If you are looking to boost your grassland production in the short to medium term, overseeding can provide a real opportunity. By improving both the yield and quality of underperforming swards, overseeding offers an early return on investment. It can increase dry matter production significantly with an increase in D-value worth 1.0MJ/kg.
Overseeding can rejuvenate pastures without taking ground out of production for long. This flexible, cost-effective option can be used in a wider reseeding programme to gain two to three more years out of a sward before a full reseed. It’s also useful where a full reseed can be challenging, such as on steeply sloping or stony ground, and when clover is being introduced into the sward.
Choose ground carefully
When choosing which pastures to renovate it is important to be selective. For overseeding to be effective, choose pastures which haven’t yet deteriorated too far and still have at least 50% perennial ryegrasses.
Where broadleaf weeds, such as docks, thistles and nettles, are a problem, they should be controlled first to open up the sward. Allow plenty of time before sowing to avoid any residual chemical affecting the seedling establishment – particularly clover. If there is an issue with weed grasses, a full reseed is likely to be more cost-effective than weed control.
The ideal period for overseeding is from now until September when conditions are warm and damp. Overseeding is less successful if followed by dry conditions, so try to pick a time when rain is forecast with no risk of drought or extended dry spells.
The right soil conditions, including fertility, structure and nutrient status, are also important. Any existing issues could be the reason your existing sward is performing poorly so it is worth taking the time to correct these first.
Carry out a soil test and examine your soil well in advance of overseeding so you have plenty of time to correct any shortfalls. For optimum sward performance, pH is 6-6.5 with P and K indices at 2 so apply fertiliser as necessary to achieve these levels. But it is important to avoid applying nitrogen to reduce the growth and competitive nature of existing species. Allow time (at least six weeks) for spring applications of organic and inorganic nitrogen to have been used.
Select the right varieties
Germinal’s Aber HSG Overseeding mixtures are specifically designed to establish rapidly by blending into the existing ley. Containing larger tetraploid seeds, the varieties are better able to grow alongside the old sward.
Mid-summer is an ideal time to add red or white clover into swards as soil temperatures are warm and grass growth is slowing down. It can be introduced using similar establishment methods or included in an overseeding mixture.
Choose the Germinal white clover blend best suited to your system. AberSheep contains smaller-leaved varieties for sheep grazing; AberPasture also includes medium-leaved varieties for cattle and sheep grazing systems; AberDairy contains medium and larger-leaved varieties for dairy grazing and cutting systems.
Red clover can also be introduced to boost silage yields and home-grown forage protein production, as well as reducing nitrogen requirements.
Sow white clover at 1.5kg/acre and red clover at a minimum rate of 2kg/acre.
Use the right method
Seed-to-soil contact is particularly important when overseeding and soil must be visible when sowing or seeds will struggle to germinate. Start by either grazing down the pasture tightly or taking a heavy silage cut. This helps reduce competition between new seedlings and the existing sward. It is important to harrow hard into the old pasture to open the sward up, remove thatch and help create some tilth. Seed can then be broadcast and rolled. Sow at 25kg/ha (10kg/acre) at a sowing depth of about 15mm. As a rule of thumb avoid drilling seeds deeper than one and half times the size of the seed. Direct drilling can work, but you must harrow well and roll to press the seed in.
Immediately after sowing, leave stock in for about a week to keep the old sward grazed off. At the first signs of germination remove livestock and monitor the establishing seedlings carefully. Graze lightly once seedlings have reached the three-leaf stage or 7-10cm and stand the ‘pull test’, i.e can’t easily be pulled out of the ground, to aid tillering.
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