Establishing white clover in grass swards
Dr. Deirdre Hennessy, a Teagasc grassland research officer based in Moorepark, Fermoy, Co. Cork, recently spoke at the Irish Grassland Association (IGA) dairy conference.
During the presentation entitled ‘Can we reduce chemical nitrogen (N) fertiliser application without impacting herbage production?’ Dr. Hennessy outlined the importance of incorporating clover into grass swards, to off-set the reduction in chemical fertiliser usage.
White clover has rhizobia bacteria in its roots that can ‘fix’ N from the air, and this can then supply up to 50-200kg N/ha/year. In frequently grazed swards (eight to 10 times/year) up to 250kg N/ha/year can be fixed according to Teagasc.
Along with this, white clover can increase the tonnes of dry matter (DM) grown; increase animal performance as it is a higher quality feed; and it can reduce the need for chemical N.
White clover is the most commonly sown legume species in grassland; it is tolerant of grazing and can grow over a fairly wide range of climatic conditions.
Some of the benefits of establishing clover in a sward:
- Increased dry matter intake – + 1.5 kg DM/cow/day;
- Increased milk solids (MS) production – + 30 kg MS/cow/year;
- Increased dry matter production – + 1.5t DM/ha;
- Potential to reduce N fertiliser with white clover contents >25%;
- Increase farm profit by €150/ha.
Something to consider before establishing white clover
Dr. Hennessy highlighted the importance of soil fertility during her presentation. She said that when establishing white clover in swards, the ideal soil pH for clover is between 6.2 and 6.5, while soil indexes for phosphorus (K) and potassium (K) should be three or four.
The farms grazing infrastructure is also important. Have you a paddock system where each paddock is grazed on a 18-21 day rotation?
Introducing Clover To The Farm
Teagasc has carried out research into how to best establish clover in grass swards including direct reseeding or over-sowing; the ideal time to introduce clover to a sward is spring or in early summer.
In terms of over-sowing, Teagasc found the best time to do this was after a really tight grazing in April or May, at a rate of 3.7-5.0 kg/ha (1.5-2.0kg/ac). It was also found that there was no difference in the germination rate between broadcasting and stitching.
Introduction of clover during reseeding, Teagasc recommends having a fine firm seedbed and a sowing depth of 10-12mm. The sowing rate is lower than if over-sowing at 1.2-3.7kg/ha (0.5-1.5 kg/ac).
Managing grass/white clover swards
Paddocks with white clover established in the sward should be grazed every 18-21 days or at a high of 9-10cm; don’t allow grass shade out white clover. Graze down to a high of 4cm to allow light down to the stolon.
Reduce N fertiliser applied from early May onwards (half-rate).
For animals accustomed to clover swards bloat is not usually an issue. But for high-risk animals introduce them gradually to clover swards. Don’t let them in hungry to clover swards and don’t move them from poor-quality swards to clover ones.
Teagasc suggests alternatively to feed roughage before grazing or graze when the clover sward is dry or use bloat oil in the water (25ml/LU/day).