Group Title: Circular
Title: The plastic wrapper is the key to making high quality round bale silage
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Title: The plastic wrapper is the key to making high quality round bale silage
Series Title: Circular
Physical Description: 6 p. : ill. ; 28 cm.
Language: English
Creator: Cromwell, Richard P
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1994
Subject: Forage plants -- Silage -- Southern States   ( lcsh )
Forage plants -- Storage -- Southern States   ( lcsh )
Silage -- Handling -- Southern States   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: R.P. Cromwell ... et al..
General Note: Title from caption.
General Note: "June 1994."
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Bibliographic ID: UF00014573
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA7039
ltuf - AKB3323
oclc - 30845859
alephbibnum - 001937398
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Circular 1072
June 1994

Institute of Food and Agricultural Sciences

The Plastic Wrapper is the Key to Making High Quality
Round Bale Silage1

R.P. Cromwell, W.E. Kunkle, G.D. Sadler and C.G. Chambliss2

In Florida and other areas of the southeastern
United States, most of the forage crops used for
livestock feed are warm-season perennial grasses:
Bermuda, Bahia, and pangola. To a lesser degree,
some producers grow higher quality legume crops:
alfalfa and perennial peanut because they are more
difficult to grow.

The producer has to store any excess forage
produced during the peak growing period to have
feed when forage production is either low or ceases
entirely. Forage crops are stored as hay, a 15- to 20-
percent-moisture material baled in rectangular or
round bales; or silage, a 50- to 70-percent-moisture
material. Silage must be stored under anaerobic
(oxygen-absent) conditions in order for the forage to
ferment to silage and remain a stable, palatable feed.
Hot, humid weather with frequent rain occurring
during the peak growth period of Florida forage
grasses makes hay production difficult. It takes 2 to 3
days of favorable drying weather to dry grass to the
15- to 20-percent moisture level required for safe
long-term storage of hay.

Storing forages as silage makes it possible to
harvest the crop after 0 hours (baled immediately
after cutting) to 4 hours of wilting in the field. This
short drying time increases chances of harvesting the
crop before it rains. Harvesting losses of most forage
crops are reduced by silage harvesting: Relatively wet
forage does not lose leaves as readily as dry forage
does when handled by the harvesting equipment (this

1. This document is Circular 1072, Florida Cooperative Extension
Publication date: June 1994.

is especially true for alfalfa). Despite this more forage
is stored as hay than silage in Florida, because
traditional silage-making methods require expensive
and specialized equipment.

Round-bale silage (or baleage) is a relatively new
method requiring little specialized equipment beyond
the round baler used by many hay producers. In this
system, wet forage (50- to 65-percent moisture) is
tightly baled, then stored in a type of plastic envelope
to keep air (oxygen) from entering the bale.

Research conducted on three different round-bale
silage storage systems at the University of Florida's
Pine Acres Research Farm is described herein.

Single-Bale Bags

A single bale of wet forage was stored in a large
plastic bag sealed to exclude air by tieing off the open
end of the bag with twine. Bags used in this system
were expensive ($6 to $8 per bag), and a lot of labor
was required to load the bales into the bags. As the
bags could only be used for one season, this method
of making silage was eliminated for economic reasons.

Multiple-Bale Plastic Tubes

Plastic tubes about 100-feet long were used to
store 15 to 20 bales of forage (depending on bale
width). The tube was tied off at both ends to keep air
out during storage. This system often resulted in

Service, Institute of Food and Agricultural Sciences, University of Florida.

2. Authors are Associate Professors of Agricultural Engineering, Animal Science, Food Science and Agronomy, Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611.
The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap,
or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean

The Plastic Wrapper is the Key to Making High Quality Round Bale Silage

6F J" silage with considerable molding, and a large portion
! 7 was not eaten by the cattle. An undetected hole in a
S multiple-bale tube would result in all of the rolls
ir spoiling. Further, it was difficult preventing and
8"#A",,patching all the holes made by raccoons and other
wildlife present in the storage area.

Stretch-Wrapped Bales

Bales were wrapped in four thin layers (each layer
1 mil or 0.001 of an inch thick) of plastic stretched by
a machine designed for this purpose. This system
showed the most promise of those investigated. The
cost of plastic wrap is about $3 per bale, significantly
less than single-bale bags, and silage quality has been
consistently better than that made with the multiple-
bale tubes. The big disadvantage to this system is the
$8,000 to $14,000 cost of the machine that wraps
plastic around the bale.

Being equipped to make round-bale silage allows
a forage producer to make hay when the weather
permits and make silage when drying conditions are
unfavorable. With this flexibility the producer can
harvest forage when the crop is at its nutritional peak,
rather than when the weather appears suitable for
making hay. Since the nutritional value of many warm
season grasses decreases rapidly after about 4 to 6
weeks of regrowth, timely harvesting is important.

Silage Quality Depends on Plastic Cover

From this point forward this circular covers
methods for maintaining the integrity of the plastic
envelope around silage so air will be kept away from
the bale. All mentions of plastic are the stretch-wrap
plastic used in the third system which was judged to
be the best from our research.

Baled silage stored in plastic has often been of
poorer quality (mostly due to mold) than silage made
using conventional silage-making equipment. Air
(oxygen) enters the plastic envelope through holes or
pores in the plastic and between layers of overlapping
plastic. In most instances holes are believed to be the
primary pathway for oxygen, since the silage quality of
bales without obvious holes in the plastic was usually
good. (There was one instance in the testing where
the plastic showed no obvious holes and yet the silage
was moldy and rotted near the outside of the bale,
indicating air had entered. This may have been unique
to the specific batch of stretch wrap used.)

The relative importance of oxygen entering
through pores and between overlapping plastic sheets
is still an unknown.

Oxygen Entry Through Holes in the Plastic

Small Holes

Eliminating small holes in the plastic is difficult,
especially after silage bales are stored. They must be
inspected regularly for holes, and any holes must be
patched with tape to limit spoilage.

Holes can develop when the wrapped bale is
dropped by the wrapping machine. The resulting hole
can. be a long split in the plastic or tiny holes caused
by sharp objects such as crop stubble puncturing the
plastic. A split is obvious to the wrapping machine
operator and needs to be patched with tape or
rewrapped, depending on the size of the hole. Stubble
punctures often go unnoticed and unpatched.

Holes can also be caused by birds walking on the
bales and pecking. In one instance a considerable
number of insect larvae emerged from holes in the
plastic. It was never determined whether the larvae
bored through the plastic or were just enlarging small
holes that were caused by birds or crop stubble.

Large Holes

There is considerable variation in how stretch-
wrap plastics withstand exposure to direct sunlight. If
the plastic contains insufficient ultraviolet light
inhibitor, it will disintegrate after a few weeks'
exposure to sunlight. This type of failure can only be
remedied by rewrapping the bales, and this is costly
and time-consuming. It may be impossible to rewrap
these bales because bales flattened on one side will
not rotate properly on the wrapping machine.

Tests were conducted in 1990-91, 1991-92, 1992-
93, and 1993-94 to determine how various plastics
endured exposure to the sun when stretched 50
percent: the recommended amount that plastic is
stretched when used to cover a silage bale. A 50-
percent stretch means that a 10-foot piece of plastic
is stretched to 15 feet when wrapped around the bale.
Samples of plastic wrapper stretched 50 percent on
frames (in the 1991-92 tests) are shown in Figure 1.

Page 2

The Plastic Wrapper is the Key to Making High Quality Round Bale Silage

Figure 1. Stretch plastics exposed to the Florida sun.

Table 1. "Stretch wrap" plastic evaluated on frames in
1990-91 tests, Gainesville, FL.a

Exposure Days or
Days to Failure

Manufacturer Color Low High Average

AEP White 375 375 375
Linear White 80 131 99
Borden Wnile 52 187 103
Bonar White 27 28 27.5
a Four samples of 20"-wide plastic (0.001" thick) were stretched
50% and mounted on wooden frames on August 14, 1990.
Plastics were exposed to Florida sun for 375 days.

Table 2. "Stretch wrap" plastic evaluated in frames in 19

Exposure Days or

Manufacturer Color Low High
AEP (20" Sunfilm) White 368 368

AEP (30" Sunfilm) White 368 368

Linear Black 151 220

Linear Clear 151 179

Linear White 199 233
Presto Black 300 368

Presto White 306 368
a Four samples of 20"- or 30"-wide plastic (0.001" thick) were st
were exposed to Florida sun for 368 days.

The first (1990-91) tests showed a great difference
in how the exposed plastics held up (Table 1). One
sample lasted only about a month, while the most
durable plastic never actually failed; that wrap was
removed after being exposed for 375 days to make
room for the 1991-92 test samples.

The second (1991-92) test samples (including
white, black, and clear plastics) were mounted on
August 23, 1991. Six months later (March 16, 1992)
the white samples of all manufacturers appeared to be
more taut and showed the least amount of ill effects
from their exposure. Table 2 lists the manufacturers
of these samples and the results.

The 1992-93 tests had three replicate samples of
10 plastics. Nine were commercially available; one was
a new formulation being tested. There were seven
white and three black samples. They were stretched
on wooden frames as in previous years and also by
wrapping on four bales of forage. All 10 on the
wooden frames had good resilience for the first eight
months (August 1992 to May 1993) then some started
developing pin holes and tears (Table 3). Degradation
accelerated during the summer, perhaps because of
the greater number of hours of high-intensity sunlight.
In June 1993, some of the plastics failed (came loose
from one end of the frame). Several had failed by the
end of the 369-day test in August. All three black
plastic samples showed some degradation at the end
of the trial. General observations for plastic wrapped
on bales was similar to that mounted on frames;

91-92 tests, Gainesville, FL.a

Days to Failure

Average Comments

368 All samples removed before failing; slill taut
and bright
368 All samples removed before failing; still taut
and bright.
201 Three samples developed small holes. One
developed a tear at the edge.
170 Failures developed where samples were
written on with marking pen.
221 All four samples failed.
342 Black color faded; tension relaxed more than
white samples. Three of four failed.
329 Two of three samples failed.
retched 50% and mounted on wooden frames on August 23, 1991. Plastics

i ry OF FLOR i1 tLIV IES

Page 3

The Plastic Wrapper is the Key to Making High Quality Round Bale Silage

Table 3. "Stretch wrap" plastic evaluated on frames and bales in 1992-1993 tests, Gainesville, FLa

Exposure Days or Days to Failure
Manufacturer /
Name or Distributor Color Low High Average Commentsb

AEP / Sunfilm

AEP / Sunfilm

Presto / Balegard

Presto / Balegard

Bonar / Silotite

Paragon / Midwest

Paragon / Midwest

not known/ Internat'l

Mobil / Regular

Mobil / 3 layer































One of 3 samples on frame failed. Plastic
356 had small holes on 2 of 4 bales, plastic
looked good after 349 days.
Many small holes in plastic on frame.
369 Plastic had 2 small holes on 2 of 4 bales,
plastic looked good after 349 days.

Two pin holes in 1 sample on frame.
369 Plastic had 4 holes in 1 of 4 bales, plastic
looked good after 349 days.

Two of 3 samples on frame failed. Plastic
352 had small holes on 2 of 4 bales, outer layer
of plastic on 1 bale partially degraded after
349 days.

369 Five small holes in 1 sample on frame. All
4 bales had small holes, plastic looked
good after 349 days.

369 Two of 3 samples on frame had one small
hole. Two of 4 bales had long tears in
plastic, plastic looked good after 349 days.

352 Two of 3 samples on frame failed. Plastic
had small holes on all 4 bales, outer layer
of plastic degraded after 349 days.

369 All samples on frame were good. Bales
had holes in plastic on 3 of 4 bales, plastic
looked good after 349 days.

346 Two of 4 samples on frames failed. Plastic
on 2 of 4 bales failed, plastic degraded on
all bales after-349 days.

330 Five of 6 samples on frame failed. Plastic
on 3 of 8 bales failed, plastic degraded on
all bales after 349 days.

a Three or more samples of 20"-wide plastic (.001" thick) were stretched 50% and mounted on wood frames on August 27, 1992. Plastics
were exposed to Florida sun for 369 days.
b Comments on bales were observations made at 349 days and some of the holes were caused by physical damage to the plastic.

although the time to complete failure was shorter for
the frame-mounted samples.

A fourth year of testing was initiated September,
1993 with 13 different samples from five different
manufacturers or distributors: AEP, Presto, Mobil,
International Plastics, and Four Seasons. After nine
months of exposure on wooden frames just two
samples of one plastic have failed.

Oxygen Entering Through the Plastic Wall

The plastic used for wrapping bales is made of
polyethylene resin. Polyethylene is more permeable to
oxygen (oxygen actually moves through the plastic)
than some other plastics. But polyethylene is cheaper
than most of the less permeable plastics and this has
dictated its use in making round-bale silage.

Page 4

The Plastic Wrapper is the Key to Making High Quality Round Bale Silage

The oxygen passing through intact plastic sheet is
usually insignificant compared to that entering actual
holes in the plastic. However, tests were conducted to
determine whether there was any difference in the
permeability of polyethylenes offered by various
manufacturers (Table 4).

Table 4. The rate that oxygen passes through various
1 mil (0.001" thick) polyethylene plastic.
Oxygen Permeabilitya,b
Manufacturer Color (cc/100 in2/24 hr)

AEP White 505
Bonar White 590
Borden White 571
Linear White 571
Linear Clear 515
Dow White 633
Union Carbide White 500
a Permeability tested on a Mocon Oxtran 1000 at the CREC,
Lake Alfred, FL.
b Plastic initially stretched 50%, then allowed to retract to some
unloaded length before being mounted on the permeability
testing equipment.

Tests showed there was some difference in
permeability, and anyone purchasing plastic might
consider relative permeability. However, this should
be a secondary consideration to the plastic's ability to
endure long term exposure to sunlight.

Oxygen Entering Between Layers of Plastic

The stretch plastic used to make round-bale silage
is "tacky" to the touch and should form a good seal
when one layer of plastic overlaps another. These
layers must seal sufficiently to keep oxygen from
leaking through and causing the bale to spoil. It has
not been proved conclusively that overlapped sheets
form a tight seal, but the good quality of bales without
obvious holes in the plastic indicates that very little
oxygen enters between the plastic layers.

Wrapping bales in the rain causes water to be
trapped between the plastic layers, providing a
pathway for air entry and subsequent spoilage.
Therefore, wrapping bales in the rain is not


The plastic used to make round-bale silage must
be carefully selected: it serves as the barrier between
the wet bale and oxygen in the air that can cause the
bale to spoil. It is virtually impossible to totally
exclude oxygen from the bale, but it is possible to
keep the oxygen crossing the plastic barrier to an
acceptable level that minimizes mold in the silage.

Good quality round-bale silage can be made. The
following suggestions about plastic selection and bale
handling, moving, and storage should increase your
chances for success.

Plastic Selection

* Choose a plastic that can withstand the ultraviolet
radiation of the sun without disintegrating. The
ability of a plastic to withstand UV radiation
depends on two factors: the plastic's containing
sufficient UV inhibitors and those inhibitors being
uniformly mixed in the batch of plastic resin by
the manufacturer. No forage producer can tell by
looking at a plastic sample whether it will hold up
when stored outdoors. Your recourse is choosing
plastic from a manufacturer whose product has a
reputation for lasting outdoors. While this
publication gives some information about the
lasting ability of several plastics, stretch plastics
offered in the future may be superior to any
tested. Ask' other forage producers in your area
(plastic that lasts outdoors in Canada will not
necessarily last in the southern United States due
to the differing intensity of the sun's rays) about
their experiences with different plastics. Buy a
small amount of the plastic for a trial run to see
how it works for you.

Bale Wrapping

* Handle wrapped bales as gently as possible to
avoid splitting or puncturing the plastic. Some
bale wrappers are designed to set the bale gently
on the ground after the wrapping operation -- a
desirable feature of this type of bale wrapper.
(Most of the machines just dump the wrapped
bale from the wrapping platform with the help of
a hydraulic cylinder.) Wrappers that dump are
sometimes equipped with an attached landing mat
that helps reduce the impact loads generated
during the dumping operation. Such a mat lessens
chances of punctures in the plastic caused by crop

Page 5

The Plastic Wrapper is the Key to Making High Quality Round Bale Silage

stubble, rocks or other things that stress the
plastic, resulting in holes after a few months.

Bale Moving

Moving wrapped bales from field to storage area
is best done with equipment designed specifically
for handling wrapped bales. A spear on a front
end loader while an excellent tool for moving dry
hay bales, is not a good tool for moving wrapped
silage bales. The hole in the plastic caused by the
spear can be patched, but almost always results in
large amounts of spoiled silage near the patched
hole. Two types of bale-handling equipment that
move silage bales without puncturing holes in the
plastic are shown in Figure 2.

!a~l 4AX dh#Ah

Bale Storing

* Once bales have been wrapped and carefully
moved to the storage area, the threat of holes in
the plastic is not eliminated. Birds cause small
holes by walking on or pecking the bales. At
night, raccoons like to run across the tops of
bales when playing; their claws can puncture
holes in the wrapper. The bale storage area
should be located where wildlife activity is less
likely, and must be fenced to prevent cattle or
other large animals from damaging the plastic.
Still, bales should be periodically inspected for
holes and patched with tape.

Lastly, the longer the storage time, the more
problems with holes in the wrapper and
consequent silage spoilage. Small holes develop
over time and the spoilage from air exposure
causes the silage to mold. Wrapping the bale with
6 layers of plastic (instead of 4) is suggested for
silage stored for 6 or more months, or in
situations where holes or punctures will likely be
a problem. Experience to date has shown that
bales should not be stored longer than 6 to 9

Figure 2. Two types of bale-handling equipment.

Page 6

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