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Making silage in a changing climate (Feb 24)

Updated: Apr 8

Successful dairying in a changing in climate requires agility, flexibility, and building more resilience into the silage-making systems. We spoke to an agronomist to find out more.


Every producer who has made grass silage for several years may feel they have got to grips with the process and can manage it like clockwork. But this winter, more than many, should demonstrate the need to adapt to a changing climate and review some silage-making practices.

A wet winter, such as 2023/2024, can have a profound effect on silage yield and quality, says independent grassland consultant George Fisher. “Cold, wet soils in spring and the resulting slow grass growth can mean either a lighter or later first cut. The latter will hit forage energy and protein levels and increase its fibre content, potentially impacting feeding throughout next winter,” he says.

But measures can be taken to mitigate these effects, and a good a place to start as any is with soil aeration. “The main problem we’ve seen this winter is compaction at the top of the soil profile,” explains Dr Fisher “Soils that are capped in this way are cold and wet and their health and microbiology will be compromised by the resulting anaerobic conditions. This results in reduced grass growth and increased surface run-off, and both are costly to dairy businesses and the environment.”

But before hitching up the aerator he says producers should go out with a spade and dig inspection pits. “This will show where compaction is and where to concentrate aeration. Even in waterlogged soils where there’s capping, it can be quite dry underneath and this means it’s worth aerating, as the field has capacity to hold more moisture.

“But if soil is saturated throughout its profile, there’s no point. Aerating could even make things worse,” he explains. “In this instance producers should wait for natural drainage to do its work.”

Spike aerator

Once areas to be aerated have been identified, he says a spike aerator should be used as soon as land will allow travel. “These aerators were popular 15 years ago, but could do a good job this spring. They may not have an instant effect on plant growth, but they will allow air into capped soils.”

Taking these early-season measures should ensure that grass growth gets off to a better start, and producers should continue to closely watch the weather and conditions through the season. “Climate change requires a change of mindset,” he adds. “We were warned by the Met Office more than 10 years ago of the wetter, milder winters to come, and a change in our approach needs to follow suit.”

When it comes to silage-making itself, Kelvin Cave’s Michael Carpenter agrees that the rule book may need to be changed. “If the wetter conditions persists, there are some specific considerations. Spoilage bacteria, such as clostridia and enterobacteria, are more likely to come in on the crop in muddy conditions. In this situation, we’d recommend using a preservative containing sodium nitrite, as this will kill these spoilage bacteria,” he says. “Using a bacterial inoculant that encourages fermentation in a certain direction may not avoid an undesirable butyric fermentation.”

Grass grown through warmer winters and through both wet and dry weather extremes is also at risk from yeasts and moulds. “These create further spoilage and nutrient loss and a particular issue are moulds that contaminate the forage with mycotoxins, which can have serious negative impact on herd health,” he says.

“Some mycotoxins are coming in from the field, particularly after a mild winter. They are entering the clamp, however good its management, and this may mean that a mycotoxin binder is required.”

That said, it is possible to kill yeasts and moulds as the crop is ensiled, and this will stop the formation of more mycotoxins. “It will also require the use of a silage preservative specifically developed to target these fungal spoilage organisms,” adds Mr Carpenter.

“This means looking for products that contain sodium benzoate and potassium sorbate, which are currently the only commonly used preservatives proven to eliminate yeast activity without compromising fermentation.”

The Safesil range of preservatives includes products that are tailored to hit both fungal and spoilage bacterial loadings.

Chop length also needs to be reconsidered in wet conditions to avoid slippage in the clamp at feed out. A longer chop of up to 10cm for a low dry matter silage (less than 22%) will help secure the clamp. “Filling the clamp in layers on a long, low ramp, rather than the traditional Dorset wedge, will also help,” says Mr Carpenter. “Spread forage evenly, in layers of between 15cm and 23cm, and compact each layer.”

Excessive compaction

While good consolidation is important in silage-making, low-dry-matter crops can be over-compacted.

“Wet silage is heavier than dry silage, and it’s possible to put too much pressure on clamp walls, which has obvious dangers, and can also increase effluent production,” he adds.

Wet weather also requires a flexible approach to cutting, and producers should be prepared to cut at any time that conditions allow. “Multi-cut systems allow for smaller, more frequent cuts to take advantage of narrow weather windows,” he says. “In drought conditions this harvesting regime will also allow swards to recover more quickly and yield more across the entire growing season.

"And don’t be afraid to bale,” he adds. “The little-and-often approach may look more expensive but if it allows better weather to be exploited at the right time for the crop, it could be more cost-effective in the long run – and balers have the bonus of causing less soil compaction than a loaded trailer.

Thinking beyond grass may also be a feature of future forage production and can help address both nutritional and agronomic needs. “We worked with a producer in 2022/2023 who direct drilled rye in September and harvested the crop as a green wholecrop in late April before drilling maize,” he says. “It made a high-energy high-protein forage and no ground was left bare during the winter".

Silage-making pointers

● Avoid overwintering bare soils, and aerate capped areas as soon as possible in spring

● Maintain a long chop-length of around 10cm in the wettest silage

● Kill spoilage bacteria and fungi with appropriate preservatives

● Compact in thin layers on a long, low ramp

● Avoid over-compaction of low-dry-matter silage to reduce effluent and improve safety

● Consider alternative forage crops for ground cover and nutrition

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