28 BULLETIN 174, IT. S. DEPARTMENT OF AGRICULTURE. 



It may be safely stated that on most soils, when they are in fit 

 condition to be worked satisfactorily with horses, the modern gas 

 tractor will cause no injurious packing. The slippage of the tractor's 

 wheels in soft ground will probably be a more serious matter than the 

 packing. 



COMPARISON OF DIFFERENT SIZES OF TRACTORS. 



Table XYIII was prepared in order to ascertain what influence 

 the size of the tractor has on the results obtained with it. In this 

 table the tractors working in the State of North Dakota have been 

 shown separately from those in other States, and only figures furnished 

 by men having two seasons' experience have been shown, for reasons 

 already given. 



In tabulating the data by sizes of tractors it was found advisable 

 to group them to a certain extent, in order to have a sufficient number 

 in each class to give reliable averages. They were accordingly 

 arranged in five classes, as follows: (a) 8 to 14 horsepower, (b) 15 to 

 19 horsepower, (c) 20 to 25 horsepower, (d) 26 to 30 horsepower, and 

 (<?) 40 horsepower and over. 



These classes were arbitrarily arranged so as to place a considerable 

 number in each group and at the same time to keep the most common 

 sizes in separate classes. The average rating of the tractors in each 

 group is shown in the table. Thus, the 8 to 14 horsepower class 

 includes three common sizes: 8, 10, and 12, although there is not a 

 very large number of any of these sizes. The 15 to 19 horsepower 

 class consists almost entirely of 15 horsepower tractors. The 20 to 



25 horsepower class includes three common sizes: 20, 22, and 25, but, 

 like the first class, none of these sizes has a very large number. The 



26 to 30 horsepower class contains 30-horsepower tractors almost 

 exclusively. Xo machines with drawbar ratings between 30 and 40 

 horsepower were reported, and the tractors in the fifth class are 

 mostly 40-horsepower outfits, as very few larger sizes were reported. 



From this tabulation it would appear that the 15-horsepower 

 tractors have a longer life than those of other sizes. The length of 

 life seems to decrease slightly with the increase in size of tractors 

 over 15 horsepower., while for the smaller sizes it is a little less than 

 for the 15-horsepower tractors. The larger sizes of tractors lose more 

 time per day than those of 15 horsepower or less, the loss increasing 

 with the size of the tractor. The amount of special equipment 

 required increases with the size of the tractor until the 30-horsepower 

 size is reached. The amount of special equipment for the 40-horse- 

 power tractor is less than for those of 30 horsepower. Previous 

 tables have shown that the amount of work done by the 40-horse- 

 power tractor, as well as the load drawn, is not commensurate with 

 its rating, but no reason is known why the value of its equipment 

 should be less than for the 30-horsepower tractor. 



