Changing weather creates silage challenges

Following the prolonged spell of dry weather across the UK, farmers are being encouraged to test the dry matter (DM) levels of their grass and adapt their silage-making plans accordingly.

Lientjie Colahan, silage technical support at Lallemand Animal Nutrition, says many farmers are reporting little or no regrowth after taking their first cut, and this year’s grass crops are unlikely to catch up once they get some rain.

“Results from our fresh grass testing service show some standing grasses have a dry matter (DM) level as high as 24%, and normally we’d say a crop is ready to cut when the level is 16-18%,” she adds.

“If you follow the standard silage-making procedure that you always do when the grass is 18% DM, you will end up with a much drier silage than you anticipate.”

She recommends testing fresh grass – either by sending a sample away to a lab or doing it at home using AHDB’s instructions for the microwave method – to understand DM levels so you can adjust your silage-making plans if necessary.

“You need to look at your crop and the weather conditions, to see how you manage it to pick it up at the recommended 30% DM,” adds Mrs Colahan.

“Dry grass is much harder to compact and if it’s left unsheeted overnight, it can spring up like a sponge sucking in more air, which means further compacting will be required before more grass is added to the clamp.”

She also advises farmers to walk through their silage fields to see if any residual slurry is present due to the lack of rain, and if a significant amount is there, she recommends increasing the mowing and tedding height to prevent contaminated grass from going into the clamp.

In instances where a grass crop receives rain after a long period of dry weather, Mrs Colahan says farmers need to be mindful of nitrate levels.

“If you’ve put down slurry and artificial nitrogen, the grass will suck up as much of that as possible as soon as there’s a bit of moisture leading to what’s called luxury uptake of nitrogen,” she explains.

“This is essentially a big spike in free nitrogen in the plant, which is measured as nitrates in a fresh grass test, and something that results in grass not fermenting as easily.”

She says a nitrate result of less than 1,000mg/kg fresh weight is required for good fermentation, however, luxury uptake of nitrogen can push this level closer to 2,500mg/kg.

“You can overcome this by waiting to make silage, using the rule of thumb that in good conditions, grass will consume 500mg/kg of nitrate per day, or wilting the grass for longer to get it as dry as possible,” adds Mrs Colahan.

“This is because the undesirable clostridia microbes, which cause spoilage, like to consume nitrates in grass; however, they struggle to be active when the grass is dry.”

In all instances, Mrs Colahan recommends the use of a crop- and condition-specific inoculant to aid fermentation, with the recent dry weather prompting many farmers to switch from a wet crop product to a dry crop one, such as Magniva Grass Dry, to reduce losses at feed-out.

“You can overcome a lot of stability issues with silage by compacting it really well, but under dry conditions, getting high compaction becomes more and more difficult,” explains Mrs Colahan.

“Once you expose the clamp to air, a gas exchange starts to happen; the CO2 seeps out and is replaced by oxygen, which causes the spoilage yeasts and moulds to come back to life again.

“The inoculant helps prevent this by producing antifungal molecules during the fermentation process.”

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