GRAZING livestock producers should re-seed five to 10 per cent of their grassland each year to achieve greatest productivity and profitability.

They should combine the most effective new sward establishment with the least time out of production, and look beyond ryegrasses – to hybrid festuloliums in particular – for the most palatable and robust seed mixtures.

The advice was given by specialists at a meeting examining the latest developments in grassland re-seeding.

Dr Michael O'Donovan, head of grassland science at Ireland's Teagasc Moorepark, said their was a direct relationship between the proportion of productive grass species in the sward and grazing livestock profitability.

"At the same level of nitrogen, we’ve recorded new perennial ryegrass swards delivering

13-15kg DM/ha compared to just 8.5 kg/ha from older pastures," he said. "They are notably more productive in both spring and autumn, extending the grazing season significantly. At the same time, the quality of grass they produce is markedly higher."

Supporting almost one extra livestock unit per hectare, the most productive swards re-grow faster and make more efficient use of applied nitrogen.

"Our studies show annual dairy herd grass utilisation rising from 7.4t DM/ha with one per cent of the grass re-seeded each year to 10.42t DM/ha at a 15 per cent annual re-seeding rate.

"We calculate the current cost of re-seeding will typically be recouped in just two years and suggest re-seeding five to 10 per cent of the grass area annually for the greatest overall value."

Re-seeding should be carefully-planned, with pastures producing the lowest levels of utilised grass – not necessarily the oldest – replaced each year.

The study found no difference between conventional plough-based, minimum tillage or direct drilling regimes in spring or autumn re-seeding; effective sward destruction and weed control is essential; careful choice of grass varieties; and recommends light early grazing to encourage the greatest plant tillering.

Barrie Hunt, Monsanto technical development manager, said less productive grasses like Yorkshire Fog, rough stalked meadow grass and creeping bent – as well as docks, thistles and other problem grassland weeds – can compromise sward output and quality.

Unless the old sward is reliably destroyed and weeds controlled re-seeding would be a costly waste of time, effort and money.

He said: "With intense pressures on dairy, beef and sheep margins, it’s equally important re-seeding takes pastures out of production for the least possible time. To address both these challenges we’ve introduced a specialist new 360 g/l Roundup for grassland farmers this season."

Roundup Biactive GL is also approved for spraying ahead of silage-making or grazing for the most rapid re-seeding turn-around.

Mr Hunt said: "You can silage or graze five days after spraying then cultivate and drill your new seeds the next day, secure in the knowledge that even the toughest weeds have taken-up enough glyphosate to kill them.

"So you can take a second silage cut or extra grazings off your old sward right up to the end of July and still re-seed at the early autumn timing that gives the best perennial weed control, rather than having to shut your ground-up for re-seeding from early June."

Rod Bonshor, DLF forage grass product manager, said on good soils with adequate rainfall and fertilisation, ryegrasses continue to be the most nutritious and productive species.

"Equally, we’re seeing festulolium (ryegrass/fescue hybrids) giving the same speed of establishment, yield, spring growth, feeding value and persistence as hybrid ryegrasses," he said. "Our most popular variety, Lofa is doing so with greater palatability and stress tolerance.

"Interestingly, grazing preference studies show the best of today’s cocksfoots and timothys to be more palatable than ryegrasses. So they continue to have a valuable place in modern seed mixtures."