52 
BULLETIN 997, U. S. DEPARTMENT OF AGRICULTURE. 
Effect of amount of work done per year on cost of using tractors. — 
Table 39 shows the cost per day and per acre of plowing with the 
2-plow machines, classified according to number of days of work 
during the year. Table 40 gives similar information for the 3-plow 
tractors. Annual depreciation, repairs, and interest charges did not 
increase in proportion to the amount of work done for either size of 
machine, and consequently the daily costs of these items were least 
for the machines which did the greatest amount of work. 
For each size the average daily charge for depreciation, interest, 
and repairs on the tractors which were used 50 days or more during 
the year was less than a third of that for machines which were used 
less than 20 days, and the cost per acre of power for plowing done by 
the machines which did over 50 days' work was less than a half the 
cost for those which did less than 20 days' work during the year. 
Such differences are reflected directly in the cost per acre or per 
bushel of producing crops and show how the man whose farm is large 
and so organized that he obtains large use from his equipment can 
produce at low cost. 
These figures do not indicate, however, that the farmer should 
endeavor to use his tractor as many days during the year as possible 
simply for the sake of reducing the cost per day of operating it. 
Even though the cost per day decreases rapidly with increased use, 
the total cost per year must increase. For instance, the cost per 
day of power for plowing with the 2-plow tractors which were used 
20 to 30 days during the year was $13.45. On the average these 
machines did approximately 25 days of work during the year and 
the total cost per year of use was $325 to $350. The cost per day of 
use of the 2-plow machines which did from 40 to 50 days of work 
during the year was only $10.81, but the total cost per year was 
$475 to $500. 
These figures further indicate that, since the number of days of 
work has only a slight effect upon the total annual charges for depre- 
ciation, interest, and repairs, the tractor owner need consider only 
the cost of fuel and oil when deciding whether or not to use his 
machine for operations where its use is of doubtful value. 
Table 39. — Effect of number of days of work per year on cost of using 2-plow tractors for 
plovjing. 
Number 
of 
tractors. 
Annual cost. 
Daily cost 
(depre- 
ciation, 
interest, 
and 
repairs). 
Cost for plowing. 
Days of work per 
year. 
Depre- 
ciation. 
Interest. 
Repair 
and 
upkeep. 
Total. 
Per day. 
Per acre. 
Less than 20 
37 
41 
54 
25 
17 
$150 
158 
168 
167 
195 
$34 
35 
34 
33 
35 
$30 
37 
39 
61 
32 
$214 
230 
241 
261 
262 
$14. 50 
8.90 
6.97 
6.08 
4.60 
$19. 14 
13.45 
11.49 
10.81 
8.55 
$3.00 
20 to 29.9 
2.24 
30 to 39.9 
1.76 
40 to 49.9 
1.76 
50 and over 
1.26 
