Best practice for waste-free maize silage

Harvesting at the right dry matter (DM), chopping to the correct length, distributing the material evenly in 30cm layers max and compacting well with the right machinery before covering with two layers of plastic film, can all help reduce energy losses and wastage from maize and grass silage clamps.


This was the advice of German silage making expert Dr Johannes Thaysen at a briefing in Cambridgeshire organised by sloping wall silage clamp specialists Bock UK.


“It is only possible to use the energy in the maize plant once – ideally inside the biogas plant or the cow,” said Dr Thaysen. “Heating in the crop is a sure sign that air has got into the clamp, and yeasts and moulds are stealing the energy, wasting the money and effort that has gone into growing and harvesting the crop. Losses could be as large as 25%.


“Growers should be aiming for waste-free silage – with no dark patches under the cover, no losses at the edges or hot spots in the lower levels. It is possible to eliminate these problems by paying attention to detail, particularly at clamp filling and covering.”


Harvesting
For best results, maize should be harvested at 30-36% DM for anaerobic digestion (AD) plants and chopped to 4-7mm in length – the higher the DM, the shorter it can be chopped. Ultimately the responsibility for this lies with the driver of the harvester. New technology such as NIRS monitors, is available for in-field DM sensing, so chop length can be altered automatically to match the state of the plants across each field.


“Biogas plants run better on smaller pieces of material, however these are harder to consolidate in the clamp and more prone to heating,” said
Dr Thaysen. “Chopping shorter also costs more in diesel when harvesting, so it is a compromise. However it is essential that all the maize kernels are destroyed.”


At the clamp
Clamp filling is often the bottleneck in the day’s operations, but it is vital it is done correctly.


The crop should be spread evenly, ideally in under 30cm layers and compacted down to a target of 250kg DM/m3. There is currently no way of measuring how compacted fresh silage is at the point of filling. Dr Thaysen’s advice is to run a minimum of two heavy vehicles – for example a tractor plus a telehandler or a four-wheel truck, with high-pressure tyres (at 2.5 bar), at a speed of 3-5km/hour, for at least two minutes on each fresh layer. This all depends on the size of clamp and silage intake.


If harvest extends beyond more than one day, sheet the first day’s intake and leave it overnight. In the morning when clamp filling starts again, care should be taken not to drive on the previous day’s silage. Do not reopen the clamp and start filling on top of it. The ensiling process will have started and driving over the previous day’s material will disrupt the process and cause significant loss of quality.


Covering
Once the clamp is full it is crucial to create an airtight seal at the top, bottom and edges. Clamps with sloping sides are best for this, as machinery can safely compact the silage right up to the edge of the sidewalls.


First place a thin, 35 micrometre (μm) under-layer of plastic that molds itself to the contours of the silage surface, as this eliminates any potential air pockets. Then sheet over with thicker 115μm plastic, and finally cover with a vermin proof net weighed down with gravel bags.

“There are now combination films that deliver a transparent underlay sheet and silage sheet on the same roll, like Bock’s Kombi2plus,” said Dr Thaysen.

“This type of covering is now commonly used on the continent. In trials in Bavaria it reduced silage losses by 15%. It is also quicker and easier to put on than two separate sheets.”