The abundance of plant pests in the tropics, including weeds and disease, makes agriculture successful mainly in the plantation system, where needed control measures can be financed. The alternative is to move from deteriorated land to newer fields; this practice of shifting agriculture has also been common, because tropical soils lose their productive capacity so rapidly.
Leasing of expensive equipment is also an option but generally is less popular except with larger producers. In the developing countries, the trend towards adoption of the tractor as the fundamental unit of agricultural mechanization systems is sure to continue. However, for many small farmers in deprived regions the transition to tractor-based mechanization is not a realistic option due to the lack of finance and basic infrastructure. In this situation, a continued reliance on human energy and animal-powered equipment for tillage, planting and harvesting will prevail for the foreseeable future.

Early tractor designs were based on the concept of substituting mechanical pulling or draft power for the draft animal classically associated with pulling plows through the soil, operating reaper and binder machines through fields of corn, or mowers through fields of grass. Cumbersome steam powered engines were soon to be replaced by the more energy efficient and compact internal combustion engine. Animals used in these operations are increasingly being replaced by diesel and electric engines. In India in 1972 the number of stationary engines for power-intensive operations was about twenty times that of tractors.

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