44 
BULLETIX 1348, U. S. DEPARTMENT OF AGEICULTUBE 
The rate paid for labor, particularly, has much to do with deciding 
the most profitable size of power unit. The lower the wages paid 
the smaller will be the most profitable size of unit, and the higher the 
wages the larger wall be the most profitable size. This partially 
explains why smaller power units are more common where relatively 
low wages prevail. 
This same condition applies when the adding of additional types 
of power to the farm equipment is contemplated. Unless the added 
power equipment is used entirely to replace human labor, or a pro- 
portionate part of the original power eq[uipment is disposed of, there 
is danger o! the load factor of the original equipment being reduced 
Average Size of Unit in Horsepower 
4 5 6 7 
$2,500 
$2p00 
$\JSOO 
|l,000 
|500 
^500 
1,800 
1,300 1,170 1,090 
Human Labor in Hours 
1,000 
930 
Fig. 48.— Effect of size of power equipment on profit or loss in crop production, a represents maxi- 
mum profit on investment, b maximum profit on labor, c probable loss in total crop value attrib- 
uted to lack of equipment (100 acres composite crops in western Corn Belt) 
and the total operating cost increased thereby through increased 
overhead to a point where the total net returns from the farm will 
be actually decreased rather than increased, even though the unit 
cost of the new power is considerablv lower than in the case of the 
old. ' . ^^ J 
This is exactly what occurs frequently when a tractor is added 
to the power equipment of a farm, unless the farming system is 
so managed that a proportionate part of the animal power formerly 
used is disposed of. Although the tractor will, und.er most condi- 
tions, develop a given amount of power considerably cheaper than 
the same amount can be developed by animal power, care must be 
taken that the load factor of the remaining ammal power is not 
