MACHINERY COST OF FARM OPERATIONS. 
strain and wear on the working parts, than for walking plows. The 
average sulky plow in this section works 119 days and plows 250 
acres of land. Its cost new is over three times that of a walking 
plow; so that the overhead charges (replacement and interest) are 
five or six times as much per acre and over five times as much per 
day. The quality of work done by the sulky plow when properly 
operated is sufficiently superior to offset the greater overhead charges. 
The decrease in cost per acre with increase of annual use show very 
conclusively the advantage of covering large acreages per plow 
annually. 
The man with a small acreage may reduce his replacement cost 
somewhat by buying a lighter plow at a lower price, but even this 
does not eliminate the economic disadvantage under which he labors. 
Sulky plows have a higher average repair charge per acre than do 
walking plows, the average being $0,069. The sulky plows in general 
use cost from $40 to $45, so that the total repair charges during life 
average 42 per cent of the first cost of the implement. The repair 
charges decrease as the acreage plowed is increased, this being in 
part accounted for by the larger plows used on the greater acreages. 
THE SPRING-TOOTH HARROW. 
In Table IV is shown the performance of spring-tooth harrows. 
The spring-tooth harrow is an implement that gives long service in 
years and also in terms of acres harrowed. Because of the large 
areas covered daily, its life in days actually worked averages only 73. 
The spring-tooth harrow is an implement that is given very poor 
shelter, its form making it awkward to house, and it often lies out 
unprotected from one year's end to another. The repair charges on 
these harrows are also very small. From the standpoint of work 
done it is a machine of very high efficiency, averaging 1 1 years of life 
and 782 acres of work. Table IV, like all of the other tables, shows 
that the larger machines which do the most work annually also do the 
greatest total of acres and days before being worn out. 
Table IV. — Spring-tooth harrows — relation of work done annually to service and cost 
per acre and per day used on 1,169 farms. 
i of area covered annually acres. 
Number of records included 
Average area covered annually .acres . , 
Years of service rendered 
Acres covered during life 
Days actually used during life 
Average width of harrow feet. 
Cost when new 
Total cost of repairs during life 
Total interest during life at 6 per cent 
Total of depreciation, interest, and repairs 
during life 
Cost of spring-tooth harrow: 
Per day used 
Per acre harrowed 
1 to 40. 
41 to 80. 
81 to 150. 
151 and 
Average. 
417 
29.5 
11.6 
342.0 
39 
5.7 
408 
61.0 
11.1 
677.1 
74 
6.5 
276 
111.6 
10.2 
1,138.3 
222.3 
8.9 
1,978.5 
149 
10.4 
$15. 00 
6.15 
5.92 
$17.00 
8.88 
6.22 
$20. 00 
9.28 
6.73 
$24. 00 
10.86 
71.1 
11.0 
782.1 
73 
6.9 
$17. 50 
8.25 
5.83 
27.07 
36.01 
43.02 
31.58 
$0. 794 
.079 
$0. 433 
.047 
$0. 375 
.032 
$0. 288 | $0. 432 
.021 ' .043 
13345°— Bull. 338—16 2 
