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II. Developments in Tillage and Seedbed Preparation

II. Developments in Tillage and Seedbed Preparation

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174



T. W. EDMINSTER AND H. F. MILLER, JR.



and Reaves (1955).Soil reaction to plowshare design is described by

Nichols et al. ( 1958),and its reaction to subsoiling equipment is shown

by Nichols and Reaves (1958).The improved means of measuring this

compaction factor have been made possible by the development of the

straingage cell by Cooper et nl. (1957).More general concepts of the

role of soil physics have been illustrated by Browning (1950). The

effectiveness of various tillage implement forms and practices in achieving

good mixing of soil was successfully evaluated through use of tracer

techniques by Hulburt and Menzel ( 1953).

Individually, none of these findings has resulted in radically new plow

design; collectively, however, they have resulted in a new awareness of

the specific criteria of design. With new understanding of the effects of

adhesion, shear, and pressure translocation, designers have new means for

improving the efficiency of plow design.

The way a plow is mounted, adjusted, and controlled also contributes

to its over-all effectiveness. In recent years there have been many advances in hitch and mounting design that give more effective results.

Heitshu (1952) presents an exhaustive analysis of the kinematics of

tractor hitches as they relate to mounted plows, disks, and subsoilers.

The ability to provide weight transfer either to the tool for improved

penetration or to the tractor for increased traction is a major advance.

Collins (1951) and Tanquary and Clyde (1957) further describe the

factors in hitch design that affect weight balance, side thrust, and suction

control. The hydraulic capacity requirements for controlling these implements have been further analyzed by Worthington and Seiple ( 1952).

These major developments in hitches and implement mounting and

control systems are the cause for the growing popularity of mounted

tillage tools. Integrally mounted on the tractor, these plows can be adjusted and controlled more effectively. This is particularly important in

conservation farming where plows must be lifted to protect grassed waterways and terrace outlets and where implement position control is important in following the contour layouts in terraced and strip-cropped

fields. With the added precision in control, plus the built-in safety

devices, higher operating speeds, particularly in turning on headlands, is

possible.

The use of two-way or reversible plows that permit turning furrows

in one direction, without leaving dead furrows or back furrows, has

become increasingly important. They are particularly valuable in maintaining a uniform surface in irrigation borders and in maintaining uniform

surface configurations under strip cropping and terracing practices. The

higher cost of these plows is offset by the reduction in special smoothing

and leveling steps that must be used to remove dead furrows made by



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175



conventional equipment. The upslope plowing with this equipment compensates for the natural downslope soil movement, particularly on the

steeper slopes. Where this has been practiced, more intensively cropped

rotations can be more safely used than when downslope plowing is

practiced.

Similar advances have been made in the design of disk plows and

harrows. Again metallurgy has played a significant role. Studies by Reed

and McCreery (1954) showed that disk life was closely related not only

to the type and hardness of steel used, but also to the directions that the

steel blank was rolled during its fabrication. By cross rolling, its resistance

to cracking and chipping could be greatly increased. The type of edge

and the method of mounting on the hub also affected disk life. A review

of recent commercial advertisements indicates that these findings have

been quickly incorporated in nearly all industrial designs. Further improvements have been the result of new understanding of the relationship between soil reaction and disk geometry as reported by McCreery

and Nichols (1956) and Thompson and Kemp ( 1958). These workers

have shown the relation between disk penetration and weight, of pressure

and forward motion on the shear forces acting on the soil, and of disk

angle as it affects the speed of rotation. A very significant relationship

between the design of the bevel on the disk edge and its effects on soil

compaction was discovered. Each of these factors when incorporated into

a new design will result in cleaner, more rapid, and more effective cutting

by disk implements.

Both Kramer (1955) and Clyde (1956) have made important contributions to a basic understanding of offset and conventional disk harrow

design. Through an analysis of the dynamic forces involved in the operation of these implements, they have proposed means of providing for

simpler construction and improved durability. Added flexibility and

greater range in adjustment to meet soil variables have also been

proposed. Another important aspect of harrow and disk plow design has

been the tremendous improvements in bearing design. Howe and Raley

(1958) stress the impact that prelubricated and “lifetime” lubricated

bearings have on the life of equipment that must operate under severe

dust and shock conditions. For example, a triple-sealed prelubricated

bearing system on a harrow that had recently completed disking 2200

acres of Arizona sand was without appreciable wear.

Other changes in design of the so-called conventional tillage equipment are imminent. For example, Brown (1957) reports on a design for

individual spring release beams for tractor-mounted moldboard plows.

Tests show that it takes at least 1 minute to rehitch a conventional

breakaway plow as opposed to only 8 seconds to relatch a spring release



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T. W. FDMINSTER AND H. F. MILLER, JR.



beam. Plows equipped with this type of beam are already commercially

available. With the continuing trend to increased power and speed for

tillage operations, this has an important economic aspect.

Draft reduction is an objective of most mechanical designers. Gunn

and Tramontini (1955) in preliminary studies have shown the possibility

of reducing draft by oscillating the tillage implement.

EQUIPMENT

AND PRACTICES

B. SPECIALTILLAGE

In recent years there has been a growing interest and awareness, on

the part of agronomists, engineers, and soil scientists, of the question of

what is the optimum in tillage and seedbed preparation. The objectives of

conventional tillage have been basically to stir and loosen the soil and to

control the weeds. While this has generally been effective in creating a

satisfactory medium for plant growth, it has also, in many instances,

resulted in destruction of soil structure, reduced infiltration capacity,

increased susceptibility to erosion, accelerated reduction of organic

matter, and other evidences of soil decline. It is with this in mind that

Melsted (1954) asks the question: “How should cultivated crops, especially row crops, be tilled and managed so that they will become soil

conserving?” He goes on to establish the importance of studying new

concepts in tillage practices that will (1) achieve erosion control, ( 2 )

maintain organic matter, (3) control weeds, and ( 4 ) provide optimum soil

tilth for plant growth.

During the period following World War I1 literally hundreds of

studies have been conducted that compared various forms of mulch tillage, trash plowing, balk tillage, ridge planting, minimum tillage, plowplant techniques, and many others with conventional seedbed preparation methods. Summaries of many of these studies are to be found in such

references as Cook and Peikert ( 1950), Jacks et al. (1955), Aldrich

( 1956), Baugh et aZ. ( 1950), Schaller and Evans (1954), Buchele et al.

(1955a,b), McCalla (1958), U. S. Dept. Agr. (1958a), Moody et aZ.

( 1952), and Willard et al. (1956). These reports stress the many variables

and problems that have been encountered in attempting to develop new

and modified tillage practices. Further discussion of these practices will

be limited to specific factors in implement design and development.

Some of the early mulch tillage work in the Southeast is reported by

Nutt (1950a), who used a tractor-mounted tool bar to carry a set of

cut-away middlebusters with disk hillers attached to throw vegetation

away from the planting furrow. This operation was preceded by heavy

disking or ripping 2 or 3 weeks in advance to kill the vegetation. Regrowth

in the row middle was further controlled at lay-by through use of broad,

flat sweeps.



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These same general principles were later incorporated in a commercially available Mulch-Till planter described by Poynor ( 1950). This

heavily constructed machine utilized a series of sweeps and rotary hoe

sections to prepare planting furrows in which the crop was planted by a

set of rear-mounted planters. High power requirements and problems of

maintaining adjustment were frequently encountered with this device.

In many areas the preceding crop that furnished the desired mulch

residue was made up largely of perennials. The conventional undercutting

by sweeps that had been effective with annual grain stubbles, as reported

by Duley (1948, 1954), did not adequately kill perennial crops when

they were substituted in the rotation in place of annual stubble crops.

The resulting regrowth of the sods and other perennials, together with the

other nutritional, temperature, and weed-control problems, caused, in

many cases, sharp declines in crop yield-too sharp to offset the advantages of increased infiltration capacity and reduced surface runoff and

erosion.

This problem of managing perennial residues led to the work of

Lillard et al. (1950) in which the double-cut plow principle was developed. Through use of the commercially available Oliver T-N-T plow,

adjustments were made in the plow to slice free and invert the top

2% to 3 inches of sod while rather thoroughly tilling the 3- to 4-inch

depth zone of soil immediately below with the plow’s extra subbase. After

drying out for a period of 10 days to 2 weeks, the ribbon of inverted sod

could be broken up with a field cultivator, disk, or other implement that

would not too deeply incorporate it in the soil. Essentially a 100 per cent

kill of the perennial residue was thus achieved. This double-cut principle

formed the basis for other work by Free (1953) in which standard plows

were modified by attachments.

In concurrent work in Ohio, Harrold and Dreibelbis (1950) found

that disking alone, or the use of field cultivator alone, would not provide

the necessary kill of the vegetation. Disking in combination with

herbicides showed some promise. Preplowing followed by the field

cultivator after a 2-week period also gave better weed control but resulted in less surface mulch. Hays and Taylor (1958) report on similar

studies in the Upper Mississippi Valley.

These are but a few examples of the great number of studies made

throughout the Humid Region in which attempts have been made to

utilize crop residues for mulches under cultivated crops. Nearly all of

the studies involved the use of standard plows, disks, or field-type cultivators, in either a modified form or in new patterns of sequence or timing.

Such studies prompted many important side studies regarding the effects

of these desired mulches upon soil structure, soil temperature, nutritional



T. W. EDMINSTER AND H. F. MILLER, JR.

178

balance, moisture relations and on runoff and soil loss. None of them

materially contributed to development or advancement in machinery

design until some more radical or drastic approaches were taken in the

mid-1950’s.

With the advent of the “minimum tillage” concept new machine

developments have rapidly taken place. The minimum tillage approach

to seedbed preparation for cultivated crops has several objectives. The

first, and most obvious, is to reduce the soil compaction caused by the

extra implement traffic. This results in improved infiltration through the

loose surface layers and a higher level of hydraulic conductivity through

the soil layers immediately beneath the surface, Both of these factors

contribute to general reduction in the soil erosion and runoff hazards

that occur when the field becomes too firmly packed and smoothed. In

some instances a reduction in the weed population is a by-product of the

minimum tillage approach.

Some of the earliest work on minimum tillage was conducted at the

Ohio Agricultural Experiment Station in 1935, where seedbed preparation was limited to use of a light smoothing harrow on plowed ground

prior to planting. Over a fourteen-year period crop yields were essentially the same under this practice as under conventional preparation.

Cook et al. (1953) reported similar results when the plow was followed by

various types of packers that would smooth and firm the surface enough

to permit accurate planting. Out of preliminary studies of this type came

the practice of tractor-track planting, as described by Peterson et al.

(1958). In this practice the tractor wheels are set to the same spacing as

the planter, thus crushing down and firming the plowed field just ahead

of the conventional planter. This practice has been further modified to put

the planting and plowing all into one operation. It is commonly referred

to as the “plow-plant” method. To accomplish this, researchers developed

several machine modifications ranging from a trailing-type planter towed

behind the plow, to planting units mounted on the plow frames, as

described by Musgrave et al. (1955) and Aldrich and Musgrave (1955).

A further development in which the planter unit is mounted on the

forward cultivator bar is illustrated by Winkelblech (no date) and by

Hansen et al. (1958). With this approach, one row can be planted with

each pass of a 3-bottom 14 inch plow, or two rows with a 5- or &bottom

plow (Fig. 1).

In the development of plow-plant devices it is important to mount

the planter in such a way as to assure accurate tracking of the planter

shoe so that the corn row will be placed directly in the middle of the

furrow slice, thus giving greater uniformity to depth-of-seed placement

and seed cover. Aldrich (1956) also points out that the degree of packing



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FIG.1. Experimental “plow-plant” equipment. ( Courtesy of the Agricultural Engineering Department, Cornell University.)



that precedes the actual opening of the seed furrow can be adjusted by

mounting an extra press wheel in front of the planter shoes or by the

use of a specially designed planter shoe that will firm the seed bed (Fig.

2 ) . Minimum tillage can also be adapted to the use of 2-, 4-, or 6-row



FIG.2. Detail of special soil-firming shoe on furrow opener. (Courtesy of the

Agricultural Engineering Department, Cornell, University.)



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T. W. EDMINSTER AND H. F. MILLER, JR.



planting equipment by trailing some type of compaction tool behind the

plow, i.e., a culti-packer, rotary hoe (pulled backward as a treader), a

spiral roller, or other seedbed finishing tools that will do a minimum of

smoothing and compaction. Conventional planting equipment can then

follow as a separate operation.

Adapting the conventional ridge planting long used in the Southeast,

Buchele et al. (1955a,b) and Lovely (1956) have proposed the ridgeplanting of corn as a further modification of minimum tillage. In this

practice two 14-inch furrows are turned to each other on top of a 28-inch

unplowed strip. A disk furrow opener replaces the conventional runnertype opener to provide for better trash cutting and to stabilize the position of the planter on top of the ridge. A disk cultivator is used in cultivating and maintaining the high ridge upon which the crop is planted.

Each of these minimum tillage practices, while still in the research and

development stage, shows considerable promise of meeting the objectives

of ( 1) lower-cost seedbed preparation, ( 2 ) improved infiltration and,

with it, better erosion control, and ( 3 ) reduced cultivation needs. While

present studies are dependent upon shop-built equipment to provide the

desired test conditions €or detailed study by soil scientists and agronomists, these practices are providing the farm machinery industry with

a challenge to develop “line” models for more extensive use.

The development of special tillage practices has not been limited to

those for Humid Region conditions. Throughout the more arid western

states modified tillage practices have long been under development and

used to provide a means of protecting the soil, both under crops and

during fallow periods, from the ravages of wind erosion and, in some

areas, water erosion caused by rapid spring snow melt and accompanying

rains. Duckfoot cultivators, “stubby” moldboard plows, and early versions

of the modem sweep cultivators paved the way for the present-day equipment.

Zingg and Whitfield (1957) have summarized the research on stubblemulch practices in the West and provided the early history and data

showing the effect of various practices on erosion control, wheat production, soil properties, and the problems of production management. A

critical analysis of the machinery requirements for stubble-mulch tillage,

particularly for the Pacific Northwest, was reported by Ryerson ( 1950).

Analysis of the operating characteristics and requirements of implements

for wind erosion control has been made by Woodruff and Chepil (1956);

and Chepil and Woodruff (1955). Krall et al. ( 1958) and Aasheim (1949)

have summarized the results of various tillage practices from the standpoint of soil and water conservation and crop production under summer

fallow conditions.



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181



The machinery-development problems for the western area are severe;

i.e., equipment must be able to handle straw residue from a few hundred



to over 12,000 pounds per acre, or residue standing over 2 feet in height,

under hard dry soil conditions. The tillage job is essentially one of undercutting so as to provide (1) minimum of mixing of the soil and mulch

except as needed to anchor the mulch in place, ( 2 ) minimum breakage

of the mulch, and (3) minimum pulverization of the soil.

Tools that are in the process of development include various types of

mulch pulverizers that will beat the straw into 8- to 12-inch lengths that

can be handled by the tillage implements’ rotary cutters, and hammer-mill

type beaters of extra heavy design, all of which have high clearance.

Sweep plows measuring 5 and 6 feet with 90- to 120-degree blade

angles are being developed for undercutting. Rod weeders have also been

effective, particularly when they are designed with a center drive which

off sets clogging problems of conventional end-drive machines. Various

types of field cultivators, particularly those equipped with coil shanks that

will provide added vibration to assist in clearing the shanks, are finding

adaptation. In areas where it is essential to break up hard soils to permit



FIG.3. Skew treader operating in heavy wheat stubble. Note straw-chopping effect

and partial incorporation of straw to provide good wind and water erosion control.

(Courtesy of the Agricultural Research Service, USDA, by T. R. Horning.)



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T. W. EDMINSTER AND H. F. MILLER, JR.



improved infiltration of the limited moisture, the rotary subsoiler has been

used. It creates a series of pits 8 to 10 inches deep that will serve as

reservoirs and points of entry for moisture. Various types of treaders,

frequently consisting of heavy-duty rotary hoes pulled backward, either

straight or on a skew, are also used to break up surface crusts, cut and

anchor mulch into the soil, and improve conditions for moisture penetration (Fig. 3 ) .

Many of these specialized tillage implements have been produced

by small, local, machinery companies, Each has added certain modifications to meet local real or assumed needs.

This section discusses only some of the major tillage equipment. Of

equal interest would be a review of developments in the special equipment lines such as the giant moldboard and disk plows capable of plowing 3 and 4 feet deep, the various developments in rotary tillage equipment, and recent trends in subsoiler design to reduce draft and increase

effective soil shatter. Since each of these lines of equipment has a more

limited area of application, their development will not be described here.

C. SEEDBED FINISHING

TOOLS

The previous discussion has been chiefly devoted to the primary tillage

operations of plowing and disking. Under conventional tillage management practices these operations are generally followed by various seedbed

finishing operations, the nature and extent of which are dependent upon

the fineness of seedbed desired. The precision seeding of fine, high-priced

vegetable seed may dictate an extremely smooth, well-pulverized soil,

while wheat might be drilled into a rough, cloddy, wind erosion-resistant

soil on the High Plains.

In recent years such conventional finishing tools as the disk and spiketooth harrows, spring-tooth harrows, floats, and drags have been supplemented by a series of specialty tools. These range from a Germandeveloped, flexible knitted-steel rod-spring-tooth harrow which, as described by Sack (1951), will conform to all surface irregularities, such as

beds and furrows, to the more functional harrows, knives, packers, and

rollers, each intended as a tool to break up clods and thus leave a smooth,

uniform soil to accommodate the planter.

111. Developments in Planting Equipment



Recent trends in planting equipment are cumulative resultants of

many separate advances in materials of construction, refinement of power

controls, and improved metering-system design. Some of the trends seen

in tillage equipment are also occurring in the planting lines, viz., the shift



RECENT DEVELOPMENTS IN AGRICULTURAL MACHINERY



183



from pull-behind units to flexible, high-speed, tractor-mounted units,

greater interchangeability of parts, and improved adjustments and controls that permit more precise operation at higher speeds.



A. ROW-CROP

EQUIPMENT

The factor of precision is becoming increasingly important. Uniformity

in the depth of seed placement is essential if uniform germination is to

be achieved. Uniformity of plant spacing, while not a critical factor from

the standpoint of crop yield, is important in mechanical harvesting to

assure an even flow of crop material into the harvester. The effectiveness

of mechanical thinners is also dependent upon uniform planting, just as

high-speed mechanical, flame and chemical weed-control practices depend on such uniformity of plant position.

There has been a significant trend toward the use of bigger multiple

planting units. Four- and six-row units (Fig. 4 ) are rapidly replacing



FIG.4. A six-row planter equipped to apply liquid fertilizer and granular insect

and weed-control chemicals. (Courtesy of the International Harvester Co. )



two-row equipment. Where land smoothing and conditioning is practiced

this trend has been most rapid. Similar trends are occurring in grain drills,

both through use of additional furrow openers and through the use of

multiple units operating on one hitch. This increased use of multiple

planting units has created several related machine-design problems.

When planting is done in multiple units the cultivation equipment must



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