Cowpeas (Warm-Season)

• Cowpeas (Vigna unguiculata) are a warm-season, fast-growing legume cover crop valued for drought tolerance, rapid canopy closure, and dependable nitrogen fixation in hot summer windows. Growers choose cowpeas to supply in-season N, suppress summer weeds, protect soil, and to fit short rotations between cash crops. [SARE “Managing Cover Crops Profitably” cowpea chapter], (sare.org) [Ohio State—Ohioline cowpea factsheet]. (ohioline.osu.edu)

• Erosion Control: On sloping land, intercropping cowpea reduced dry soil loss by 40% on gentle slopes and 58% on steep slopes versus monocropping in a replicated field study (Vietnam, 2018 season). More broadly, legume cover crops have reduced soil loss 38–69% across studies, with average sediment loss reductions of 20.8 tons/acre under conventional till conditions. (so01.tci-thaijo.org, sare.org)
• Weed Suppression: Cowpea quickly shades the soil; typical biomass of 3,000–4,000 lb dry matter/acre helps smother summer annuals. Recent research reports >80–90% reductions in weed dry weight where cowpea covers established dense canopies; residues can add allelopathic effects for continued suppression. (sare.org, mdpi.com)
• Soil Structure Improvement: A vigorous taproot can reach nearly 8 feet within eight weeks, creating biopores and helping relieve shallow compaction; legume cover crops have increased water infiltration 39–528% in compiled studies. (sare.org)
• Water Management: Dense summer cover and residue reduce crusting and runoff while increasing infiltration; the deep taproot helps plants access subsoil moisture and improves water storage. Legume covers commonly increase infiltration (39–528%) and reduce runoff compared with bare soil. (sare.org)
• Disease/Pest Break: Selected cowpea cultivars (e.g., ‘Iron Clay’, US-1136/1137/1138) are resistant to some root‑knot nematodes (Meloidogyne incognita), helping reduce nematode pressure before susceptible vegetables. However, cowpea can be a host for soybean cyst nematode and for guava root‑knot nematode (M. enterolobii) depending on cultivar—manage rotations accordingly. (edis.ifas.ufl.edu, content.ces.ncsu.edu)
• Nitrogen Management: Properly inoculated stands commonly accumulate about 70–150 lb N/acre (total N in biomass), with N availability to the next crop maximized when terminated at early bloom. As with other legumes, actual fertilizer N credit depends on biomass, C:N, and termination timing. (ohioline.osu.edu, sare.org)
• Biomass Production: Typical dry matter yields range from about 2,500–4,500 lb/acre in the Midwest/East; North Carolina trials measured ~3,500 lb/acre and ~75 lb N/acre in above‐ground biomass. (ohioline.osu.edu, content.ces.ncsu.edu)

• Seeding Rate:
• Drill: 50–90 lb/acre (pure live seed), 1–1.5 inch depth; use higher end in cooler/drier conditions or with larger seed. (ohioline.osu.edu)
• Broadcast: 70–120 lb/acre; incorporate shallowly for best stands. General cover crop guidance is to increase broadcast rates 10–25% over drilled to compensate for poorer seed‑to‑soil contact. (cms.ctahr.hawaii.edu, midwestcovercrops.org)
• Seeding Depth: 1–1.5 inches is typical; up to ~2 inches on coarse, sandy soils to reach moisture. (ohioline.osu.edu, sarep.ucdavis.edu)
• Soil Type and pH: Performs best on well‑drained sandy loams; avoid waterlogged soils. Optimum pH is roughly 5.5–6.5; cowpea tolerates moderately acidic to neutral soils but is less adapted to alkaline conditions. (corn.agronomy.wisc.edu, sare.org)
• Planting Time (seasonal windows by region):
• Upper Midwest (MN): May 20–Aug. 15. (mosh.umn.edu)
• Midwest/Ohio Valley: Reliable establishment in Ohio from about June 10–Aug. 16. (ohioline.osu.edu)
• Iowa Corn–Soy region: Often used July–September after small grains or prevented‑planting acres. (crops.extension.iastate.edu)
• Southeast/Mid‑South: Spring after last frost through late summer; Mississippi guidance lists May 1–June 30 for warm‑season forage legumes like cowpea. (content.ces.ncsu.edu, extension.msstate.edu)
• General Temperature Rule: Wait until soils are consistently ≥65°F for reliable emergence. (sare.org)
• Termination:
• Winter‑kill in frost‑prone regions; otherwise terminate before seed set to avoid volunteers. Mowing alone may not kill cowpea; combine mowing/rolling with herbicide or shallow tillage for reliable control. (sare.org)
• For crop‑insurance compliance, follow USDA NRCS/RMA cover crop termination guidance by zone: in most of the Midwest/East/South (Zone 3) terminate at or before planting; in the Southeast/Gulf (Zone 4) within 5 days after planting but before cash‑crop emergence. Local Good Farming Practice determinations allow flexibility—confirm with your NRCS/insurance agent. (nrcs.usda.gov, rma.usda.gov)
• Rotational Considerations:
• Nematodes: Where soybean cyst nematode (SCN) or guava/southern root‑knot nematodes are concerns, either choose resistant cowpea cultivars (e.g., ‘Iron Clay’, US-1136/1137/1138) or plant a non‑host cover crop (e.g., sunn hemp for RKN; small grains for SCN). Avoid placing susceptible cash crops immediately after a susceptible cowpea cultivar. (edis.ifas.ufl.edu, content.ces.ncsu.edu)
• Allelopathy: Cowpea residues can contribute to weed suppression; in sensitive vegetable systems, test on a small area or allow a short interval before direct‑seeding small‑seeded crops. (sare.org)
• Water Requirements and Drought Tolerance:
• Once established, cowpea is a “rugged survivor” of dry spells; taproots can extend nearly 8 feet in eight weeks, enhancing drought tolerance and access to deep moisture. It is more drought resistant than common bean and performs well under non‑irrigated conditions, but avoid waterlogging. (sare.org, corn.agronomy.wisc.edu)
• Cover crops, especially legumes, can substantially increase infiltration (often 39–528% in compiled studies), improving soil water storage for subsequent crops. (sare.org)
• Nitrogen Management:
• Inoculate with a “cowpea group” Rhizobium each time cowpeas are new to a field. Well‑managed stands typically accumulate 70–150 lb N/acre in biomass; terminate at early bloom to optimize plant‑available N to the next crop, recognizing that realized fertilizer credit depends on biomass, C:N, placement, and weather. (sare.org, ohioline.osu.edu)
• Biomass Production:
• Expect roughly 2,500–4,500 lb dry matter/acre in single‑species stands under Midwest/Eastern conditions; NC trials reported ~3,500 lb DM/acre and ~75 lb N/acre. Biomass and N are higher with earlier planting and adequate moisture. (ohioline.osu.edu, content.ces.ncsu.edu)

Practical notes:

• Seed size is large; drilling gives the most uniform stands. If broadcasting, incorporate lightly and increase seeding rate relative to drilling. (midwestcovercrops.org)
• Use in mixtures (e.g., with sorghum–sudangrass or millets) when longer‑lasting residue or extra weed suppression is desired. (sare.org)
• For erosion control goals, maintain continuous cover and minimize bare periods; cover crops have reduced sediment losses dramatically in many systems. (sare.org)

This description draws on university Extension, USDA/NRCS guidance, SARE publications, and recent peer‑reviewed research to provide regionally adaptable, number‑driven recommendations for cowpea as a warm‑season cover crop.