Overseeding, or sward rejuvenation, can be a good way to improve the yield and quality of grassland whilst minimising any time out of production, according to David Little of Germinal.
It should be used selectively, he says, on leys past their best but still with a good proportion of perennial ryegrass present.
Done correctly, and in the right circumstances, overseeding will provide a return on investment within a year.
“Overseeding is a tactic that is best used alongside full reseeding, particularly as it generates additional forage quickly that takes the pressure off when other leys are being completely renewed,” he explains. “It can cost effectively extend the life of a ley by two or three years, adding flexibility to a sward renewal programme.”
The best time for overseeding is when the ley is deteriorating but has not gone too far (50% perennial ryegrass still present), or in situations when ground is difficult to fully reseed due to slopes or stones for example.
“It can be done in the May – September period, following a tight grazing or silage cut, using a seed rate around two-thirds of a full reseed,” adds David. “Good soil-to-seed contact is important, as with any method of reseeding.”
The uplift in dry matter yield possible from overseeding will depend on the state of the old sward, but David Little conservatively uses a figure of a 10% increase. Alongside this, he expects an improvement in the D-value of the rejuvenated grass, estimated to be worth around 0.5MJ/kg ME, which means overseeding will provide a good return on investment.