Laboratory assessment of bunker silo density. I. Alfalfa and grass

Muck, R.E.; Savoie, P.; Holmes, B.J.

Laboratory assessment of bunker silo density. I. Alfalfa and grass

2004

Muck, R.E. | Savoie, P. | Holmes, B.J.

A laboratory apparatus was developed to simulate pressure, time of compaction, and layer thickness as applied in a bunker silo. Chopped alfalfa or orchardgrass was placed in layers of 0.15, 0.30, and 0.45 m in a 482- x 584-mm rectangular container simulating the footprint of a tractor tire. Pressure between 20 and 80 kPa was applied to the forage by a platen. The total time of compaction varied between 2 and 10 s. A total of 23 tests (17 with alfalfa, 3 with grass, and 3 with mixed alfalfa-grass) were conducted; dry matter (DM) concentration ranged between 20% and 54%. The pre-compressed density of the first layer (0.30 m high) averaged 72 and 55 kg DM/m3 for alfalfa and grass, respectively. The highest compressed density ranged between 138 and 339 kg DM/m3 with an average of 220 kg DM/m3. After releasing pressure, the relaxed density of the first, uppermost layer ranged between 81 and 152 kg DM/m3 with an average of 127 kg DM/m3. After six layers, the average relaxed density was 181 kg DM/m3, 18% lower than the average highest compressed density. As successive layers were added, the cumulative DM density increased according to a logarithmic model. The model suggested that density would continually increase, slowly but without reaching a plateau, as the silo height increased. Within the experimental range, parameters of the logarithmic model were significantly affected by pressure, DM content, crop species and chop length, but not by layer thickness or time of compaction. More laboratory data are needed to understand interactions between the variables while field validation is necessary to extrapolate results to deep bunker silos.

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