Legume green manure raises available N for the subsequent crop.
Promising A person has checked it against its sources. If you skip this, it still grows, just less well. The planner suggests it.
How it works
A legume fixes atmospheric nitrogen into its tissue as it grows. When the crop is killed and its residue decomposes, soil microbes mineralize that organic nitrogen, converting a form plants can't use into one they can, and release it for the next crop. How much depends on how well the legume grew, and it is lower on sandy soils.
The evidence
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
When cover crops are killed and begin to decompose, nitrogen can be released from the residues back into the soil where it can feed the next crop
The nitrogen credit depends on the amount of crop growth and when the legume was planted. Nitrogen credits are 50 lb N/a lower on sandy, coarse-textured soils.
Plant teams that rest on it
- Melon Sisters (small bed)
- Milpa
- Rotation break
- Summer legume break
- Sweet-potato milpa (small bed)
- Three Sisters (small bed)
- Winter cover pair
Read next
- Cover crops and green manure for the home gardenA cover crop is a plant you grow to feed the soil. Here's what they do, which kind fixes nitrogen and which just builds organic matter, and how to fit one into a small garden's off-season.
- Growing beans: pole or bush, and what the roots leave behindThe same bean is a knee-high bush or an all-season climbing vine, and the packet says which. How to grow both, and the truth about the nitrogen everyone repeats.
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Sources updated
- Wording made clearer
- Sources updated
- A person read the sources and confirmed it
- Added to the rules
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Cite this page
Milpa Gardens. “Legume green manure raises available N for the subsequent crop.” Evidence grade: Promising. https://milpa.garden/rules/legume-green-manure-raises-available-n-subsequent/
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
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- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.