Successful grassland rejuvenation

Rejuvenating tired, low-performing pastures by topping them up with fresh, productive grass species has been a success for some and, it has to be said, a disaster for others. Andy Collings reports

Grassland rejuvenation sounds easy. Instead of having to spend time and money ploughing up old pastures to reseed them, new grass seed is sown into the existing sward and the job is done; just stand back and wait for the increased production to arrive.

No surprise perhaps, to learn there is more to grass rejuvenation than this. In fact, to ensure any degree of success there is quite a bit of preparation involved along with some luck with the weather.

The first point to appreciate is that existing, well established grass, while not perhaps being the most productive in terms of growth, can still dominate the proceedings. It can be a big ask for a small grass or clover seed to germinate and grow away in such competitive conditions.

So reducing the competition to a minimum is a priority and this can be achieved either by tight grazing or by taking a hay or silage cut. Just topping grass is a definite no-no – the resulting residue will tend to stifle the germinating grass seed.

In terms of timing, the optimum is probably July/August when the initial vigour of existing grasses has waned although, with proper management, it is possible to seed pastures both earlier and later than this.

It makes sense during the planning stage to ensure soil pH indices are adequate along with phosphate and potash levels. An application of herbicide to reduce the broad-leaved weed population could also be considered.

And for those who have not yet worked out that this is a competition between small seed and established grass, applying a dose of nitrogen is not going to be a good idea at this time.

It may possible to deal with compaction problems if the right kit is available – such as the Opico Sward Lifter or Ritchie’s Actisol Grassland subsoiler, for example.

So, with the existing grass down at ground level and soil status and structure all OK, it’s time to get some grass seed sown.

Broadly speaking, there are two ways of planting grass seed into an existing pasture one is slot seeding and the other is overseeding.

Of the two, overseeding appears to now be the most popular system, not perhaps because it is any way more successful at establishing new grass than slot seeding – but more to the fact that it calls for less expensive equipment and it can be a faster job overall.

Key to the overseeding operation is a set of tine harrows which have the task of pulling out the dead thatch in the base of the grass sward and create a mini-tilth on the soil’s surface.

Grass seed is then broadcast into this tilth – delivered by a series of outlets across the width of the harrows from a pneumatic seeder unit. Normal practice is for the field to then be flat-rolled to provide soil/seed contact.

Slot seeding probably comes into its own when there is a dense mat of weed grass present in the base of the sward – conditions where the overseeding system could struggle.

Instead, discs are required to cut a slot through the mat and into the soil below. Contenders for this task are .

The Sulky Easydrill’s claim to fame is its ability to exert up to 250kg on each of its disc coulters and to do so without causing excessive disturbance to the surrounding soil, which is just about what is needed when slot seeding into turf.

Opening discs are also employed on the Aitchison SimTech T-Sem but these are followed by spring tine coulters. Not your average seed coulters though; these have an inverted “T” shape which creates a slot that is wider at its base than at the surface and, as a bonus, severs the roots of neighbouring plants.

Seed dropped into this warm, damp housing germinates quickly and has, says Aitchison, reduced competition in the immediate vicinity.

Both seeding systems require soil moisture to have any chance of success; the worst scenario is for the seed to chit and then die off from insufficient moisture. In an ideal world, a light shower or two of rain would be provided during this critical establishment period.

How much seed should be sown when overseeding or slot-seeding? Opinions differ but the important detail is how much will germinate and actually survive into adulthood. As a rule though, current thinking is that somewhere between half and three-quarters of the rate applied for a full re-seed is about right.

In terms of species, there appears to be no specific varieties recommended, with a standard four year ley of a rye grass/clover mix being chosen by the majority.

The case for re-seeding

* There are about 6m ha of grassland in the UK which has been down for more than five years and about 1.2m ha of shorter-term grassland.

* 15% of weed grasses are established at the same time as a new sward is sown. After five years these unproductive grasses – Yorkshire fog, creeping bent and annual meadowgrass, for example, dominate the sward and output is significantly reduced. 

Case study

Contractor, Mike Simpson reckons to overseed up to 160ha (400 acres) of pasture land each year for customers and says that, with only one or two exceptions, the operation is normally successful.

Based at Winterborne Kingston, Blandford, Dorset, Mr Simpson emphasises that it is not a system which suits all situations but believes it can have an important role to play.

“In this part of the country there are large areas of pasture which cannot for one reason or another be ploughed and re-seeded,” he says. “Estate parklands, steep terrain, small paddocks and so on, and there are those who simply cannot afford to have a pasture out of production for several months while a full re-seed is established.”

Mr Simpson offers a choice of two systems: a slot-seed and an overseed using a grass harrow seeder.

The slot-seeder is a Moore Unidrill which uses angled discs to cut the slot into which the seed is placed; the design of the drill allows significant pressure to be applied to the discs and ensure adequate soil penetration in most conditions.

“I would use the slot-seeder where the existing pasture is particularly matted,” he says. “In these conditions it’s essential to get the incoming seed in contact with the soil and create a path for it to grow through.”

If the pasture is more open though, his choice is to use his harrow-type seeder which is based on a Dalbo triple flat roller unit he purchased a few years ago.

“I fitted a set of tines to run in front of the water ballasted rolls and bolted an Opico pneumatic seeder unit on to the main frame which broadcasts the grass seed from five delivery points along the tine-bar,” he explains.

With a working width of 6m and a transport width of 2.5m this unit, he considers, has the ability to travel safely along Dorset’s narrow lanes and also produce acceptable work rates in the field.

“This system is not soil dependent; it just tickles the top half-inch and rakes out any crop residues there may be. Sometimes we make two passes at right angles, not to improve the seed spread but to create a better tilth if there is some matting present.”

Mr Simpson concedes that over seeding is just a top-up and not a re-seed – a way of introducing modern and more vibrant grass species which will respond better to fertiliser applications and hopefully increase production.

“It’s an operation which can be done more than once,” he says. “I have customers who I overseed their grassland perhaps every four or five years.”

Mr Simpson says he charges about £35/ha to overseed which does not include the price of seed. This, he estimates would be less than half the cost of a plough/cultivate/drill operation.

Pasture rejuvenation

* Advantages:

Minimum down time of pasture

Cheaper than total re-seed

Can be used where cultivation is not possible

* Disadvantages:

Results can be variable and at best, a top up of new varieties

Does not remove weed grasses

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