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Trench or silo bags: two silage options

The different silage solutions meet the different technical and economic requirements of the companies. A point to consider regarding the silage system concerns possible product losses, which are also linked to environmental sustainability

by Jacopo Bacenetti
July - September 2019 | Back

Modern silage, especially of cut corn, is generally made in trench silos, an extremely common structure in the business centers of the Italian provinces with the highest livestock density.

Nevertheless, it is quite evident the more and more frequent use of a new solution for stocking the shredded: the so-called silo bags, long cylindrical containers made of plastic film arranged horizontally on the ground, which contain considerable quantities of cut corn. Basically, it is a bag, of considerable length (up to 70-75 m), consisting of several layers of co-extruded polyethylene film which, due to its versatility, it can be profitably used in different settings. Both trench silo stocks and silo bags have their strengths and weaknesses, so the choice of the most suitable solution depends on the specific business situations. Trenches require less maintenance, but a considerable initial investment, and is a "final" choice that is little or not at all flexible concerning possible changes in the barn's production needs. With the trench, the possibility of coping with production peaks is limited to the increase in the heap, an option that poses several problems, both from the storage security point of view and the need to uniformly press the forage. Trench sizing is, therefore, the key aspect: if it is too large, it can lead to a reduction in the quality of the grains due to the impossibility of desiling all what was collected in a reasonable time, while if it is too small it does not allow to properly store the required amount of shredded, or it may be insufficient to enshrine all forages produced in particularly favorable years.

Silage packed into long round bales in polyethylene bags, on the other hand, makes it possible to easily adapt to variable production, and does not require the initial investment for the trench, but on the other hand it involves the purchase or rental of the bagging machine, as well as the consumption and disposal of the film plastic (which is not reusable).

Silo bags are manufactured in diameters and lengths of different size, so it is possible to collect in silos small quantities as well as significant amounts.  Compared to trench ensilement, compaction is generally more uniform; furthermore, silo bags typically have a reduced desiling front, so they are more suitable for small stables.  On the other hand, ensiling times and costs are higher, it is necessary to have specific types of machinery both for storage and collection, and finally, it must not be forgotten that silo bags must be disposed of properly.


Machinery for tubular silage

There is a very considerable range of models of machineries for tubular silage, both self-propelled and coupled to the tractor. In the first case, labor productivity is undoubtedly higher as it can exceed 100 t/h.

Among other things, manufacturers provide types that are also suitable for bagging grains. Work productivity also depends on the type of forage, on the degree of compaction required and on the standard diameters of the silo bags (they can be of 1.83 and 3.66 meters, or 6 and 12 ft) and with a length normally of 60 or 75 m, but which can be adapted according to the volumes of forage to be ensiled by simply cutting the sack.

Regardless of the version, it is possible to identify a central body to which the bag-holder bell is fixed at the rear, and at the front the feeding system, which can be constituted either by a hopper filled from above with a loader, or by augers and/or a conveyor belt, to which the product arrives directly from the forage transport wagons (e.g. with side discharge). Depending on the type of forage, the feeding system can also be equipped with one or more hammer or roller mills.


Trench vs silo bags: which has the least environmental impact?

As for the economic evaluation, it is possible to compare the two silage solutions also from the environmental impact point of view, therefore from the sustainability one, according to the Life Cycle Assessment (LCA) approach which makes it possible to convert both the amount of production factors consumed and the emissions into the environment into a limited number of environmental impact indicators, such as for example the carbon footprint, soil acidification, and water eutrophication.

The two compared siling modes also differ in the average size of the product loss (typically 11% for trenching and 3.5% for silo bags storage), so the environmental impact must also take into account the productive aspect of the crop. The cultivation technique taken into account, in this case, is that typically practiced in the irrigated areas of the Po plain for class 700 Corn Hybrids.

Although the largest proportion of the impact of shredding production is related to the cultivation phase (between 90 and 98% of the total), silage can also have an impact because of product losses. In the proposed comparison, the silo bags solution reduces the impact from 4.5% to 9.3%, a decrease essentially due to shredding losses.

Basically, even if silo bags cause the consumption of the plastic film to be unfavorable, the impact of its production and the use of the operating machine dedicated to the formation of silo bags is lower than that of the construction of the trench and increased product losses.

The ideal silage solution does not exist (yet ...), but by adequately examining the operating conditions it is possible to identify the solution that best meets the specific needs. The use of silo bags involves greater flexibility, an excellent ability to preserve the quality of the forage and greater integration in the management of intensive and "modern" livestock farms, but it is more expensive than traditional horizontal silos. With silo bags, it is possible to better contain product losses, as long as the ensiling is performed correctly, i.e. with the most appropriate level of compaction and no damage to the plastic film.

The widespread adoption of silo bags will probably reduce the initial investment costs for the necessary machinery, thus increasing its convenience, to the advantage of greater flexibility in managing the silage resource, especially for those companies subject to production peaks that, next to the traditional trench silos, will be able to use this innovative opportunity for the storage and conservation of the product.


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