Take five: a step-by-step guide to reseeding

A properly managed reseeding programme can boost grass growth by 20-40pc

Reseeding leads to longer growing seasons
Reseeding leads to longer growing seasons

Tom Coll

There are many benefits to reseeding old pasture. Research has shown that newly reseeded grazing swards can produce 20-40pc more grass.

It is also more palatable, has a higher DMD value and delivers more rapid regrowth than old swards

Reseeding will also lead to longer growing seasons as ryegrasses have a distinct yield advantage at the shoulders of the year in early spring and late autumn.

Silage produced from high ryegrass swards will be easier to preserve due to higher sugar content, will recover faster and give higher yields with quality generally 6+ units higher in DMD than old swards.

However, reseeding is a significant farm investment and can cost over €300/acre. So it is important to evaluate whether reseeding is cost effective for your farm.

Why reseed?

For highly-stocked farms the answer is simple - reseeding will improve grass yield, increase the number of days at grass, increase silage yield and quality and, ultimately, improve animal performance.

However, on lower-stocked farms greater economic gains may be obtained from correcting soil fertility with additional N, P, K, plus S and applying lime to existing swards.

Significant increases in sward ryegrass content can be achieved through improvements in soil fertility combined with better grassland management and adopting a rotational grazing system.

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On the heavier soil types in the north-west it is common practise for farmers to reseed the drier more productive land on the farm to maximise its potential and counter act the lower production capacity of the remainder of the farm.

When the decision is made to reseed a particular area of the farm it is vital that it is carried out correctly to give the seed the best chance possible to maximise its potential in a newly-established sward.

As advisers we are often called out to assess situations where reseeding went wrong at substantial expense to the farmer. Following the correct procedure and management of the established crop will greatly reduce the risk of failure.

STEP 1: Soil test

A soil test carried out prior to cultivation will give a good indication of the lime, P and K requirements. Its use is more valuable where minimum cultivation is the method used.

As when ground is ploughed, the top four inches, where the soil sample was taken, is now generally replaced by less fertile soil. So the general rule of applying 3-4 bags of 10:10:20 and two tonnes of lime per acre may be more applicable.

STEP 2: Spraying

Spraying off the sward with glyphosate is essential as it will reduce the competition from old permanent grasses and weeds and allow the new grasses to establish.

3 Lime

Liming at this stage is also essential to counteract the acid that is produced as the old sward decays which can reduce germination. Lime can be applied at 2t per acre to neutralise the acids.

Trash should be kept to a minimum when using min-till techniques as it will release acids that can impact germinations.

4 Method

There are many different cultivation and sowing methods available for reseeding. All methods, when completed correctly, are equally effective.

In all cases, a fine-firm seed bed is required and good seed soil contact.

You should be able to ride your bicycle across it with ease. Soft fluffy seed beds can result in poorer germination with seeds, especially clover, being buried too deep.

Minimum cultivation works well on shallow soils and reduces the work load of picking stones. Deep ploughing can bury the top four inches which is normally the most fertile area and can result in reseeds that need additional P and K.

Ploughing makes field levelling easier and can improve drainage.

Rolling with a light roller after reseeding will ensure good seed-to-soil contact.

5 Post emergence weed control and grazing

Post emergence spraying, where weeds are present, is essential for a successful reseed.

Weeds in new reseeds are best controlled when the grass is at the two-leaf stage, normally around five weeks after sowing.

The crop should be assessed for the presence of leather jackets and appropriate control taken immediately.

A top dressing of nitrogen should be applied three to four weeks after sowing. Grazing can take place as soon as the crop cannot be pulled out of the ground.

It is important that all reseeds are grazed at low covers around 1000kg in the first year after sowing to encourage tillering and establishment.

It is better to avoid cutting the new reseed in the first year.

The main reasons for ryegrasses to disappear from newly-established reseeds is where soil fertility is poor, where poaching takes place, where heavy silage cuts are taken and where extremely heavy applications of thick slurry are applied.

Avoid these and reap the benefits of adequate grass supplies in the shoulders of the year, better quality grass and silage and better animal performance from high ryegrass swards.

Tom Coll is a Teagasc advisor based in Mohill, Co Leitrim

Indo Farming