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number of variations survive. In cultivation itself, as above defined, there is no selection.

The principal effect of cultivation on the growth of wheat is through its influence upon the physical condition of the soil, to which great importance is attached. By physical condition is meant friability or openness, capacity for absorbing and retaining water and heat, and permeability to roots. Air, which is necessary to the roots, is excluded by hard, water-soaked, baked or puddled soils, and such soils are also impermeable to roots. Stirring or cultivating the soil enables the air to circulate and the roots to penetrate through it. Tillage has been known to increase the yield of wheat over eight bushels per acre.1 Richardson claimed that it increased the nitrogen content of wheat. Generally about 50 per cent of the volume of soils is empty space. That is, in one cubic foot of soil there is about a half a cubic foot of space into which air and water can enter.

The Motor Power first utilized was the muscular energy of man himself. Its application requires the least intelligence. The abundance of human labor, and hence its cheapness, coupled with a lack of intelligence to utilize other forces, are conditions still existing in vast regions of the earth where it is impossible for any other motor power to compete successfully with man himself. India, largely using human labor, often at a cost of but 4 to 8 cents per day, has been so successful in competing with more civilized nations using other forms of power as to assume fourth rank among the wheat raising nations, and to be able to undersell many of them in the world markets. Hand labor is used almost exclusively in raising wheat in China, Japan, Siam, Syria and Colombia, and very extensively in Egypt and parts of Greece, Spain, Mexico, and some of the South American republics.2

Animal Power.—The first one of the forces of nature which man subdued and utilized in relieving himself of some of the drudgeries incidental to agriculture was that of the domesticated beast. There are no marked periods of progress in this. Animal power is by far the most universally used in agricultural operations. As a rule, oxen are found in communities

1 R. C. Bui. 56. p. 12.

'U. S. Dally Consular Repts., Oct. to Deo.. 1903.

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less developed agriculturally and horses in the more developed ones. For example, oxen were preferred to horses in England from 1250 to 1650.

Steam.—After nearly two centuries of projection and invention, steam was successfully used for agricultural operations in England in 1832. The system adopted was that of dragging the implements by the aid of pulleys and a cable revolved by a stationary steam engine. This method in improved form is still found in Europe. The movable engine appeared before 1850. In the United States, activity in the invention of steam plows began in 1861, and it was perhaps entirely confined to the use of the traction engine. On the Pacific coast, steam is used quite extensively in the cultivation of wheat, especially on the larger farms. In Germany and Hungary there was about one steam plow to every 10 small plows in 1900. There have also been experiments with electricity as a motor power in agriculture.

Plowing.—The first plow was simply a "sharpened piece of wood or the crotched limb of a tree," and was evolved from the hoe. Some of the earliest plows were drawn by two men, while two others kept them in the ground. The form represented on Egyptian monuments (3,000 B. C.) is an improvement on the hooked stick. Chinese historians say that the first plows in China were made 2,737 B. C. The plow described by Homer was a composite piece drawn by oxen or mules. The early Romans had no cast steel or iron, and their implement was essentially like that of the Germans. The first use of metal on a plow is unknown, but before the time of Christ the Romans yoked the steer to one with a "shining share." The ancient Egyptians and Assyrians had plows pointed or edged with iron. These primitive implements turned no furrow, but simply stirred the ground. Those of the Greeks 2,000 years ago had wheels supporting the beams, and similar forms are found depicted in Saxon manuscripts.

The rude primitive plow seems to have been almost universally the first agricultural implement drawn by beasts of burden. The constancy of the type among different peoples is remarkable. Under uncivilized or frontier conditions it nearly always appears, and its persistence is very great. In the United States plows were worked in Virginia as early as 1617. Twelve years after the landing of the Pilgrims, the farmers about Boston had no plows. The first ones used by French settlers in Illinois were of wood with a small point of iron tied on with straps of rawhide. The oxen were yoked to them by the horns. This method of hitching was rivaled only in Saxony and Ireland, where the horses were fastened to the plow with their tails. An attempt was made to abolish this practice in Ireland by act of Parliament in 1634. Arthur Young (1741-1820) mentioned it in his time, however, and Gibbons maintained that it was still to be found in remote parts of Ireland as late as 1896.

In England, from one to eight oxen were used in the eleventh century, while four horses or oxen were usual in the seventeenth century. The first plow in California (about 1835) was a crooked branch with an iron toe. On the whole, the American form before 1767 was practically the same as that used by the Romans before the Christian era, and this type was still found in Europe in 1867. It was the only agricultural implement of France in the eleventh century, and of Sicily in 1863. In southern Greece many plows similar to those of the age of Pericles (450 B. C.) are still being used. Many of those in Russia are equally primitive, while the Spanish, South French and Italian forms resemble the Roman type.

There was little improvement in the plow during the middle ages, perhaps largely on account of legislative restraint. Many popular prejudices also existed. In England, for example, after the farmers hrd experimented with iron plows of good construction, they concluded that the iron made the weeds grow; and in America iron plows were supposed to poison the soil and to prevent the growth of crops. It was not until the end of the seventeenth century that plows began to be improved. The moldboard was then made of iron and steel and given its proper form. While the plow was always essentially a wedgeshaped instrument forced through the soil to loosen it, these improvements perfected it so that the draft was reduced by one-third and the implement was also much more complete in its operation on the topsoil, which it gradually loosened, raised and completely turned over to one side. Coulters were known in England at least as early as the eleventh century. Fitzherbert writes of different kinds of plows for different soils in 1534. The date of the first English patent on this implement is 1720. The cast iron plow was first patented in the United States in 1797. A patent on an adjustable cast iron point in 1818 marks the introduction of the most useful economy in plow manufacture, the interchangeability of parts.

Modern Plows are practically the same in principle as those described above. The only improvements which have been made are in minor details. The draft and friction have been reduced to a minimum, and forms have been invented which are best suited for different types of soil and for the application of different kinds of motor power. The common hand plow is undoubtedly most widely used, and the small farm rarely ever has any other. It is drawn by two horses. Another widely used form is the sulky plow, having two wheels to carry the beams, and a seat for the driver. Two or three horses are required. The acreage covered depends on the condition of the soil, and varies from one to two acres per day. These are the common forms used by all the large wheat raising countries. Another common type used on large farms is the gang plow, drawn by horses or steam. This is merely a number of common plows combined in one frame. A usual plow in the Red river valley is a gang cutting 16 inches in two furrows, drawn by five horses and turning 250 acres in from four to six weeks. Steam is not used, as mud was found to cut out the plow bearings when it was wet, and the expense of keeping horses is necessitated by other farming operations. In some parts of California, plows are set in gangs of as many as 14. They are drawn by eight mules, and plow three inches deep at the rate of 10 or 15 acres per day. A traction engine with large gangs of plows or discs is often used on the larger farms, accomplishing an enormous amount of work in a little time.

Special forms of plows adapted to the use of a stationary engine have been evolved in Europe. The Fowler plow is perhaps the best known and most effective of these. It consists practically of eight turnover plows yoked together, and is capable of plowing 40 acres of land a day and accommodating itself to the mcst uneven ground. The electric plow of Austria is also worthy of mention.

Time of Plowing.—In general, it may be said that in the spring wheat area of the United States, fall plowing slightly

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