Green manure means growing a crop specifically to turn into the soil.
Good species
Sesbania, sunn hemp, cowpea, mung bean and berseem clover are widely used, depending on climate.
How it works
Sow densely, let it grow to flowering (when biomass and nitrogen peak, usually 6–8 weeks), then cut and incorporate it into moist soil. Wait 1–3 weeks for decomposition before planting, since fresh residue can briefly tie up nitrogen.
When it pays
On depleted or sandy soil, in rotations with demanding crops like rice or maize, and where mineral fertilizer is costly. It reduces the nitrogen you must buy and improves soil structure.
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