Silage Insights - Bale Silage Production
Improving silage quality and reducing CO₂ emissions

Climate change is currently having a number of effects on the farming community and will, if all the predictions are correct, continue to do so for some time to come.

There are 3 key impacts: firstly, livestock producers, like the rest of society, are being encouraged to reduce their carbon emissions. Alongside this the weather is becoming more unpredictable with a situation in 2006 of silage shortages due to a very hot summer and that of 2007 being one of the wettest on record, with flash floods devastating silage making. Warmer winters also result in forage continuing to grow at times when previously it would have been dormant. Microflora associated with the forages, particularly undesirable microbes such as yeasts and moulds that cause spoilage of silage when oxygen is present also continue to grow at times when they previously would have been dormant or dying. Finally, there is the economic impact with both fertiliser and cereal based concentrates becoming increasingly costly. In addition, the drive for bio-fuel production and increased demand for meat and milk from China has also meant that less livestock products are available to the consumer.

So now is the time more than ever to make the best use of both freshly grazed and conserved forages within the farming system. Doing so will capture the increased value of livestock products for the farmers' benefit rather than pass the increased value on to a sales representative from a feed or fertiliser company.

So we now have 3 targets/problems to consider/overcome when making our silage this year.

1. To reduce carbon emissions.
2. To harvest forage for silage with increasingly unpredictable weather conditions.
3. To maximise the conservation of nutrients present in the fresh forage during silage making so that more of these nutrients can be converted into saleable product - namely meat and milk - to maximise profitability.

To hit all three targets may seem like a tall order. Luckily most decisions about how you make your silage will have positive impacts on all 3 criteria.

One key factor that affects both silage quality and carbon emissions during silage production and feeding are dry matter (DM) losses. These occur at all stages of the silage making process, from the field through respiration and fermentation to feed-out. In clamp silage these are often as high as 25% where as in baled silage they will be much lower at around 8%.

Improving control of the process will reduce these losses and improve silage quality resulting in more silage being converted into meat and milk and less being wasted. Figure 1 shows the relative proportions of losses at each stage of the silage making process. If we consider field, silo filling/baling and wrapping and aerobic spoilage then make the assumption that all these losses are due to aerobic respiration, the result is forage dry matter will be converted completely to CO₂ and water. So for every tonne of clamp silage with 25% DM losses then 250kg of DM will be lost and 61 kg of CO₂ will be produced (see Table 1.).

Table 1 - Clamp vs. bale silage: DM losses and CO₂ production per ton of silage

Source: IGER

However comparing the losses often associated with the baled system for the same tonne of silage with an average 8% DM loss equates to 80 kg of DM lost and 19.5 kg of CO₂. Losses of effluent should be eliminated by ensuring the DM content of the silage is above 28%. However, achieving this is not always easy and rapid wilting to the required DM is essential to ensure that field losses of DM are not increased by excessively long wilting times. Fermentation DM losses are more difficult to convert to CO₂ losses because there are so many different pathways that can result from the silo fermentation.

To minimise these losses inoculation with an inoculant containing strains of homofermentative lactic acid bacteria is required as these maximise the production of the 'good' silage acid - namely lactic acid- and reduce other 'bad' acids -namely acetic and butyric acids. Again we can assume that for every gram of acetic acid in the silage analysis 0.733 g of CO₂ is also produced. Data taken from a recent publication from the Institute of Grassland and Environmental Research (IGER) showed that the acetic acid concentration in inoculated silage (10 g/kg DM) was significantly lower than that of the concentration in untreated silage (27g/kg DM). If we convert this back to 1 tonne then the inoculated silage would have produced 7.33 kg of CO₂ compared to 19.79 kg CO₂ for the untreated silage. Oxygen ingress into the silage will also encourage acetic acid rather than lactic acid production and the same DM losses and CO₂ production.

Whilst these calculations represent a gross over simplification of the ensilage process and associated losses they do give an idea of losses on farms from the point of cutting forage to feeding it. They do not take into account the impact on climate change of the products brought in to make the silage.

So we can clearly see that the DM losses not only represent a loss of forage to feed to your stock but also represent production of carbon dioxide. Reducing these losses not only affect your bottom line, but reduce the carbon footprint of your business. Air, or more correctly oxygen, is one of the main culprits in all of this. So methods to remove oxygen from the silage as quickly as possible and maintaining an oxygen free environment right up to the silage being fed will benefit everyone. Attention to detail will enable reduction of these losses in both clamp and bale silage systems. However, baled silage production systems offer many opportunities to reduce losses whilst increasing silage quality. Baled silage production systems can be flexible enough to both ensure maximum use of grazed grass (which in itself will reduce carbon emissions whilst increasing productivity), and give more flexibility in harvesting opportunities even in a poor summer.

If you only take one message from this remember 'It's crucial to exclude oxygen throughout the silage process.' Everything you do to achieve this will improve your silage quality, reduce your forage losses and reduce your impact on the environment.

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