How cultivated arable margins help rare plants and biodiversity
© GNP Cultivated margins, or areas of fields that are cultivated annually, but not drilled, are one of the best ways of encouraging rare arable plants and the wildlife that depends on them.
Whether they are part- or whole-field areas, the key to their success is to only disturb the soil once a year and then rely on the seed bank, which will build up over time.
That allows rare arable plants – the fastest declining suite of plants in the UK – to germinate and thrive, rather than be outcompeted by crops growing in highly fertile situations.
See also: Why trees in hedges improve arable farm landscapes
In terms of their location, sites around the edges of fields are preferred, as this is where the arable plant seed bank is at its best.
It is also likely to be the least productive part of the field, with minimal effect on farm profit.
What do cultivated margins offer?
- The support of rare arable plants
- Habitat for invertebrate species
- Pollen and nectar food sources and nesting habitat for pollinators
- Seed and insect-rich foraging for farmland birds
- Nesting habitat for certain farmland bird species.
Regenerate naturally
Annually cultivated to at least 3m wide, but then undrilled and left to regenerate naturally, the best results have come from the use of non-rotational margins on lighter soils, where farmers have committed to them.
A sunny south or south-west facing aspect will support the highest number of plant species, but no two cultivated margins are likely to look alike.
Weedy sites, such as long-term fallows or former winter bird food plots are unlikely to be suitable, due to species such as ragwort and thistles likely to be present.
Included in the expanded Sustainable Farming Incentive offer for 2024 as AHW11 when the scheme was still open for applications, it is one of the limited area actions (restricted to 25% of the farmed land), with a payment rate of £660/ha.
Top tips for cultivated margins – establishment and management
- Cultivate annually either in the spring or autumn – consider doing a 50/50 split of autumn and spring cultivation on the farm.
- Carry out cultivation as you would for normal field operations and to fit cropping patterns – cultivation outside of these windows is not required.
- Cultivations should produce a fine, firm level seed-bed – such as you would prepare for drilling barley.
- Margins will re-generate naturally – do not sow seed mixes on them.
- Going forward, margins need to be cultivated every year.
- Once established, most margins should be left alone all season.
- Preventing a single species dominating may be achieved by varying cultivation depths and timings occasionally.
- Fixed margin locations are more beneficial to the species they support but they may need rotating if perennial weeds are a problem.
- High topping (30cm minimum) of weeds such as thistles can be done before they set seed.
Case Study: John Secker, West Norfolk
A cultivated margin on a Brecklands farm © Breckland Farmers Wildlife Network
Cultivated margins were first included as one of the options in a stewardship scheme back in 2012, recalls John Secker, who works on an arable farm on the edge of the Brecklands.
A member of the 60-strong Breckland Farmers Wildlife Network, John believes there is no better way to increase biodiversity on an arable farm in the area, providing they are sited and managed correctly.
It took trial and error to make them work well, he says.
A total of 328 insect species were found in the margins on the farm compared to 67 species in cropped areas.
In addition, roughly 100 different species of flowering plant have been recorded, some of which are nationally scarce.
Perennials and certain weed species will proliferate if the timing of cultivations is wrong, he warns.
“We initially thought carrying out cultivations just as the soil was warming up would be perfect.
“In fact, we were preparing the perfect seed-bed for fat hen, which then dominated.”
Breckland Farmers Wildlife Network
Biodiversity audit work done by the University of East Anglia documented the species that were found in the Brecks and grouped them according to the management required for them to thrive.
A key finding was more than 600 of the species needed soil disturbance to complete their life cycle, which is why cultivated margins have since become a focus for the group.
Timing
By changing the timing to early February or late October, the results came.
There was a far greater number of species, and both fat hen and annual mercury – which had been big problems before – were kept at an acceptable level.
“We found ploughing to be best on this farm, as it buries perennials and brome seed,” reports John.
“Where we just cultivated, brome was able to dominate.”
To prevent perennials building up, he uses a single application of glyphosate in late September, after the annual plants have set seed.
“We would rather not spray but it controls the perennials and keeps the diversity of annuals in the margins.”
Fertiliser should be avoided, adds John. “Cultivated margins work best in low fertility situations – the species we want to bring back do better on nutrient-poor soils.”
Fiddleneck, which can smother annual plants and originally came in with carrot seed, is easier to manage where there is less compaction, he continues.
“We used to plough to 6m and then use a 4m harrow, creating a 2m overlap. The fiddleneck grew strongly in the central 2m.
“When we switched to a 3m harrow, it didn’t break the soil down too much and there was far less of the weed. In fact, ploughing and no follow-up cultivation has been the best approach.”
Flowering
The margins are full of colour from late March until October, he reveals, with mid-June being the time of year that they are at their best.
“It’s possible to get 50-60 species in these margins and you can get a diverse range in a very small area. We have found nine species in just 1sq m.”
On Glebe Farm, this includes some very rare plants, including corn gromwell and dwarf spurge, as well as others that were threatened by the advent of herbicides and fertilisers.
John has also seen remarkable results with insects. The farm has two county first records for beetles, and a county second record beetle.
It is one of only three sites in the UK where a new species of leaf hopper has been found, while it is the third site to record flixweed flea beetle.
He also reports turtle doves are back.
“Birds benefit from an abundance of invertebrates and turtle doves will eat a variety of seed.
“The margins are a very good feeding habitat for them. They don’t like feeding in dense vegetation.”
John Secker was speaking on an RSPB Hope Farm webinar.
Making the Most of Nature
This article is the third in the series, which looks at natural on-farm features and the contribution they make to wildlife and biodiversity, as well as highlight funding opportunities and sources of specialist advice.
The first article in the series focuses on land ditches for wildlife and the second looks at hedges.
