Multiple gains from sward diversity

Friday 28.06.2019 , News

The government recently published the Climate Action Plan to tackle Ireland’s rising emissions and to comply with international obligations.

This plan targets all sectors including agriculture. The target for agriculture is high with mitigation strategies focused on a broad range of issues including improved grassland management, correcting soil pH and the inclusion of clover in swards. With the increased focus on the environmental agenda, the concept of increased plant diversity has been gaining momentum in recent years.

One of the challenges for farmers looking to sow a multi-species ley is to know exactly what the composition should be. Many mixtures currently on the market being promoted as herbal or multi-species leys may contain well over a dozen components. Ideally the mixture should include nitrogen-fixing and nitrogen-lifting plant types, and a combination of species with complementary root and leaf architectures, so that we are maximising the capture of sunlight, water and nutrients.

Including nitrogen-fixing species such as clovers alongside ryegrasses, for example, has been shown to result in comparable or higher animal performance than is achieved from ryegrass-only swards with higher nitrogen fertiliser inputs. There is also evidence showing that plants with different – but complementary – root structures can lead to more effective use of soil nutrients, giving an overall advantage compared to monoculture swards. Using deep-rooting species such as perennial chicory or plantain, for example, means nutrients are being taken up from a different part of the soil profile than is the case with shallower rooting ryegrasses. Having several different species will also mean multiple sources of protein, energy and minerals, presenting a more complete nutritional profile.

These benefits can translate into improved animal performance and help reduce reliance on bought-in feeds and fertilisers, and there are tangible benefits for soil health too. But the gains are only likely if mixtures are comprised of the best performing varieties. Wherever possible it is advisable for at least half the seeds mixture to be a high-ranking perennial ryegrass.

Recent research from UCD has shown benefits of reduced anthelemintic use in lambs and faster growth rates, leading to a quicker time to finishing from weaning. In New Zealand, plantain has been shown to reduce N leaching, where it has been included in swards. Issues of weed control and seasonal growth rate may mean multi-species swards are not broadly suitable to all systems. On-going research in Ireland will give a more definitive answer on the role of these swards into the future.