Do you have too much waste in your clamp this winter?

Published 23 March 18

I have recently been involved in a project funded by AHDB  which aimed to examine the variability in grass silage quality in clamps from 20 farms in England. We wanted to see what factors were associated with differences in quality, both within a clamp on a single farm, and between clamps on different farms.  

The height of grass in the clamp, clamp width and length was assessed first. In addition, ambient temperature in front of the clamp was measured as was the geographical orientation of the clamp and the open face. From the clamp dimensions, the sampling points in each clamp were then marked out as shown below.

At each sampling point, silage density (kg of fresh matter (FM) per metre squared (kg FM/m3)) was assessed using a cored sample.

Silage Density Sampling

Waste silage

Top and shoulder ‘waste’ silage was assessed on all farms and samples collected. The top waste sample was collected by walking across the top of the clamp and taking a core vertically down, approximately 30cm depth every third or fourth step and mixing all cores taken together. These samples were analysed by wet chemical procedures for Dry Matter (DM) and Ash.

For clamps, the vulnerable zone is 0.5m from the side wall or the top sheet of the clamp. Many producers disregard this portion of the clamp as being the ‘bits around the side’ but these evaluations show a significant proportion (on average 27 per cent of the volume and 21 per cent of the fresh weight) of all the silage is in these vulnerable zones. For the clamps assessed, the average cost of filling the clamp was around £21,000, which means on average over £4,000 worth of silage is in the vulnerable zone. 

The proportion of the clamp within 0.5m of the wall increases as the silage clamp width and height reduces. The crucial factor is management at filling and rapid feed-out irrespective of clamp size.  The data highlights the importance of silage in this region to the overall quantity of silage and its effect on losses of both DM and quality. By knowing this, management process can be put in place to reduce losses.

Silage density

The density of silage is key to many of the problems associated with storage. Poor density leads to poorer preservation quality and secondary fermentation (not to be confused with aerobic spoilage). This is where products of the primary fermentation, normally lactic acid, are converted to secondary fermentation products such as acetic and butyric acids by undesirable silage microorganisms, because of the presence of trapped oxygen at the beginning of the storage period. Poor density also increases the ingress of oxygen during the entire storage period if sealing is inadequate and increases the risk of aerobic spoilage or deterioration at feed-out due to the ability of oxygen to penetrate further into the silage from the open clamp face. 

Figure 1 shows the variation in density for all 20 farms. At each of the nine sampling sites density was measured. The graph indicates the mean values of the three right hand side, left hand side, top and vertically central samples. The target density is 750 kg/m3, which suggests most of the clamps were below target.

Variation In FM Density

In terms of waste, nine of the 20 farms had no visible top or shoulder waste, with the range for the other clamps being 0.2 per cent to 36.7 per cent, which equates to £44 to over £8,000 of lost production due to visible waste in the clamp.

Top tips to ensure good consolidation:

  • Fill the clamp rapidly, spread silage evenly and consolidate well. The pressure exerted under the wheels of a heavy tractor will only be effective down to approximately 15cm depth
  • If silaging continues the next day, sheet down overnight
  • DO NOT ROLL the following morning as this creates a vacuum and pulls more air into the silage, when the aim is to get all the air out
  • Prevent soil contamination by cleaning tractor tyres before rolling. Keep tipping area clear of mud
  • Aim for 250kg DM/m3 or 750kg FM/m3. This will improve quality, reduce DM losses and aerobic spoilage at feed-out
  • Do not over fill a clamp. Compaction above the walls is at least 10% lower than if the silage is level with the walls. Poor compaction increases silo losses both during storage and at feed-out

More information can be found in the BRP manual Making Grass Silage for Better Returns