**3. Lining bunker walls with plastic**

Livestock farms can store silage in various ways such as horizontal silos (bunker and stacks), tower silos, bagged silos, or wrapped bales. Several farms prefer horizontal silos due to relatively low construction costs, greater safety compared to tower silos and high work rates for filling and unloading [2]. Nevertheless, their design allows large areas of the ensiled material to be exposed to the environment and prone to spoilage, especially in the upper layer

In horizontal silos, during the storage period, a spoiled layer is formed below the sealing sheet, known as "surface waste." Although there is also some evidence that invisible oxidation losses occur throughout the whole mass of silage during the storage period. A large percentage of the silage mass (about 25%) can be within the top 1 m depending on silo size and depth.

The most common material used to seal horizontal silos is the plastic film. The principal function of the film is to seal the forage and allow anaerobic conditions to establish [4]. Plastic films of 150–200 μm thickness have been used for this purpose. Although polyethylene (PE) sheeting has been the most common method used to protect silage near the surface, the protection provided is highly variable and often changes during storage [5]. Thus, the effectiveness of covering methods is very important to limit aerobic deterioration and losses

This chapter presents the main factors related to sealing methods that affect the extent of aerobic deterioration in horizontal silos. Furthermore, the chapter review aims to identify

Along with proper harvesting and filling techniques, it is also equally important to properly cover a bunker silo. Previous studies have demonstrated that the quality and recovery of silage

A study summarized the DM and nutrient losses when bunker and stack silos are not sealed [6]. From 1990 to 1993, the top 0.90 m of silage from 127 horizontal silos was sampled at three sites throughout the silo face. Sampling depths from the surface were 0–0.45 m (depth 1) and 0.45–0.90 m (depth 2). The silos were sealed with a single PE film of black or white-on-black

Losses were higher in bunkers and stacks that were not sealed. Silage locates in the peripheral area of the unsealed silos showed pH values ranging from 4.75 to 8.55, which were typical of spoiled silage. When a plastic film was applied, the organic matter losses in the upper layer (top 0.45 m) were reduced. Silage sealing also reduced spoilage losses in the second 0.45 m. The aerobic deterioration is initially limited to the top 15–30 cm in an uncovered silo. The reason for this is that aerobic microbial activity is great enough in the upper layer to remove all of the oxygen entering into the crop either by diffusion or by convection. As the readily degradable components of the crop in the top layer are exhausted, the rate of microbial activity declines allowing oxygen to move deeper in the silo and cause deterioration at that level [7].

proper management strategies to improve silage quality on commercial farms.

are compromised if horizontal silos are not covered with plastic film.

(from 100 to 150 μm thick) secured with tires, sidewall disks or soil.

and near the walls [3].

54 Advances in Silage Production and Utilization

in the large mass being protected.

**2. Unsealed silos**

A large part of the silage stored in horizontal silos is exposed to air and is prone to spoilage, especially in the upper part near the walls (at the shoulders of the silo), which are difficult to seal properly. A research reported silage DM losses near the surface of bunker silos to be the highest (76%) near the silo wall and the lowest (16%) in the core [9]. Thus, a problem still not fully solved is the connection of the cover to the bunker silos.

The best results are achieved by putting an additional film 1–2 m deep (depending of the silo size) between wall and forage, and then over the forage, before the main sheet is attached (**Figure 1**). The result of this additional effort is that silage quality along the wall is similar as that throughout the silo [10, 16].

**Figure 1.** Bunker lining diagram. Step 1 = before silo filling, place a plastic sheet along the length of the sidewall with approximately 2 m of excess draped over the wall; Step 2 = sidewall plastic should lap onto the forage top at the end of filling; and Step 3 = cover the bunker with additional plastic film.

There are limited studies showing the effects of bunker silo sidewall plastic on silage characteristics. A survey in 20 dairy farm bunker silos, 10 without and 10 with sidewall PE plastic, demonstrated that lining bunker wall improves fermentation and produces silage with greater digestibility [11]. Sidewall plastics have more effects on forage preservation; however, it will be addressed in Section 4.2 of this chapter.
