EQUIPMENT ASPECTS OF FORAGE HARVESTING
D. R. Buckmaster1
Abstract
This paper and its associated presentation are intended to be a complement to numerous excellent
printed and internet publications and reference materials. In this paper, aspects of forage
machinery selection and machine operations are briefly presented for both hay and silage
harvest; in-field and handling/transport operations are considered. Capacity considerations and
equipment matching are the focus and a list of resources is provided.
Forage equipment needs: Equipment for hay and silage harvest and handling may be very
different from one farm to the next, but some aspects will be similar. Since a standing hay crop
is typically 70 to 80% moisture, forage equipment systems are specifically designed to facilitate
crop drying. For hay making, a mower-conditioner, rake, and baler are a minimal set. Handling
and transport systems must match the package size. Swath manipulation with a tedder,
swath/windrow inverter, and/or merger may be performed to manage swaths to increase
harvester performance or improve drying. For whole-plant corn silage, a harvester, transport,
and packaging equipment is needed; for grass or alfalfa silage, a mower or mower-conditioner,
and perhaps swath/windrow manipulation tools are also needed. A good set of forage machinery
not only accomplishes harvest in a timely fashion, but also provides flexibility for sequencing
operations; equipment should be sized for the labor available and to meet timeliness goals based
on crop quality targets.
Features, adjustments, and safety considerations during operation of these machines are best
described by advertising literature and operators manuals. Particular attention should be given to
tailoring equipment choices and machine settings to the crop (grass vs legume), the harvest
method (hay vs silage), and the market or animals to which the crop will be fed all within the
context of capacities needed and anticipated climate and crop conditions. The market or feeding
system will drive the package type (small bales, large bales, bulk silage) and the package type(s)
on the farm will narrow the field of options regarding transport and handling. Shinners (2003) is
an excellent reference regarding principles of machine operations and design.
Equipment Capacity: In general, capacity of field equipment can be limited by one or more of
the following four principles:
 Traction: sometimes the draft force required for implements limits the speed, hence capacity,
of the implement – it should not be the case with forage harvest that traction is limiting.
 Speed: sometimes mere speed poses an upper bound on the rate of the operations – for
example, sickle mowers don’t work well above some speed, for example, 8 mph.
_______________________
1
Associate Professor of Agricultural and Biological Engineering, Purdue Unviersity,
West Lafayette, IN 47907

Throughput capacity: even if there were plenty of power to the implement, some implements
have a “throat” through which crop must flow and this can limit capacity – balers and forage
harvesters have this limitation.
 Power: if there is insufficient power with a particular harvester or tillage implement, the lack
of power can limit speed and/or throughput. Balers and forage harvesters can have this
limitation.
There is a fifth element in capacity evaluation when harvesters must interact with transporters
and those transporters must interact with unloading sites; this interaction can limit system
capacity to levels lower than capacities of individual machines within the system.
Good selection of forage machinery doesn’t require calculation, but the insight from a
mathematical treatment of the topic can certainly improve the quality of these expensive
investment decisions. For many machines, thinking of capacity as field capacity (area covering
rate) for field going machinery is most appropriate; it is simply a function of speed, width, and
field efficiency (which accounts for overlap, turning, etc.):
Carea, ac/h = (Smph Wft Edecimal)/8.25
A rake, swath merger, or tedder fits this approach well because power would rarely be a
limitation. Speed may be a limit (for example, you can go too fast for some devices or perhaps
any faster and safety becomes compromised), but the capacity is simply related to width and
speed. For some machines, it is not area capacity which is of concern, but, rather, material
capacity which incorporates crop yield:
Cmaterial, t/h = (Smph Wft Edecimal Ytons/ac)/8.25
In harvester or baler operations, it is material capacity and the related power requirement
which often limit capacity. Manufacturers don’t generally report material capacity limits, but
equipment operators will soon find their operating comfort limit which can be related to
throughput capacity either limited by the power available or the machine throughput limit. In a
well matched tractor-harvester pair, power and throughput should provide a similar limit (that is,
there is neither excess capacity “wishing” for more power nor excess power “wishing” for a
bigger implement).
For mowers and mower conditioners, the capacity-limiting factor is not always clear or
consistent. If a tractor and disc mower pair has plenty of power for a low yield crop, capacity
may be speed limited. In different crop conditions, the throughput of the conditioner may limit
speed, hence capacity. In yet different crop conditions, the power for cutting may be high and
the reason the operator cannot go faster (particularly up-hill) is insufficient power.
Proper machine selection is a balance of machine capacity (area or material rate) to the
capacity needed. The capacity needed is a function of the area (or total amount) to be harvested
as well as the time constraints for that harvest which include calendar days (D), hours per day for
this particular operation (H), and the probability (or likelihood) that a given day is suitable for
this particular operation (P, often referred to as probability of a working day). Using the area
basis:
Carea,needed, ac/h = Aacres/(Ddays Hh/day Pdecimal)
As with capacity from a particular machine, the material capacity needed incorporates
yield:
Cmaterial,needed, tons/h = (Aacres Ytons/ac)/(Ddays Hh/day Pdecimal)
Capacity example 1:
Consider a situation where 120 acres of haycrop should be mowed within 14 calendar
days and the operator is willing to mow for up to 6 hours each day during a time of the
year for which 30% of the days seem suitable for mowing. Suppose the anticipated
mowing speed is 7 mph and the field efficiency of mowing (taking into consideration
overlap, turning, etc.) is 0.8.
Carea,needed, ac/h = Aacres/(Ddays Hh/day Pdecimal) = 120 /(14x6x0.3) = 4.8 ac/h
Matching this need with the capacity from a mower, we have:
Carea, ac/h = (Smph Wft Edecimal)/8.25 = 4.8 ac/hour = (7xWx0.8)/8.25
W = 7 ft, so a 7 ft mower would be sufficient.
Where do the numbers for situations like this come from? Typical speeds would come
from experience or an informed salesperson. Probability of a working values are tabulated in
different sources, but most forage producers likely have a reasonable feel for values. The other
values are farm specific.
Capacity example 2:
Considering the same farm with 120 acres of haycrop …raking likely needs to occur in
less time within the day because baling also needs to happen that day. Although the
mower was sized with 14 calendar days in mind and the 30% probability of a working
day, we could likely assume something like the raking needs to take place on a total of 5
days with only 2 hours available each raking day. If this is the case, the capacity needed
is the 120 acres in 10 hours or 12 acres/hour. With an assumed raking speed (e.g., 8
mph) and raking field efficiency (0.8), the width needed is:
Carea, ac/h = (Smph Wft Edecimal)/8.25 = 12 ac/hour = (8xWx0.8)/8.25
W = 17 ft, so a 15 to 20 ft rake would be needed.
Capacity example 3:
Continuing with the same farm situation, let’s consider the baler. If there was a 7 ft
mower and a 20 ft rake, perhaps each baler windrow came from about 20 ft of field width
collected by the rake. Or perhaps, the rake made two windrows each from about 10 ft of
field width. Either way, the baler capacity requirement isn’t really set by area but is
more determined by throughput capacity and power available. Just as an example,
suppose the goal with the 120 acres, which has a per-cutting yield of 3 tons/acre, is to get
it baled on 5 days (which might fall over a 14+ day calendar window) with up to 5 hours
devoted to baling on a “baling day”. This means the total of 360 tons (120x3) needs to
be baled in about 25 (5x5) hours. This capacity of 14 tons/hour might mean more to
some operators expressed as 28 1000 lb bales/hour or 480 60 lb small bales/hour.
A capacity like this requires both a baler with the capacity and a tractor with enough
horsepower. The capacity to transport and put away the forage into storage cannot be
ignored either. It may be that these considerations force a stretch to the harvest window.
The principle illustrated through these examples is that the capacity of machines in a
“good set” of forage equipment (mower, rake, baler) are not likely the same. The hours available
for the operations dictate the capacities needed. If forage equipment manufacturers reported
material capacities of equipment, selecting machinery might be easier, but recognize that this
capacity is very much a function of crop type and conditions. Informed dealers should be able to
help match implements to capacity needs and match tractors to those implements.
Equipment matching: For haymaking equipment, the key matching considerations are related to
capacity needed, power needed, and having transport and logistics which can keep up with the
harvest. The examples above illustrate the interrelationships, but good operators will consider
creative solutions. Use of preservatives can extend the baling hours in a day. Multiple rakes or
balers may be required to “match” larger mowers. Handling systems may need to be highly
mechanized to keep the forage from weather damage after packaging.
For silage making, equipment matching is very much driven by harvest-time logistics.
Sufficient wagons or trucks are needed to keep up with harvester capacity. Blower size and
power, bagger size and power, or bunker packing tractor weight must be sufficient to keep up
with harvester capacity. If silage is baled, then the capacity to transport and wrap or seal bales
must match so there is no more than a couple hour delay between packaging and sealing.
Table 1. Approximate sizing of silage harvesting equipment to match harvester power
(Buckmaster, 2009).
Harvester Power (hp)
Approximate
Power
Power
Bunker Packing
system capacity, needed to a needed to Tractor Weight1 (with
transport nonblower (hp)
a bagger
1 tractor, good
limiting (tons/h)
(hp)
packing practices, lb)
Haycrop silage
PHHhp
PHH/4
0.5(PHH)
0.4(PHH)
21,500 + 83(PHH)
Example, PHH=250 hp
62 tons/h
125 hp
100 hp
42,000 lb
Corn silage
PHChp
PHC/2.5
0.6(PHC)
0.4(PHC)
27,000 + 105(PHC)
Example, PHH=300 hp
120 tons/h
180 hp
120 hp
58,000 lb2
1
3
Assuming 65% moisture, 6” layers to reach 16 lb DM/ft target (Holmes and Muck, 2002).
2
Most tractor manufacturer warranties end when tractor ballast weight exceeds about 150 lb/PTO
hp. This 58,000 lb tractor would need to be a 390 hp or larger 4WD unit – if one wasn’t
available, two lighter packing tractors would be needed.
Silage equipment matching was addressed by Buckmaster (2009). A summary of that
work is in Table 1. Using cycle analysis, the number of transport units required to keep the
forage harvester from having idle time was also estimated (Buckmaster, 2009). Resulting
equations were:
Haycrop silage, with dump cart:
Nt,req'd = 0.44 + 0.061[PHHhp*Dt,mi/(Vt,tDM*St,mph)]
Haycrop silage, direct to transporters: Nt,req'd = 1.50 + 0.061[PHHhp*Dt,mi/(Vt,tDM*St,mph)]
Corn silage, with dump cart:
Nt,req'd = 0.44 + 0.098[PHChp*Dt,mi/(Vt,tDM*St,mph)]
Corn silage, direct to transporters:
Nt,req'd = 1.50 + 0.098[PHChp*Dt,mi/(Vt,tDM*St,mph)]
Where:
Nt,req’d = number of transport units required
PHC = power of the forage harvester in
to keep the harvester busy (must be
whole-plant corn silage
rounded!)
Dt = round trip transport distance, miles
PHH = power of the forage harvester in
Vt = capacity of the transporters, tons DM
haycrop silage
St = speed of the transport units, mph
Literature Cited:
Buckmaster, D.R. 2009. Equipment matching for silage harvest. Appl. Eng. In Agr. 25(1):31-36.
Holmes and Muck. 2002. Documentation of bunker silo silage density calculator. Univ. of
Wisconsin, Madison. http://www.uwex.edu/ces/crops/uwforage/bunkdens‐Doc.PDF.
Accessed 30 Oct. 2012.
Shinners, K.J. 2003. Engineering principles of silage harvesting equipment. Chapter 8 in: Silage
Science and Technology. Buxton, Muck, and Harrison, eds. Amer. Soc. of Agronomy.
Related Educational Internet Sites:
UW Madison forage website: http://www.uwex.edu/ces/crops/uwforage/storage.htm
Integrated Farming System Model reference manual:
http://www.ars.usda.gov/main/docs.htm?docid=8519#Reference
Encyclopedia entry on Forage Harvesting Systems:
http://books.google.com/books?id=fCRpUZzT2hMC&pg=PA358&dq=forage+harvesting+sy
stems+buckmaster+encyclopedia&hl=en&sa=X&ei=61aPUKaRNKX50gGJqYCwDQ&ved=
0CC8Q6AEwAA
Simple primer on haying equipment:
http://counties.cce.cornell.edu/washington/Ag/Haymanual/Hay%20Manual/4-HayMachinery/Hay%20Making%20Equipment.pdf
Author’s outreach page: https://engineering.purdue.edu/~dbuckmas/index.html
Penn State forage publications online:
http://pubs.cas.psu.edu/PubSubject.asp?varSubject=Forage, Pasture, and Silage
For historical perspective … 1919 Hay: http://books.google.com/books?id=Mu9Ye_HFbucC
For historical perspective … 1903 Silage: http://books.google.com/books?id=kTdEAAAAYAAJ
Haymaking 101, A Deere publication:
http://www.deere.com/en_US/docs/zmags/agriculture/online_brochures/hay_forage/haym
asters/haymasters_zmags.html
New Holland Haymakers Handbook (excerpts only online):
http://agriculture.newholland.com/us/en/information-center/haymakershandbook/Pages/default.aspx
EQUIPMENT ASPECTS OF FORAGE HARVESTING
D. R. Buckmaster1
Equipment for hay and silage harvest and handling may be very different from one farm
to the next, but some aspects will be similar. Since a standing hay crop is typically 70 to 80%
moisture, forage equipment systems are specifically designed to facilitate crop drying. Particular
attention should be given to tailoring equipment choices and machine settings to the crop (grass
vs. legume), the harvest method (hay vs. silage), and the market or animals to which the crop
will be fed all within the context of capacities needed and anticipated climate and crop
conditions. The market or feeding system will drive the package type (small bales, large bales,
bulk silage) and the package type(s) on the farm will narrow the field of options regarding
transport and handling.
A good set of forage machinery not only accomplishes harvest in a timely fashion, but
also provides flexibility for sequencing operations; equipment should be sized for the labor
available and to meet timeliness goals based on crop quality targets. The capacity of machines in
a “good set” of forage equipment (mower, rake, baler) are not likely the same because different
hours available for the operations dictate the capacities needed. Key matching considerations are
related to capacity needed, power needed, and having transport and logistics which can keep up
with the harvest. Capacity considerations and equipment matching are discussed and a list of
resources is provided.
_______________________
1
Associate Professor of Agricultural and Biological Engineering, Purdue Unviersity,
West Lafayette, IN 47907