AN APPKAISAL OF POWEK USED OX FABMS 
45 
reduced to the point where the increased cost of this power per unit 
of work done amounts to more than the saving accomplished through 
the use of the cheaper tractor power. Tables XIX and XX show 
the average cost of horse and tractor power on farms in the United 
States under 1924 conditions for different amounts of power produced 
annually; and Figure 49, based on these tables, illustrates graphically 
the reason for increased rather than decreased power costs that fre- 
quently takes place when a tractor is added to the farm equipment 
without disposing of a proportionate part of the original animal 
power equipment, as has been determined by many cost-accounting 
studies. 
Figure 50 shows the average crop-acres per farm worker in the 
various States. (The type of farming followed and the topography 
100 200 300 400 500 600 700 
Horsepower-Hours Developed Annually per Drawbar Horsepower 
800 
Fig. 49.— Effect of power load factor on cost per unit of power developed and effect of using horses and 
tractors on same farm under average conditions. An equivalent quantity of animal power should 
be disposed of when adding mechanical power to the farm equipment if the total power costs or 
the average cost per unit of all power utilized is to be reduced 
of the land available for farming are also factors that affect the 
size of power units used and the crop-acres per w^orker.) 
CHOICE OF POWER 
In choosing a type of power for farm use, the kind of farnaing 
followed and local conditions should be given first consideration. 
The power should, of course, be adapted to the kind of work to be 
done and the proportion of the total work on the farm that can be 
done by each kind of power under consideration is a matter of im- 
portance. Other factors that should be considered are the local 
cost of fuel, feed, etc., attention required by the power plant while 
in operation, care required while not in use and adjustments to be 
