Legume green manure raises available N for the subsequent crop.
Promising · suboptimal if ignored → advise
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: confirmed against 2 sources in the research-based literature.
the 2 sources
Penn State Extension, 'Growing Cover Crops for Nitrogen on Vegetable Farms', extension.psu.edu/growing-cover-crops-for-nitrogen-on-vegetable-farms (read 2026-07-11): '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'; 'Mineralization is the process where organic nitrogen, which is largely not available to plants, is converted by soil microorganisms' into a plant-available form.
Univ. of Wisconsin-Madison Extension (Crops & Soils), 'Late Summer Planting Legumes to Produce Nitrogen Credits for Next Year', cropsandsoils.extension.wisc.edu/articles/late-summer-planting-legumes-to-produce-nitrogen-credits-for-next-year (read 2026-07-11): '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.'
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- legume green manure — fill the stub mechanism from its own sources
- promote to verified — legume green manure raises next-crop N
- cite Penn State + Wisconsin for legume green-manure N credit (rule confirmed)
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/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.