Red clover's role in silage swards

Red clover can contribute substantially to organic, low-input and conventional animal production systems due to its ability to fix atmospheric nitrogen and support of higher animal performance.

Swards with a high red clover (RC) content (75% on a dry matter (DM) basis) are capable of fixing 24-36kg N/t (DM) produced, meaning swards of high clover proportion and DM production are potentially fixing in excess of 200 kg N/hectare (ha) per year.

Given the cost of fertiliser and feed, and increasing environmental constraints, incorporating RC into swards can offer significant benefits to ruminant production systems. Despite the many benefits of RC inclusion, it has had limited uptake on pasture-based production systems in Ireland. The poor on-farm uptake of RC is likely due to its more complex management requirements, unsuitability to frequent grazing, reduced persistence (approximately 3-4 years), and the relatively low cost of chemical N fertiliser in the previous years.

Agronomy

Unlike perennial ryegrass (PRG) and white clover varieties, no Recommended List currently exists for RC varieties in Ireland, with Irish producers relying on information from the UK Recommended/National List to identify suitable varieties.

Red clover should be grown in rotation, allowing for a four-year break to control diseases such as stem eelworm and Sclerotinia fungus (clover rot). Typically 7.5 to 10 kg/ha of RC in addition to 20 to 22 kg/ha of PRG should be sown on well drained soils with a soil pH of 6.5 to 7.

Depending on soil moisture and temperature, seedbed preparation and sowing, establishment may be slow but not necessarily a failure. Spring reseeds offer the greatest window of opportunity to optimise pre and post-sowing management.

Red clover has a deep taproot, an erect growth habit, with a low density of large shoots. Stems are formed from the growing points located on the crown on top of the taproot. Reserves of carbohydrates and N are stored in the crown and taproot, where they are remobilised to fuel regrowth after defoliation.

The crown/growing point of RC is solitary and exposed, making it vulnerable to physical damage by machinery and animals. This means that RC is best suited to infrequent silage cuts rather than regular grazing.

Cutting intervals of six to eight weeks allow sufficient time for the canopy to intercept sunlight to replenish energy reserves. Increasing the defoliation frequency beyond three cuts can reduce yield due to insufficient replenishment of plant reserves and thus persistence.

‘Late’ silage harvests (beyond mid-September) can be difficult to ensile (insufficient wilting) and are of relatively low yield making it difficult to justify economically. Red clover has a low water soluble carbohydrate concertation and high buffering capacity, reducing its ensilability. The inclusion of perennial ryegrass as a companion species will improve the overall ensilability of RC silages as well as wilting (24-48 hours) to increase DM concentration, while ensuring that the leaf is not damaged (shattered) as a result of over wilting and excessive machinery passes.

Feeding value

Red clover silage can support higher animal performance than PRG-only silage. The feeding value of RC silage appears lower than that of PRG, with lower levels of digestibility because of high fibre levels. The elevated fibre levels are likely due to the higher levels of stem required to support the plants erect growth habit. Despite overall lower digestibility, increased DMI and animal performance can be achieved due to the faster rate of digestion of plant fibres and increased particle break down contributing to increased passage rate and lower rumen fill.

DM yield

Recent research from Grange has shown that mixed RC and PRG swards receiving no chemical N were found to have similar annual DM production to PRG swards receiving up to 412 kg N/ha per year (15.8 and 15.7 t DM/ha, respectively).

Conclusion

The inclusion of RC into silage swards has great potential across Irish pasture-based production systems of all intensities. These swards have an enhanced ability over grass only swards to maintain high levels of herbage production and animal performance in the absence of chemical N fertiliser.

This article by Nicky Byrne, Peter Doyle and Donall Fahy was first published in the Irish Dairying – Securing a Sustainable Future Moorepark 2023 Open Day Book. Access the full publication here