12 BULLETIN 1004, U. S. DEPARTMENT OF AGEICULTUEE. 
To determine this point the rate of the use of water for the period 
"when the moisture content of the soil neared depletion was com- 
pared with the rate of use of water for the two periods preceding. 
The conditions necessary for obtaining data on this point were as 
follows: (1) All three periods must have been within the period 
of rapid growth, (2)' the last period must have ended before the soil 
moisture was depleted, and (3) the samples must have been taken 
deep enough to include all soil in which a change in water content 
took place. 
The number of years in which data on this point could be obtained 
was small, and the experimental error due to the short lengths of the 
periods was large. In order to obtain data for the consecutive 
periods within the period of rapid growth, the three periods selected 
were necessarily short. Data were obtained for an average of about 
two years at each station. 
It was found that when the results of all stations were averaged 
the use of water for each period was nearly the same. It can not be 
said that anything conclusive was shown by the data, however. 
The experimental error in the rate of use per day was so large that 
it obscured any small differences there might have been between the 
different periods. No consistency in water use in the different 
periods is shown either between the different stations or the different 
years at the same station. 
The conclusion drawn from this study is that though there may be 
a slight decrease in the rate of use of water as the soil becomes drier, 
such decrease is too small to be measured by the means employed. 
The wheat crop can exhaust nearly all the available water without 
any serious reduction in its rate of use. 
RATE OF THE USE OF WATER DURING THE GROWING SEASON. 
Under the second preceding heading the rate of the use of water 
under certain conditions and for a part of the growing season was 
considered. The conditions were such as to permit or require the 
use of water at maximum rates per day. Under the present heading 
the rate of the use of water for the entire growing season under 
conditions that obtain for the entire season will be considered. 
The use of Avater was determined, in terms of inches used, for 
each period between successive samples, beginning with the one near- 
est seeding time and ending w^ith the one at or near harvest. The 
same method was used as in the preceding study. While the primary 
calculation was in terms of use for each period, the material so 
obtained was prepared for use by successive additions of the water 
from period to period. The sum at any sampling date represents 
the total quantity of water used by the crop from the first date of 
sampling until the date in question. The successive sums from date 
to date show the cumulative use of water during the growing season 
from zero at the beginning to the total quantity at harvest time. 
The data so assembled were further prepared for study by charting 
on cross-section paper with calendar dates as abscissa and quantities 
of water used as ordinates. The first sampling is indicated by a 
point on the zero line of ordinates at the given date. The second 
sampling is indicated by a point the abscissa of which is the date 
and the ordinate of which is the quantity of water used to that date. 
