All techniques › Soil cover & moisture
Cover Crops & Green Manure
Growing a crop to feed the soil rather than to sell. Works well above roughly 700 mm of annual rainfall, can cost you yield below it, and frequently loses money even where it works.
The short answer
Check your annual rainfall first. Roughly 700 mm is the dividing line. Above it, cover crops work: a European meta-analysis finds legume covers give a significant grain-yield increase in the following cereal. Below it they can cost you — −12% in dry climates, −11% in temperate drylands — because a growing cover crop transpires water your cash crop needed. Those two figures come from a dryland meta-analysis, which is what it was built to measure; its +4% continental figure describes continental drylands, not Atlantic Europe.
Termination timing is the whole technique. Early termination gave +12% yield in trials; late termination gave −61%. Decide the date before you sow, not after.
They often lose money even where they work agronomically. UK trials found gross margin reduced in 95% of situations, averaging −£150/ha over two cash crops. So plant cover crops when you have a reason beyond the margin: an eco-scheme payment that genuinely pays, a nitrate-leaching or erosion problem with its own cost, or livestock that can graze the cover. Soil improvement alone is not a business case we can support with the evidence.
What it is
A crop grown to cover and feed the soil rather than to be harvested and sold. It goes in between cash crops — as a catch crop or winter cover — or in the inter-row of a vineyard, olive grove or orchard. Then it is terminated: mown, shredded, roller-crimped, grazed or incorporated, before or as the cash crop goes in.
Green manure is the same practice with the emphasis on incorporating the biomass for fertility. Living mulch is the same practice with the cover kept alive alongside the cash crop. And a cover crop terminated and left flat on the surface simply becomes mulch. These are one system with different termination choices rather than separate techniques.
How it helps
Living roots stay in the soil year-round, feeding soil biology and building the aggregate structure that lets water infiltrate instead of running off.
The surface is protected from raindrop impact and crusting. In Mediterranean vineyards and olive groves, cover crops cut soil and runoff loss substantially compared with conventional tillage.
Soil organic carbon builds over years, raising water-holding capacity. This is the largest, slowest and most reliable benefit.
Nitrogen that would leach away over winter is captured, and legume covers fix their own.
After termination the residue becomes surface mulch, cutting evaporation for the crop that follows.
The water trade-off: read this before deciding
A growing cover crop transpires water. In a wet climate that does not matter, because the water is replaced. In a dry spring it comes straight out of the reserve your cash crop needed. This is the central honest finding about cover crops and it cuts against how they are usually promoted.
A dryland meta-analysis found that averaged across drylands globally, cover cropping reduced cash crop yield by 7%, soil water content by 18% and soil mineral nitrogen by 25% (Agronomy for Sustainable Development, 2022).
Broken out by climate, the sign of the effect flips entirely:
| Climate | Effect on the following cash crop |
|---|---|
| Tropical | +15% |
| Continental | +4% |
| Dry | −12% |
| Temperate dryland | −11% |
The 700 mm rule
That same analysis identifies roughly 700 mm of minimum annual precipitation as the break-even point. Below it, cover crops in dryland systems stop delivering a yield benefit compared with simply leaving the ground fallow.
Much of Mediterranean and south-eastern Europe sits below that line — which is exactly where the drought problem is worst. If you farm in Andalusia, or Dobrogea, or inland Portugal, the common advice to "just plant a cover crop" is not supported by the evidence for your conditions. That is why this page is filtered to Atlantic and Continental Europe only.
If you are below the line, prioritise residue retention and mulching instead, which give you surface cover without a growing plant drinking your water.
Termination timing is the lever
Early termination largely resolves the water conflict. The difference is dramatic:
| Termination | Soil water at wheat sowing | Yield | Carbon |
|---|---|---|---|
| Early | +1–4% retained (0–45 cm) vs. fallow | +12%, water-use efficiency +10% | modest gain |
| Late | −7% depletion at planting | −61% | best: total organic carbon +17%, particulate +72% |
Source: PLOS One / PMC10241367, read in September 2026; publication year not captured.
That table is the whole technique. Late termination maximises biomass and carbon and can destroy the following crop in a dry year. Early termination gives up most of the carbon gain to protect water and yield.
Note the tension honestly: the practice cannot optimise carbon and water in the same season. In drought-exposed conditions we advise terminating early and accepting the smaller carbon gain — but that is a choice with a real cost, not a free win.
Does it pay? Often not
This is the part most cover-crop advocacy leaves out.
The AHDB/ADAS "Maxi Cover Crop" project (2016–2020) measured margins across two consecutive arable cash crops in the UK — a climate comfortably above the 700 mm line, where the agronomy is favourable:
| Metric | Result |
|---|---|
| Average gross margin change | −£150/ha |
| Range across species and soil types | +£64/ha to −£476/ha |
| Situations showing a reduced margin | 95% |
AHDB's own explanation: the cash-crop yield benefit was not large enough to cover the cost of establishing the cover crop (AHDB).
Nor does subsidy obviously close the gap. The only European eco-scheme figure we have been able to verify is a €20/ha French increment between standard and superior scheme levels, which the researchers who examined it judged insufficient to offset the cost of changing practice. Rates are set nationally across 28 CAP Strategic Plans, so check your own country's scheme rather than trusting a European average — there isn't one.
So the honest position is that cover crops improving your soil and cover crops paying for themselves are two different claims. Plant them where you have a second reason: a scheme payment that genuinely covers the cost, a nitrate-leaching or erosion problem that is already costing you, livestock that can graze the cover, or a straw contract you want to protect while still building soil.
What else the evidence shows
| Finding | Source |
|---|---|
| European cereals: legume covers give the most pronounced significant grain-yield increase in following cereals; brassicas also positive in southern European climates; the effect is positive under conventional tillage but not significant under reduced or no-till | European cover crop meta-analysis, Agriculture 2023 |
| Cover crops cut soil and runoff loss versus conventional tillage in vineyards and olive groves across several Mediterranean countries | Maetens / Cerdà et al. |
| Vineyard termination: shredding decomposes fast and lets Cynodon dactylon take over and compete with vines in summer. A one-pass roller-crimper is the practical compromise between effectiveness and efficiency | Pest Management Science, 2024, AgriEngineering 7(9):295 |
| Cover-crop mixtures enhance several ecosystem functions at once, compared with single-species covers | Journal of Applied Ecology, 2025 |
| Mediterranean evidence gap: most trials are winter covers, tomato is the most-studied cash crop, and most studies are short — little is known about Mediterranean perennials over long horizons | Sustainability 16(17):7362 |
Which species? Legumes first if you want the yield and nitrogen benefit in a European cereal rotation. Brassicas are a viable southern-European option. Mixtures deliver more functions than single species. And in perennial inter-rows, well-managed spontaneous vegetation costs nothing in seed and performed as a legitimate comparator in European vineyard trials — worth considering before buying anything.
Where it fits
| Context | Fit | Why |
|---|---|---|
| Atlantic, maritime and continental Europe above 700 mm | Best case | The water trade-off barely applies; European trials show a significant yield gain in cereals after legume covers |
| Sandy leaching soils, any zone | Excellent for nitrogen capture | The catch-crop benefit is largest here, and has its own value |
| Irrigated horticulture | Good | Water competition is manageable when you control the water |
| Mediterranean perennials — vineyard and olive inter-rows | Good, with early termination | Real runoff and erosion gains; manage summer competition with the vines |
| Mediterranean and south-east European arable below 700 mm | Often negative | Early termination becomes mandatory. Consider residue mulch instead |
| Farms with a tight rotation window | Difficult | See below — the window, not the cost, is what usually stops this |
What it costs
The cost structure is simple: seed, one sowing pass, one termination pass. Seed is the dominant variable and swings enormously between plain cereals and complex multi-species mixtures.
We do not have reliable European per-hectare figures, and would rather say so than publish American ones. The best-documented costings are North American (total direct cost ranging $14–285 per acre, median $48, with plain cereals such as oats or rye at the bottom of that range), and European seed, contractor and machinery markets differ enough that converting them would be misleading.
What we can say is where the real constraint lies. Two extra field passes are affordable for most farms; fitting the cover into a tight rotation is what actually stops adoption. A late cash-crop harvest leaves no window to establish a cover before winter, and covers forced into too short a window establish poorly and deliver little.
On timing: nitrogen capture and erosion protection arrive in year one. Soil carbon and water-holding gains take 3–10 years — and note that the largest measured carbon gains came from the late-terminated treatments this page otherwise advises against.
Commitment
Fully reversible, and that is a genuine strength. Cover cropping is an annual decision. If it does not suit your rotation or your margin, you simply stop, and nothing is left behind but whatever soil improvement you achieved.
Given the financial evidence above, that reversibility matters: this is a practice worth trialling on a field or two and measuring, rather than committing the whole farm to. Unlike earthworks or agroforestry, a wrong answer here costs you one season.
How to start
- Check your annual rainfall against 700 mm. Above it, proceed. Below it, treat this as a precision practice needing early termination — or use mulching instead.
- Work out your second reason before you sow. If the only benefit is soil improvement, the UK margin data suggests you will be disappointed. An eco-scheme payment, a leaching or erosion problem, or grazing livestock all change the calculation.
- Check whether you are already required to do this — and already paid for it. Cover crops may fall under GAEC soil-cover conditionality and separately attract a national eco-scheme payment. Getting paid changes the economics entirely.
- Use the cheapest species that fits the goal. Plain cereal rye or oats for winter cover and nitrogen capture; a legume where you want the yield benefit in a cereal rotation; spontaneous vegetation in perennial inter-rows for nothing at all.
- Decide the termination date before sowing. This single decision is the difference between +12% and −61% yield in the trial data.
- Leave the residue on the surface rather than incorporating it, in drier regions. It becomes your evaporation barrier and you keep the water benefit.
- In vineyards, plan the termination machinery. A one-pass roller-crimper is the documented compromise; shredding alone risks a perennial weed problem by summer.
- Trial it on one or two fields and measure the margin, not just the soil.
Risks and failure modes
Soil water depletion in a dry spring is the main agronomic risk — up to 7% depletion at planting, and catastrophic yield loss when terminated late. This is not a marginal caveat.
A negative gross margin is the main business risk, and the UK evidence says it is the likely outcome rather than the exception.
Nitrogen tie-up during decomposition, the same carbon-to-nitrogen mechanism as straw mulch — soil mineral nitrogen fell 25% on average in the dryland analysis. Legume covers reduce this but do not eliminate it.
The rotation window is often simply too tight. A late harvest leaves no time to establish, and a rushed cover delivers little while still costing seed.
Weed shift rather than weed control. In vineyards, fast-decomposing shredded residue let aggressive perennial weeds take over in summer.
Volunteer regrowth in the following crop if termination is incomplete.
A pest and disease green bridge — a cover in the same family as your cash crop can carry pathogens over. Watch brassica covers ahead of oilseed rape.
The carbon–water conflict is unresolved, not solved. Advising early termination protects your water and yield while knowingly giving up most of the carbon benefit. We think that is the right trade in drought-exposed Europe, but it is a trade.
Claims checked. Two circulating claims about cover crops are run down to their sources: cover crops are always good for the soil and eco-schemes pay €40 to €120 per hectare.
Measured on farms. On five rainfed almond farms at 300–400 mm (Spain, 2016–18), an unmown living understory produced the lowest net revenue of four floor systems and compost the highest. See the case studies page.
Where a living cover does not pay. On rainfed almonds at 300–400 mm (Spain, 2016–18) an unmown understory gave the lowest net revenue of four floor systems and compost the highest. Below the rainfall line, compost adds organic matter without competing for water.
The harvested cousin. Growing a cereal and a legume together for grain is intercropping: more grain per hectare at low input, but the seven-site European trial found its stability gain only in productive conditions, the same shape as this page's rainfall line.
Graze it. The one route this site has found that turns the cover-crop margin loss into a positive without a subsidy is livestock: grazing at moderate stocking on dry soil showed minimal soil cost in a 2020 review. Details, and the CAP grassland rule that goes with them, on the ley–arable page.
Free fungi. A winter cover crop raises native mycorrhizal colonisation of the following cash crop by about 30% across 54 field studies, the same as reduced tillage; see mycorrhizal inoculation for why that beats buying fungi in a bag.