8 BULLETIN 1139, II. S. DEPARTMENT OF AGRICULTURE, 
available moisture lias been removed by harvest time. This represents full 
use of water and soil and is indicated by the symbol F. 
(2) A condition where available moisture was present in the soil during the 
growing season and where the moisture content was reduced but not ex- 
hausted at harvest. It is indicated by the symbol PW and represents partial 
utilization of the moisture in the soil and the presence of available water in 
the soil at harvest. In some cases, particularly in the first foot, it may in- 
dicate a condition where all of the available water has been removed at some 
time before harvest but where precipitation near harvest time has again 
raised the moisture content above the minimum point. 
(3) A condition where the soil was only partly filled with moisture and all 
of the available water was removed by harvest. This is indicated by the 
symbol PD and represents partial use of water and a soil dry at harvest. 
(4) A condition where available moisture was present in the soil but was not 
used. It is designated by the symbol OW representing zero use, although 
water was present. In a very few cases, particularly in the* first foot of soil, 
it indicates a year with so much rain neur harvest time that the soil at harvest 
is at its field carrying capacity. 
(5) A condition where no moisture has been used and no available moisture 
has been present in the soil during the growing season. This is designated by 
the symbol CD, representing zero use of water and a dry soil. 
It is apparent that there is no definite line of demarcation between 
these classes, In some cases the classification of a foot section of soil 
might have been changed by a moisture determination at some date 
when none was made. In general, however, the designations give 
a very close approximation of the status of any foot section of soil 
for the season, and the large number of cases makes up to a great 
extent for the lack of refinement of data. 
Making application of these symbols to the data illustrated in 
Figure 1, the first foot section would be classified as F; the second 
as PD ; and the third, fourth, fifth, and sixth sections as OD. 
In Table 1 these symbols are used to indicate the moisture history 
of each foot of soil each year at each of the 17 stations. The yield 
in bushels per acre is given for each plat each year, to indicate to 
what extent drought injury has reduced the yield of the different 
plats, as practically all low yields were the result of drought injury. 
As stated before, years when some factor, such as hail, was respon- 
sible for a low yield are not included. Years when the moisture 
determinations were so infrequent as to leave a material doubt as 
to the classification of the different foot sections of soil are likewise 
omitted. 
It must be understood that close comparisons can not be made be- 
tween corresponding plats at different stations in any one year. The 
stations are in most cases rather widely separated and subject to 
local conditions of rainfall and other climatic factors. In many cases 
the differences between two stations, even in one State, during the 
same season may be greater than those between different seasons at 
one station. Each station must be considered as a unit both in soil 
and climate in this study. 
No attempt will be made to describe the soil of the different sta- 
tions further than is necessary to indicate the facility of its pene- 
tration by water and roots. Peculiarities that inhibit the soil from 
functioning in these respects are perforce noted. 
A brief summary of the soil utilization at each station will be 
made, and points of special interest considered. 
