What the research measured
Wisconsin corn N-rate trials measured nitrogen credits of 46 to 100 lb N/ac after frost-seeded red clover across four site-years, with a 16 bu/ac corn yield drag in one of them. A 12-location Ontario study reported an 82 kg/ha credit to the following corn, and a 20-year Ontario rotation experiment reported 5% higher corn yield after wheat underseeded with red clover under moldboard tillage. Penn State measured 91 lb N/ac (range 45–137) in red clover biomass at spring termination.
Four Wisconsin site-years of corn N-rate trials (2010–2019), a 12-location University of Guelph wheat-management study, a 20-year Ontario tillage-by-rotation experiment, Penn State’s biomass-N table and SARE’s species chapter. No meta-analysis specific to frost-seeded red clover was found.5 independent sources.What it is. A short-lived perennial legume broadcast onto frozen or honeycombed soil in standing winter wheat in late winter, where freeze–thaw cycles work the seed in. It grows under the wheat canopy, takes off after wheat harvest and is killed in fall or the next spring ahead of corn.
Study conditions and limitations
- The credit moved from year to year: 46 lb N/ac at Janesville in 2010 and 57, 75 and 100 at Arlington in 2016, 2018 and 2019; SARE cites a two-year Michigan trial that logged a fertilizer replacement value of 36 lb N/ac.
- A credit does not rule out a yield drag: Arlington 2016 measured a 57 lb N/ac credit alongside a 16 bu/ac drag, 2018 showed some yield loss under no-till, and 2019 none.
- Biomass N is larger than the fertilizer credit: Wisconsin measured 80 to 110 lb N/ac in red clover top growth, and Penn State 91 (45–137), against credits of 36 to 100.
- Wheat management sets the stand: in the Guelph study conventional tillage before wheat gave 48% more red clover dry weight than no-till, and the 5% corn yield gain in the 20-year experiment was reported for the moldboard system.
- Kill date changes what is in the stand: an Ohio measurement cited by SARE found about 75 lb N/ac on May 15 rising to 130 by June 22, and SARE notes 50% of the cover-crop N was released in the first month after incorporation.
- SARE lists frost-seeding at 10 to 12 lb/ac into wheat in February, hardiness to Zone 4, a minimum pH of 6.0 and persistence of three to four years, so a stand left uncontrolled becomes a weed in the next crop.
Read the sources · 5
- Quantifying the benefits of legume cover crops ↗
Corn N-rate trials after frost-seeded red clover measured N credits of 46 lb N/ac at Janesville (2010) and 57, 75 and 100 lb N/ac at Arlington (2016, 2018, 2019), with 80 to 110 lb N/ac in the clover’s above-ground biomass; the 2016 site also had a 16 bu/ac yield drag.
- Impact of Winter Wheat Management on Underseeded Red Clover ↗
Red clover under-seeded to winter wheat in Ontario provides an 82 kg/ha nitrogen credit to the following corn; across twelve locations with four wheat N rates, conventional tillage gave 48% more red clover dry weight and 6.7% more wheat yield than no-till.
- Impact of Tillage and Rotation on Yield and Economic Performance in Corn-Based Cropping Systems ↗
In a 20-year Ontario experiment comparing seven rotations under moldboard and chisel plowing, corn yield in the corn–soybean–wheat rotation was 5% higher when the wheat was underseeded with red clover, in the moldboard system.
- Soil Organic Matter and Cover Crop-based Nitrogen Recommendations for Corn ↗
In Pennsylvania measurements at maximum spring growth before termination, red clover biomass averaged 91 lb N/ac with a range of 45 to 137, against 79 (53–105) for crimson clover and 164 (134–194) for hairy vetch.
- Red Clover, in Managing Cover Crops Profitably (3rd edition) ↗
Full-season over-wintered red clover can produce 2 to 4 tons of dry matter and fix 70 to 150 lb N/ac; a two-year Michigan trial logged a fertilizer replacement value of 36 lb N/ac. An Ohio farmer frost-seeds 10 to 12 lb/ac into wheat in February; winter hardy in Zone 4 and warmer.
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
- October 12, 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 →