What the research measured
Published Extension measurements describe roughly 50–100 lb N/ac in crimson clover biomass in some regions. Biomass nitrogen and fertilizer-equivalent nitrogen credit are different measures. Winter survival, planting date, and termination timing affect the reported results.
The meta-analyses cover legumes generally rather than crimson clover specifically, the multi-year peer-reviewed crimson-clover corn trial found is a single Ontario site, and the Midwest N-credit and winter-survival numbers come from Extension summaries.5 independent sources.What it is. A winter-annual legume seeded in late summer or fall that fixes nitrogen and, where it overwinters, supplies part of the following corn crop’s N when killed in late spring.
Study conditions and limitations
- Winter survival by region: dependable in Zone 8, survivable in the lower reaches of Zone 6, winter-killed in Zone 5 and colder; Michigan lists winter kill and seed cost as the main drawbacks.
- Variety matters: in a one-year Illinois trial the older Dixie survived winter 69% versus 94% for Kentucky Pride, with 14 versus 187 lb N/ac in spring biomass. That write-up is by the seed company, so treat it as company data.
- A winter-killed stand releases much of its N before corn can use it, so fall-only growth gives erosion and organic-matter benefits but little spring credit.
- Kill late: N accumulates through spring, and the 2026 meta-analysis found termination under 7 days before planting roughly doubled the unfertilized-corn benefit versus early termination.
- Ohio’s reliable establishment window is June 10 to September 28, which rules out seeding after most Corn Belt corn harvests; it needs true-clover rhizobium inoculant where clover has not been grown in three years.
Read the sources · 5
- Corn responses to nitrogen fertilization as influenced by cover cropping: a meta-analysis ↗
Across 392 corn-yield observations from 55 site-years, legume cover crops raised corn yield 51% when no N was applied, a benefit that shrank as N rate rose; grass covers cut unfertilized corn yield 20%. Late termination gave a larger unfertilized-yield benefit than early termination.
- Corn yield response to winter cover crops: an updated meta-analysis ↗
Across 268 observations from 65 studies (1965–2015), grass covers such as rye neither raised nor lowered corn yield on average. Legume covers raised corn yield 30–33% only where fertilizer N was low or the system was no-till.
- Legume Cover Crops Provide Nitrogen to Corn During a Three-Year Transition to Organic Cropping ↗
In a three-year southwestern Ontario rotation, summer-seeded crimson clover carried 119 kg N/ha at spring plow-down (hairy vetch 240, red clover 199). Corn after the legumes averaged 13.1 Mg/ha versus 6.4 for organic plots with no cover crop.
- Soil Organic Matter and Cover Crop-based Nitrogen Recommendations for Corn ↗
From hundreds of Pennsylvania measurements, crimson clover biomass at spring termination averaged 79 lb N/ac (range 53–105), against 164 (134–194) for hairy vetch and 91 (45–137) for red clover. Penn State calls its cover-crop N recommendation system highly experimental.
- Crimson Clover, in Managing Cover Crops Profitably (3rd edition) ↗
As a winter annual in Zone 8 crimson clover fixes 70–150 lb N/ac by mid-May; a Michigan summer-annual stand made only 50–60 lb N/ac. It overwinters dependably in Zone 8, can survive the lower reaches of Zone 6, and winter-kills in Zone 5 and colder.
Before you buy, ask
- What seeding rate, date, and termination timing did the cited studies use?
- How does termination timing before my cash crop change the nitrogen and moisture picture?
- Which species or mixture fits my rotation window and equipment?
Record
- Sources checked
- September 26, 2026. Every figure shown is printed on the linked page; unit conversions are noted on the chart.
- Company response
- None yet. Makers and suppliers of this product can send corrections, additional trials, or a statement; it is published here, labelled, and never edits the research summary. Send a correction →