Calculate how much cover crop seed you need per acre, estimate nitrogen fixation credit from legumes, project seed cost with a 10% buffer, and get a biomass and termination timing summary. Enter your field size, choose a single species or build a mix of up to three, and select your seeding method and primary goal.
Cover crops are planted between cash crop cycles to keep living roots in the soil, build organic matter, and address specific agronomic problems. The four most common goals are weed suppression, nitrogen fixation, erosion control, and soil biology improvement — and choosing the right species for your goal makes the difference between a successful cover and wasted seed money.
Weed suppression works through allelopathy and canopy competition. Winter rye is the gold standard: its dense canopy shades out early-germinating summer annuals, and its roots release allelopathic compounds that suppress weed seed germination. Sorghum-sudangrass delivers similar suppression in warm-season windows. A thick rye stand terminated at heading — before seed set — provides weed control windows of four to six weeks into the following crop.
Nitrogen fixation is the flagship benefit of legume covers. Hairy vetch fixes 100–200 lbs of nitrogen per acre under ideal conditions, crimson clover fixes 80–150 lbs, and cowpea fixes 50–150 lbs in warm-season systems. Legumes must be properly inoculated with the correct Rhizobium strain before planting — uninoculated seed on soils with no prior legume history fixes little to no N. Approximately 40–60% of fixed N becomes plant-available to the following crop after termination and decomposition.
Erosion control requires rapid establishment and ground cover. Annual ryegrass, oats, and winter rye establish quickly and produce extensive root systems that bind soil through the winter. Radish and turnip break up compaction layers and leave channels that improve water infiltration. Phacelia is excellent in specialty crop rotations where residue management is critical.
Termination timing matters as much as species selection. Winter-kill species — oats, radish, phacelia — die naturally after hard frost with no action required, leaving flat mulch for spring planting. Roll-crimping works best on rye and hairy vetch at anthesis (full flowering), when plants are most susceptible to mechanical termination without regrowth. Premature rolling leads to poor kill rates and re-tillering. Spring tillage incorporates residue and is the most flexible option across all species. Herbicide burndown is fastest and most consistent but requires proper product selection and timing relative to planting the cash crop.
Grazing cover crops adds another dimension. Sorghum-sudangrass, oats, and crimson clover all provide high-quality forage when managed with rotational grazing. Graze covers when plants reach 12–18 inches and pull livestock when grazed to 6 inches to protect root systems and ensure regrowth. Incorporating livestock into a cover crop program can partially offset seed costs through reduced purchased feed.
Yes, in most cases. Crimson clover, hairy vetch, and cowpea all form symbiotic relationships with specific Rhizobium bacteria to fix atmospheric nitrogen. If your soil has no prior history with that legume species — or if you're planting a new field — uninoculated seed will germinate and grow but fix little to no nitrogen. Purchase pre-inoculated seed or coat seed yourself with the correct inoculant at planting. Inoculant is inexpensive ($10–20 per bag) and the yield impact on the following cash crop is significant on soils with no native Rhizobium population.
Yes. Broadcast seeding works well for small-seeded species like crimson clover, annual ryegrass, phacelia, and radish. The key is seed-to-soil contact — broadcast onto a tilled or disturbed surface and cultipack or drag to press seed into the soil. For larger-seeded species like oats, rye, and cowpea, broadcast seeding requires a 25–40% increase in seeding rate to compensate for poor germination on the surface. Aerial seeding is used for interseed applications into standing corn or soybeans at canopy closure — timing is critical, and seed-to-soil contact is poor, so aerial rates run 40% higher than drill rates.
A conservative and defensible nitrogen credit is 40–50% of estimated fixation, applied at the time the following cash crop needs it. For hairy vetch terminated in spring before corn, a well-established stand fixing 120–150 lbs N/acre can justify crediting 50–75 lbs N/acre toward the corn nitrogen budget. Your state extension service publishes N credit guidelines for common legume covers — follow those values rather than the maximum fixation estimates when making fertilizer decisions. Factors that reduce actual credit: poor stand, early termination, wet soils that slow decomposition, and fall-applied legume residue that mineralizes before spring planting.
Roll-crimping uses a large roller equipped with blunt crimping blades to mechanically terminate cover crops without tillage. The roller lays the biomass flat, creating a thick mulch that suppresses weeds and retains soil moisture for the following cash crop, which is no-till planted through the mulch. Roll-crimping works reliably on winter rye and hairy vetch when plants are at or past anthesis — typically late May in the Midwest. Rolling too early results in regrowth, particularly with rye. It does not work well on oats (which are typically winter-killed) or on species that don't form a dense enough canopy to suppress weeds once flattened.