2 BULLETIN 1139, U. S. DEPARTMENT OF AGRICULTURE. 
The present study is not intended primarily to establish the maxi- 
mum depth to which a wheat crop is capable of feeding. The pur- 
pose is rather to determine and present the actual depth to which 
the wheat crop has utilized the soil in a series of seasons, on a wide 
range of soils, and under radically different cultivation methods. 
The data are classified to show whether this depth was limited by the 
depth of the soil itself, by the quantity of water available for storage, 
by the physiological limitations of the crop, or by the character of 
the season. 
The material was obtained in connection with the preparation of 
United States Department of Agriculture Bulletin Xo. 1004, entitled 
" Use of Water by Spring Wheat on the Great Plains," by John S. 
Cole and O. E. Mathews. All the members of the technical staff 
of the Office of Dry-Land Agriculture Investigations from 1906 to 
date have contributed to the publication by the data they have ob- 
tained at the stations where they have been located. 
E. C. Chilcott, 
Agriculturist in Charge. 
SOURCES OF INFORMATION. 
At the time the work of the Office of Dry-Land Agriculture Investi- 
gations was inaugurated it was recognized by those in charge that a 
measure of the water content of the soil would be of great value in 
interpreting crop yields. For this reason frequent determinations 
of soil moisture were made at the stations then in operation, on plats 
receiving different cultural treatments. This work has been carried 
on continuously at these stations and at all stations where experi- 
ments have been subsequently started by the office mentioned except 
one, where the character of the soil prohibits soil sampling by the 
usual method. Moisture determinations have been made on all of 
the principal crops, but at the stations where wheat grows well it 
has been considered the basic crop and has been sampled more regu- 
larly than any other. It should not be inferred, however, that wheat 
is the most important crop at all the stations from which data are 
presented. At some of them it is, in fact, of little importance, but 
even at these certain data have been obtained on it for purposes of 
comparison. The moisture reactions of spring wheat and winter wheat 
have been found to be somewhat different. Spring wheat alone is 
considered in this publication, as more moisture determinations have 
been made with it than with winter wheat. Some of the stations 
having the best soil-moisture records have been necessarily omitted 
because the major part of their work has been with winter wheat. 
The data presented consist of moisture determinations at 17 sta- 
tions in different portions of the Great Plains on three plats of spring 
wheat, known as plats A, B,' and C or D. The moisture history of 
these three plats constitutes a total of 135 crop years, after omitting 
years when some factor, such as hail, was responsible for crop dam- 
age and years when the number of samples taken was not great 
enough to determine the changes in moisture content of the plats. 
The plats indicated by the same letter receive the same cultivation 
at all stations. They represent systems of tillage so different that 
they should show maximum differences in their moisture relations. 
