Laboratory Assessment of Bunker Silo Density Part Ii: Whole-plant Corn

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 482584-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 1 and 10 s. A total of 25 tests were conducted with crop dry matter (DM) content ranging between 33% and 44%. The pre-compressed density of the first layer (0.30 m high) averaged 95 kg DM/m3. The highest compressed density ranged between 169 and 261 kg DM/m3 with an average of 216 kg DM/m3. After releasing pressure, the relaxed density of the first layer ranged between 117 and 153 kg DM/m3 with an average of 131 kg DM/m3. After six layers, the average relaxed density became 185 kg DM/m3, a density 14% lower than the average highest compressed density. A logarithmic model fit the data very well (R2 0.93 in 24 out of 25 tests), indicating that density increased continually as the number of layers increased. Model parameters were significantly affected by pressure, layer thickness, and crop processing while time of compaction had a small effect. DM content 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.