6 BULLETIX 218, IT. s. DEPARTMENT OF AGRICULTURE. 
Summer tillage is of the intensive type. The land lies fallow for 
a year. It is kept clear of weeds and as far as practicable a mulch 
is maintained on it during the time between the harvest of the pre- 
ceding crop and the seeding of the oats. This involves a period in 
some cases as long as 21 months. In some cases it is necessary to 
plow the land more than once during this period, in order either to 
maintain a surface receptive to water and that will resist blowing or 
to prevent the growth of weeds. The long period of summer tillage, 
together with the intensive methods practiced, have made this an 
expensive system of production. Experiments are under way to 
determine the most economical method of summer tilling. Indica- 
tions are that a less intensive method than that practiced in the work 
here reported will give practically as good returns. 
The yields given in these tables begin with the second year of crop 
production at each station. The first year's crop is produced on 
land uniform in its treatment. 
In cases where an entire crop has been lost by hail or other agency 
that could not possibly be overcome by cultivation the years are not 
considered in computing averages. Such failures must of course 
enter into the final results of agricultural endeavor. They are, how- 
ever, of such uncertain occurrence that the series of years here con- 
sidered is too short to permit an attempt to establish their normal 
frequency for any locality. This is in effect what would be done by 
including them in averages. It is believed that less error is intro- 
duced by recognizing their occurrence and excluding them from aver- 
ages. When the loss of a crop is due to conditions that might pos- 
sibly have been overcome by cultural practices a zero yield for that 
year is included in the calculations. 
Embodying the basic data given in Tables II, III, and IV, the 
second part of the table for each station has been compiled. In this 
are brought together in summary form the yields detailed in the first 
part of such table. The value of the average yields thus obtained is 
calculated and given, together with a computation of the cost of pro- 
duction. The last line of the table gives the profit or loss resulting 
from the production of oats by the method stated. Loss is indicated 
by the minus sign. In this second part of each table there are two 
general headings : "Tillage treatment" and "Previous crop." Under 
the first general heading the plats are grouped entirely by treatment 
without considering the previous crop. Under the second heading 
treatment is not considered, and the grouping is entirely governed by 
the crop immediately preceding the oats. This really makes two 
tables combined in one, with subdivisions common to both. 
Figure 2 shows a diagram of the dry-land rotation field at the 
Belle Fourche Field Station. This station being a representative 
one will serve to illustrate the general scheme and plan of work. 
