Farmers are being urged to assess the dry matter (DM) content of their grass and adjust silage-making plans accordingly, despite recent rainfall, following an extended dry spell across the UK.
According to Lientjie Colahan, silage technical support at Lallemand Animal Nutrition, many are reporting minimal or no grass regrowth after their first cut. She warns that the crop is unlikely to recover fully, even though rain has now returned.
“Results from our fresh grass testing service show some standing grasses have a dry matter (DM) level as high as 24%,” says Mrs Colahan. “Normally we’d say a crop is ready to cut when the level is 16-18%. This means if you follow the standard silage-making procedure that you always do when the grass is 18% DM, you’re going to end up with a much drier silage than you anticipate.”
To avoid this, she strongly recommends testing grass before cutting - either by sending samples to a lab or using AHDB’s microwave method at home.
“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,” she adds.
Drier grass poses challenges: it’s harder to compact and, if left unsheeted overnight, can spring up like a sponge, drawing in air and requiring extra compaction the next day.
Mrs Colahan also advises walking silage fields before cutting to check for residual slurry, which may not have been washed in due to previously dry conditions. If slurry is present, raising mowing and tedding heights can help reduce contamination.
Where rain does return after a dry period, farmers should be wary of nitrate spikes in the grass.
“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 leads to elevated nitrate levels in the plant, making fermentation more difficult. For successful silage, nitrate levels should be below 1000mg/kg fresh weight - but luxury uptake can push this to 2500mg/kg or more.
“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,” advises Mrs Colahan.
Alternatively, wilting the grass for longer can help, as clostridia microbes - responsible for spoilage - struggle to thrive in dry conditions, especially when nitrates are present.
To aid fermentation under these challenging conditions, Mrs Colahan stresses the importance of using an inoculant tailored to crop type and moisture levels. For drier grass, she recommends switching to a product like Magniva Grass Dry, which is formulated to reduce dry matter 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,” she notes.
“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.”
An effective inoculant, she says, helps by producing antifungal compounds during fermentation - offering a vital line of defence as dry weather conditions continue to challenge normal silage routines, even after some rain.
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