Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2003
Publication Date: 3/1/2004
Citation: Savoie, P., Muck, R.E., Holmes, B. 2004. Laboratory assessment of bunker silo density, part ii: whole-plant corn. Applied Engineering in Agriculture. 20(2):165-171. Interpretive Summary: For farmers making silage in bunker silos, achieving a high density when putting the crop in the silo has several benefits: better preservation of the silage in the silo, a silage that is less likely to heat and spoil during feeding, and reduced overall storage costs. However, most of the strategies for achieving a high density are based on experience or the results of silo surveys. Consequently, it is not known which factors are truly most important. Earlier we began to study several of these factors (pressure, time/layer, layer thickness) in alfalfa and grass in a pilot-scale compactor that allows us to compress up to six feet of compacted forage. In the current study, we used chopped whole-plant corn in the same compactor. Dry matter density in corn silage was increased most by higher pressure and thinner layers of crop. Compaction time and dry matter content had less effect on density than pressure or layer thickness. Our next step is try similar experiments on field-scale bunker silos in order to confirm the results. If confirmed, the results will be incorporated in a spreadsheet model that will help farmers decide the best way to make high density silage in their particular circumstances.
Technical Abstract: The density of forage crops in bunker silos can vary between 100 and 400 kg DM/m^3 and is affected by variables such as packing tractor weight, time of compaction and layer thickness. To better understand and predict silage density in bunker silos, chopped whole-plant corn was placed in layers of 0.15, 0.30, 0.45 and 0.60 m in a rectangular container 482 mm by 584 mm simulating the footprint of a tractor tire. Pressure between 20 and 80 kPa was applied to the forage by a platen. The most frequently used pressure of 40 kPa corresponded to the weight of a 4600 kg tractor spread over four tires. The total time of compaction varied between 1 and 10 s; the most frequently used time of 5 s was equivalent to two tires passing four times at a speed of 3.4 km/h. A total of 25 tests were conducted. The crop dry matter ranged between 33 and 44%. Results showed the pre-compressed density of the first layer (0.30 m high) averaged 95 kg DM/m^3. The highest compressed density ranged between 169 and 261 kg DM/m^3 with an average of 216 kg DM/m^3. After releasing pressure, the relaxed density of the first layer ranged between 117 and 153 kg DM/m^3 with an average of 132 kg DM/m^3. After 6 layers, the average relaxed density became 185 kg DM/m^3, a density 14% lower than the average highest compressed density. A logarithmic model fitted the data very well (R^2 > 0.97 in all 25 tests), indicating that density increased continually as the number of layers increased. Model parameters were significantly affected by layer thickness and pressure while time of compaction and processing had a smaller effect. DM concentration was not significant. A model based on extrapolation of laboratory results is proposed to predict density for deep bunker silos, but field data are required to validate the model under such conditions.