Forage Focus April 2015

Exploring the world of high quality forage production and utilisation with specialist agricultural merchant Morton’s.

Improving Silage Performance Next Winter

How has your silage fed this winter? On many farms silage quality has been variable with some top quality silage producing good results whereas others, perhaps cut past the ideal stage due to weather, have required additional supplementation.

Looking at all the elements required for producing quality silage is important as this has a direct impact on the bottom line.  Typical losses on a three cut grass silage system can be around 20% of the harvested dry matter of the material, made up of 12% in-silo losses and 8% feedout losses.  On the best managed farms this can be reduced by half to around 10% total losses.

A 20% wastage rate on a 100 acre first cut averaging 8 tonnes freshweight per acre would mean 160 tonnes are lost.  Kingshay put the cost of grass silage at over £30/t FW so reducing this by half will save over £2400, in addition to savings due to less concentrates being required.

There are three main components of losses at silage making (see graph).  The first type are the losses that occur in the field and include respiration losses while the cut crop is waiting to be picked up, leaching of nutrient losses when crop is rained on and leaf shatter when the crop is harvested.

Speed is the key to reducing in field losses.   The sooner the crop is picked up after mowing, the lower the respiration losses will be. Wilting is a way of managing the compromise between low dry matter, effluent losses and high dry matter respiration and leaf shatter, so go for a quick wilt and don’t over wilt the crop.  The target dry matter for ensiling is 25-30% so there is little benefit from over-wilting.  Also don’t move the crop too often, especially if it is dry as this will increase leaf shatter, a particular problem with clovers. More movements increase the risk of soil contamination.

The second category is in-silo losses and the key to reducing these is managing the fermentation process and avoiding post-fermentation spoilage. 

The simple aim when making silage is to ferment the sugars in the crop to produce fermentation acids, which are needed to drop the pH as quickly as possible from the 6.5 of the cut grass to pH 4.0 in the clamp. Ideally this occurs within 24 hours.  The greater the crop’s resistance to acidification (buffering), the more difficult it is to achieve a rapid and subsequently stable fermentation. Excess nitrates significantly increase the buffering capacity of the crop. A high concentration of nitrates normally means there is also a low sugar content. When this occurs it is difficult to achieve stable fermentation and the resulting silage is likely to have high ammonium N and butyric acid. Nitrate levels should be below 0.1% (1000 ppm) before cutting.

Using a crop and condition specific inoculant to achieve a lactic acid dominated fermentation to ensure a rapid pH drop is really a prerequisite of efficient fermentation and wastage reduction.

It is vital to compact the grass thoroughly to exclude oxygen as under-compaction increases in-silo dry matter losses. Most clamps are under-compacted and there is no such thing as an over-compacted clamp. Build the clamp in thin layers and roll continually to produce the anaerobic conditions required. Then cover the clamp quickly with an effective oxygen barrier.

Finally there are losses as effluent which everyone will be familiar with. As mentioned earlier wilting correctly is the main method to reduce the amount of effluent produced. Effluent contains valuable minerals and trace elements in addition to protein and amino acids. Work at Hillsborough showed that using a specific inoculant that opened the fibre structure of the grass by breaking down the hemicellulose linkages making the grass more absorbent reduced effluent losses from 250l per tonne to 100l per tonne in low dry matter silage.


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