Cover crop and soil FAQ

It depends heavily on the species and on how much ground is covered. The most reliable measure is %Ndfa, the share of the plant's nitrogen that came from the air rather than the soil:

• Pueraria javanica reached 85 to 93% Ndfa in one four-year trial under young rubber in northeast Thailand, accumulating up to 250 kg N/ha/yr in above-ground biomass.
• Mucuna bracteata derived 67 to 84% of its nitrogen from fixation under three-year-old oil palm on Jawa Series soil in Malaysia (15N isotope dilution); no routine annual rate is asserted for it.
• Calopogonium caeruleum averaged 49% Ndfa (range 28 to 75%) in a survey of oil palm plantations in Papua New Guinea.

For legume cover as a whole rather than a single species, two study-level records exist: an extra 151 kg N, 10 kg P and 20 kg K per hectare per year compared with a grass cover, for a mixture of Pueraria, Centrosema and Calopogonium mucunoides in Malaysian rubber trials reviewed by Broughton (1977); and 48 to 102 kg N/ha/yr for legume cover in young oil palm plantations in Papua New Guinea, annualised by the authors from four months of growth. Neither is a rate for any one species.

Pipai's 2014 work, as reported by Pardon et al. (2016), measured only above-ground biomass and found just 0.3 to 34.2 kg N/ha, while older Malaysian estimates run several times higher. The difference is largely method, which is why a figure means little without its method attached.

Sources: Clermont-Dauphin et al. 2016, Agriculture, Ecosystems and Environment 217; Cheah et al. 2010, Oil Palm Bulletin 60 (MPOB); Pipai et al. 2023, Plant and Soil 491; Vrignon-Brenas et al. 2019, Agronomy for Sustainable Development 39, reporting Broughton 1977; Pardon et al. 2016, Agronomy for Sustainable Development 36.

We are not able to give you one, and we would rather say that than invent it.

In a literature search across the peer-reviewed record, these two species appear almost exclusively as components of mixtures. We found no primary study measuring their fixation in isolation under plantation conditions. Figures circulating for them trace back to secondary sources we cannot verify.

For Centrosema pubescens and Calopogonium mucunoides, no verified species-specific nitrogen figure is published. Both are also established components of mixtures, including the Malaysian mixture record above.

Yes, and negatively. Across 13 plantations, the proportion of nitrogen derived from fixation was strongly negatively correlated with soil nitrate, and dropped significantly wherever soil nitrate-nitrogen exceeded 5 mg/kg.

Put plainly: the more mineral nitrogen you apply, the less your legume bothers to fix. Heavy fertilisation and a legume cover partly work against each other. This is one of the least-known findings in the field and it matters for how you plan the two together.

Source: Pipai et al. 2023, Plant and Soil 491, R² = 0.55.

Pueraria phaseoloides produced about 8 t/ha/yr of above-ground biomass over four years under young rubber in northeast Thailand. For Mucuna bracteata, the biomass harvested in a 24-month trial under mature oil palm at Rembau, Negeri Sembilan depended strongly on cutting frequency; we do not quote a single tonnage for it.

Calopogonium caeruleum yields about 3 to 7 t DM/ha/yr in the open but only about 1 to 1.5 t/ha under mature oil palm (about 10% light). That sounds poor until you note it is often the only species still alive under a closed canopy. Its value is persistence, not tonnage.

Sources: Clermont-Dauphin et al. 2016, Agriculture, Ecosystems and Environment 217; Mohd Noor et al. 2021, Pertanika Journal of Tropical Agricultural Science 44(1); Tropical Forages (CIAT and ILRI 2020).

On mineral soil in a Selangor trial, Mucuna bracteata planted at 680 seedlings per hectare reached about 100% ground cover at 6 months.

On peat, the picture is completely different. An MPOB bulletin, with 320 seedlings per hectare on deep peat, recorded only 31% cover at 6 months, 58% at 12 months, 75% at 18 months and 78% at 24 months for the same species. Both studies are Malaysian.

So a single “covers the ground in X months” claim is not something anyone can honestly make. Soil type, planting density and maintenance change the answer substantially.

Sources: Samedani et al. 2015, International Journal of Agriculture & Biology 17(2); Hasnol Othman et al. 2012, MPOB Information Series TT No. 501 (extension bulletin, peat soil).

Calopogonium caeruleum. In a survey of 13 Papua New Guinea plantations it was the only species still present in blocks over five years old. Pueraria phaseoloides was found only in younger plantations. Separately, Tropical Forages records C. caeruleum still producing about 1 to 1.5 t of dry matter per hectare a year under mature oil palm at about 10% light.

This is the practical argument for sowing a mixture rather than a monoculture: fast species close the ground in year one, and a shade-tolerant species is what carries the block through year six.

Sources: Pipai et al. 2023, Plant and Soil 491; Tropical Forages (CIAT and ILRI 2020).

A note on Mucuna bracteata. A review of the Mucuna genus notes that shade affects its growth and nodulation. But MB is the species Malaysian estates plant because it holds under a maturing oil palm canopy, where Pueraria javanica thins well before. Our position is that MB is shade-tolerant through the maturing phase, and that CC and CP are the species that persist once the canopy is fully closed.

Sources: Pipai et al. 2023, Plant and Soil 491; Tropical Forages (CIAT and ILRI 2020); Dissanayaka et al. 2024, Circular Agricultural Systems 4 (review of the Mucuna genus).

All five are grown on the acidic, heavily weathered soils typical of Southeast Asian plantations, but tolerance differs by species and by site, and we do not publish a pH range for each species.

Soil pH is worth testing before you order rather than assuming. Our climate suitability calculator will narrow the species list for your site, and we will check the result with you.

Yes, and this is the trade-off most suppliers will not mention.

In a four-year Thai rubber trial, Pueraria phaseoloides improved tree nutrition and growth at the bottom of the slope where soil water storage was good. At upper positions with low water-holding capacity, the same cover crop reduced the trees' ability to survive intense drought.

On shallow or light soils, plan the cover to the soil rather than to the block, and talk to us about species and density before you commit the whole estate.

Source: Clermont-Dauphin et al. 2016, Agriculture, Ecosystems and Environment 217.

Very well, once the cover is established. In a Selangor trial under oil palm, across all cover treatments from 9 to 24 months, weed dry weight under cover was 97.3 to 99.9% lower than an unweeded control, and weed density 94.77 to 99.73% lower.

The establishment phase is the hard part. Until the cover closes over the ground, weeds compete with it. Budget for weeding in the establishment phase.

Source: Samedani et al. 2015, International Journal of Agriculture & Biology 17(2).

Ground cover helps, but on the published Malaysian evidence slope and frond management dominate.

Oil palm soil loss runs at 13 to 78 t/ha/yr on Oxisols and 1 to 28 t/ha/yr on Ultisols. Runoff was 30.8% with fronds stacked down the slope, 17.9% with contour frond stacking, and 10.7% with silt pits added.

In one of the earlier studies the bulletin reviews, legume cover produced 5,370 kg/ha of dry matter against 1,930 kg/ha for natural weed cover, contributing 113 kg N, 11 kg P and 106 kg K per hectare. A cover crop is one contributor to erosion control alongside terracing, frond stacking and silt pits, not a replacement for them.

Source: Afandi et al. 2017, Oil Palm Bulletin 75 (MPOB review of Malaysian studies 1977 to 2014).

This is the weakest link in the case for cover crops, and we would rather flag it than oversell it.

Few plantation trials compare cover with no cover over enough seasons to settle it. A 24-month Malaysian trial under mature oil palm compared how often Mucuna bracteata was harvested, so every plot had cover; it does not test cover against bare ground. A 2025 systematic review of cover crops, drawn largely from temperate studies, reported gains in soil organic carbon on average, with yield effects that varied between studies.

The better-supported benefits are nitrogen contribution, weed suppression after canopy closure, and surface protection. Buy on those.

Sources: Mohd Noor et al. 2021, Pertanika JTAS 44(1); Salisu et al. 2025, Agronomy 15:2865.

We will not put a percentage on that, and we would be cautious about anyone who does.

A legume cover contributes nitrogen, and that contribution is real and measurable. But it varies with species, ground cover, soil nitrate and season across the wide range set out in the first answer on this page, and the fixation itself is suppressed by the mineral nitrogen you apply. Treating a cover crop as a fixed fertiliser credit is how estates end up under-nourishing a block.

The sound approach is to establish the cover, measure your own leaf and soil analysis over two to three seasons, and adjust the programme against your own data. Our agronomists will help you set that up.

The best-cited published mixture is MPOB TT No. 501 (Information Series 588, June 2012), Table 1 treatment C2: PJ 4 : CP 3 : CC 1, total 8 kg/ha, which MPOB calls conventional LCC, with 5 g of Rhizobium (RRI strain) inoculant per kg of seed. Read that as an institutional best-management-practice recommendation from a peat trial rather than a primary field measurement: MPOB gives no mineral-soil rate, and does not state whether the total is per gross hectare or per interrow hectare actually sown.

PROSEA 4 (1992) gives calopo, centro and kudzu at 5:4:1, or centro and kudzu at 4:1, sown at 2 to 5 kg/ha in the interrow. Three distinctions are worth holding onto when you compare quotations: a mixture total is not a per-species component rate, a gross hectare is not the interrow hectare you actually sow, and grazed-pasture rates are not cover crop rates. There is also no Philippine institutional rate: PNS/BAFS 238:2018 recommends legume cover cropping but gives no figure, so any Philippine number is an extrapolation from Malaysian practice. Our seed calculator will work the quantities for your area, and we check the output on estate-scale quotations.

Yes. These are hard-seeded tropical legumes and untreated seed will disappoint you regardless of its quality.

For Mucuna bracteata, a laboratory germination test reported in 2024 recorded 88 ± 9.1% germination from shell nicking combined with a fungicide treatment, with mean germination time of 4.25 days.

We supply scarification guidance with the seed and will walk your team through it. Germination test certificates are issued per lot on request.

Source: Hastuti et al. 2024, BIO Web of Conferences 94:06002 (laboratory germination test, conference paper).

Cool, dry and off the floor. Store on elevated pallets rather than in contact with a concrete slab, keep seed moisture low, and protect against storage pests and humidity.

Viability declines with time and with storage conditions, so we do not quote a shelf life. What we do instead is issue a germination test certificate for the specific lot supplied, dated. If you are holding seed for a later planting window, tell us and we will advise on retesting.

Selection comes down to canopy stage and shade, not crop alone. An immature block and a closed-canopy block on the same estate want different species.

Generally no. Most tropical legume covers are perennial and are managed rather than killed. Periodic slashing controls biomass, circle weeding maintains clearance around young palms and trees, and cut material is left as mulch.

Mucuna bracteata in particular is vigorous and needs active management. A 2024 review of Mucuna cover cropping notes that Mucuna needs proper maintenance and pruning because of its aggressive vegetative growth, and that it can compete with young seedlings of the main crop. A cover that establishes well is a cover you will need to manage.

Source: Dissanayaka et al. 2024, Circular Agricultural Systems 4.

Yes, and they are the buyer's responsibility to confirm before ordering. Import and export both require permits, and most destinations require a phytosanitary certificate for a seed consignment. Some species are restricted in some jurisdictions on invasiveness grounds.

Chemiseed exports from Malaysia, so the certificate is issued by Malaysia's national plant protection organisation, the Department of Agriculture Malaysia (Jabatan Pertanian Malaysia), under the IPPC framework. That certificate is the document described by ISPM 12. ISPM 7 is a different standard covering how an NPPO runs its certification system: it applies to national authorities, not to companies, so no seed company is or can be "ISPM 7 certified". SoilBoost EA is a mined mineral product rather than plant material, so a phytosanitary certificate is generally not the applicable document for it.

We supply phytosanitary certificates, certificates of origin, germination test certificates and technical documentation to support your import. Check your destination country's rules before placing an order, and tell us the destination early so we can prepare the right paperwork. Our terms of service set this out in full.

SoilBoost EA is a humic soil conditioner derived from leonardite ore. Humic acid is typically 96.55% by laboratory analysis. Sulfur is 0.45% as sent (25.81% sample moisture) or 0.61% on a dry-weight basis, and pH is 3.84. It is a separate product from the seed, used to condition the root zone.

Leonardite is a mined mineral and batch-to-batch variation is significant, so analysis is run per batch, on request, and the figures above are typical values rather than guaranteed constants. Typical analysis. A certificate of analysis for the batch supplied is available on request.

It is a soil conditioner, not a fertiliser, and not a substitute for a fertiliser programme. Response to humic substances is real on average but variable: meta-analyses report roughly +12% crop yield and +19 to +22% biomass, while about half the trials in the largest meta-analysis improved growth by less than 5%. Source material matters more than dose, and overdosing reduces the response rather than increasing it. Those meta-analyses, including Ma, Cheng and Zhang (2024), tested humic acid products as a class and did not test SoilBoost EA, and the response diminishes outside roughly pH 6 to 8.

Our honest read of that evidence, with the caveats intact, is on the research page. Trial it on a limited area with an untreated comparison strip before committing an estate.

Sources: Rose et al. 2014, Advances in Agronomy 124; Ma et al. 2024, Agronomy 14:2763.