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II. Developments in Tillage and Seedbed Preparation
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
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
RECENT DEVELOPMENTS IN AGRICULTURAL MACHINERY
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
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
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.
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,
RECENT DEVEIXlPMENTS IN AGRICULTURAL MACHINERY
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
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.
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
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
RECENT DEVELOPMENTS IN AGRICULTURAL MACHINERY
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.)
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
RECENT DEVELOPMENTS I N AGRICULTURAL MACHINERY
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.)
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
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
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.
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