5 common mistakes to avoid when making silage for biogas

Does your silage have an unpleasant odour? Does your clamp suffer from excessive losses, effluentor mould? Are your biogas yields lower than they should be? If so, you may beguilty of making one or more of the most common mistakes when producing silage for biogas production.

Here, Tim Elsome, General Manager of FM BioEnergy, explains howcrop-fed biogas plants are only as good as the silage put into them –and how you can prevent poor silage from affecting your bottom line.

While the direct costs of poor silage production (such as low dry matter) can be significant, disposing of sub-standard feedstock brings additional financial and time burdens. Yet the alternative option – feeding poor quality silage into your digester – is far worse, potentially causing significant damage and disruption to the resident microbe population. In some cases, it can take many months to repair the damage and get the digester back to a healthy condition, costing the operator thousands of pounds in lost biogas production.

If you experience issues with your silage, you may be making one or more of the following mistakes:

1. Harvesting the crop at the wrong maturity of dry matter

Harvesting maize too soon is one of the most common errors, particularly when trying to balance crop maturity against weather conditions and the ability to harvest it.

It is difficult to get good fermentation in maize silage at moisture levels above 70%, and harvesting immature kernels will reduce the starch content of the silage, in turn reducing the amount of food for the bacteria in the digester.

Low dry matters will increase the potential for liquid draining from the clamp and could lead to environmental issues with run-off. Conversely, maize silage that is too dry (typically above 36% dry matter) can be difficult to compact.

2. Incorrectly applying additives

When used correctly, additives and inoculants can greatly improve silage quality and help to mitigate the effects of some of the mistakes outlined in this article. However, their incorrect usage is one of the most common errors we see.

It is important to follow the manufacturers’ instructions in terms of dilution and application, as well as regularly maintain, calibrate and check applicators. Applying too little additive, or uneven application, will adversely affect its performance, while applying more than is necessary is a waste of money. Choosing a biogas-specific additive which is independently approved and easy to store, dilute and apply, such as Silasil Energy XD, should also be a key consideration when comparing products.

3. Inadequately packing the clamp

There can be many reasons why a clamp is not properly packed or consolidated, such as loading too much material too fast or using machinery of insufficient weight. Poor compaction results in the formation of oxygen-containing air pockets in the clamp, which allow aerobic bacteria to grow and spoil the silage. It is also important to avoid over-filling the clamp, as this may mean that it cannot be sealed correctly.

Matching clamp-loading machinery and capacity to harvesting rates is also crucial. In addition, a silage additive, such as Silasil Energy XD, will ensure an optimal population of anaerobic bacteria, helping the silage to resist aerobic breakdown and improving quality where the clamp may not have been fully compacted.

4. Skimping on sheets and sealing

Sealing the clamp properly is essential to create the anaerobic conditions necessary for fermentation to take place in the top and side layers.

Financial losses from these areas can soon add up, with up with every 1.3 sq. m of surface area representing around 1 tonne of silage, with a value around £40/t.

Using specific oxygen-blocking covers, ensuring that sheets have sufficient overlap (especially at the clamp edges), and using side covers are all essential.

5. Poor feed-out practice

It is easy for good silage to turn bad through being exposed to the air, and this is most likely to occur when feeding out from the clamp. Some estimates suggest that up to half of all dry matter losses occur at this stage. Try to keep exposed surfaces as small and smooth as possible; ideally removing the entire open area surface to a depth of 2m each week. Process any spilled material immediately and do not take more material than can be instantly fed into the plant.

Removing two- or three-days’ worth of feedstock at once may seem like a time-saving operation, but material which has been left in the open and exposed to the air will not perform as well in the digester and is more likely to become contaminated.

When combined with good silage management practices, using a silage additive, such as Silasil Energy XD, will speed up fermentation in the clamp, improve the storability of the silage, and help to protect against deterioration associated with poor clamp management, such as sealing and out-loading.