22 BULLETIN 1139, U. S. DEPARTMENT OF AGRICULTURE. 
vidual sections of soil in their water relations without lack of mois- 
ture being the determining factor. 
In the first foot plat, C or D closely approaches the other plats in 
its moisture relations. The chief difference has been a slightly greater 
number of cases where the soil was filled with moisture and all avail- 
able moisture used (F), and a correspondingly lesser number of cases 
where the soil was only partly filled with water and all the water 
used (PD). The soil was dry at harvest practically the same propor- 
tion of the time as on the other plats. 
The data for the second foot of plat C or D almost duplicate those 
from the first foot. This seems to indicate that the second foot of 
soil is normally filled with roots when moisture is present and that 
water is used as freely from this section as from the soil above it. 
The difference shown between the second foot of plat C or D and that 
of the other two plats appears to be solely due to the quantity of 
moisture present in the soil. 
The third foot of soil evidently differs but little from the first 
and second in regard to the demands which the wheat crop has 
made upon it for moisture and the extent to which it has respond- 
ed. It is only slightly lower in the proportion of time that the soil 
has been filled with water and the water all removed by harvest. 
This decrease is accounted for by the fact that the soil has not 
always been moist to a depth of 3 feet even in fallow. The same 
decrease in- the proportion of the time the available water has not 
all been used is found in this plat as in plats A and B. 
In the fourth foot full use of water has taken place only 43 per 
cent of the time. That this is due to lack of penetration of water rather 
than to other factors is indicated by the greater percentage of cases, 
as compared with the upper sections, when the soil was dry or partly 
dry. There is, however, a small increase in the number of times 
the available moisture has been only partly exhausted (PW) and a 
corresponding decrease in the percentage of the time all available 
moisture has been removed from the soil before harvest. 
In the fifth and sixth foot sections full use of the soil is not fre- 
quent. There is a marked increase in the proportion of the time 
the available water has been only partly used (PW) and in the 
number of times no use has been made of available moisture (OW). 
There are, too, an increasing number of cases where no available 
moisture has been present (OD). In the fifth foot sections available 
water has been present in the soil 81 per cent of the time. In 47 
of this 81 per cent the water has been unused or only partly used 
before harvest. In the sixth foot section available moisture has 
been present 67 per cent of the time. Only 13 of this 67 per cent 
represent cases where all available moisture was removed from the 
soil. The remainder of the time the available water was only partly 
removed or not used at all. 
As a whole, there is a greater use of water in the lower depths 
of plat C or D than in the other two plats. This is largely due to 
the fact that water has been present in the fifth and sixth foot 
sections more frequently. The quantity of water used by the crop 
from these depths in an average year must be small, since full use 
of water is so infrequent. 
