Historically, AgriSearch’s forage work has focused on grazing systems such as GrassCheck and multispecies swards. However, more NI dairy farms are shifting towards housed and autumn-calving systems — making silage quality and home-grown protein increasingly important for profitability.
Research in AFBI and Teagasc previously showed that red clover/grass silage can match the yields of high-input grass systems with slurry as the sole nitrogen source. What remained unclear was how the crop performs across commercial NI farm.
Twelve farms joined the project (six dairy, six beef/sheep), with three additional lucerne farms in Co. Down. Eleven of the red clover farms continue in 2025, while lucerne performance was more challenging, with only one site continuing due to establishment and persistency issues. ZeroNsile aims to determine how this translates on commercial farms across NI.
Establishment: Findings from Year One
Swards were established in autumn 2023 or spring/summer 2024, both in challengingconditions. While most farms relied solely on slurry or FYM, a small number used low-N compounds where zero-N products were unavailable.
Typical seed mixture/acre:
• 8–9 kg grass seed
• 4 kg red clover
• 1 kg white clover
Key establishment recommendation
• Control docks/weeds in the year before sowing
• Avoid overseeding: less suitable for stitching in than white clover
• Fine, firm seedbed — roll before drilling
• Drill very shallow (5–10 mm)
• Soil temperature ≥8°C (late April–June ideal)
• Maintain soil pH 6.5–7.0
• Apply P & K only — avoid chemical N
Harvest Management: Protect the Crown & the Leaf
Red clover requires a slightly different approach when it comes to management especially around harvesting. The crown sits close to the soil surface — scalp it with a mower and persistency suffers. The leaf is where the protein and energy is, but it can be easily shattered and lost through aggressive tedding or raking. Farmers within the project have already noticed lines in their fields were clover has been significantly impacted by machinery particularly in poor weather conditions.
Best practice for cutting and conservation:
• Aim for 3–5 cuts at 6–8 week intervals.
• Mow at 5–7 cm to protect the crown.
• Leave in swath, minimize raking and tedding.
• Expect a longer wilt to achieve 35% DM.
• Consider additives in poor weather to reduce fermentation risk.
Nutrient management
Red clover can fix up to 200 kg N/ha each year from the atmosphere. When combined with nitrogen supplied in slurry, this typically removes the need for chemical N. Teagasc research has shown that red clover/grass silage can even produce higher yields without chemical nitrogen, achieving 15 t DM/ha at 0 kg N/ha compared with 14.8 t DM/ha where 50 kg N/ha was applied.
However, as with any high-output silage system, nutrient offtakes must be replaced. Potassium (K) demand is particularly high — approximately 25 kg K per tonne DM removed. For example, a three-cut system yielding 12 t DM/ha (around 24 bales/acre) requires 240 units potash/acre. Slurry alone often cannot meet this requirement after heavy first cuts, so many farmers in the project supplemented with MOP to maintain soil K levels.Sulphur (S) is another key nutrient that is often overlooked. Slurry contains relatively little plant-available S, yet sulphur is essential for nodule formation and effective biological nitrogen fixation. Without enough sulphur, both yield and protein suffer. Where zero-N fertiliser blends were unavailable, several ZeroNsile farms applied calcium, potassium and sulphur fertilisers ahead of first cut. Recommended SO₃ rates are 40 units/acre for first cut and 20 units/acre for second cut, with later cuts usually supplied through mineralisation.Finally, red clover performs best at pH 6.5–7.0, higher than grass-only systems. Maintaining this pH ensures full nutrient availability and supports strong N-fixation. Lime offers one of the best returns on investment on farm — £1 spent can return around £7 through improved yield and reduced fertiliser costs.
2024: A challenging year for clover
The red clover swards established the previous year faced difficult growing conditions in 2024. A cold, wet spring delayed growth and created strong temptation for farmers to apply chemical nitrogen to help crops get moving.
Despite the slow start the red clover/grass crops delivered comparable yields and forage quality to the grass-only control fields — but without the need for chemical nitrogen. Instead, slurry alone supplied the necessary nutrients. As a result, these crops received approximately 97 units/acre less nitrogen, equivalent to 3.6 bags of CAN. With CAN priced around £300 per tonne, this represents a saving of roughly £53 per acre.
2025: Clover shows what it’s capable of
This year farmers seen what red clover can do in much more favourable conditions both for growing and harvesting. On William and Andrew Crawford’s dairy farm one of our Dale Farm farmers within the project, the red clover/grass silage area produced around 20% more dry matter per hectare than the conventional grass silage (13.8 vs 11.5 t DM/ha). Despite this higher yield, gross energy concentration was very similar between the two swards (around 18.3 vs 18.4 MJ/kg DM), meaning the red clover system delivered more total energy per hectare as well as more dry matter.
Across the three cuts, the red clover silage averaged about slightly higher crude protein than the grass (15.2 vs 13.5% CP). Fibre profiles differed slightly, with higher ADF but lower NDF in the red clover, suggesting a small trade-off in digestibility but potential benefits for intake.
However, the red clover silages were generally wetter, with higher ash and lower sugar concentrations than the grass, particularly in later cuts.William & Andrew achieved this performance with the red clover swards receiving only a small amount of chemical nitrogen — 12 units/acre in total. Across the three cuts, this amounted to 144 units/acre less N than the grass only system, equivalent to 5.33 bags of CAN per acre. At a CAN price of £300/t, that represents a saving of approximately £80 per acre.
What’s next
A beef feeding trial is currently underway within the project to compare animal performance from red clover silage versus grass-only silage. The next key focus will be persistency — assessing how well red clover maintains yield, quality and clover content over multiple years. This will provide the true test of its long-term value on Northern Ireland farms.