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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Various Factors on Bunker Silage Density

item Savoie, Philippe - AGRICULTURE AND AGRI-FOOD
item Muck, Richard
item Holmes, Brian - UW-MADISON

Submitted to: World Wide Web
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2003
Publication Date: March 15, 2003

Technical Abstract: Previous models to predict density in bunker silos were developed from empirical data and a limited number of variables. To develop a more general relationship, a laboratory apparatus was developed to simulate how pressure, time of compaction and layer thickness affect density in bunker silos. Chopped alfalfa, grass and whole-plant corn were placed in layers of 0.15, 0.30, 0.45 or 0.60 m in a rectangular container 0.48 m wide by 0.58 m long, simulating the footprint of a tractor tire. A pressure between 20 and 80 kPa was applied to the forage by a platen. The most frequently used pressure, 40 kPa, corresponded to a 4600 kg tractor with weight equally spread across four tires. Compaction time per layer varied between 1 and 10 s. The most frequent time, 5 s, was equivalent to two tires passing four times at a speed of 3.4 km/h. A total of 23 tests were conducted in alfalfa and grass and 25 tests in corn. The latter are not reported here. The pre-compressed density of the first layer averaged 72 and 55 kg dry matter (DM)/m^3 for alfalfa and grass, respectively. The highest compressed density within a trial ranged between 138 and 339 kg DM/m^3 with an average of 220 kg/m^3. After releasing pressure, the relaxed density of the first layer ranged from 81 to 152 kg DM/m^3 with an average of 127 kg/m^3. After six layers, the average relaxed density was 181 kg DM/m^3. As successive layers were added, the cumulative relaxed density increased according to a logarithmic model. Within the experimental range, parameters of the logarithmic model were not significantly affected by layer thickness or time of compaction even though short compaction times and thick layers reduced density in trials. These parameters were significantly affected by pressure, DM content, crop species and chop length. More laboratory data are needed to understand interactions between variables while field validation is necessary to extrapolate results to field conditions.

Last Modified: 5/5/2015
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