EQUIPMENT TO RAKE
AND MERGE HAY
K. J. Shinners and R.T. Schuler 1/
Today, hay and forage producers have a
wide variety of equipment options for raking and merging swaths or
windrows. Selecting the proper equipment
and operating it correctly will help to insure high quality forage and a cost
effective harvesting system. Several studies have been conducted evaluating the
equipment performance and provide useful information in selecting the equipment
that best fits a specific forage harvesting system.
SEGMENTATION OF RAKES AND RELATED EQUIPMENT
Rakes are often used for four purposes:
to invert the crop to allow wet hay on the bottom of the swath to be exposed to
sun and wind, to displace the swath from wet to dry ground, to merge swaths
together to match the windrow density with harvester or baler capacity, and to
narrow the swath into a windrow narrow enough to meet the width of the
harvester or baler pick-up. The North
American market for equipment that is used to rake forage crops after cutting
can be illustrated as follows:
1/ Professors in Biological Systems Engineering
Department, University of Wisconsin-Madison.
The tractors PTO or hydraulics are generally used to power
rotary and parallel-bar rakes. This
gives them sufficient power to manipulate wet, heavy swaths or windrows that
will be harvested as silage. Wheel rakes
are not powered directly by the tractor.
Rather, forward motion of the tractor and the engaging of the wheels in
the crop or soil drive the wheels and because of this they often have
difficulty moving wet, heavy swaths or windrows. Therefore, wheel rakes are often limited to
raking drier crop that will be harvested as dry hay.
Wheel rakes are available in a wide variety of designs that
can be generally grouped into the three categories above. Because they do not require a powertrain,
wheel rakes are the lowest cost segment and are designed to rake widths up to
36 ft. This width allows two swaths from
a 18 ft. cut mower-conditioner to be merged in a
single pass. No other rake type offers
such size at such low cost. The mounted
and single frame wheel rakes are dominated by imports from Italy and are low feature and low cost units. These units are not common in the Upper Midwest
because they lack the needed width or capacity to manipulate swaths from the
typical mower-conditioner or windrower.
The most common type of wheel rakes is the twin frame design. The twin frame rake can be further divided
into low, high and premium feature rakes.
Low feature rakes typically have the wheels mounted on the rear of the
frame, must be folded manually and also have manual width adjustment. Hay will be rolled in front of the wheels, so
locating wheels on the rear of the frame limits capacity because of potential
for crop interference under the frame.
High feature rakes typically have wheels mounted in front of the frame
to handle larger crop volumes and have hydraulic controls for folding and width
adjustment. These rakes will also
feature articulated frames that allow wide rakes to follow ground contours with
less crop loss. Premium wheel rakes
feature larger diameter wheels with stiffer teeth and larger overhead frames to
accommodate these larger wheels. These
rakes are more typically seen in the arid western US and are popular with
commercial hay producers. No matter the
design, the wheel rake will have springs whose tension can be adjusted to
change the weight carried on the wheel.
If wheel float is set too light, the wheels will float over the crop and
leave some crop behind. If wheel float
is set too heavy, tooth wear will be accelerated and the wheels will dig into
the ground, creating greater soil and rock contamination. Most designs require that spring tension be
adjusted manually on each wheel, so this adjustment is often neglected in the
heat of the hay making battle. A concern
often expressed with wheel rakes is the tendency for the hay to be “roped”
after the raking operation, which can reduce air movement through the windrow
and slow the drying rate. Data on drying
rate and leaf loss of various rake types will be covered later.
Parallel-bar rakes were the dominant machines used to
manipulate forage crops in the Upper
Midwest for many years, but sales
of these machines are declining annually.
Although parallel-bar rakes are considered less aggressive than wheel
rakes, parallel-bar rakes are more expensive and are not available in wider
widths. The parallel-bar rake also has a
powertrain and many moving parts to maintain.
Twin frame parallel-bar rakes are more expensive than single frame rakes
because they typically have larger baskets and also have added frame, controls
and hydraulics. Although parallel-bar
rakes will continue to have a place in the rake market in the future, the share
of these rakes will continue to erode toward rotary rakes.
Rotary rakes originated in Europe to
handle the heavy, wet grasses that are harvested there. Other rake types could not handle the tough
conditions experienced in Northern
Europe. Rotary rakes were introduced to the North
American market in the 1980’s and they have slowly but surely gained market
share since that time. Single rotor
rakes are the most popular. Although
mounted or pull-type rotary rakes are available, the pull-type type is dominant
in the Upper Midwest. The two primary
features that differentiate single rotor rakes are the rotor diameter and the
number of arms. Larger diameter rotors
will improve the swath width handled and more arms will increase the
capacity. Standard feature twin rotor
rakes are typically designed to sweep two swaths toward the center forming a
single merged windrow and the distance between the rotors is not
adjustable. The distance between the two
rotors, and hence the coverage width, is adjustable on the high feature twin
rotor rake. Some twin rotor rakes have
identical rotors on both sides so that all hay is moved in the same
direction. This allows merging to the
side of the machine, rather than the center, so that when the next pass is
made, another merged windrow is laid beside the first. This may be done to meet the capacity of a
self-propelled forage harvester. Four
rotor rakes have a retail price of over $40k, so they have limited market in
the Upper Midwest. These machines
would typically be used to merge crop for large self-propelled forage
harvesters. Rotary rakes have a deserved
reputation for creating a well-formed, less roped windrow that allows good air
circulation and good crop drying. For
this reason, these rakes are becoming increasingly popular to merge the crop
for large square balers because of the need to get hay very dry in these large
bales. Care must be taken with this rake
type not to sweep the ground to aggressively to avoid
soil and rock contamination of the windrow.
Another important adjustment is the rotor to ground speed ratio. The correct combination of tractor gear and
engine speed must be found so that all the crop is
swept into the windrow, but the rotor is not turning so fast that leaves are
battered from the stem. Rotary rakes are
the most expensive rake type discussed because they are the heaviest and
require the heaviest frame, and the cam-actuated gearbox that drives the rotor
is more complicated and expensive. The
cam/gearbox can be quite expensive to repair if failure occurs.
Many forage producers in the Upper Midwest
who chop silage know the expense and frustration of running a rock into the
forage harvester cutterhead. Merging
multiple swaths into a single windrow with a rake can add to this risk because
the crop is dragged along the ground as it is merged. Also, soil contamination into the windrow can
lead to problems with clostridia fermentation and high ash content in the dairy
ration. As forage harvesters have grown
in capacity, there has been a need for merging more swaths into a single
windrow. This has led to the development
of a machine referred to as a windrow merger.
The major difference between this machine and a rake is that the merger
lifts the crop onto a belt conveyor that is used to move and deposit the swath
into the desired position so that the crop is never dragged along the
ground. The windrow merger can be used
for either silage or dry hay although its primary use is silage crops. Most machines can deposit crop to the left or
right simply by changing the direction of the hydraulically driven belt
conveyor. Before purchasing a windrow
merger, it is important to consider the compatibility of the mower-conditioner
width, merger pick-up width and the forage harvester or baler pick-up
width. Some mergers can be configured
with a belt extension to help width compatibility. Windrow mergers are configured as either
single or double windrow machines.
Single windrow machines can merge either two swaths into one with one
pass or three swaths into one by making a return pass on the other side of the
new doubled windrow. Double windrow
mergers are more expensive at retail list price than single mergers because
they have much heavier frames and complicated folding or swiveling features for
transport. Most double windrow mergers
can be configured to deposit crop to the left, right or to the left and right
simultaneously. Operating by depositing
to the left or right exclusively provides the option of merging either three or
five windrows into a single windrow. Lifting
two and depositing onto a third merges three windrows. Lifting another two on the return pass on the
other side and depositing on the newly tripled windrow merges five windrows. Windrow mergers are configured with either
conventional tine-type pick-up or tine-belt pick-up similar to a windrow
pick-up for a grain combine. Some
mergers also have optional inverter shield that can be mounted on the output of
the cross-conveyor to help invert crop for better drying.
Windrow inverters pickup one windrow and lay it on the
ground up side down. They are configured quite similar to windrow mergers with
a conventional or belt-type pick-up, cross-conveyor belt and inverter shield at
the conveyor output. The primary differences between a merger and inverter is that the
inverters have a narrow pick-up width that can only accommodate a narrow
windrow and the inverter is quite a bit lighter-duty than a merger. The inverter is not intended as a merging
device. Rather, the inverter is intended
to move an already formed windrow off of wet ground and invert it for faster
drying to dry hay moisture.
The final type of hay manipulation tool that should be
mentioned is the tedder. The modern
tedder was developed in Europe and most tedders that are sold in the Upper Midwest
are imported from Europe. Tedders are used
to spread crop into a swath as wide as the cut width of the
mower-conditioner. This not only aerates
the swath, but more importantly it allows all the sunlight that is striking the
field to be used to dry the crop. When
crop is placed in a narrow windrow, much of the sunlight strikes bare ground
and does not aid in the crop drying.
Besides good crop conditioning, the most important factor in achieving
fast forage drying is the width of the formed swath. If tedding offers so many benefits, why isn’t
it a common practice in the Upper
Midwest? There are several reasons for this. First, tedding is an aggressive action and is
acceptable for grasses where leaf loss is less of a concern. But for alfalfa there is concern that tedders
will cause unacceptable leaf loss, especially if the tedding is done when the
crop is partially dry and the leaves are brittle. Second, tedding adds an additional step in
the hay making process: cutting, tedding, raking and baling. Third, a tedder adds an additional machine
expense to the already substantial line-up of hay making equipment. Lastly, sometimes it is beneficial to lay the
crop in a narrow swath so that damp ground can be dried out. This will allow a dry location for a raked
windrow to be placed. There are so many
different designs and configurations of tedders available that it is not
possible to cover all of them here. The
most common types in the Upper
Midwest are pull-types with two
or four rotors. These are relatively
simple machine with relatively low retail list price. The larger six rotor machines are more
complicated and much more expensive because of the folding requirements for
transport. Six rotor machines are often
fully mounted, so they require a fairly large tractor to operate. Although there are some downsides to using a
tedder, forage producers in the Upper
Midwest, especially those with
alfalfa-grass mixtures, who are looking for fast drying to dry hay moisture may find the tedder quite beneficial.
Another tedder design, sometimes referred to as a fluffer, does not move
the windrow nor changes its width. The machine has parallel rake bars that
engage the windrow at a faster rearward speed than the forward travel speed. This action causes the forage in the windrow
to be moved rearward and slightly upward resulting in a
aerated windrow that allows air to move through it for improved drying. This machine can be helpful in increasing the
drying rate after a heavy rainfall.
MACHINE PERFORMANCE STUDIES
Rakes and related equipment can be
evaluated based on field losses, drying rates, windrow shape and condition,
ability to move heavy swaths and ability to create windrow free of rocks and
other debris typically found in the field.
When evaluating this equipment the forage producer must evaluate their
situation to ensure high quality forage and to meet their needs with respect to
their yields and cutting and harvesting equipment size.
This equipment should be selected and operated
based on the criteria to create minimal losses and maintain rapid field drying
which will ensure high quality forage.
The manner in which the equipment handles the swath impacts the level of
loss and the resultant windrow. Handling methods range from picking up the
swath and laying it down to rolling the swath across the ground surface.
Most of the research has involved the losses and drying
rates associated with these machines. In
numerous cases the forage quality was evaluated which may be related to the
losses, usually high quality leaves, and drying rate.
In a study by Savoie et al. (1982), a
parallel-bar rake was compared to a rotary rake in conditioned and
non-conditioned alfalfa. They found no
difference in the drying rate but the rotary rake had slightly higher
losses. Raking was done near 40 percent
moisture, wet basis. They found tedding
increased the drying rate slightly but the results were not very consistent. During good drying conditions, tedding did
not appear to be beneficial but may be beneficial after a heavy rain, which
creates a windrow that was dense and matted.
Using artificial stubble, Buckmaster
(1993), evaluated a parallel-bar and a wheel rake. The parallel bar rake had
about two percentage units less loss throughout a forage moisture range of five
to fifty-five percent, wet basis. In an Ohio study reported
by Claas, three rakes (wheel, rotary and parallel-bar) were compared with
respect to drying rate based on moisture content as forage dry down approached
baling moisture. In the first cutting
for a orchard grass-alfalfa mix, the rotary rake had
the lowest moisture (20.9 percent) while the wheel rake had the highest
moisture (25.0 percent). The parallel-bar rake was intermediate. For the second cutting alfalfa, the rotary
rake had lower moisture (20.4 percent) than the other two rakes (22.5 percent
for the parallel-bar and 23.0 percent for the wheel rake). In a third cutting of alfalfa of a orchard grass mixture, the differences in moisture between
rake types were not significant.
Garthe et al. (1988) compared a parallel-bar rake with a windrow
inverter and found no difference between the two devices in terms of drying
rate or crop quality (based on crude protein content). Shearer et al. (1992) compared
a parallel-bar rake with two different windrow inverters. They found no difference between the three
machines with respect to the drying rates or losses. In a study of several rakes and a windrow
inverter, Hoover (1996) found
that the inverter and the parallel-bar rake had significantly less loss than
the other rake types which included a wheel rake and several rotary rakes. In this study, the drying rate among the
different rakes was very similar.
Savoie and Beauregard (1988) studied
four windrow inverters that significantly increased the drying rate compared to
a control with no manipulation of the forage in a windrow. In addition they
indicated that an inverter could advantageously replace a hay tedder.
Although no research has been reported
on windrow mergers, their losses would be expected to be similar to the windrow
inverters because they both pickup the windrow and do not move it across the
ground. The drying rate of forage
gathered with a windrow merger is generally not an issue because merging
usually takes place right before the forage harvester.
To produce a
consistent, high quality forage the raked or merged windrow must be
uniform to ensure the moisture is the same throughout the windrow. Based on field experience and observations,
the rotary rakes produce a more uniform and less roped windrow than wheel or
parallel-bar rakes. Windrow inverters and mergers will not produce a roped
windrow, but can often produce a non-uniform windrow if the belt does not
properly take the crop off the pick-up. In all cases the equipment must be
properly adjusted operated to obtain the most uniform windrows.
It is important to produce windrows free
of rocks, soil and other debris to avoid problems with forage harvester knife
wear, knife damage, clostridia fermentation (especially in high moisture
silages) and excess ash content in the feed. Equipment that rolls or slides the
windrow across the ground will have a greater risk of having rocks and soil
contaminate the windrow. This becomes
more important with high capacity forage harvesters requiring a greater
distance for swaths to be moved.
Machines that pickup the swath, displace it
with a cross-conveyor and then lay it down on the ground at another location
will have less risk of contaminating the windrow. In a study of rock movement caused by rakes
and a windrow inverter, Hoover (1996) found
that the inverter and wheel rake moved significantly fewer rocks than the other
rake equipment. The rotary rake moved
significantly more rocks than the other rakes.
Although no studies have been done with windrow mergers and since they
are handle the windrow similar to an inverter, it is safe to imply that the
merger would move fewer rocks.
With increased forage yields, raking and merging equipment
must be sufficiently aggressive to move the large quantity of forage. Equipment that is ground driven will have
greater difficulty picking these swaths.
These would include the wheel rakes and ground driven parallel-bar
rakes. PTO and hydraulic driven rakes
and mergers can become more aggressive by maintaining a higher operating speed
relative to the forward travel speed.
Today, forage producers have many
options in equipment for moving swaths and creating windrows. Careful selection of this equipment should be
made to choose a system the machine that best meets the needs with respect to
crop yield and cutting and harvesting machine size. Also it is extremely important to properly
adjust and operate these machines to insure minimum losses and rapid drying.
Buckmaster, D. R. 1993. Alfalfa raking losses as measured on
artificial stubble. Transactions
of the ASAE. 36(3):645-651.
Garthe, J. W., P. M. Anderson, R. J. Hoover and S. L.
Fales. 1988. Field test of a swath/windrow hay inverter. ASAE Paper 88-1549. ASAE, St. Joseph, MI. 15
1996. A comparative
rake study of dry matter loss, drying rate, and rock movement in alfalfa
Honors Thesis. The Pennsylvania State University. 33 pp.
Rotz, C. A. and P. Savoie. 1991. Economics
of swath manipulation during field curing of alfalfa. Applied Engineering in Agriculture. 7(3)316-323
Savoie, P. C. and S. Beauregard. 1988. Hay
windrow inversion. ASAE Paper 88-1548. ASAE, St. Joseph, MI. 13 pp.
Savoie, P., C. A. Rotz, H. F. Bucholtz and R. C. Brook. 1982. Hay harvesting system losses and drying
rates. Transaction of
the ASAE. 25(3)
Shearer, S. A., G. M. Turner, M. Collins and W. O.
Peterson. 1992. Effect of swath and
windrow manipulation on alfalfa drying and quality. Applied Engineering in Agriculture. 8(30) 303-307.