Advice for rejuvenating grassland if reseeds failed during the drought

Grass seed sales have spiked over the past six months following reseeding efforts on farms to repair scorched and patchy leys after the 2018 summer drought.

Seed merchant and grass breeder Germinal has reported a 50% rise in sales. Mild autumn conditions allowed reseeding as late as November in some areas.

See also: How to maximise your farm’s spring or autumn reseed

However, due to persistently dry conditions, some grassland didn’t establish, with some farmers drilling too deep in a bid to capture moisture. Others were caught out by leatherjackets, with spray treatments no longer available.

Shallow drilling required

Helen Mathieu of Germinal said deeper drilling meant soil temperatures were not sufficient to get seeds growing and that 1cm drilling depths were enough

“The temptation last year was to drill deeper because some people thought they needed to get closer to the moisture deep down,” she said.

“But the deeper you go the cooler it gets and perennial ryegrass needs a soil temperature of 5-6C to get growing.”

Italian ryegrass grows at 3C while clover needs 7C. Depths of 2cm can leave you with 80% establishment, and seeds sown at 6cm can result in lower establishment rates of just 20%, trials have shown.

With a range of situations and challenges presenting themselves on UK farms, soil and grassland consultant Nigel Howells, of Nigel Howells Consultancy, stresses that it is vital to know your soil health before spending money on seed, fuel and labour.

Mr Howells gave the following suggestions for rejuvenating grassland this spring:

Scenario 1: Failed pasture/reseed – grass has failed to establish 

Step 1

  • Work out why the reseed has failed.
  • If it is due to moisture then that problem can naturally correct itself, but if you suspect there is something else going on or lacking then a soil test should be done.
  • Reseeding can cost £370-£500/ha including all contracting costs, so make sure this investment is maximised. Successful reseeds will pay you back in the first year with a 15-20% increase in DM production.

Step 2

  • Think carefully about your cultivation method.
  • If there is a heavy weed burden then glyphosate should be applied, but if they are not deep-rooting weeds such as chickweed then they could be ripped out with one pass of a spring tine. Make your decision based on the weed burden, the type of weeds and the competition the seedlings will face.
  • Don’t plough unless you have to – it damages soil structure. If you are on light land or in a moisture deficit then ploughing could dry out land further.
  • Direct drilling is the most cost-effective option if soil structure is good, weed burden is low and the sward is open enough to allow seedlings to compete. This isn’t suitable if the ground is hard and dry.
  • A compromise might be discing or tining as this is cheaper and disturbs soil structure less than inversion ploughing. This is most effective if soil moisture is present, although avoid doing this straight after heavy rain as you can smear and compact top soil.

Step 3

  • Soil temperatures are sufficient to reseed so get started (up to 7C for clovers).
  • Even if some grass patches are present reseed fully at the prescribed rate on the pack.
  • After drilling seed always roll to achieve good seed-to-soil contact. Cambridge rolls are best.
  • Don’t drill too deep. A maximum of 1cm is sufficient.

Scenario 2: Partial reseed needed

Step 1

  • Assess soil structure and weed burden in parts of the field that have failed.
  • Assess how open/bare the sward is.
  • Investigate suggested overseeding rates for certain varieties. They are often half the full seeding rate, depending on how bare the sward is.

Step 2

  • Graze the old sward hard and harrow the ground to fluff up the soil. This reduces competition from existing plants and opens up new space for seedlings.
  • Avoid working after heavy rain as this leads to compaction and can create a hard pan on the top soil.

Step 3

  • Once you’re happy with the seed-bed, drill.
  • Work quickly to patch up swards as necessary because seedlings will have increasing competition from existing grasses as the growth increases through May.
  • Roll the seed into the soil.
  • Keep stock off until new grass has become firmly anchored in the soil.

Species options

Mr Howells advices that, ideally, permanent pasture is followed by a break crop (brassicas or short-term Italian ryegrass) before going back to permanent pasture.

  • Cutting leys: A red clover and tetraploid mix.
  • Grazing leys: Late heading diploid perennial ryegrass/timothy/white clover mix tailored to the farm.
  • Resilient leys: Farms experiencing crop failure from shallow-rooting ryegrass could try more varied swards comprising cocksfoot, timothy, plantain and other native grasses.

Forage options

With some farms looking to replenish feedstocks, Mr Howells says cereals and wholecrop mixes might be an option. Drilling a 75% rate of wholecrop with barley and peas and 100% rate of a perennial ryegrass variety could work well.

“This will provide shade and shelter for the young grass crop,” he says. “You can take the wholecrop in July and then graze or silage the ryegrass underneath.”

He says cereal/wholecrop mixes undersown with ryegrasses should be harvested 10 weeks after sowing so the pasture can thrive in late summer and not be shaded out.

Dealing with leatherjackets

With no spray treatments available for leatherjackets it is important to assess if they are the reason why your grassland swards are patchy, says Mr Howells.

“They are laid as cranefly eggs between July and September and eat grass roots and stems, and April/May is when most damage and activity occurs,” he says.

“If you’ve had poor grass regrowth then the chances are leatherjackets won’t be a problem as their habitat is grassland.”

The best advice is to have a break crop to disrupt the fly’s life cycle, he says. Brassicas or a fast-growing Italian ryegrass are good ways to do this before returning to grass.

Mr Howells recommends digging a test hole and inspecting the top 5-8cm of soil. If the problem is bad, it’s best to let the birds feed on them after inversion ploughing.

Other issues farms may face this spring

Addressing compaction

Nigel Howells advises: Lots of farms are suffering from shallow compaction from livestock and tractors. A lack of worm casts can be a giveaway that your soil is short of air and oxygen.

If you think shallow compaction is an issue then aerators can be used when soils are damp and drying – avoid doing this after heavy rain.

Most shallow compaction is in the top four inches, so getting the fins of the aerator down six inches should suffice and if the soil is drying it will create cracks deeper than that.

Assessing soil health

Nigel Howells advises: Basic soil tests are a good start, but a more detailed Albrecht test can be used across similar fields. This works out not just what is present in the soil, but what is available to plants and can cost as little as £10-£11/ha.

Fertilise accordingly, making sure phosphate and calcium are provided to give the plants the best start they can get. Calcium is needed for plants to access nutrients, and phosphate is needed to drive root growth.

Aim for

  • pH: 6-6.5 – should be nearer 6.5 if growing brassicas
  • Calcium levels should be sufficient and at a 7:1 ratio with magnesium
  • Phosphate should be at an index level of 2
  • Potassium should be at an index level of 3.