Sorghum-Sudangrass

Sorghum-sudangrass (Sorghum bicolor × S. bicolor var. sudanese) is a fast-growing, warm-season annual grass used widely as a summer cover for rapid soil cover, high biomass, and strong root growth. Growers choose it to smother summer weeds, loosen compacted layers, scavenge nutrients, and provide a short-season “reset” between cash crops, especially in hot, dry windows when cool-season covers struggle (SARE, Managing Cover Crops Profitably).

• Erosion Control: Winter trials in Salinas Valley (2023–2024) showed sorghum-sudangrass cover reduced storm-season sediment loss by 96–98% vs. bare fallow and cut runoff roughly 70% (more rainfall infiltrated), despite low winter biomass; suspended sediment in runoff was 77% lower than bare fallow (UC ANR, 2024). Similar vegetative filter work found “Sudex” strips reduced total suspended solids by 73% during runoff events in Hawai‘i (Journal of the American Water Resources Association, via K-State database).
• Weed Suppression: Dense summer canopies and allelopathy (notably the root exudate sorgoleone) suppress many annuals. In an Oklahoma field trial, sorghum-sudan cover reduced weed counts 82% at V2–V3 soy (189 vs. 34 weeds/3 ft²) and 86% at R2 (398 vs. 56) compared to no cover (Oklahoma State Univ. Extension). Mechanistically, sorghum/sudangrass residues and exudates inhibit species such as pigweed, crabgrass, barnyardgrass, ragweed, and more (USU Extension, SARE).
• Soil Structure Improvement: A single mowing at 3–4 ft height increases sorghum-sudangrass root mass 5–8× and pushes roots deeper (to ~10–16 in. vs. 6–8 in. unmowed), creating “wormhole-like” channels that enhance drainage and fracture shallow compaction (SARE).
• Water Management: The tall canopy and residue reduce raindrop impact and evaporation, while living cover improves infiltration; in storms, cover plots had ~70% less runoff than bare fallow in the Salinas trial (UC ANR, 2024). Plants are inherently drought-tolerant (waxier leaves, more secondary roots than corn) and can go semi-dormant under stress (SARE).
• Disease/Pest Break: Many sorghum-sudangrass cultivars are poor hosts for root-knot nematodes (M. incognita, M. arenaria, M. javanica), lowering pressure through rotation; best suppression occurs when used as the rotation crop and, for residue-mediated effects, when green tissues are chopped and incorporated promptly (UF/IFAS EDIS).
• Nitrogen Management (non-legume scavenger): As a non-legume, it scavenges available N; tissue N uptake averages about 7 lb N per ton of biomass (e.g., 4–10 tons DM/A = ~28–70 lb N/A taken up) (Penn State Extension). In low-biomass winter plantings, cover captured 45–55 lb N/A by mid-March in California trials (UC ANR, 2024). Note the high C:N residues can temporarily immobilize soil N; plan termination timing and supplemental N accordingly (SARE).
• Biomass Production: Typical dry matter is 4,000–8,000 lb/A under rainfed Midwestern conditions (Ohio State Univ. Extension, 2023), with 4,000–5,000 lb/A commonly reported by SARE; under irrigation/high fertility, 8–18 tons DM/A have been measured in research trials (SARE; UNL CropWatch, 2023–2024, 2024 summary).

• Seeding Rate (cover crop objectives):
• Drill: 20–40 lb/A; for fast smothering, many programs target 35–40 lb/A drilled (SARE; NC State Forage Planting Guide).
• Broadcast: 30–50 lb/A (use the high end for weed suppression; incorporate lightly or cultipack) (SARE; UGA Forages).

Notes: Ohioline lists 16–30 lb/A drilled and 18–30 lb/A broadcast (PLS) for Ohio; increase rates on slopes or for forage use (Ohio State Univ. Extension, 2023). Always follow state NRCS Appendix A seeding standards when cost-shared.

• Seeding Depth: 0.75–1.5 in. in medium/heavier soils; up to 2 in. in sands to reach moisture (Virginia Tech; UGA Forages; NC State).
• Soil Type and pH: Performs best on well-drained, fertile soils; intolerant of flooding/ponding (Ohio State Univ. Extension). Tolerates a wide pH range (~5.0–9.0), though near-neutral (6–7.5) is optimal for growth (SARE; Univ. Wisconsin Extension).
• Planting Time (seasonal windows by region):
• Upper Midwest/North: Generally after soils reach 60–65°F; typical windows May 20–July 25 in Minnesota (UMN Extension, reviewed 2024) and late May–early June in Wisconsin (Univ. Wisconsin Extension).
• Great Plains: Plant once soils are 55–60°F; in western Nebraska avoid planting before ~June 1; acceptable through mid-July depending on moisture (UNL Extension; UNL CropWatch).
• Mid-Atlantic/Southeast: NC seeding window ~May 1–June 30; rates B: 35–40, D: 20–30 lb/A; depth 0.5–1 in. (NC State Planting Guide). In Georgia: Coastal Plain Apr 1–Aug 15; Piedmont Apr 15–Aug 1; Limestone Valley May 1–July 15 (drill 15–20; broadcast 25–30 lb/A) (UGA Forages).
• General Rule: Plant when soil is 65–70°F and you still have at least ~60 days before expected frost for meaningful biomass (SARE).
• Termination (methods and timing):
• Winterkill in cold climates (first hard frost), leaving manageable residue for spring planting (Ohio State Univ. Extension).
• Mow or flail chop (3–4 ft stage encourages tillering and deeper roots during the season; mowing after heading can terminate stands) and/ or incorporate with tillage; dense roots may require multiple tillage passes (SARE; Ohio State Univ. Extension).
• Herbicide termination is an option in conventional systems; follow label and local guidance. For nematode suppression via residues, incorporate while green and chop finely to hasten breakdown; immediate incorporation improves biofumigant effect (UF/IFAS EDIS).
• To avoid allelopathic effects on small-seeded crops, allow roughly 3–4 weeks after incorporating fresh green residues before direct seeding sensitive species like lettuce (UVM Extension).
• Rotational Considerations:
• High C:N residues can temporarily tie up N and slow early growth of the next crop; consider adding N at incorporation or following with a legume cover to offset immobilization (SARE).
• In an 8‑year Kansas study, a summer sorghum-sudan cover removed ~47 lb N/A from the plant-available pool; subsequent grain sorghum needed ~120 lb N/A vs. ~80 lb N/A after other treatments—plan N accordingly (Kansas State Univ. eUpdate).
• Avoid planting in fields infested with johnsongrass; sorghum-sudangrass can complicate management of this perennial grass (Ohio State Univ. Extension). In warm regions and potato systems, monitor for wireworms when using sorghum covers and adjust harvest/termination timing if needed (UF/IFAS EDIS).
• Water Requirements and Drought Tolerance: Among summer annual grasses, sorghum-sudangrass is highly drought tolerant—more so than corn—due to waxy leaves and robust secondary roots (SARE). However, it is generally more water‑demanding and less drought‑tolerant than pearl millet in the Southeast (UC Davis SAREP; UGA Forages).

Practical Notes:

• Manage for biomass and timing: For maximum soil building without spring delays, mow once at 3–4 ft to keep tissues vegetative and easier to handle later, then terminate 2–4 weeks before planting the next crop to minimize N tie-up and any allelopathic carryover (SARE; UVM Extension).
• Forage/grazing caution: All sorghums can accumulate prussic acid and nitrates under stress; do not graze until 24–30 in. tall, avoid immediately after frost/drought, and test suspect forage (Missouri Extension; MSU Extension).