Grassland reseeding: formulating grass mixtures

Read our information on the benefits of grass mixtures and top tips for using mixtures in a grassland reseed.

Most grass leys are sown as a mixture of diploid and tetraploid ryegrasses, perhaps with a small amount of other species, such as clover or timothy. Mixtures are commonly sown for three reasons:

• Risk management – to minimise the risk of a crop of seed failing
• To ensure sward quality throughout the grazing season
• To achieve a balance of desirable traits

Studies undertaken in Northern Ireland have shown that over a three-year period, under simulated grazing (in year two) and silage management (in years one and three), there was little difference between the annual DM yield of nine varieties grown as straights or in a range of mixture combinations.

However, heading date is important when considering mixtures. When varieties with close heading dates are sown together, this increases competition between varieties, resulting in an increase in DM yield compared with the average yield of the component varieties sown separately. In contrast, mixtures with a wide heading date range have a lower yield than the corresponding weighted average of their components.

Results from experiments in Northern Ireland comparing straights and mixtures

In the first year after sowing, most mixtures are likely to change in their composition from what was sown. Early studies suggest that in mixtures managed for grazing, later-heading varieties become more dominant, while, in silage mixtures, the contribution of earlier-heading varieties tends to increase. In addition, mixtures with a greater heading date range will change more than those with a smaller heading date range. However, much remains unknown about mixtures and how these changes can be minimised through variety selection and management.

• For grazing mixtures, choose varieties with a heading date range less than 15 days
• For cutting mixtures, choose varieties with a heading date range less than seven days
• Open-growing diploids tend to be more aggressive than dense-growing diploids, when sown with tetraploids in a mixture
• Have a minimum of 3 kg of an individual variety in a mixture