Turnip

Turnip (Brassica rapa subsp. rapa) is a fast-growing brassica cover crop valued for rapid fall canopy, nutrient scavenging, and the option to graze leafy tops and bulbs. Growers choose turnip to protect soil going into winter, capture leftover nitrogen, alleviate shallow compaction, and provide economical fall forage. Ohio State University Extension—Ohioline, 2023; UMass Extension—Brassica cover crops

• Erosion Control: Multiple studies show non-legume cover crops substantially reduce soil loss; mustard (a brassica) cut soil loss by up to 82% compared with no cover, and cover crops reduced sediment losses by an average of 20.8 tons/acre (conventional till), 6.5 tons/acre (reduced till), and 1.2 tons/acre (no‑till). Turnip provides living cover in fall and, where it overwinters, into spring. SARE “Cover Crops at Work: Covering the Soil to Prevent Erosion”
• Weed Suppression: Brassicas establish quickly and shade the soil; research has documented 52–56% reductions in weed density/biomass with mustard covers and up to 98% early-season weed biomass reductions with brassica covers in certain vegetable systems. Recent field work also found fall cover crops (including mixes with canola) cut weed biomass 86–99% in semi-arid systems. Expect strong fall suppression from turnip; spring suppression depends on winter survival and residue. HortTechnology (yellow mustard) 2008; SARE project report LNE03‑192; Crop Science 2022
• Soil Structure Improvement: Turnip’s enlarged taproot and bulb create macrochannels that improve near-surface porosity and ease root penetration for the next crop; brassicas are widely used to relieve surface hardness. UMass Extension—Brassica cover crops
• Water Management: Cover crops increase infiltration by 8%–462% across systems and can reduce runoff two- to four-fold under no-till; the macropores left by brassica roots help water move into the profile, reducing crusting and ponding. SARE “Increasing Infiltration”; UMass Extension—Brassica cover crops
• Disease/Pest Break: Brassica residues release isothiocyanates that can suppress some soil-borne pests and diseases; in certain systems brassica covers reduced Columbia root‑knot nematode up to 80% and have shown suppression of pathogens like Rhizoctonia and Phytophthora when managed as green manures. Turnip is also listed as a non‑host for soybean cyst nematode. Results vary by species, timing, and incorporation. SARE Managing Cover Crops Profitably—Brassicas & Mustards; SARE nematode section; Ohio State—Ohioline
• Nitrogen Management (Scavenging): Fall‑planted brassicas (including turnip hybrids) commonly accumulate 31–136 kg N/ha (≈28–121 lb N/acre) in biomass, capturing residual nitrate and lowering off‑season losses; across systems, cover crops reduced nitrogen losses to water by an average of 48% (up to 89% in one study). Agronomy Journal (brassica N uptake); SARE “Cover Crops Improve Soil Conditions and Prevent Pollution”
• Biomass Production: Typical dry matter production for turnip cover crops is 1,200–3,000 lb DM/acre in the Midwest, driven by planting date, fertility, and moisture; forage-oriented plantings can yield more total (fresh) tonnage. Ohio State—Ohioline

• Seeding Rate (monoculture):
• Drill: 1–3 lb/acre PLS at 0.25–0.5 inch (Ohio) for basic soil cover/grazing; use higher rates for steep slopes or heavy grazing. Ohio State—Ohioline
• Drill (for aggressive fall weed suppression/grazing focus): 4–7 lb/acre about 0.5 inch. SARE—Brassicas & Mustards
• Broadcast with shallow incorporation: 2–4 lb/acre (Ohio). Broadcast without incorporation: 3–4 lb/acre (Ohio). For broadcast generally increase rates 20–50% over drilled to ensure stands. Ohio State—Ohioline; Midwest Cover Crops Council—Planting
• Regional brassica category guidance lists 8–14 lb/acre single‑species for “brassica (rape, turnip, kale)” and 3–6 lb/acre in blends; depth 0.25–0.75 inch. Use local NRCS Appendix A where program dates/rates apply. Mississippi State Extension—Seeding Rates & Depths
• Seeding Depth: 0.25–0.5 inch is ideal; do not exceed 0.75 inch, especially in finer soils. Good seed‑to‑soil contact is critical; cultipack after broadcasting. Ohio State—Ohioline; Mississippi State Extension
• Soil Type and pH: Prefers well‑drained to moderately well‑drained soils; avoid poorly drained/wet spots, which hinder stands (especially bulb types). Optimal pH is about 5.3–6.8 (acceptable roughly 5.5–7.5). Mississippi State Extension—Forage Brassicas; Ohio State—Ohioline; Texas A&M—pH table
• Planting Time (typical windows; adjust to local frost/soil temps):
• Midwest (Ohio): March 29–June 11 for spring; July 24–Sept 6 for fall establishment. Ohio State—Ohioline
• Upper Midwest (Minnesota): Forage turnip July 25–Sept 15; 1–4 lb/acre. Reviewed 2024. University of Minnesota Extension
• Northeast (Pennsylvania): Latest fall seeding dates by zone—Area 1 Sept 1; Area 2 Sept 7; Area 3 Sept 15. Penn State Extension
• Southeast (Mississippi/North Gulf): Aug 15–Oct 1 typical for turnip/brassicas. Mississippi State Extension—Forage Establishment Guide
• General rule of thumb where specific dates aren’t listed: seed ≈4 weeks before the average first 28°F freeze so plants reach 6–8 leaves (rosette) before hard frosts. UMass Extension—Brassica cover crops
• Termination:
• Winterkill: Many turnip stands winterkill with sustained lows below about 25°F; survival varies by variety, planting date, snow cover, and latitude. UMass Extension—Brassica cover crops
• Herbicide: Turnip can be terminated with a full rate of paraquat, or with multiple glyphosate applications; glyphosate plus 1 pt/acre of 2,4‑D is also effective on brassicas. Always follow label/rotation restrictions. SARE—Brassicas & Mustards
• Mechanical: Flail mowing or tillage can be used; rolling/crimping alone is unreliable on broadleaf/brassica covers unless at full flower. SARE—Brassicas & Mustards; Southern Cover Crops Council
• Timing note for cash crops: In water‑limited settings, consider terminating 2+ weeks before planting to conserve seedbed moisture; later termination can boost biomass but may increase moisture/pest “green bridge” risks. SARE—Building Soils for Better Crops, Ch. 10; NC State Extension—Termination timing
• Rotational Considerations:
• Disease bridge: Avoid planting turnip (or other brassica covers) close in rotation with brassica cash crops (e.g., canola, cole crops); manage volunteers. Many universities advise a 3‑year or longer break to reduce clubroot/black leg risk. UMass Extension—Brassica cover crops; PNW Plant Disease Handbook—clubroot/black leg and Turnip/Rutabaga—clubroot
• Biofumigation notes: If your goal is disease suppression, optimum effects require chopping and immediate incorporation of high‑biomass brassica tissues; responses are pest- and site‑specific. University of Missouri IPM—Biofumigation; Oregon State Extension, 2024/2025 update
• Water Requirements and Drought Tolerance:
• Establishment needs firm seedbed and adequate moisture; brassicas do poorly on wet, poorly drained soils. Once established, brassicas are generally considered cold‑hardy with moderate drought tolerance, but their relatively high water use means they can deplete soil moisture if allowed to grow long into a dry spring. Plan termination to balance biomass benefits with moisture conservation. Wisconsin Agronomy—Turnip; Oregon State Forage Information System; SARE—Building Soils for Better Crops, Ch. 10
• Additional Practical Notes:
• Increase rates on slopes or when using for forage/weed suppression. Mix with a winter‑hardy grass (e.g., cereal rye) if spring ground cover is needed where turnip winterkills. Ohio State—Ohioline
• For grazing, many state extensions seed 1–3 lb/acre turnip in mixes; tops are typically ready 60–70 days after planting, bulbs 12–14 weeks. Introduce livestock gradually and provide fiber. Mississippi State Extension—Forage Brassicas

This description prioritizes data from U.S. university extension, NRCS/USDA, and SARE, and incorporates recent research where available (for example, 2022 Crop Science findings on weed suppression).