2025 – AFBI reports a bumper year for white clover

Date published: 04 November 2025

‘Clovercheck’ trial results from AFBI, Hillsborough show that 2025 has been a productive season for white clover. CloverCheck is part of the GrassCheck project, funded by DAERA and Agrisearch.

The work records white clover performance throughout the growing season compared with Nitrogen (N) fertilised grass-only plots. Figure 1 shows that grass/clover plots, even with no fertiliser, out-yielded fertilised grass plots, including those receiving 270kgN, by approximately 1tDM/ha from April-October.

Much greater yield benefits were recorded when compared to lower rates of N fertiliser such as grass+135kgN/ha and grass+67kgN/ha. The reduced use of fertiliser N results in considerable financial savings as well as environmental benefits. GrassCheck/CloverCheck plots do not receive any manure (to ensure the long-term integrity of data) and thus their absolute levels of forage yield tend to be lower than those on grazing fields.

Figure 1: Cumulative herbage yield of GrassCheck and CloverCheck plots in 2025

The AFBI trial data is based on simulated grazing plots, with grass-only plots cut every 3 weeks and grass/clover plots every 4 weeks throughout the growing season. Fertiliser N applied to clover plots is skewed towards early season, to boost spring herbage production and minimise any negative impact of fertiliser on naturally occurring fixation of N in clover-based swards. Results also show that clover content was <10% of dry matter in April but increased quickly from June onwards with >50% of dry matter recorded in August which helps to explain the overall yield differences recorded. From a herbage quality perspective the Crude Protein and Metabolisable Energy (ME) of grass vs grass-clover was similar in 2025. Recently, in mid-October crude protein was 22 vs 22.1% DM; ME was 12.3 vs 12.1 MJ/kgDM for grass and grass/clover respectively. 

Future articles will quantify the full economic and environmental impact of grass/clover production.  

Despite these results and other trial findings, many farmers are not yet adopting grass/clover in their grazing systems. Some pros and cons of white clover are considered below. 

Pros

1. Free Nitrogen ‘fertiliser’ -  N Fixation is a naturally occurring process

• White clover has a symbiotic relationship with Rhizobium bacteria in its root nodules that can draw down atmospheric nitrogen (N₂) which is then made available for grass uptake.  This represents an economic saving and reduces the emissions of nitrous oxide, a potent greenhouse gas.

2. Improved Forage Quality

• Herbage is typically higher in protein and digestibility compared to many grass species, which, enhances animal performance often equating to greater weight gain and milk production.

3. Increased Pasture Productivity

• Inclusion of clover boosts total dry matter production in a mixed sward with grasses, if well managed. And improves yield and sward resilience in changeable weather.

4. Extended Grazing Season

• In a year like 2025 the sward can remain productive late into the season which extends the grazing season and reduces the demand on conserved feed and reduces the volume of slurry produced.  Extended grazing also reduces ammonia emissions.

5. Soil Health and Structure

• Root systems of clover improve soil aeration, organic matter content and earthworm populations which enhances water infiltration and builds long-term soil health and resilience.

6. Biodiversity

• Cover supports pollinators (bees) and contributes to agroecosystem diversity.

Cons

1. Bloat Risk

• High levels of soluble protein and rapid fermentation in the rumen can cause ruminal bloat especially in cattle. Daily checks are required in high risk periods – prevention includes anti-bloat agents, long fibre from hay/haylage and controlled grazing strategies.

2. Establishment and Persistency

• Clover is vulnerable to competition during establishment from grasses and sometimes gives inconsistent performance in the long term.  As such reseeding and/or over-seeding may be required in poor performing fields.

3. Spring growth

• The growth of clover is temperature and moisture dependent – a cold, late spring results in poor clover performance in March/April. However, it can contribute positively to the sward, as noted above, when grass growth is challenged during the main growing season. 

To address some of these issues a new project called ZeroNfarm started in 2025 at AFBI Hillsborough, funded by DAERA. Initially it will examine all the existing published scientific information on clover, followed by plots trials to test a range of clover:grass species compatibility and evaluate pre-release varieties.  The work will extend to including these swards in a dairy cow system study at AFBI Hillsborough with zero or very low use of synthetic N fertiliser for grazing and silage. Ultimately this will reveal scientific, technical and practical outputs on the management and reliance on clover-based grassland farming systems in N Ireland.  

Tips for managing clover this autumn:
 

1. Ensure grass/clover fields are clean grazed before the onset of winter - this will reduce the competition and shading from grass and stimulate clover stolon branching which sets the clover potential for next spring.

2. In the last grazing round prioritise grazing clover swards when ground conditions are good, to minimse poaching and clover stolon burial.

Plan ahead – soil test in December/January to check acidity (ph=6.5) and P/K levels are on target (index 2+); early slurry can be applied in spring to boost early season performance.