30 BULLETIN 174, U. S. DEPARTMENT OF AGBICULTUBE. 
These facts, together with others shown in the tables, seem to 
indicate that the 15-horsepower tractor is giving better average 
results than any other size. It will be seen that the 15-horsepower 
tractors also give more favorable operating figures than any other 
size of tractor. 
While the figures for the different sizes of tractors in Table XVIII 
show other variations, it is believed most of them are due to causes 
other than the size of tractor. For example, the number of horses 
kept, the percentage of night work done, and the percentage of custom 
work done, increase with the size of the tractor, but this increase is 
probably due largely to the fact that the larger tractors are usually 
found on the large farms, as will be noticed by the average sizes of the 
farms shown in the table. 
SIZE OF FARM. 
In North Dakota, tractors are seldom found on farms of less than 
320 acres, the average size of the farm on which tractors are used in 
that State being between 700 and 800 acres. In other States, par- 
ticularly in Iowa, tractors are frequently found on farms as small as 
160 acres. As will be seen from Table XIX, however, a very large 
percentage of tractor owners do custom work with the tractor, indi- 
cating that the home farm does not furnish sufficient work to keep 
the tractor busy during the entire working periods. It will also be 
noticed that the farms ol less than 480 acres show a greater percentage 
of owners doing custom work than do those of larger size. 
Table XIX was prepared in order to ascertain what effect the size 
of the farm had upon the results obtained from the tractor. The 
figures used in its preparation are those furnished by tractor owners 
in North Dakota who have used their outfits for two seasons. A 
similar table for other States was not made because of the many types 
of farming which would be represented, as it was believed the many 
and varying factors involved would vitiate the results obtained. 
In North Dakota, however, as has already been stated, the conditions 
are very similar throughout the State, and the averages in the table 
are believed to show the relation of the size of the farm to the results 
obtained, as far as it is possible to do so. 
In this connection, attention is invited to the fact that there is a 
close relation between the size of the tractor and the size of the farm, 
the larger tractors usually being found on the large farms. In both 
the tabulation by size of farm and by size of tractor, therefore, it is 
impossible to determine to just what extent each of these factors 
influences the result. 
From the table it would appear that slightly better results are being 
obtained on the larger farms. It will be noticed that the' percentage 
of owners reporting that the tractor is a good investment is greatest 
