All of my Grandpas Fancy New Tractors

Human and animal powered mechanization systems (Figures 2 and 3) are described in detail in Human and Animal Powered Machinery, EOLSS on-line, 2002. The drudgery, long hours and low pay typically associated with these systems make rural life in the developing countries an unattractive career for young men and women.
Because mechanization of harvesting is directly dependent on labor costs, it is rarely profitable in low-wage countries. The higher the control intensity of the operation, the higher must labor costs be to warrant using a machine. Crop husbandry. Weeding and cleaning of crops, fields, and orchards are control-intensive operations. In animal systems, people go on weeding by hand long after the introduction of the plow and cart-until rising wages make herbicides profitable.

Tractors were mainly used for tillage and as power sources for stationary machines such as threshers, saws, silo fillers, and choppers. The same pattern of tractor use was common in Europe until about 1960 and is now common in South Asia, Southeast Asia, and China. The only differences are that direct power takeoff has replaced the belt and pulley and that tractors are now more frequently used for transport. Although modern tractors are more efficient than prewar ones, wages in Asia are much lower than in the prewar United States. Asian countries are therefore likely to make continued use of animals along with tractors, until rising wages make the animals' drivers, and thus the animals, too expensive. On a smaller scale, responses have been equally rapid in economies as diverse as Thailand and Mexico. In the developed world, government policy toward mechanization has been confined to patent laws for enforcing innovator's rights and encouraging disclosure; testing of machinery, support of standardization measures, and dissemination of information; and support of agricultural engineering education and some university-based research. These are clearly appropriate interventions. Unlike the case of agricultural research, it is difficult to make a case for any further intervention on the grounds of economic welfare. Where governments have intervened more, they have either had little success, as in numerous publicly funded research efforts, or they have made wrong or controversial choices.'

Early methods of weed control included mowing, flooding, cultivating, smothering, burning, and crop rotation. Though these methods are still important, other means are perhaps more typical today, particularly the use of herbicide (plant-killing) chemicals. Another technique is to introduce insects that attack only the unwanted plant and destroy it while leaving the crop plants unharmed.
Agricultural mechanization has involved the partial or full replacement of human energy and animal-powered equipment (e.g. plows, seeders and harvesters) by engine-driven equipment. Most of this is tractor driven and to a lesser extent self-propelled equipment (including harvesters, sprayers, fertilizer applicators, planters and seeders). Agricultural mechanization has been pioneered in North America and Europe and more recently in Japan, and is now spreading rapidly throughout the world. Notwithstanding such progress, a significant element of human and animal powered mechanization remains, particularly in the poorer regions of the world.

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Pakistan not only subsidized big tractors, but also prohibited imports of all but a few brands.12 Its trade policies restricted imports of many smaller machines and implements and made it almost impossible for small innovating firms to import foreign designs for local adaptation.The process of burning fuel to generate power in a tractor engine is known as the Otto cycle. It involves four basic steps: intake, compression, power, and exhaust. During the intake stroke, a mixture of fuel and air is drawn into the cylinder through an intake valve. During the compression stroke, the mixture is compressed by the upward movement of the piston. During the power stroke, the compressed mixture is ignited by a spark plug, and the explosion pushes the piston down, generating torque. During the exhaust stroke, the exhaust gases are expelled through an exhaust valve.

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