conducted at this station show 
that an application of ten tons of manure per acre worked to a depth 
of six inches into the soil when apparently no other influences are at 
work results in a temperature rise of about 0.15 degrees F. In sunshiny 
weather the temperature of the soil receiving this ten tons of manure 
per acre is raised over two degrees, apparently because of the increased 
capacity of the soil to absorb the sun’s heat. For the reasons named 
above, we deem it advisable to make a careful study of the details of 
soil temperature. 
A very important question that has suggested itself, is the possibility 
of what might be called a critical soil temperature, beyond which the 
result in crop yield may increase very rapidly. It must be admitted 
that the question strictly speaking is but a hypothetical one and yet 
there is ground for such question. Fig. 1 illustrates the idea. The 
horizontal dimension represents temperature, while the perpendicular 
