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United States Department of Agriculture

Agricultural Research Service

Research Project: Evaluation of Oxygen Barrier Wraps for Large-Round Silage Bales
2013 Annual Report


1a.Objectives (from AD-416):
Compare (EVAL-containing) oxygen-barrier and standard polyethylene silage wraps for large-round bales through a series of challenge experiments emphasizing heating characteristics, losses of dry matter, and indices of forage quality that are closely associated with spontaneous heating.


1b.Approach (from AD-416):
We propose to do a series of three challenge experiments, each designed to place increasingly difficult challenges on the oxygen-limiting properties of the two types of silage wrap (oxygen-barrier and standard polyethylene). In moist hays, spontaneous heating, dry matter loss, and changes in concentrations of fiber components and crude protein fractions are closely related to spontaneous heating/aerobic deterioration. In addition, the energy density of the resultant hay is depressed markedly, and this energy depression also is associated closely with spontaneous heating. Processes of spontaneous heating and aerobic deterioration require oxygen; as such, differences in oxygen permeability should be quantifiable in terms silage producers can easily understand on the basis of these (and related) response variables. We propose to utilize these documented relationships to assess the oxygen-limiting properties of oxygen-barrier and polyethylene silage wraps.

Challenge #1 – Based on previous work, six layers of silage wrap will support satisfactory storage characteristics for both polyethylene- and oxygen-barrier-wrapped silages. We propose to wrap 40 bales of alfalfa-orchardgrass forage wilted to approximately 50% moisture with six layers of either polyethylene or oxygen-barrier silage wrap (20 bales each). The challenge to each wrap type will be initiated by delaying wrapping, thereby allowing spontaneous heating to occur. Bales will be wrapped immediately after baling, or after intentionally delaying wrapping by 12, 24, 48, or 72 hours. Each wrapped bale will be fitted with thermocouples at baling, and temperatures will be monitored daily. Internal bale temperatures will rise with time delay for this type of forage, and will likely reach 60C or more within 72 hours. This form of heating is generated by aerobic respiration within the bale, and requires oxygen. Theoretically, bales wrapped with oxygen-barrier plastic should exhibit a more rapid temperature decline following wrapping, lower internal bale temperatures throughout the ensuing 180-day storage period, as well as reduced losses of dry matter relative to polyethylene-wrapped bales.

Challenge #2 – This challenge will be structured in an identical manner to Challenge #1, except that only four layers of silage wrap will be used to wrap each bale. Previous work showed that silage bales wrapped with four layers of oxygen-barrier wrap exhibited satisfactory fermentation and storage characteristics, but this approach was clearly marginal for polyethylene wraps. This additional challenge to the oxygen integrity of the wrap should accentuate differences between oxygen-limiting and polyethylene wraps over an identical 180-day storage period.

Challenge #3 – The integrity of the plastic wraps will be challenged even further by maintaining the four layers of plastic wrap used in Challenge #2, but wilting the forage to 35% moisture before baling. This should create bales that undergo a restricted fermentation, and are particularly sensitive to heating and external surface mold. Any conduit for entry of oxygen into these bale packages should produce measurable temperature and/or other responses.


3.Progress Report:

This project supports Objective 2: Develop new alfalfa production systems that are less costly, more productive, and of greater value for livestock and biomass conversion. During FY12, several (~20) prototype formulations of commercial plastic wraps fitted with an internal oxygen-limiting barrier were evaluated for physical characteristics on three different occasions. This preliminary evaluation effort was extended through FY13, with a final assessment of five formulations occurring on 29 May 2013. This is critical to the project because too much oxygen-limiting barrier makes the product brittle and unsuitable for commercial use, while too little negates the purpose of including the barrier in the plastic. A satisfactory formulation must be selected prior to making a production run of enough plastic wrap to begin the three challenge studies. We anticipate enough plastic containing the proper formulation will be produced during the summer of 2013. This may allow the field studies to begin by the fall of 2013 and continue through 2014.


Last Modified: 7/10/2014
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