Compaction of silage commodities using the silage bag technology

The advances in technology with a much higher throughput allow its use in a more powerful silage chain. As with all silage technologies and also in use of silage bags the compaction of silage commodities has a decisive influence on the silage quality. Thus, press pulp silages, corn silages and ground husk silages were investigated on farms to evaluate their compaction performance.

The silage compaction is amongst others an important influencing factor, stability and consequently on the silage quality. During the storage phase the totally enclosed tube excludes air as long as this tube is not mechanically damaged. The storage density affects the gas exchange on the open silo with a decisive impact during the extraction phase. According to Honig silage commodities have to be compacted so that the remaining pores allow a gas exchange of not more than 20 l/h m² at the face. From the requirements in relation to the gas exchange it is possible to derive recommendations for the compaction of different silage commodities. Density measurements on practice silos, however, revealed that only about 20% of the investigated silages showed a storage density within the recommended area. To evaluate the procedure of ensiling in bags and to classify the current state of engineering in comparison to other methods, storage density in silage bags of various silage commodities at farms was measured by sampling. On one hand to find out how dry matter content of silage commodities affect the compactibility in silage bags and on the other hand it was to determine how evenly the compaction over the cross-section tube occurs.

What was done?

An electrically driven boring tool, developed at the Institute for Agricultural Technology, was used for extracting the samples (internal diameter 102 mm, screwing depth 50 cm).
Due to the large diameter and an inward cutting crown the displacement of silage to the side, and plugging of the boring rod can be prevented. In the following silage bags distributed at 10 positions over the incision area. Figure 1 shown model in April 2007 and 2008 were sampled. Altogether 10 press pulp silages and corn silages at any one time as well as 7 crushed husk silages were investigated. In this connection the temperature in the borehole was measured with an electronic thermometer after the extraction of the drilling core to record the silage temperature of the incision area.

Results:

 Lastly the storage density of corn in silage bags measured at the 10 sampling points was on average the same level as the investigations made in clamp silos. Relating to fresh mass storage densities around 520 kg/m³ - 680 kg/m³ have been achieved, which accords in case of a dry matter content of 32% to 38% with density values of 180 kg/m³ to 230 kg/m³ relating to the dry matter.

Furthermore, a significant rise in dry mass density with increasing dry matter content, as is required, was not observed in the mentioned investigation with clamp silos as well as with ensiling in bags. During the storage of press pulp in bags with dry matter content of approximately 22%, average densities of the original substance of up to 800 kg/m³ were measured.

The differences in storage densities between the core, edge and upper bag segment are with press pulp vary from the core to the upper bag middle up to 30% slightly higher than for corn and ground ear. These silage commodities show differences in densities of about 20% from the core to the upper bag middle, whereas the average storage density of ground ear in the bag was between 580 kg/m³ and 750 kg/m³ related to the original material. 

The larger differences in density of the core to the edge in press pulp silages can be explained by a greater weight of the stored silage mass, which results from the high water content of the silage. The silage in the core will be stronger after compaction as silages with a higher dry matter content and lower fresh mass density. A considerable after warming of the sampled silages could only be assessed if the bag near the incision area was damaged, so that atmospheric oxygen could enter in the silo over a long period of time. Damages of the silage bag affect especially the upper part, because air can enter more easily through the silage commodity and little voids.

Given that the tube extents elastically during the storage process, after extracting the silage at the edge of the incision area the tube puckers up itself a little bit, so that the bag lies against the silage commodities tightly and the direct air access under the bag can be reduced.

Conclusion:

To sum up the average storage densities of the sampled silages in bags were nearly at a comparable level to clamp silos. In the flank area of the bag and on the upper edge the storage density is about 20 % to 30 % lower than in core depending on the silage commodity. The main cause of after warming is a damage of the bag, which could be prevented by a covering with a protecting net. The smaller incision surface usually allows a sufficiently large feed to prevent the after warming near the incision area.

Figure 1: Boring rod (left) and position of the 10 boreholes on the incision area of the bag (right)

Figure 2: storage density of dry and original substance depending on the dry matter content (arithmetic average in each case with 10 samples)

Figure 3: storage density of press pulp (n=10), silo corn (n=10) and grinded husk (n=7) of the tube’s cross-section area