28 March 1997


Is that grass ley ready to rip up and reseed or could it be rejuvenated to increase its density and introduce some modern high yielding grass varieties? Jessica Buss reports

GRASS swards kept in optimum condition give the most economic response to nitrogen and the highest yields. The difficulty is assessing swards that are under-performing and need reseeding.

Dr Robin Turner of the Grassland Research and Advisory Service (GRAS) advises reseeding a proportion of the grass acreage each year. This ensures some fields are in tip-top condition, with better disease and drought stress resistance than older crops. New varieties also have higher yield potential.

"If other fields visibly need reseeding due to poaching damage, drought, winter kill when there is no option but to reseed," he says.

The difficulty is knowing when to reseed because of low yields. He advises a sward assessment of broad-leaved weed levels, grass cover and disease pressure – all of which can reduce yields by up to 30% because the grass is less responsive to nitrogen.

"When the preferred grass species, either perennial or Italian ryegrass, falls below 25% of the sward, its response to nitrogen is uneconomic," says Dr Turner. "The composition of the mixture sown changes and the grasses left may not be the highest yielding or the most digestible."

Leys can have shortened lives, when cut three or more times a year, and a four or five year leys response to nitrogen may be uneconomic after three years, he warns.

"Measure yields objectively in terms of the trailer loads of silage taken or grazing days of each field to check if the return to fertiliser is economic," he says. Following the swards annual yield changes allows optimum timing of reseeding before its nitrogen response is uneconomic.

However, a full reseed can be deferred by one or two years by rejuvenating swards. Mechanical aeration can rejuvenate leys as can effective fertiliser policy, he adds. Potash is particularly important for plant health, tiller development, palatability and nitrogen uptake.

Introducing new seed by slot seeding can be hit and miss but can work when there is little build up of thick matter in a sward, he says. It works best when grass growth is slower such as after first cut silage and mid-summer up to mid-August – providing there is enough moisture. But avoid September when the seedling has less time to compete and spring slot seeding is difficult unless there are bare patches, he adds.

When slot seeding, he advises using larger seeded tetraploid varieties that compete well in the sward and in an Italian ley using Italians and hybrids.

Rejuvenating swards may increase their life by one or two years

before a full reseed is needed,

says Robin Turner of GRAS.


&#8226 Gives up to two years extra life.

&#8226 Not suitable for thick pastures.

&#8226 Slot seed tetraploids, Italians or hybrids.

&#8226 Best after first cut or mid-summer.