WBD4Arable reversion to grassland with low fertiliser input

What it actually is

You take arable ground that is working against you, land at risk of erosion or surface runoff, or land that sits against a watercourse, SSSI or priority habitat, and you sow it to grass and keep it there for three years. The seed mix must include at least five grass species, sown by early autumn within 12 months of the start date. GOV.UK's stated aim is a dense and diverse grass sward throughout the year, with varied heights through autumn and winter and minimal bare ground, holding the soil, cutting nutrient losses and reducing flooding risk.

The sward is not shut away: you graze it or cut it through spring and summer, with cuttings removed in late summer after the bird breeding season. What you cannot do is graze it through autumn and winter, GOV.UK gives usually early October to mid-March, or apply fertilisers and manures from late summer to mid-winter, usually mid-August to the end of January. Across the year the nitrogen stays below the limits rather than at them: livestock manure nitrogen below 100 kg per hectare, or, where you use no livestock manure, fertiliser nitrogen below 50 kg per hectare. GOV.UK prohibits applying 100 kg or more, and 50 kg or more, so 100 kg exactly is over the line and not on it.

Source: GOV.UK, WBD4 action page, checked 23/08/2026.

What it pays, and what that comes to

The rate is in the panel at the top of this page. Multiplied out:

Source: arithmetic on the payment rate shown at the top of this page, which comes from Tilth's copy of the GOV.UK action catalogue and carries its own last-checked date. The 5 hectares is an illustration.

Is it worth it on your ground?

Step one: what it costs to put in. A five-species grass mix, the cultivation and the drilling, at your own prices, once, in year one. There is no published seed figure we are willing to put against a mix this open-ended, but a plain grass mix sits at the cheap end of anything sown for these schemes, well below a herbal ley or a flower mix.

Step two: what the ground would otherwise return. Gross margins per hectare for England, non-organic, in the 2023/24 crop year, with variable costs already taken off:

Source: Farm Business Survey, Crop Production in England 2023/24, Rural Business Research, England, non-organic, 2023/24 column, checked 02/08/2026.

Step three: the gap, and the thing the gap forgets.

Source: arithmetic on the crop gross margins in step two set against the payment rate at the top of this page. The rotation averages are the same three illustrations used across this site's arable pages.

The thing the gap forgets is that the field is still producing. The action requires grazing or cutting through spring and summer, so the sward is keep for stock or a cut of forage, and that has a value on any farm that can use it. What that value is depends on your stocking and your forage market, so it is your figure, but it belongs in the sum, and it only pushes one way.

Two things to set against those figures. What follows is Tilth's own reading rather than scheme guidance.

The action is aimed at ground that is not making the average. The eligibility test does the targeting for you: land at risk of erosion or runoff is usually the land whose real margins sit a long way below the survey table, between the drowned headlands, the capped seedbeds and the passes it takes to keep it in crop. The honest comparison is against that field's own figures, not the national ones.

Three years is a commitment, and so is what comes after. The action is static, and at the end of it you have a three year old sward on ground you chose because it was fragile. Nothing in the action requires what happens next, but the practical question of whether it ever goes back to the plough is worth answering before entry, not after.

Does it work, and what makes it work better

This section is what we have found in published sources about the practice this action pays for. It is not scheme guidance, it is not Defra's or the RPA's view, and it adds no requirement beyond what the GOV.UK action page sets out. We have named every source and given the date we checked it. What it means for your ground is your decision.

None of the work below is about WBD4 by name, but the practice assessed, reverting arable land to sown agricultural grassland, is unusually close to what this action pays for. The results deserve stating plainly, and then locating carefully, because they are the bleakest on this site and they are measuring the wrong outcome for this particular action.

The graded assessments. Conservation Evidence, based at the Department of Zoology at the University of Cambridge, assesses this practice twice. In the Bird Conservation synopsis, reverting arable land to permanent grassland is in the category Likely to be ineffective or harmful, on 5 studies, scored 0 per cent for effectiveness, 64 per cent for certainty and 10 per cent for harms. In the Farmland Conservation synopsis, the same practice across all wildlife is in the category Unknown effectiveness (limited evidence), on 8 studies, scored 0 per cent for effectiveness and 20 per cent for certainty. An effectiveness score of zero means the studies reported no clear benefit at all to the wildlife measured.

Source: Conservation Evidence, action 210, Revert arable land to permanent grassland, Bird Conservation synopsis, and action 561, Convert or revert arable land to permanent grassland, Farmland Conservation synopsis, both checked 23/08/2026. Cite as Williams et al. (2020), Bird Conservation, pages 137 to 281, and Dicks et al. (2020), Farmland Conservation, pages 283 to 321, both in What Works in Conservation 2020, Open Book Publishers.

What the studies found. Every one of the individual studies found no clear benefit to the wildlife it measured. The sharpest result is a controlled before-and-after study across 28 square kilometres of Sussex farmland from 1970 to 1994: grey partridge numbers fell from an average of 6.5 coveys per square kilometre to 1.1 after arable fields were reverted to grassland, a far steeper fall than on arable fields left in crop, with the reverted fields going from favoured to avoided. Foraging brown hares on the South Downs avoided farms converted to scheme grassland. Skylarks, corn buntings and meadow pipits were not consistently more abundant on reverted fields than on winter wheat or intensive grassland. Breeding waders in Denmark did not increase on reverted fields. A Czech comparison found a reverted field held the fewest plant species of 47 grassland sites, five species against up to 26, with no increase over five years. And a 2000 review reported that breeding corn buntings and skylarks abandoned reverted fields that were mown or grazed during the nesting season.

Source: Conservation Evidence, actions 210 and 561, key messages and supporting evidence, checked 23/08/2026.

Why that is not quite the verdict it looks like. The assessed outcome is wildlife. This action's stated aim is not wildlife: it is soil stabilisation, reduced nutrient loss and flood risk, on ground picked for being erosion-prone or for buffering water and sensitive habitats. None of the studies above measured soil loss, nutrient movement or flooding, and we have not found an equivalent graded assessment for those outcomes for this practice. So the honest position is uncomfortable in both directions: the wildlife case for a plain grass reversion is poorly supported by the published record, and the soil and water case, which is the case the action is actually built on, is unmeasured in the source we lean on across this site. What the evidence does firmly say is that a field of sown agricultural grass should not be counted as a wildlife gain when the application is being weighed.

Source: the aim, GOV.UK, WBD4 action page, checked 23/08/2026; the assessed outcomes, Conservation Evidence, actions 210 and 561, checked 23/08/2026. The reading is Tilth's own.

Conservation Evidence say themselves that studies are not directly comparable or of equal value, and that study size, design, reported metrics and relevance to your own situation matter more than "simply counting the number of studies that support a particular interpretation".

Source: Conservation Evidence, the note under key messages on the action pages cited above, checked 23/08/2026.

What you actually have to do

Establish a sward using a seed mix with at least five grass species, sown by early autumn and within 12 months of the action's start date, and keep it at the same location for the full three years. Keep the sward dense and diverse through the year, with varied heights in autumn and winter and minimal bare ground. Graze or cut it during spring and summer, removing cuttings in late summer after the bird breeding season. Stay within the nitrogen limits: no fertilisers or manures from late summer to mid-winter, which GOV.UK gives as usually mid-August to the end of January, and across the year livestock manure nitrogen below 100 kg per hectare, or fertiliser nitrogen below 50 kg where you use no livestock manure. GOV.UK prohibits applying 100 kg or more, and 50 kg or more, so 100 kg exactly is over the line and not on it.

You also have to hold evidence that the land qualifies: that it is at risk of erosion or runoff, or that it buffers a watercourse, SSSI or priority habitat.

Source: GOV.UK, WBD4 action page, checked 23/08/2026.

What you cannot do on it

No grazing through the autumn and winter, which GOV.UK gives as usually early October to mid-March. No fertilisers or manures from late summer to mid-winter. No pesticides, except herbicides to control injurious weeds, invasive non-native species, nettles or bracken. No supplementary feeding apart from mineral blocks.

Source: GOV.UK, WBD4 action page, checked 23/08/2026.

Where it can go

Arable cropland, temporary grassland (TG01) or fallow (FA01) below the moorland line, identified by you as at risk of erosion or surface runoff, or as important for buffering sensitive habitats: watercourses, SSSIs, priority habitat. SSSIs need Natural England's consent before agreement. Land with historic or archaeological features needs an SFI HEFER first. It is static: the same field for all three years.

Source: GOV.UK, WBD4 action page, checked 23/08/2026.

What you can stack it with

The same-area list on the GOV.UK page is short: the agroforestry actions AGF1 and AGF2, the organic actions OFC1 and OFM1, and the precision actions PRF1 and PRF2. The boundary list is the usual four: CHRW2, BND1, BND2 and WBD2.

Source: combinations, GOV.UK WBD4 action page, checked 23/08/2026.

Things worth watching

This section is Tilth's own reading of where this action is easy to get wrong. It is not scheme guidance, it is not sourced from Defra or the RPA, and none of it adds a requirement beyond what the GOV.UK action page sets out.

The eligibility case is a document, not a feeling. The land has to be identified as erosion-prone, runoff-prone or buffering something sensitive, and GOV.UK expects you to keep the evidence for that identification. A soil management plan, a runoff map or the parcel's position against a watercourse is the paperwork; the memory of a wet winter is not.

Two calendars run at once. The grazing ban runs early October to mid-March; the fertiliser ban runs mid-August to the end of January. They overlap but they are not the same window, and the pair of them is easy to hold wrong in the head. Both carry GOV.UK's "usually" wording rather than fixed dates, which cuts both ways: room to manage, nothing to point at afterwards except your records.

The summer management is compulsory, and it has a wildlife edge. Grazing or cutting in spring and summer is a requirement, not an option. The published review noted above found breeding corn buntings and skylarks abandoned reverted fields mown or grazed in the nesting season, and the action threads that needle by requiring cuttings to be removed in late summer, after the bird breeding season. How you sequence the grazing and the cut within the requirement is left to you.

The five species are grasses. The mix requirement is at least five grass species. It is not a legume or herb requirement, and if you are picturing a flowering ley, that is a different action and a different payment. What goes in the mix beyond the five is your choice within the requirement.

Static means the fragile field is the committed field. The action cannot move. The field you enter is the field for three years, and it was chosen because it was the one that struggles. That is the point of the action, and also the reason to be sure about the boundary of what you enter: part of a parcel is allowed, and the eligible part may not be the whole field.

Keeping the evidence

Also Tilth's own reading. GOV.UK sets the requirements; what follows is a practical suggestion about record keeping.

GOV.UK's list is longer than most: the eligibility evidence for the land, field operations with seed mix details and invoices, stocking records for the grazing, nitrogen application records, and photographs. The nitrogen ledger is the one to keep carefully, because the caps are annual and split by source, and the record that shows what went on is also the record that shows the closed window was honoured. Dated photographs through autumn and winter carry the sward-density and no-grazing side.

Source: evidence requirements, GOV.UK, WBD4 action page, checked 23/08/2026. The suggestion is Tilth's own.

The part only your own ground can answer

Everything turns on which field you are looking at. Against the farm's average arable margin this payment falls short; against the real returns of the field that floods, caps and washes, plus the forage the sward will still give you, the sum can land the other way entirely. That field's true figures live in your own records, margin by margin, season by season, which is what Tilth is for. Request an invite.