Chopping grass for silage
Introduction
All forages are composed of dry matter (DM) plus water. Therefore, a silage which has a DM content of 45%, contains 55% moisture, for a total of 100%.
When completely dried in an oven, only the DM remains.
It is the DM that contains the energy, protein, fibre, minerals and vitamins that livestock require for maintenance and production.
Target DM content at harvest
A good silage fermentation depends on the forage being harvested in a target DM range.
The target DM content will vary with factors such as crop type, growth stage at harvest, and the type of equipment and storage method being used.
The DM content for baled silage is usually higher than that recommended for silage harvested with a forage harvester and stored in pits or bunkers.
The maximum DM content recommended for most Australian silage storage systems does not exceed 50% DM, the level for most baled silage systems.
If the forage becomes over-dry, very fine chopping and using balers that can compact the material well may allow an adequate preservation of the silage.
However, harvesting at DM contents above the target ranges in Table 6.3 is not recommended because of the high field losses that can occur.
In reality, if most of the crop is to be harvested at the desired DM content, harvesting will usually start when it is slightly lower than recommended.
Chopping silage
Minimising time delays – by using extra or larger equipment, or contracting operations, for example – ensures quality losses during harvesting are kept low, and that most or all the silage is harvested within the target DM range.
Effluent loss can be a major problem with low DM silage, but is less significant when DM content of the silage is more than 28-30%. The contamination of waterways and groundwater with silage effluent is a potential problem that can be avoided with good wilting management.
Contamination of water systems is a growing concern, receiving increasing attention from the various environment protection authorities. As well as being an environmental concern, effluent loss results in a decline in silage quality.
Silage effluent contains many nutrients, with up to 5-10% solids, comprising soluble crude protein (20-30%), soluble sugars (4-30%), fermentation products (0-30%) and ash (20-30%) on a DM basis. A silage of 20% DM may lose 5% of its DM as effluent, most of which is highly digestible.
- Legumes have relatively low WSC content and, for chopped silage, grasses or cereals, at the lower end of the target range.
- More mature plants with lower leaf:stem ratio need to be ensiled at the lower end of the recommended DM ranges to ensure adequate compaction (see Table 6.3).
- Haylage is an American term used to describe high DM silage system. The enormous weights inside the towers compacts the silage.
Some producers have successfully ensiled large square bales at 55-70% DM. However, field losses (DM and quality) at these high levels are greater
