The inclusion of red clover within a new reseed has helped to lift forage yields and also milk production on the Tyrone dairy farm, operated by David and Philip Clarke.

The Clarkes are among a group of 12 farmers taking part in the ZeroNsile project managed by AgriSearch, which aims to examine the feasibility and practicality of producing silage without the use of manufactured nitrogen (N) fertiliser.

The 110-acre Clarke farm outside Augher has approximately 80 spring-calving dairy cows, with land around the yard all grazed.

Silage is taken off a separate block consisting of four main fields, with one of those fields, extending to 12-acres, now in red clover.

As part of the ZeroNsile project, red clover is sown out in a mix, with around 3kg included alongside 8kg of perennial ryegrass and 1kg of white clover per acre. The 12-acre field on the Clarke farm was sown out on 15 June 2023. The field was ploughed, made ready and rolled before sowing. Red clover is a small seed that should be established in a fine, firm seedbed and not buried too deeply (beyond 10mm).

An Einbock seed drill was used, with the field rolled again post sowing. Ideally, sowing should be done before the end of June, to allow the crop to get well established.

To avoid the red clover being out-competed by perennial ryegrass, fertiliser containing phosphorus (P) and potassium (K), but with no N, should be applied.

However, David was unable to source product at the time, so it received two bags per acre of 9.7-24-24. Soil pH is ideal at 6.7.

The wet summer meant no spraying was possible. A total of 51 bales were taken off on 16 August.

“It was a clean-up cut to take out red shank,” says David, with the Clarkes managing to get a further 60 bales made on 2 October. Slurry was applied after each cut.

The bales were wet, “but fed very well” having been offered as a night feed to cows late in the grazing season. When cows came off the red clover silage, milk yield dropped 1l/cow.


Management this year started at the end of January with muriate of potash (0-0-60) applied to try to front-load K requirements for the season.

However, in hindsight, David thinks he should potentially have used potassium sulphate (0-0-50), as subsequent soil analysis shows the field is low in sulphur.

Slurry was applied in February and again after first cut taken in early May. Grass clips taken just before first cut showed there was 3.5t dry matter per hectare (DM/ha) in the field with red clover, compared to 3.2t DM/ha in the remaining silage block. All grass was ensiled in a pit.

“It is maybe not a fair comparison, as some of our existing silage swards are tired, but if you are able to grow more grass with no N fertiliser and it is higher quality, then red clover makes a lot of sense. Even if it goes wrong, you are still left with a field of new grass and white clover,” suggests David.

His plan is to sow out one field in a red clover mix within his silage block every other year, so it will probably be eight to 10 years before the first field is sown again.

Red clover is likely to die out of the sward within four years, but the crop cannot be grown continually in the same field, with a four-year break necessary to avoid the build-up of stem eelworm and clover rot.

As a result, an eight to 10-year rotation, as planned on the Clarke farm, will fit in with this cycle.

The other main issue with red clover is that it has a crown just above the surface and if this crown is damaged by livestock or machinery, the plant dies.

At cutting, the mowers are set to leave stubble of three inches.

The Clarkes hope to get four cuts this year, followed by a light grazing in autumn.