Sudangrass

INTRODUCTION

Sudangrass (Sorghum bicolor ssp. drummondii), often sold alone or as a sorghum–sudangrass hybrid, is a fast-growing warm‑season annual grass used widely as a summer cover. Growers choose it for rapid biomass, strong weed suppression, compaction relief, and its ability to scavenge residual nitrogen while protecting soil between cash crops. SARE—Managing Cover Crops: Sorghum-Sudangrass

Benefits of Sudangrass as a Cover Crop

• Erosion Control: In a 2023–24 on‑farm trial in California vegetables, winter‑planted sudangrass or sorghum–sudangrass reduced total sediment loss 96–98% and reduced runoff ~70% compared with bare fallow during storms; suspended sediment concentrations were 77–90% lower under the grass cover crops. UC ANR Salinas Valley Agriculture More broadly, cover crops used with conservation tillage have reduced soil loss up to 89% vs. conventional tillage systems. SARE—Covering the Soil to Prevent Erosion
• Weed Suppression: Dense, quick canopies and allelopathy suppress many annual weeds. Sudangrass/sorghum–sudangrass seedlings, shoots, leaves, and roots exude the allelochemical sorgoleone; effects can persist for weeks and are strong enough to inhibit sensitive small‑seeded vegetables if planted immediately after termination. UVM Extension fact sheet; SARE—Sorghum-Sudangrass
• Soil Structure Improvement: Mowing at 3–4 ft increases root mass 5–8× and drives roots deeper (to roughly 10–16 in vs. 6–8 in unmowed), creating “wormhole‑like” channels that help alleviate compaction and improve surface drainage. SARE—Sorghum-Sudangrass
• Water Management: Grass cover crops consistently increase infiltration; across studies, non‑legume covers increased infiltration by 8–462%, while residue cover alone increased infiltration up to 180%. Greater infiltration lowers runoff and associated erosion. SARE—Increasing Infiltration. In the UC ANR field trial above, cover‑cropped plots infiltrated more rain and lost much less runoff than bare fallow. UC ANR
• Disease/Pest Break: When finely chopped and incorporated green before frost, sudangrass can suppress plant‑parasitic nematodes (e.g., northern root‑knot, Meloidogyne hapla) via poor host status and release of nematicidal compounds during decomposition; timing and quick incorporation are critical. Plant Disease, APS; SARE—Nematode management notes within Sorghum‑Sudangrass
• Nitrogen Management (scavenging): As a non‑legume, sudangrass is an excellent summer N scavenger; UGA notes sorghum–sudangrass as the “best” summer scavenger, and a CA winter trial measured 45–55 lb N/ac taken up by sudangrass by mid‑March. Plan for possible short‑term N tie‑up from high‑C residues if terminated late. UGA—N Availability Calculator bulletin; UC ANR trial; SARE—residue N tie‑up management
• Biomass Production: Typical single‑season biomass is about 4,000–5,000 lb dry matter (DM)/ac, with 18,000 lb DM/ac possible under fertile, moist conditions and multiple cuttings. Recent Nebraska research (2022–2024) found top sorghum–sudangrass varieties frequently exceeded 8–10 tons DM/ac in favorable summers; across years, strong performers averaged ≥4.5 tons DM/ac. SARE—Sorghum‑Sudangrass; UNL CropWatch 2025 study

Planting and Management Advice

• Seeding Rate (pure stand):
• Drill: 30–40 lb/ac when the goal is fast cover/smothering; lower rates (e.g., 15–20 lb/ac) are used in some forage programs. USDA‑ARS Southeast Fact Sheet; UGA Annual Forages Bulletin B1584
• Broadcast: 40–50 lb/ac; use the high end for weed suppression or if seedbed/coverage is marginal. USDA‑ARS Southeast Fact Sheet; UVM Extension fact sheet
• Notes: Drilling is more efficient and typically requires less seed than broadcasting; increase broadcast rates if seed–soil contact is poor. UVM Extension fact sheet
• Seeding Depth: 0.5–1.5 inches; plant shallower on heavier soils and deeper on sandy soils. UVM Extension fact sheet; NRCS Cover Crop Table 1
• Soil Type and pH: Prefers fertile, well‑drained soils; optimal pH is near neutral (6–7), but sorghum–sudangrass relatives tolerate pH ~5.0–9.0, offering flexibility on acidic or alkaline sites. SARE—Sorghum‑Sudangrass; UVM Extension fact sheet
• Planting Time (by region; plant after soils reach ≥60–65°F):
• Upper Midwest (MN): May 20–July 25; 25–30 lb/ac typical for sorghum–sudan in commodity systems. UMN Extension—Getting started with cover crops
• Northeast (ME): Mid‑June to mid‑August for sorghum × sudangrass; 35–50 lb/ac recommended when drilled; winter‑kills with frost. UMaine Extension Bulletin #1170 (Table 2)
• Southeast (GA): Warm‑season forages (including sorghum × sudangrass 15–20 lb/ac drilled) are generally planted April–June depending on sub‑region (Coastal Plain/Piedmont/Mountain); plant when 2‑inch soil temps exceed 65°F. UGA Annual Forages Bulletin B1584
• Central Great Plains (eastern NE): After winter wheat harvest (early–mid July) through summer; sorghum–sudangrass was a top biomass producer in 2022–2024 research plantings. UNL CropWatch 2025
• General NRCS guidance for warm‑season, winter‑killed species: May 1–Aug 5 (adjust locally). NRCS Cover Crop Table 1
• Termination (choose method based on goals and next crop):
• Frost: In cold regions, sudangrass winter‑kills with the first hard frost, leaving manageable residue. UVM Extension fact sheet
• Mow/Flail: Mow at ~3–4 ft to encourage tillering and deeper rooting; for final termination, flail chop and incorporate (or herbicide‑terminate) to speed residue breakdown. Earlier termination reduces N tie‑up risk. SARE—Sorghum‑Sudangrass management
• For nematode suppression: Finely chop and incorporate while still green before frost; immediate incorporation is needed to retain bioactive compounds. SARE—Nematode notes; UF/IFAS—Nematode Management Using Sorghum and Relatives
• Rotational Considerations:
• Residue/N tie‑up: High‑C residues can temporarily immobilize N. If planting an early, N‑demanding crop next, terminate earlier, add some starter N, follow with a legume, or allow a decomposition window. SARE—Sorghum‑Sudangrass, Crop Systems notes
• Allelopathy: Delay direct seeding of sensitive small‑seeded vegetables (e.g., lettuce) for several weeks after termination to avoid carryover suppression. UVM Extension fact sheet; SARE—weed suppression/allelopathy
• Herbicide carryover: As with any cover crop, check labels for rotational restrictions from herbicides used in the preceding or cover‑crop phase.
• Water Requirements and Drought Tolerance:
• Compared with corn, sorghum–sudangrass has waxier leaves, more secondary roots, and can endure drought by going semi‑dormant once established; biomass depends on rainfall or irrigation. SARE—Sorghum‑Sudangrass. Recent Nebraska work underscores that summer biomass is highly rainfall‑dependent; grass covers led the pack for biomass and durable residue. UNL CropWatch 2025

Practical tips

• Fertility: For vigorous summer growth, many programs apply 40–60 lb N/ac at establishment if residual N is low; avoid pushing N excessive to limit lodging and nitrate accumulation if the stand will be grazed. UVM Extension fact sheet
• Seeding method: Drill for best stands and lower seed cost per acre; increase rates if broadcasting or when a fast “smother crop” canopy is the goal. UVM Extension fact sheet; USDA‑ARS Fact Sheet
• Safety if used as forage: Do not graze young regrowth or frost‑injured plants due to prussic acid risk; this is a livestock‑management note, not a soil‑health limitation. SARE—Sorghum‑Sudangrass

Typical performance snapshot (what to expect)

• Biomass: 2–5 tons DM/ac in a single summer window; higher (8–10+ tons DM/ac) possible in long, moist summers or with multiple cuttings. SARE—Sorghum‑Sudangrass; UNL CropWatch 2025
• Erosion/infiltration: Order‑of‑magnitude drops in sediment loss and large infiltration gains documented under grass covers; site‑specific results vary with slope, rainfall intensity, and management. UC ANR trial; SARE—Increasing Infiltration

This guidance draws on recent research (2023–2026) and established extension/NCRS/SARE publications to provide actionable numbers for on‑farm decisions in U.S. regions.