Cover Crops and Soil Glossary

Cover crop concepts

Cover crop

A plant grown to cover and protect the soil rather than for harvest. In tropical plantations, leguminous cover crops are sown between young oil palm, rubber, coconut, and cacao to reduce erosion, suppress weeds, retain moisture, and add nitrogen to the soil. See our complete cover crops guide.

Legume cover crop (leguminous ground cover)

A cover crop from the legume family that hosts nitrogen-fixing rhizobia bacteria in its roots. Legume cover crops add biologically fixed nitrogen to the soil while covering the ground, which is why they are the standard ground cover for immature plantations.

Biological nitrogen fixation

The process by which rhizobia bacteria in legume root nodules convert atmospheric nitrogen into a form plants can use. It reduces dependence on synthetic nitrogen fertiliser. Fixation rates vary by species, ground cover, and conditions, and are highest at full cover in immature plantings. Two different things are often reported under this heading and should not be confused: the proportion of a plant’s nitrogen drawn from the air (percent Ndfa), and the quantity of nitrogen accumulated in biomass per hectare. A percentage is not a quantity, and nitrogen accumulated in biomass is not the same as nitrogen measured as fixed.

Ndfa (nitrogen derived from the atmosphere)

The share of a legume’s nitrogen that came from biological fixation rather than from the soil, usually measured by 15N isotope dilution. It is expressed as a percentage. On its own it tells you nothing about kilograms per hectare, which depend on how much biomass the cover actually grew.

Ground cover establishment

The period from sowing until a cover crop forms a continuous living mat over the soil. Faster establishment means earlier erosion and weed protection. Establishment speed depends on species, light, rainfall, and seeding method.

Inter-row

The strip of ground between the planted rows of a plantation crop. Cover crops are usually established in the inter-rows so they protect the soil without competing directly with the main crop in the planting row. Note that a seeding rate quoted per hectare may refer to the gross hectare or to the interrow hectare actually sown; the two are not the same, and published sources often do not say which they mean.

Replanting (immature phase)

The stage when old palms or trees are removed and young ones established. Bare replanted ground is highly exposed to erosion, so cover crops are sown early in the immature phase to stabilise and enrich the soil before the canopy closes.

Cogon grass (Imperata cylindrica, lalang)

An aggressive perennial grass that competes with plantation crops and is difficult to manage once established. A dense legume cover crop helps suppress cogon by shading it out, supporting reduced reliance on repeated herbicide passes. See weed suppression.

The five cover crop species

Mucuna bracteata (MB)

A vigorous creeping legume that gives the fastest canopy closure of the common species, reaching full ground cover in about six months. It derives roughly 67 to 84 percent of its nitrogen from the atmosphere by 15N isotope dilution (Cheah, Zaharah & Aminuddin 2010, Oil Palm Bulletin 60); that is a proportion, and no traceable measurement supports an absolute kilograms-per-hectare figure for MB, so we do not publish one. MB is the shade-tolerant species of the group, which is why it is used under maturing oil palm. Established by nursery transplant at about 320 seedlings per hectare (roughly 85 to 100 g of seed per hectare), never broadcast. View MB.

Pueraria javanica (PJ)

A fast trailing legume valued for erosion control and nitrogen fixation, with deep roots reaching 2 to 3 metres. The best-measured reference point is about 250 kg N per hectare per year accumulated in aboveground biomass at 85 to 93 percent Ndfa, from a single rubber-intercrop trial in northeast Thailand (Clermont-Dauphin et al. 2016, Agriculture, Ecosystems & Environment 217:79-88). That is an upper reference point from one site, not a design value, and the same trial found the cover reduced the drought resilience of the young rubber on water-limited ground. PJ thins as the canopy closes. Pure-stand seeding is 4 to 6 kg per hectare. View PJ.

Calopogonium mucunoides (CM)

A fast-establishing trailing legume that provides quick early ground cover, often sown in a mixture with PJ and CC for layered establishment. PROSEA reports about 65 kg N per hectare accumulated in biomass by a 3-month green manure crop in one experiment; there is no annual fixation rate for CM in any source we can trace. Pure-stand seeding is 4 to 6 kg per hectare. View CM.

Centrosema pubescens (CP)

A shade-persistent creeping legume that carries the cover under closing canopies, tolerating up to about 80 percent shade. Suited to older stands and shaded systems such as cacao. PROSEA cites 120 to 270 kg N per hectare per year, which is an institutional compiled estimate rather than a field measurement. Pure-stand seeding is 3 to 4.5 kg per hectare. View CP.

Calopogonium caeruleum (CC)

A persistent perennial twining legume used for long-term cover, especially on slopes and in maturing plantations, and the second of the two shade-persistent successors alongside CP. It is slow to establish (up to about 20 months to full cover) and is commonly the persistence component of a mixture. CC has not been separately quantified for nitrogen fixation in any source we can trace, so we publish no figure for it. View CC.

Conventional LCC mixture

The standard multi-species legume cover sown at plantation establishment. The best-cited published example is MPOB TT No. 501 (Information Series 588, June 2012), Table 1 treatment C2: PJ 4 : CP 3 : CC 1, total 8 kg/ha, with 5 g of Rhizobium (RRI strain) inoculant per kg of seed. Treatment C4, with Mucuna bracteata carrying part of the cover, is PJ 3 + CP 1 = 4 kg/ha. These are institutional best-management-practice recommendations from a peat trial, not primary field measurements. Published totals run 5 to 15 kg/ha and cluster at 6 to 12; every published mixture is PJ-dominant, and an equal-parts blend is not a standard.

Soil inputs

Soil conditioner

A product that improves the physical, chemical, or biological condition of soil rather than primarily supplying nutrients like a fertiliser. SoilBoost EA is a humic acid soil conditioner that supports soil structure, nutrient holding, and root-zone conditions. See soil conditioner vs fertiliser.

Humic acid

A group of stable organic molecules from decomposed organic matter that improve nutrient availability, soil structure, and microbial activity. Humic acid is the active basis of SoilBoost EA. See SoilBoost EA vs compost.

Leonardite

A soft, oxidised lignite (brown coal) that is one of the richest natural sources of humic acid. SoilBoost EA is derived from leonardite ore.

Biostimulant

A substance that supports a plant’s natural processes, such as nutrient uptake, root development, or stress tolerance, without being a fertiliser or pesticide. Rootlife and Seed Activator are biostimulant-type products.

Cation exchange capacity (CEC)

A measure of the soil’s ability to hold and exchange positively charged nutrients such as potassium, calcium, magnesium, and ammonium. Higher CEC means the soil retains more nutrients against leaching. Humic substances can help raise effective CEC.

Seed quality and trade

Tested to ISTA and AOSA methods

ISTA (International Seed Testing Association) and AOSA (Association of Official Seed Analysts) publish standardised methods for testing seed germination and purity. Seed lots tested to these methods give buyers a consistent, comparable quality basis. Lot results are available on request.

Germination rate

The percentage of seeds in a lot that germinate under standard test conditions. Some species, such as Mucuna bracteata and Pueraria javanica, have hard seed coats and benefit from scarification to improve and synchronise germination.

Phytosanitary certificate

An official document issued by a national plant protection organisation (NPPO) confirming that exported plant material meets the importing country’s plant health requirements. The certificate itself is the subject of ISPM 12. Chemiseed exports from Malaysia, so the issuing authority is the Department of Agriculture Malaysia (Jabatan Pertanian Malaysia), under the IPPC framework. Import permits and admissibility remain the buyer’s responsibility.

ISPM 7

The IPPC standard that governs an NPPO’s export certification system: how a national authority organises, staffs, and audits its phytosanitary certification. It is a standard for national authorities, not a credential a seed company can hold. No exporter is or can be “ISPM 7 certified”. The document that travels with a consignment is the ISPM 12 phytosanitary certificate.