10 
BULLETIN 338, U. S. DEPARTMENT OF AGRICULTURE. 
The approximate cost of new spring-tooth harrows of the average 
sizes shown in Table IV is $17.50. The replacement cost for each 
time an acre is harrowed with the spring-tooth harrow is $0,023, and 
the interest charge per acre averages about $0,007. 
The repair charges on spring-tooth harrows are very small per acre 
covered, being only $0,011 on the average. The total repairs made 
during the life of the average spring-tooth harrow cost about 47 per 
cent as much as the harrow itself when new. 
THE SPIKE-TOOTH HARROW. 
The spike-tooth harrow (Table V) is not hi such general use in this 
section as is the spring-tooth harrow. It is a longer-lived implement 
than the spring-tooth harrow by about 27 per cent in terms of years, 
but it does about one-third less work in terms of acres. The class of 
soils on which the spike-tooth harrow can be used is lighter, and the 
character of work required of it is much less severe. In this section 
the spike- tooth harrow lasts an average of 14 years, doing 43 days 
of work and covering 676 acres of land. Like the spring-tooth har- 
row and walking plow, it is a low-priced implement, so that the 
interest charge, as well as the machinery or replacement charge per 
day and per acre, is relatively low. 
Spike-tooth harrows of the average size given in Table V cost when 
new about $10.50. The average cost for harrowing an acre is $0,016 
for replacement and $0,007 for interest. 
Table V. — Spile-tooth harrows — relation of work done annually to service and cost per 
acre and per day used on 824 farms. 
Range of area covered annually acres. . 
1 to 20. 
21 to 40. 
41 to 60. 
61 to 100. 
101 and 
over. 
Average. 
193 
15.7 
18.4 
288.9 
24 
6.3 
301 
33.3 
13.6 
452.9 
37 
7.3 
151 
52.8 
12.9 
681.1 
40 
9.5 
138 
86.4 
12.4 
1,071.4 
64 
10.6 
41 
166.6 
10.0 
1,666.0 
79 
13.8 
Average area covered annually acres. . 
Years of service rendered 
48.3 
14.0 
676.2 
43 
Average width of harrow feet. . 
8.5 
Cost when new 
87.75 
2.76 
4.42 
$9.00 
4.22 
3.94 
$12. 00 
3.35 
5.29 
$13.00 
7.32 
5.21 
$17. 00 
7.70 
5.60 
$10. 50 
Total cost cf repairs during life 
4.76 
Total interest during life at 6 per cent 
4.76 
Total of depreciation, interest, and 
14.93 
17.16 
20.64 
25.53 
30.30 
20.02 
Cost of spike-tooth harrow: 
Per day used 
$0. 622 
.052 
SO. 464 
.038 
SO. 516 
.030 
SO. 400 
.024 
$0. 383 
.018 
SO. 465 
.029 
The spike- tooth harrow is an implement having lower repair 
charges per acre than does the spring-tooth harrow, the average 
being only $0,007 per acre. It is not subjected to the severe strains 
met by the spring-tooth harrow, as the latter is used on much heavier 
and more stony land where the spike-tooth harrow would not work 
