Practical implications

At Greenmount Campus many of the practical problems associated with harvesting, ensiling and utilising high dry matter silage have been assessed during the last few years.

In order to meet the target of 25 to 30% dry matter it is essential to be able to assess the dry matter of the crop at various stages. Walking through the standing crop should enable you to assess initial dry matter. As a general rule, if your boots are wet the dry matter content of the crop is approximately 15 percent. If, however, your boots remain dry after walking the field, then the dry matter content is approximately 20 percent.

Once the grass has been mown it is important to monitor the wilting process so that the crop is ensiled at the correct stage. To assess the dry matter of the cut grass take a representative sample from the swath (grass on top will be drier than grass at the bottom). Wring the grass firmly in your hands and if moisture is yielded the crop is below 25 percent dry matter. Conversely, if no moisture can be detected on your hands the crop is probably at least 25 percent dry matter.

Having assessed the dry matter content of the standing crop, you will be in a position to make a decision on how to achieve the target dry matter of 25 to 30% within 24 hours. A standing crop with an initial dry matter of 20 percent will reach the target in 24 hours if left in single swaths. If conditions are ideal for wilting, i.e. dry with bright sunshine, such a crop will reach the target within five to six hours if spread across at least 75 percent of the field area. Very heavy crops and those with low initial dry matter contents will require to be spread across the available field area in order to reach the target dry matter content within 24 hours.

Silage making conditions are typically variable and it is therefore essential to monitor the dry matter content of the crop regularly and ensile when target dry matter content is obtained. Remember, overwilting can cause problems of its own. If it is not possible to ensile immediately, or if harvesting is prolonged, then rowing up the grass will effectively halt the wilting process.

As wilted silage is generally less well fermented than unwilted silage it is very sensitive to aerobic deterioration. This is the process of spoilage after air is introduced into the silo when opened for feed-out. In this situation, not all the sugar in the crop is fermented to acid. High quality/high intake potential silage tends to have higher levels of residual sugars than is the case with extensively fermented silage. The remaining sugar presents a suitable substrate for the growth of aerobic yeasts, moulds and bacteria.

Silage leaving a sticky consistency, once squeezed in the hand, indicates a high content of residual sugar.

Moulds prefer drier to wetter conditions, so their growth can be slower in the wetter silages than in wilted silage. Yeast growth can continue under anaerobic conditions throughout the storage period. Rapid development on opening the clamp is assisted by having a high population at the outset. Prolonged field wilting for over 24 hours may result in elevated yeast counts.

The silo as well as the sheeting must be airtight to prevent deterioration. If a lot of air is left in the crop at ensiling, as a result of poor chopping and poor consolidation, then the silage will be more prone to rapid heating and moulding once the silo is opened. Short chopping and careful consolidation of thin layers of grass to remove air from the crop can help reduce growth of undesirable aerobic micro-organisms.

To assess the degree of spoilage due to aerobic deterioration in a silage clamp, dig into the face about 0.5m (1.5 ft). If the silage gets progressively hotter as you move into the silage mass, spoilage is occurring with significant nutrient loss.

Loss of nutrients due to spoilage after the silo is opened may result in significant reductions in feeding value. Spoilage can only be prevented once it has started by increasing the speed of feeding-out and by keeping the face as smooth and undisturbed as possible. Smooth silage faces can help to restrict the penetration of air into the silage mass in the clamp. During feed-out, the silo face should ideally be moved back 2 m per week.

Rate of aerobic deterioration during feed-out depends on: