46 BULLETIX 99*, U. S. DEPARTMENT OE AGRICULTURE. 
were obtained. Interest was charged at 6 per cent on the average 
investment. 
The total annual cost for depreciation, repairs, and interest was 
divided by the number of days of work done by the tractor during 
the year to obtain the cost per day of work for these items. To this 
was added the cost of fuel and oil used per day to obtain the total 
cost per day of use, and the sum divided by the number of acres 
covered in a day to obtain the acre-cost of using the tractor on the 
different operations. Xo charges for shelter, insurance, and taxes 
are included. These charges would amount to only a small per- 
centage of the total cost, however. 
In the following discussion the 2-plow and 3-plow machines are 
treated separately in order to afford a comparison between the two 
sizes. On all the 286 farms there were only 8 tractors of sizes other 
than these (see page 9). and no figures for them are given. The 
286, however, are included in every case in the figures for "All 
tractors." 
First cost. — The average first cost of the 174 2-plow machines was 
$972; of the 104 3-plow machines, $1,354, and of the entire 286, 
$1,140. These figures include the first cost of all extra equipment, for 
the tractors themselves, but do not include the cost of new implements 
purchased. Every farmer owned a tractor plow and a majority had 
also purchased tractor disks. Some had also procured belt machines 
for use with the tractors. On the average the amount which had 
been spent by the owners of the 2-plow tractors for implements and 
machines was $271, and by the owners of 3-plow tractors $430. For 
all farms this item amounted to an average of $343. 
Life. — The average estimated life of the 286 tractors was 6.7 years. 
The average of the estimates for the 2-plow tractors was 6.4 years, 
and for the 3-plow 7.0 years. 
Table 31. — Estimated life of tractors. 
Estimated life of tractor (rears). 
^Number of owners 
estimating life of 
tractor as speci- 
fied. 
. 
Owners Owners 
of 2-plow of 3-plow 
tractors, tractors. 
3 
4 
37 i 
3 
5 
37 
51 
33 
17 
22 
21 
A . . 
1 
5 
30 
6 
13 
7 
13 
8 
14 
9 
9 
10 
16 
11 
1 
12 
1 
3 
15 
3 
