PJ vs CM vs CP vs MB vs CC: cover crop comparison guide

PJ: Pueraria javanica

Use PJ on open and immature blocks with neutral to slightly acidic soils. Moderate drought tolerance suits areas with 1500-2500 mm rainfall. Nitrogen: about 250 kg N/ha/yr accumulated in aboveground biomass at 85-93% Ndfa in one rubber-intercrop trial in northeast Thailand (Clermont-Dauphin et al. 2016, Agriculture, Ecosystems & Environment 217:79-88). Treat that as a measured upper reference point from a single site, not a design value. The same trial found the cover reduced the drought resilience of the young rubber trees on water-limited ground. Biomass: 6-12 t DM/ha/yr. PJ thins as the canopy closes, so plan a shade-persistent successor.

CM: Calopogonium mucunoides

Select CM as a fast pioneer on acidic soils (pH 4.0-6.0). Good early biomass (8-15 t DM/ha/yr). Nitrogen: PROSEA reports about 65 kg N/ha accumulated in leaves, shoots and roots by a 3-month green manure crop in a single experiment. That is nitrogen accumulated in biomass, not nitrogen measured as fixed, and no annual rate for CM exists in any source we can trace.

CP: Centrosema pubescens

Use CP in dense shade where other legumes struggle. Best for mature rubber and dense cocoa canopies, and one of the two shade-persistent successors. Nitrogen: PROSEA cites 120-270 kg N/ha/yr, which is an institutional compiled estimate rather than a field measurement, so do not plan against the top of that range. Biomass: 4-8 t DM/ha/yr.

MB: Mucuna bracteata

MB is the shade-tolerant species of the group, which is why it is used under maturing oil palm, and it carries heavy biomass (up to 28 t/ha open, ~13 t/ha under 60-70% shade, MPOB). Nitrogen: 67-84% of its nitrogen comes from the atmosphere by 15N isotope dilution (Cheah, Zaharah & Aminuddin 2010, Oil Palm Bulletin 60). That is a proportion, not a quantity: we do not publish an absolute annual kilograms-per-hectare figure for MB because none we can trace is sound. Requires nursery preparation and adequate moisture.

CC: Calopogonium caeruleum

Choose CC for the deepest shade and longer-term ground cover under mature canopies. It is more drought tolerant than CM and PJ and persists where faster species thin out, though it establishes slowly and can take up to 20 months to reach full cover. Suits mature oil palm and rubber, plus sloping blocks where erosion control matters. Nitrogen: CC has not been separately quantified in any source we can trace. The figure we used to publish was a fertiliser-nitrogen equivalent from a Nigerian maize green-manure screening with no primary citation, so we have removed it rather than replace it with another number. Biomass: 3-7 t DM/ha/yr.

The best-cited published mixture (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. Treatment C4, where Mucuna bracteata carries part of the cover, is PJ 3 + CP 1 = 4 kg/ha. MPOB TT 501 is a peat trial and this is an institutional best-management-practice recommendation, not a primary field measurement; no mineral-soil rate exists, and MPOB does not state whether the 8 kg/ha is per gross hectare or per interrow hectare actually sown.

Defensible totals: published mixture totals run 5-15 kg/ha and cluster at 6-12 kg/ha. Per-species component ranges are PJ 3-7.5, CM 1-3, CP 0.5-3, CC 0.6-1.5 kg/ha. Every published mixture is PJ-dominant - an equal-parts blend is not a standard, and we no longer publish one.

Three distinctions worth stating before you order: the total rate is not the per-species component rate; a gross hectare is not the interrow hectare you actually sow; and grazed-pasture rates (0.5-1.0 kg/ha) are not cover crop rates.

PJ + CM: fast establishment with high early biomass. Suits newly opened and immature blocks.

Adding CP or CC: blend a shade-persistent species in from the start so it is established before the canopy closes and PJ thins out.