Agricultural Machinery

I

Introduction

Agricultural Machinery devices used to till soil and to plant, cultivate, and harvest crops. Since ancient times, when cultures first began cultivating plants, people have used tools to help them grow and harvest crops. They used pointed tools to dig and keep soil loosened, and sharp, knifelike objects to harvest ripened crops. Modifications of these early implements led to the development of small hand tools that are still used in small-scale gardening, such as the spade, hoe, rake, trowel, and scythe, and larger implements, such as plows and larger rakes that are drawn by humans, animals, or simple machines. See Agriculture.

Much of the world's arable land is still tilled under conditions that do not permit use of expensive modern machinery. However, modern machinery is used extensively in the United States, Canada, the United Kingdom, Western Europe, and Australia.

Modern large agricultural implements, adapted to large-scale farming methods, are usually powered by diesel- or gasoline-fueled internal-combustion engines. The most important implement of modern agriculture is the tractor. It provides locomotion for many other implements and can furnish power, via its power shaft, for the operation of machines drawn behind the tractor. The power shafts of tractors can also be set up to drive belts that operate equipment such as feed grinders, pumps, and electric-power generators. Small implements, such as portable irrigators, are often powered by individual motors.

II

Implements for Growing Crops

Many types of implements have been developed for the activities involved in growing crops. These activities include breaking ground, planting, weeding, fertilizing, and combatting pests.

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Ground is broken by plows to prepare the seedbed. A plow consists of a bladelike plowshare that cuts under, then lifts, turns, and pulverizes the soil. Modern tractor plows are usually equipped with two or more plowshares so that a wide area of ground can be broken at a single sweep. Harrows are used to smooth the plowed land and sometimes to cover seeds and fertilizer with earth. The disk harrow, which has curved, sharp-edged steel disks, is used mainly to cut up crop residues before plowing and to bury weeds during seedbed preparation. Rollers with V-shaped wheels break up clods of soil to improve the aeration of the soil and its capacity for taking in water.

Some cereal crops are still planted by broadcasting seeds—that is, by scattering the seeds over a wide area. Machines for broadcasting usually consist of a long seedbox mounted on wheels and equipped with an agitator to distribute the seeds. Broadcast seeds are not always covered by a uniform or sufficient depth of soil, so seeding is more often done with drills, which produce continuous furrows of uniform depth. Specialized implements called planters are necessary for sowing crops that are planted in rows, such as corn. Corn planters and other similar machines have a special feed wheel that picks up small quantities of grain or separate kernels and places them in the ground.

Fertilizer can be distributed during the winter or shortly before seeding time. Commercial fertilizers are commonly distributed, along with seeds, by drills and planters. Manure is distributed most efficiently by a manure spreader, which is a wagon equipped with a bottom conveyor to carry the fertilizer back to a beater attachment, which disintegrates it and then scatters it on the ground.

After crops have begun to grow, a cultivator is used to destroy weeds and loosen and aerate the soil. A flame weeder, which produces a hot-air blast, can be used to destroy weeds growing around crops, such as cotton, that have stems of tough bark. The weeds are vulnerable to the hot air, but the tough stems protect the crops from damage. Chemical herbicides applied in the form of a spray or as granules are used extensively for destroying weeds (see Weed Control).

Insecticides are applied to soil and crops in the form of granules, dust, or liquid sprays (see Pest Control). A variety of mechanical spraying and dusting equipment is used to spread chemicals on crops and fields; the machinery may be self-powered, or drawn and powered by a tractor. In areas where large crops of vegetables and grain are grown, airplanes are sometimes used to dust or spray pesticides.

Chemical pesticides are used in nearly all modern farming operations. However, increasing concern over the harmful effects that pesticides may have on the environment has led to the use of alternative forms of pest control. For example, farmers use crop rotation to prevent pests that feed on a certain crop from becoming entrenched and infesting the field. Also, certain pests are controlled by introducing an organism that damages or kills the pests, but leaves the crops unharmed. Finally, scientists genetically engineer crops to be more resistant to troublesome pests. See also Environment.

III

Implements for Harvesting Crops

Most cereal crops are harvested by using a combine—a machine that removes the fruiting heads, beats off the grain kernels, and cleans the grain as the combine moves through the fields. The cleaned grain is accumulated in an attached grain tank.

Corn is harvested by a combine or a machine called a corn picker. As the corn picker moves along the rows, the ears are picked from the stalks and are husked. The ears are then transferred either to a sheller, which removes the kernels from the ear, or to a wagon trailing behind the machine.

Hay harvesting usually requires several steps. First, the hay is cut close to the ground with a mower. After drying in the sun, most hay is baled. In baling, the pickup baler lifts the hay to a conveyor that carries it to a baling chamber, which compresses the hay into bales weighing up to 57 kg (125 lb) and ties each bale with heavy twine or wire. A machine called a field chopper cuts down green hay or field-cured hay for use as animal feed. After being cut down, the hay is stored in a silo and allowed to ferment; this type of animal feed is nutritious and resistant to spoilage. Alfalfa and other legume hay is harvested in some areas with a hay cuber. This machine cuts the plants close to the ground and, after field curing, chops them into a fine mash and compresses the mash into cubes that are more easily shipped and stored than are bales.

Specialized machinery is used to harvest large root crops such as potatoes and sugar beets. Mechanical cotton pickers and strippers are used in harvesting nearly all of the cotton grown in the United States. Mechanical pickers have rotating spindles that twist the cotton fiber from the boll. Before picking, the leaves of the cotton plant are removed by means of a chemical defoliant spray. Light-boll, stormproof cotton is harvested by strippers that comb or brush the cotton from the plant and lift it into a trailed wagon. More efficient mechanical pickers continue to be developed. See also Cotton Gin.

Specialized machines are also used to harvest fruits and vegetables. Some mechanical fruit pickers that are used to harvest deciduous tree fruits, such as plums, cherries, and apricots shake the fruit tree, causing the fruit to fall onto a raised catching frame that surrounds the tree. Nut crops can also be harvested in this manner. In addition, plant breeders use modern methods such as genetic engineering to develop varieties of fruits and vegetables that are tougher and hardier for easy harvesting by machines. For example, a variety of tomato has been bred for a tougher skin that reduces bruising.

In addition to the kinds of agricultural machinery being used on large modern farms, a wide range of automated devices became available to farmers through the revolution in electronics. Today, an increasing number of farmers use personal computers to keep records, manage their farms' business, and connect to information centers that can help them solve the problems they confront in the operation of their farms.

IV

Practical Significance

Use of agricultural machinery substantially reduces the amount of human labor needed for raising crops. The average amount of labor required per hectare to produce and harvest corn, hay, and cereal crops has fallen to less than a fourth of what was required only a few decades ago. Mechanization, together with improved crop varieties, better techniques, and more efficient food processing, has enabled the small percentage of the U.S. population living on farms to produce enough food to feed the nation.

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