A research trial was conducted at Teagasc Moorepark from 29 September 2023 to 31 October 2024 to examine the effects of autumn closing date and initial spring defoliation strategy on white clover persistence.

The study compared four autumn closing dates: September 29 (very high), October 16 (high), November 1 (medium) and November 14 (low). Two spring defoliation strategies were implemented – an early defoliation on February 14 and a late defoliation on March 19.

The trial was established on two paddock types differing in initial white clover content – low clover (18%) and high clover (41%) – to assess treatment effects across contrasting scenarios. All plots were mechanically harvested, with measurements taken for herbage mass and white content to monitor seasonal and treatment driven changes. Each plot received a standardised nitrogen (N) application of 150 kg N/ha annually.

Results

In the low clover paddock, white clover content remained below the minimum threshold of 15-20% until the fifth rotation in July, with only the medium and low autumn closing treatments successfully reaching this threshold at this stage, with white clover contents of 15% and 23%, respectively (Table 1).

The very high and high treatments were delayed, only reaching this threshold by the sixth rotation in September, both at 15%, just meeting the minimum. This in turn can reduce the level of white clover contribution in the sward during the subsequent year.

Table 1: Clover contents (%) as affected by autumn treatment across seven rotations in a low clover content sward (18%) and their overall average for the year

In the high clover paddock, both medium and low treatments had reached the target, each at 18% by May, with the very high and high treatments recovering to >20% by the fourth rotation in June (Table 2).

Table 2: Clover contents (%) as affected by autumn treatment across seven rotations in a high clover content sward (41%) and their overall average for the year

Conclusion

Autumn closing date can have a significant impact on subsequent sward clover content, with a greater impact in swards with a lower clover content initially. In high clover content swards, the later closing treatments also supported faster early-season white clover recovery; however, the earlier closing dates (very high and high) did recover to the required 20% clover content by June. Deciding on a closing rotation order in autumn needs to be considered in order to reduce the impact on sward clover content during the subsequent year.

The above was adapted for use on Teagasc Daily from the paper titled: ‘The impact of building herbage masses in autumn and initial spring grazing strategy on overall sward white clover content’ authored by Fiona Beamish, Frank Buckley, William Burchill and Michael Egan and first appearing in the proceedings from the Moorepark 2025 Dairy Open Day (PDF).