Grassland Reseeding

By Nicholas McKenna, Teagasc Walsh Fellowship Masters Student, Teagasc Longford

With the fine weather this Spring farmers should be considering some reseeding on their farm this year. So why should I reseed my grass fields? Reseeding is extremely important to increase the productivity of a farm. High quality reseeds can carry more stock, increase live-weight gain, regrow faster, use nitrogen fertiliser more efficiently, begin growing earlier in the year and also grow later in the year. Reseeding also helps to improve silage quality. With silage being the main feed on farms over the winter months it is important to have the highest quality possible. Increase silage DMD % from 68-72 will reduce meal feeding by 1kg/head/day. Reseeding can be done either in the Autumn or Spring, in most drystock and beef farms Spring reseeding has more advantages than Autumn. Lower stocked farms can afford to have a block of grazing/silage grounds closed during reseeding and not find themselves with a grass deficit.  Old swards will in fact grow more grass after Spring reseeding than they would have grown had they not been reseeded. If sowing clover it is important to sow earlier in the year as it takes up to 10 weeks for it to establish properly, heavier wet soils also need to be reseeded earlier in the year and for this reason Spring reseeding is ideal. Increasing soil temperatures and hours of sunshine will help improve grass/clover establishment. Opportunity to graze the reseed several times over the summer months allows the sward to tiller and thicken out meaning the following spring the sward will be of higher quality than a reseed carried out in the autumn.

The first stage of carrying out a reseed is to take soil samples from the area to be reseeded. One soil sample should be taken from every 5 ha planned for reseeding, the samples should representative of the entire field/paddock. If ploughing samples should be taken after ploughing as this will give the most accurate result. Soil tests are crucial to find out what levels of Lime, Phosphorous and Potassium are needed at reseeding, over applications are wasting money but also can have huge negative environment impacts while under application will lead to poor sward growth, establishment and overall production.

There are two main methods of reseeding, conventional and minimum cultivation. Conventional is using a plough and minimum cultivation techniques are carried out without a plough, most commonly direct drilling and power harrowing. The paddock/field for reseeding should be sprayed off with a glyphosate product in order to kill off any existing vegetation present. Where ploughing has been done without spraying off it is common for weed grasses to regrow quickly and are then very hard to control. Where minimum cultivation is being practiced the vegetation needs to be either grazed off or topped to allow a cleaner surface with little trash as possible. 

Ploughing:

• Once the vegetation has died off about 10 days after spraying the field is ready for ploughing, during ploughing any trash on the surface is buried. After ploughing it is time to spread lime and fertiliser based on the soil sample results.
• Surface is then power harrowed to produce a fine, firm and level seed bed which will give the optimal conditions for sowing.
• In order to achieve a firm seed bed the field should be rolled before sowing.
• Avoid having a fluffy seed bed as this will cause the grass seed to go too deep into the soil and lead to poor germination/establishment.
• Weather permitting the reseed should be rolled again in an opposite direction to compress the seedbed and increase seed/soil contact.

Direct drilling:

• Existing sward needs to be sprayed off as well as grazed tightly or topped
• Very successful if drilled after a crop of silage is removed
• Some direct drills place seeds in a slit 2-5cm apart, others rotavate a 4cm slot and place in both seed and fertiliser
• Both work very well but it is recommended to do an additional run over the field in a diagonal direction
• Slug pellets are recommended to be added in order to protect the reseed when it is establishing

Power Harrow:

• Involves using a power harrow to cultivate soil surface to a depth of 2-3 inches.
• Ideally the field should be harrowed 3 times in different directions to ensure a fine tilt and to break up old sods sufficiently.
• After harrowing, the field should be rolled before seeding to ensure seedbed is firm.
• Seeding should then take place with the seed being placed on the soil rather than deep in the soil.
• The field should then be rolled again in the opposite direction to optimise soil/seed contact.

Post reseeding: Post sowing management is as important as the sowing itself. It is important for weeds to be kept to a minimum and the best way to do this is to encourage the new grass to tiller as much as possible. A successful sward will have 10,000 tillers/m². Tillers are what will lead to overall establishment success.

Nitrogen and grazing are the main areas that will increase tiller numbers. Nitrogen should always be applied at seeding along with P & K, according to soil test results the amount will vary for every reseed. Once the grass roots have strengthened and you can pull the grass without the roots pulling also you can graze the reseed. Short grazing intervals with young light cattle or sheep will encourage tillering while also reducing surface damage in the field. 

Weeds should be monitored in the reseed and targeted with spraying if they begin to spread, through grazing and applying sufficient N the grass plant should be able to compete with weeds and not let them become an issue in the reseed.

Reseeding in the Spring/early summer followed by proper management with targeted fertiliser and grazing will allow the sward to thicken and thrive leading to a well-established and successful reseed. Grazing during the summer and autumn months and resting over the winter will have the best possible results for the reseed and mean it will increase grass production on the farm immediately for the years to come.

Teagasc provides a Local Advisory and Education service to farmers. They have offices based in Longford Town (Tel: 043 3341021), Roscommon Town  (Tel: 090 6626166) and Castlerea (Tel: 094 9620160), You can find us online at on Facebook @Teagascroscommonlongford.