What the research measured
Maryland trials reported an economic nitrogen rate of about 27 lb/ac after vetch versus 179 lb/ac without a cover crop. Pennsylvania measurements averaged 164 lb N/ac in vetch biomass at termination. These are different measures; the linked studies describe their locations, management, and sampling methods.
Two-site, two-year replicated Maryland kill-date trials, a two-site USDA-ARS mixture study, a 55 site-year meta-analysis and the legume-cover meta-analyses.5 independent sources.What it is. A winter-hardy annual legume seeded in late summer or fall, alone or with rye, that fixes the largest spring N supply of the common winter legumes when killed at early bloom before no-till corn.
Study conditions and limitations
- Kill date drives the credit: vetch added about 2 kg N/ha per day from late March to early May in Maryland; Wisconsin and Minnesota credit about 60 lb N/ac when incorporated before June 10 versus 120 for a full season.
- N release is fast, about 70 lb N/ac within four weeks of corn planting in an Illinois study, which fits corn demand but can be lost in a wet spring; mixing with rye slows release and adds cover.
- Winter survival: hardy to Zone 4 per SARE, but the Wisconsin and Minnesota bulletin says it often fails in the northern Midwest, and Nebraska stands measured only 12–29 lb N/ac.
- Stand N is not fertilizer-replacement N: Extension credits range from 75–150 lb N/ac (Maryland) to 80–100 (North Carolina); at full N rates expect the return to be the fertilizer saved, not extra bushels.
- Seeding: 15–20 lb/ac drilled or 25–30 broadcast; for maximum N in a mix the USDA-ARS study used 27 kg/ha vetch with 34 kg/ha rye.
Read the sources · 5
- Kill Date of Vetch, Rye, and a Vetch–Rye Mixture: II. Soil Moisture and Corn Yield ↗
At the Maryland Coastal Plain site the economic N rate for no-till corn was 30 kg/ha after hairy vetch, 65 after a vetch–rye mix, 161 after rye and 201 with no cover; late-April or early-May kills consistently out-yielded earlier kills.
- Kill Date of Vetch, Rye, and a Vetch–Rye Mixture: I. Cover Crop and Corn Nitrogen ↗
Between late March and early May hairy vetch added about 2 kg N/ha per day, reaching 144–203 kg N/ha in topgrowth; corn N requirement was lowest after vetch, intermediate after vetch–rye and highest after rye.
- Biomass Production and Nitrogen Accumulation by Hairy Vetch–Cereal Rye Mixtures: A Meta-Analysis ↗
Across 55 site-years from 21 US studies, vetch–rye mixtures produced 63% more biomass than vetch alone and held 150% more N than rye alone; with vetch above 46% of the seed mix by weight, the mixture accumulated as much N as the best monoculture.
- Biomass and Nitrogen Content of Hairy Vetch–Cereal Rye Cover Crop Mixtures as Influenced by Species Proportions ↗
At two Maryland sites, spring N content rose from 64 to 181 kg N/ha as the vetch share of biomass went from 0 to 100%, plateauing once vetch reached about half the stand; biological fixation supplied 63% of vetch N in monoculture and 86% in mixture.
- Hairy Vetch, in Managing Cover Crops Profitably (3rd edition) ↗
Maryland vetch–rye mixtures accumulated 130–180 lb N/ac, and late-April or early-May kills with corn no-tilled 10 days later consistently out-yielded earlier kills. Winter hardy through Zone 4; drill 15–20 lb/ac or broadcast 25–30.
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 →