454 
Journal of Agricultural Research 
Vol. XIV, No. IX 
A statement of the average moisture content of the surface foot as a 
whole may be very misleading. Thus, at a time when the average for 
the whole foot section indicates a fair amount of available moisture, the 
soil of the first 3 or 4 inches may be too dry to permit germination of 
seeds, and at another time the optimum condition may be found in the 
first few inches, while in the lower portion of the section the soil may be 
too dry to permit the penetration of roots. Therefore detailed moisture 
studies of the sur- 
Lnfnmft _ 
■ 4nnmtf tn inch**. ~ Atmvnf Inch—. 
...,, ■— MumhnA nf Onafhf* in • £rp*r»mni Stnthnn 
Fiq. i.—M ap of a portion of the United States, showing annual 
precipitation,^ evaporation from a water surface,* and fre¬ 
quency of drouths in a 20-year period, 1893-1914,* to indicate 
the especially favorable location of the Nebraska Agricultural 
Experiment Station for soil-moisture studies. 
face soil during pe¬ 
riods of exceptionally 
dry weather are of 
special interest. 
For such studies the 
Nebraska Experiment 
Station Farm at 
Lincoln probably pro¬ 
vides as good a place 
as is to be found any¬ 
where in the portion of 
the United States to be 
considered as strictly 
humid, as it lies almost 
as far to the west as the 
strictly humid climate 
extends on the Ameri¬ 
can prairies (fig. i). 
WEATHER CONDITIONS 
From the autumn of 1906 forward we had watched at Lincoln for 
weather conditions that would develop a very dry surface soil, but not 
until late in the summer of 1909 did these appear, and then at a time 
when sampling could not be undertaken. They ceased just before 
meeting the definition of a drouth as used by the United States Weather 
Bureau: Thirty consecutive days between March 7 and September 30 
without a total precipitation of 0.25 inch in 24 hours (7, chart). Then 
ensued a remarkably wet autumn, to be followed in turn by a record- 
breaking period of dry weather, which was terminated by May rains. 
We secured some sets of samples during this, but during the dry periods 
of the following year (1911) we failed to get any. Then we decided upon 
a detailed study of the moisture variations in the season of 1912, no matter 
whether it opened wet or dry, beginning the sampling as soon as the 
frost was out of the ground and taking samples at such times as would 
1 Henry, A. J. climatology of the united states. U. S. Weather Bur. Bui. Q, pi. 26. 1906. 
* Kimball, H. H. evaporation observations in the united states. In Mo. Weather Rev., v. 32, 
DO. 12, p. 558. 1904. 
* NATIONAL WEATHER AND CROP BUL-, 19x5, HO. 7, 4 p., 4 maps. 1915. 
