The agricultural tractor (tractor) is the most important machine of a farmer, with which he performs numerous tasks. A tractor is capable of hauling, mounting, and powering attachments. The first tractors, steam-powered and internal combustion, were invented during the second industrial revolution. Later, the development of genetics and chemistry led to the explosion of agricultural production.
There are many manufacturers on the market with a range of tractors in terms of size and horsepower. The modern farmer should consider many parameters before settling on the right one.

The Size of the Farm 
The size of the farm is the key factor in choosing an agricultural tractor. In the US, the average farm is 180 hectares and rising (1). In the European Union, the average is 16.6 hectares, while in some members, the farmers who own arable land of fewer than 5 hectares represent 77.3% of the total (2). Today, there are tools and spreadsheets to calculate the required power of a tractor. Sumner and Williams created such a tool from the University of Georgia (3). In the file they created, the user can add some hypothetical parameters such as: farm size (100 hectares), tillage tool (heavy-duty disc harrow), available working hours (40 hours), soil type (clay) as well as some more.

Figure 1. Printscreen from the Sumner and Williams program shows some of the parameters we choose and the horsepower result.

Land fragmentation
Large plots of land favor the mechanization of crops, making the work of machines more efficient as they do not consume unnecessary fuel for transportation and save time. In other words, the use of larger machines is favored. On the contrary, the subdivision of the land leads to small farm roads and fences that reduce the mobility of tractors and waste time. As a result, smaller tractors are preferred. In many countries, like Greece, Malta, and Romania, the phenomenon of parcel fragmentation is observed (4, 5).

Horsepower Requirements of the Equipment
Implements like plows, rippers, and stone crushers require comparatively increased horsepower, either engine or PTO (Power take-off). Machines such as fertilizer spreaders, small transport buckets, ditchers, and inter-row cultivators require relatively less powerful motors.

Task Execution Speed needed
A factor affecting the choice of a tractor is the need to perform tasks quickly. A short window of time to perform tasks such as seeding, haying and harvesting require faster farm coverage; therefore, larger tractors with larger implements. Cutting hay, for example, is a process that sometimes must be carried out immediately because of impending rainfall, as it requires cutting the forage, turning it, and finally baling. Farmers who are also stock breeders have limited time daily due to animal care.

Investment for the future
Many farmers choose larger tractors than indicated to anticipate future investments in larger acreage crops. This, in a growing farm, is correct. However, the choice should be made with reasonable criteria, as a larger agricultural tractor requires more capital to acquire, operate and maintain, possibly absorbing valuable capital. Apart from future needs, farmers choose larger tractors as they believe the excess power will be needed at some demanding time, such as a heavy load or a difficult job.

Economies of Scale
In today’s production model, each farmer usually has his agricultural tractor. It makes sense as it gives freedom of movement to the grower to change crops and carry out the necessary work when he sees fit. However, producer groups and cooperatives following specific crops can purchase larger agricultural tractors making the work more cost-effective and achieving economies of scale. By replacing several small tractors with a larger one, the economy is achieved both in the purchase of the machine and in its cycle of use.

Farm Contracting
Many farmers who own a tractor choose to undertake work on other farmers’ properties. This way, they get more use out of the machine, making the investment more profitable and giving them an additional supplemental income. In countries such as the United Kingdom, there are organized groups that are fully engaged in the subject of crop contracting. A grower with such a business will usually purchase a higher-horsepower tractor.

Special applications of an agricultural tractor
Certain uses of the agricultural tractor require special adjustments or specifications to it. Cultivation of the land, apart from the plains, occurs in mountainous areas with sloping lands. In such terrains, a tractor that uses crawlers for movement instead of wheels can be chosen for greater ground contact and traction. Crawlers are also suitable in plains (both on tractors and combines) where muddy soil is a frequent problem. A change in the wheels is also required in other cases, like in rice cultivation, where thin metal wheels a few centimeters thick are used. In orchards and vineyards, the distances between the lines, in some cases, are narrow, so special tractors are required. The grower can find high-power tractors (100 hp) and a width of only 1,5 m in the market. The agricultural tractor can also be used in other farm work requiring a front loader. With this additional machine, materials, manure, and hay can be loaded. It is a function that must be foreseen in advance as front hydraulics are required on the tractor. Finally, an additional feature of modern agricultural tractors is the possibility of adjusting implements in their front part. However, an extra hydraulic system and PTO should be installed.

Figure 2. PTO system on a tractor where the lift arms can be distinguished

Proximity to Brand Agency and Resale Value
Finally, a factor in choosing an agricultural tractor, mainly in terms of manufacturer and less in terms of size and horsepower, is proximity to a certified and reliable repair shop. Modern farm tractors are complex machines with many electronics and mechanical differences between manufacturers. For this reason, the maintenance workshops repair only certain brands. The grower should choose a manufacturer that is or has an official agent (store) within a short distance of his/her farm. This way, it will be easier to find spare parts for the tractor and perform maintenance and repairs.

The manufacturer’s company influences another important financial factor; that of resale. When purchasing a tractor, the producer calculates the purchase cost, operating costs, and the profit he will have when he resells it in the future. In addition to the condition of the machine and the hours of use, the brand has a significant influence on the selling price. This is because some manufacturers have better reputations for their capabilities, credibility, aftermarket availability, and fuel consumption.

From the above, the choice of an agricultural tractor is a complex decision that should be made with the proper criteria of ergonomics and economy and not with hasty calculations.



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