Green Manure: What It Is and the Best Crops for the Tropics

Green manure is a crop grown to be returned to the soil, rather than harvested, to build fertility and organic matter. In the tropics, the leguminous cover crops used in oil palm and rubber double as green manures: they fix nitrogen, add large amounts of biomass, and improve soil structure when slashed, incorporated, or left as a living mulch.

What is green manure?

A green manure is any crop grown primarily to improve the soil rather than to be sold or eaten. The crop is grown for a period, then either slashed and incorporated into the topsoil or left on the surface as a mulch, returning its nitrogen, organic matter, and nutrients to the soil. Legumes are the most common green manures because, in addition to biomass, they fix nitrogen from the air.

How green manure improves soil

• Nitrogen: legume green manures fix atmospheric nitrogen and release it as the residue breaks down.
• Organic matter: biomass and litter feed soil organic matter and the soil food web.
• Structure and water: added organic matter improves aggregation, aeration, and moisture retention.
• Weed suppression: a dense green manure shades out weeds while it grows.

Best green manure crops for the tropics

The tropical legume cover crops used in plantations are the workhorse green manures of Southeast Asia and similar climates:

• Mucuna bracteata: highest biomass, deep-rooting; see the MB guide.
• Pueraria javanica: fast cover, strong nitrogen contribution.
• Calopogonium mucunoides: rapid early growth, good nurse crop.
• Centrosema pubescens: shade-tolerant, high biomass-nitrogen.
• Calopogonium caeruleum: hardy, persistent perennial.

For full detail on each species and selection, see the cover crops guide and the five-species comparison.

How to use a green manure

1. Establish the crop. Broadcast or transplant the chosen legume into the inter-rows or a fallow block.
2. Grow it. Allow it to build biomass and fix nitrogen over the season.
3. Return it to the soil. Slash and incorporate, or leave it as a living or cut mulch, so the nutrients and organic matter feed the soil.

Pertanyaan yang Sering Diajukan

What is green manure?
A crop grown to be returned to the soil for fertility and organic matter, rather than harvested. Legumes are common because they also fix nitrogen.

Best green manure crops for the tropics?
The legume cover crops Mucuna bracteata, Pueraria javanica, Calopogonium mucunoides, Centrosema pubescens, and Calopogonium caeruleum.

Cover crop vs green manure?
A cover crop protects and covers soil; a green manure is grown to be returned to soil for fertility. The same species often serve both roles.

How much nitrogen does a legume green manure add?
Roughly 100 to 290 kg N/ha biomass-nitrogen, depending on species and method.

Related reading

• Pupuk Hijau pada Padi: Cara Cerdas Mendapatkan Nitrogen Tanpa Menggunakan Pupuk
• Fiksasi Nitrogen di Perkebunan Tropis: Bagaimana Tanaman Penutup Keluarga Kacang-kacangan Dapat Mengurangi Biaya Pupuk
• The Role of Leguminous Plants: Nature's Soil Fertility Boosters
• Cara Mengurangi Penggunaan Urea pada Kelapa Sawit Tanpa Mengorbankan Hasil Panen

Sources: MPOB; Tropical Forages database (CSIRO, CIAT, ILRI); Philippine field studies on legume cover crop soil-nitrogen contribution. Figures are given with method and context; results depend on site, soil, rainfall, and management. Last reviewed May 2026.