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plant-foods if it must be purchased on the market; and when converted into nitric acid, the form in which it is available to crops, it is in the greatest danger of being lost by surface washing, by leaching and by denitrification. Moreover, it is and must be sold off the farm in larger quantities than either potash, phosphoric acid or lime; next to soil moisture, the variations in its available amounts are oftenest responsible for high and low yields.

Not only is the nitrogen, in the form in which is it chiefly available to crops, derived largely from the organic matter incorporated with the soil, but when the amount of organic matter in the soil is large the soluble forms of most of the other essential plant-food materials are likely also to be large.

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through its physical effects, in giving to the soil that granular structure which constitutes good tilth, leading to better reception of rain, better drainage, better ventilation, stronger capi lary movement of water, deeper root penetration, less loss of plant-food by leaching, and a much higher efficiency of soil moisture. Thus, aside from mere plant-food, it is of the greatest importance to maintain incorporated thoroughly and deeply in the soil an abundant supply of organic matter slowly undergoing decay.

To maintain the high content of organic matter, dependence must be placed on the root systems of the crops grown on the field; on turning under judiciously the roughage and waste of the

field in the form of stubble, weeds and crops not harvested; on green-manures and covercrops, especially of the leguminous type: on soil organisms which have the power of fixing free nitrogen; and, best of all, on the manure of live-stock, because it is made up of the richest parts of all the others, reenforced, perhaps, with grain bought from outside, and all combined in superlative condition for thorough incorporation with the soil, and highly charged with the best of available plant-food materials.

The great problem of tillage in this regard is how to incorporate deeply the largest amount of organic matter rich in nitrogen. Much more attention needs to be given to turning under more deeply and more completely all roughage and waste, stable and green-manures, using the jointer on the plow, and a chain if necessary, to bring all such material completely under cover where it will have the maximum effect physically, chemically and biologically. The still deeper incorporation, which is needed, must be secured largely by growing grasses and legumes in rotation with other crops.

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Fig. 494. To show the granular character of a soil in good tilth after cultivation. The granules were sorted by a series of sieves. The relative amount of each size of granules is represented by the dotted line in each vial. It will be seen that the largest size, No. 1, constitutes the smallest part of this soil, and No. 5 the largest.

That such a relation should exist is to be expected for the reason that within the plant tissues, whose decay yields the organic matter, there has been collected from the soil moisture taken up by the crop and transpired through the foliage much of the soluble salts carried by the water in the soil at the time. And it is not unreasonable to expect that we shall yet learn that other and more valuable combinations with these plant-food ingredients are formed during their association under the vital processes of the plant, and that, when the tissues are again breaking down in the soil when closely associated with active roots, they are again absorbed and may contribute in an important way directly to plant growth.

In the case of stable manure, too, which must be regarded as finely comminuted organic matter brought into admirable condition for incorporation with the soil, there is a very high percentage of readily soluble substances concentrated first by the crop and then by the animal fed on it. Some of these, because they have recently been functional in plant growth or in animal nutrition, may remain for some time in the soil in forms directly utilizable by the crop on the ground and by the microscopic soil organisms.

But organic matter is of great importance,

Maintaining the best soil structure, or good tilth.

Next in importance to an abundance of moisture well charged with the essential plant-food materials, is the best structure of the soil itself, by which is meant a good bunching or gathering of the ultimate soil particles into granules such as are shown in Fig. 494, which represents the granules of a clay loam in fair tilth which were sorted by screens from the loose earth as left after cultivating three inches deep. The relative amounts of the several sizes are shown by the heights of the dotted lines in the respective vials. There was present least of the No. 1 and most of No. 5. Even of the finest grade, No. 8, very many of the kernels are large enough to be readily distinguished with the unaided eye, although they are made up of particles of microscopic size. When a soil has its structure or tilth destroyed, the granules are more or less completely broken down, and in a thoroughly puddled condition the destruction of the kernels is carried to the extreme limit, and so long as a fine-grained soil is in this state it will remain entirely unproductive. This must be so (1) because

with the close packing of such minute grains the movement of both water and air is too slow to meet agricultural requirements; (2) because the spaces between the grains are too minute for even root hairs to place themselves between them; (3) and because it is impossible for soil organisms, essential to fertility, to develop and spread through a medium so poorly aërated.

Fig. 495. Showing the principle of the

pulverizing action of the plow.

For developing and improving the structure of the soil we now have two types of tools which are admirably suited to the purpose, the moldboard plow for depths of 5 to 12 inches, and the revolving disc harrow for more shallow work. The principle underlying the pulverizing action of the moldboard plow is illustrated in Fig. 495. A plow is there represented as running under a pile of eight flexible layers or sheets. As they are forced up by the plow in its advance, each sheet is compelled to slide over the other, and even if the several layers were pinned together as represented at 1, 2 and 3, they would tend to shear off the pins as indicated in the cut. This action is very clearly shown by abruptly bending a lot of leaves in a book. Each leaf is then seen to have slipped on its neighbor, and the further the more abruptly the bending is done. The action of the moldboard plow on the furrowslice is of the same character, tending to force the soil particles to slide or roll over one another, and through a greater distance the steeper the moldboard of the plow. The revolving disc harrow or plow, with its concave discs moving obliquely through the soil, tends to shear the soil layer much more than the ordinary plow, but its best service is rendered when used as a shallow tool and when the soil is not too wet.

In plowing to correct texture and to improve tilth, it must be remembered that very much depends on the shape of the mold board, the wetness of the soil, and the depth of the furrow-slice. If a soil is the least amount too dry to puddle, a steep moldboard plow, such as shown in Fig. 243, will shear it into thinner layers and pulverize the soil most; if the soil is still drier, the layers will be thicker and the granules coarser. When the soil is much too dry no shearing will take place, and the furrow-slice will break into coarse lumps. If the soil is much too wet the pulverizing will be so great that the soil will be puddled. With a given plow the deeper the furrow-slice the greater will be the pulverizing effect and the greater the danger of puddling the soil if the soil is too wet. So if the plowing is done with a low, flat moldboard, like that of Fig. 496, the pulverizing effect on the soil will be much less than if a plow like the one in Fig. 243 is used, and the danger of puddling will be much less if the soil is very wet.

It is clear from the mechanical action of the plow that its form should be adapted to the type of soil. If the soil has a tendency to be too open and porous, and is naturally coarse-grained, like the sandy soils, it should be plowed with a steep moldboard when a little over-wet, and as deep as conditions will permit, so as to break down the granulation and secure a finer, closer texture. If the soil is generally too close in texture, is heavy and soggy, it needs to be plowed with a less steep moldboard and when the soil is a little drier, so as to shear into thicker layers and form granules of larger size. If the plowing must be done when the soil is a little too wet, a less steep moldboard should be used and the depth made as shallow as the conditions will permit. If the soil has become too dry and is not pulverizing enough, a steeper plow run at a greater depth will do the work better.

There are other ways of improving the structure of the soil, and there is, perhaps, none so effective and so enduring as that of thoroughly incorporating organic matter in one way or another. The organic matter falling into the spaces of the soil establishes parting planes which prevent the grains from reuniting when expansion follows with the wet season. The very great advantage of stable manure, in this direction, arises chiefly from its extremely comminuted condition which permits a thorough dissemination through the soil; partly also from the flocculating tendencies of the salts carried in it. Lime, especially, acts in this way on clay soils, and some of the mineral fertilizers do also, while others have an opposite effect. Some crops, as blue-grass and timothy, which are perennial and form a dense mat of roots that closely cross-divide the soil, exert a very pronounced granulating effect that is very helpful to

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Fig. 496. Type of sod plow, which pulverizes but little. heavy soils, largely in this physical way but also, perhaps, in providing conditions which enable some forms of soil organisms to add to the store of nitrogen in the soil. This is suggested by some of the results of the Rothamsted Station recently reported by Hall.

The action of freezing during the winter and of surface-drying in the summer are other conditions that act especially to overcome the bad effects of puddling, and they are agencies that may be employed, acting on the subsoil, in the methods of progressive deepening of the soil to which reference has been made. In these cases, the water held so firmly by the extremely fine clay particles is driven out and then, when wetting occurs again, the fine clay and also, perhaps, some of what had

been colloid matter, no longer returns to that state but is gathered about other granules; in this way, the soil becomes more open and friable.

Soil moisture, available plant-food, soil temperature. Many of the operations of tillage influence in important ways, and are often specifically directed

able nitrogen is developed in the loosened tilled soil and in the layer just below it, as the effect of better aëration and a higher temperature following the stirring. For this early fitting of the seedbed, which has not been spring-plowed, it is doubtful whether there is a more effective tool than the disc harrow. It may readily be made to pulverize the soil to a depth of four inches, and, by lapping half-way, the work is very effectually done.

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Fig. 497. Method of plowing. The furrow-slices turned on edge and left comparatively unbroken. Sod land.

toward effecting a control of or improvements in the conditions of soil moisture, available plant-food and soil temperatures. Surface tillage, as applied early in the season, particularly in the fitting of the seed-bed, should be made to influence the conservation of soil moisture, the development of available plant-food, and the temperature of the seed-bed.

In the very early fitting of the surface soil in the spring for the small grains, and for seeding to grass and clover, the shallow tillage that is given to fields plowed the previous fall and to land that had been in corn or potatoes the year before, that are to be seeded without plowing, should exert an important influence on the productive capacity of the field for that season. This influence results from the very large reduction in the loss of soil moisture by surface evaporation, which is effected by loosening the soil to a depth of three to four inches. The amount of evaporation from naked soil when wet and firm, as it is before tillage in the spring, is very large, and in clear, warm, windy weather may easily exceed two inches of rainfall per week. The writer has measured rates exceeding three inches, and mean rates for the growing season ranging from 1.1 inches to 1.5 inches on naked, firm soil maintained continually saturated by capillarity. This influence results also from the increase in the rate at which avail

In the case of intertilled crops which are planted considerably later than the small grains, there is opportunity to develop the advantages of tillage to a greater extent. Very much may be gained by beginning the fitting of the field two or three weeks ahead of planting time in order to take advantage of naked fallow in increasing available plantfood and in giving opportunity once or twice for weed seeds to germinate; the weeds should be killed before the crop is planted. It is especially important, when green crops are turned under and when stable manure is applied, that early fitting should precede the planting by a considerable interval of time.

The tillage given to intertilled crops to conserve moisture through the development of earth mulches and the killing of weeds is very helpful along another important line, namely, in restraining the rise of nitrates and other readily soluble salts to the very surface, where they are above the reach of roots and in danger of being lost by surface washing in times of heavy rains. An earth mulch two to three inches deep has its effect in restraining the soluble salts to a level just below its surface; and apparently, through the slower rate of capillary rise, the nitrates diffuse downward again so as to be found more abundant six to twelve or more inches below the

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Fig. 498. Poor plowing in the same field as Fig. 497, but not in sod.

and the land too dry.

surface, where the roots are also more abundant than they are in soil where no mulch has been maintained.

Literature.

The following publications should be consulted. in this connection: Agriculture, by F. H. Storer, Vol. 1, Chapters V and VI; Agriculture, by William P. Brooks, Vol. I; Fertility of the Land, by I. P. Roberts; The Soil, by F. H. King; Irrigation and Drainage, by F. H. King, Chapter III; Physics of Agriculture, by F. H. King, Chapters VIII, IX and XI.

tillage is a plow, and as it is one of the first devices invented by man it will be considered first. The plow.

The first plow was only a modification of the hoe of that age, a crooked stick so shaped that it penetrated and loosened the soil as it was drawn along. Man, at first, furnished the power, but later he enlarged this crude plow and drew it with the beast that he had been able to

TILLAGE MACHINERY
By J. B. Davidson

When man first turned his attention to agriculture and had fields in which grain was planted, he began to devise tools to aid him with his work. It was found that plants grow larger and produce more when the ground is stirred. The tools first used were simple and inefficient, but they have been developed until now they seem almost perfect. Agricultural tools and implements used in preparing the soil for the seeding, planting or growth of crops may be classed as tillage machinery.

The objects sought by the use of tillage machinery are many and have been enumerated about as follows: first, to produce various textures of the soil that will render the most plant-food available; second, to cover under the surface green crops and other vegetable matter where it will decay quickly and add to the supply of humus in the soil and not hinder further cultivation; third, to destroy and prevent the growth of weeds and other vegetation not desired; fourth, to regulate and retain the moisture in the soil; fifth, to change conditions, as to modify the temperature of the soil; sixth, to modify the soil as regards root-penetration.

Too much stress cannot be laid on the importance of tillage machinery, for much of the increase in

Fig. 500. A Spanish Plough, with one of which, and one Horse they will in Spain plough two or three Acres of their light Lands in a day.' "" Mortimer, The Whole Art of Husbandry," London, 1708.

production is due almost entirely to its introduction. By its proper use a given area is made to produce more and a larger area can be tilled. By the intelligent use of modern machinery the objects as set forth may be accomplished almost perfectly. The tool used in the preliminary operation of

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Fig. 499. Rodgers Improved Scotch Plough,' on which a report was made on March 24, 1818, by the Agricultural Committee of the Society for the Promotion of Useful Arts in the State of New York.

train for draft and burden. The ancient Egyptians had such a plow, and pictures of farmers plowing are to be found among the oldest records. They developed the plow until it had a beam, a shank and a handle. (Fig. 491.)

The next step in the development was to shoe the point and wearing parts with iron, and this was done very early, for it was written, 1,100 years B. C., that the Israelites, who were not skilled in the working of iron, "went down to the Philistines to sharpen, every man, his share and his coulter."

The Romans were among the first to develop the plow, and the Roman model remained for a long time as the standard plow. Vergil describes the Roman plow in the Georgics as having a point made of two pieces of wood meeting at an acute angle and being plated with iron.

During the middle ages the plow was developed very little, and those used resembled very much the Roman. The Dutch, owing to the conditions which they had to meet, were among the first to make changes of importance. The crude Roman

type of plows did not give satisfaction on their soils. They found it necessary to give the moldboard a more perfect form and protect it with iron. Some of the early Dutch plows were imported into Yorkshire, England, as early as 1730. The Dutch plow was improved by Small, of Berwickshire, Scotland, until the major part of it was made of iron.

Small established a factory at Black Alder Mount, Scotland, and developed a large trade. The moldboard of this plow was finally made of cast iron, and the beam, handles and share of wrought iron. The English patent records show that a patent was granted to Robert Ransome, of Ipswich, England, for an improvement in the construction of the cast-iron share. This was followed in 1803 by one to the same man for case-hardening and chilling the share. In 1840 a plow factory was established by Mr. Howard, and the firm is still in existence. At about the same time a factory was established to manufacture Ransome's plow;

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and this factory also remains to this day one of the largest in England. It is reported that the Howard and Ransome plows won prizes at the London and Paris Expositions of 1851 and 1855.

Fig. 501. Daniel Webster's plow.

Some of the early forms of plows are shown on pages 206-210.

The plow used by the colonists before the Revolutionary war did not differ much from those used in England at the time. Conditions were not such as to encourage the invention and manufacture of new tools. During the later colonial times the Cary plow was used, and it seems to be representative of the type then employed. It was described as having "wrought iron share, wooden landside and standard, and wooden moldboard plated over with sheet iron or tin, and short upright handles." In the Yearbook, Department of Agriculture, 1899, it is stated that the Old Colony plow, which was used in the eastern states in 1820, "had a ten-foot beam and a four-foot landside" and that it made the "furrows stand up like the ribs of a lean horse in the month of March."

Thomas Jefferson was among the first to give thought to the improvement of the plow. When abroad in France, he wrote "Oxen plow here with collars and harness. The awkward figure of the moldboard leads one to consider what should be its form." Later he specified the shape of the plow by stating: "The offices of the moldboard are to receive the sod after the share has cut it, to raise it gradually and to receive it. The fore end of it should be as wide as the furrow, and of a length suited to the construction of the plow." Jefferson made elaborate mathematical studies of the proper shape for the working parts.

Daniel Webster also designed and helped to build a plow in the year 1836 to be used. on his farm at Marshfield, Massachusetts. The plow was very large and cumbersome. It was designed to plow 12 inches deep or more, and required several men and yoke of oxen to run it. It was described as being "12 feet long from the bridle to the tip of the handles; the landside was 4 feet long; the bar and share were forged together; the moldboard was of wood with strip of iron; breadth at heel of moldboard to landside was 18 inches; the spread of the moldboard was 27 inches; the lower edge of

the beam was 2 feet 4 inches above the sole; the width of the share was 15 inches." Webster, in speaking of his work with the plow, is reported to have said: "When I have hold of the handles of

my big plow in such a field as this, with four yoke of oxen to pull it through, and hear the roots crack and see the stumps all go under the furrow out of sight, and observe the clean, mellow surface of the plowed land, I feel more enthusiasm over my achievement than comes from my encounters in public life in Washington." A picture of this plow is given in Fig. 501.

The first letter patent on a plow was granted to Charles Newbold, of Burlington, N. J., in 1797. (Fig. 502.) His claim read as follows: "The subscriber, Charles Newbold, of Burlington county and state of New Jersey, has an improvement in the art of plow-making, viz., the plow to be, excepting the handles and beam, of solid cast iron, consisting of a bar, sheath and mold-plate. The sheath serves the double purpose of coulter and sheath, and the mold-board serves for share and mold-board, i. e., to cut and trim the furrow." It is an amusing fact that the history of the times records that the farmers rejected Newbold's plow on the theory that so much iron being drawn through the soil poisoned it, retarding the growth of plants but stimulating the growth of weeds.

For some time there was little development from these simple wooden plows with the wearing parts protected with strips of iron. About 1830, what was known as the Diamond plow was brought into general use. The name was derived from the shape of the slab of iron that formed the moldboard.

The next step in plow development was recorded by a patent granted to Jethro Wood. (Fig. 242.) Wood's plow was made almost entirely of iron and the parts were made interchangeable. The form of the moldboard was also more perfect, the pressure being more evenly distributed over it, thus increas

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Fig. 502. The Newbold plow. The first plow "that was made of cast iron in this country," according to the work on the Utica Plow Trials.

ing its life. Wood's plow served as a model for the many designs to follow, but the inventor failed to be rewarded for his work; it is said he finally died in want. William H. Seward, Secretary of State under Lincoln, said: "No citizen of the United States has ever conferred greater benefits on his country than Jethro Wood; none of her benefactors have been so inadequately rewarded."

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