Weed Suppression and Cover Crops on Organic Farms Michael Bomford, PhD Kentucky State University College of Agriculture, Food Science and Sustainable Systems
Cover Crops Advantages Build organic matter to enhance soil tilth Fix nitrogen Prevent erosion Prevent nutrient loss and recover nutrients from deep soil horizons Suppress weeds Characteristics Rapid establishment and growth Competitive Drought tolerant Deep rooted Nitrogen fixing
Cover crops for Kentucky Purpose N source Soil builder Erosion fighter Subsoil loosener Pest fighter Weed fighter Crops Hairy vetch, crimson clover, subterranean clover, berseem clover, cowpea Rye, sudex, subterranean clover Subterranean clover, cowpea, rye Sudex, forage radish, sweet clover Rye, sudex, mustard/rape Buckwheat, subterranean clover, rye, sudex Adapted from SARE, 2007. Managing Cover Crops Profitably.
Competition Light Water Nutrients Space Chemical warfare How Cover Crops Suppress Weeds Allelopathy = Production of chemicals toxic to other plants Allelopathic crops Rye Wheat Oats Sorghum Sunflower Tobacco
Timing Fall Planting Early Spring Planting Summer Planting Cereal rye Oats Buckwheat Winter wheat Forage radish Sudex Winter barley Mustards Millets N-fixing Hairy vetch Field peas Cowpea Crimson clover Bell beans Sunnhemp Austrian winter pea Soybean
Rye-Vetch Mix (late May)
Hairy Vetch vs. Crown Vetch Strings of flowers Narrow, pointed leaves Cold tolerant; fades in heat Excellent spring N fixer Weak roots; N stored in tops Clusters of pea-like flowers Rounded leaves Aggressive invasive perennial weed Do not plant!
Wheat-Vetch Mix (mid-may)
Wheat-Crimson Clover Mix (mid-may)
Hairy vetch superior Crimson clover superior Transition zone moving north with changing climate From SARE, 2007. Managing Cover Crops Profitably.
Pacific Gold Mustard (July 1)
Sunflower (August 1)
Sudex (August 1)
Buckweat (August 1)
Cowpea (August 14)
Cowpea (September 7)
To till or not to till? No-till drilling works well when crop residues and weed pressure are light. Tillage helpful otherwise. Till at, or immediately before, planting to ensure clean seedbed and give cover crop head start. Light, shallow tillage sufficient for good seed-soil contact. No need to pulverize soil. Chisel plow or subsoiler may be needed to break subsurface hardpan.
Smother crops Do not try to stretch seed below recommended rate. Increase seeding rate if: Weed pressure is high Soil fertility is low Seedbed is poorly prepared Planting dates are not optimal Seed quality is poor
Depth Use recommended planting depth unless: Soil is hot and dry plant 50% deeper Soil is cold and wet plant shallow.
Acid or alkaline soil? Acid soil (ph<5.0) Apply limestone Plant acid-tolerant cover crops: Oat Buckwheat Cereal rye Hairy vetch Cowpea Alkaline soil (ph>8.0) Apply sulfur Plant alkaline-tolerant cover crops Barley Brassicas (mustards, forage radish) Sweet clover Woolypod vetch
Manure Plant cover crop after raw manure application Satisfies organic standards by giving more than 120 days until next edible harvest Manure fertilizes cover crop Cover crop retains nutrients until next vegetable planting Cover crop reduces manure runoff, volatilization
Nitrogen fixation Inoculate legume seed with correct strain of Rhizobium or Bradyrhizobium (not genetically modified, irradiated, or containing synthetic ingredients) Check for vigorous nodulation of legume cover crops
Nitrogen fixation Inoculate legume seed with correct strain of Rhizobium or Bradyrhizobium (not genetically modified, irradiated, or containing synthetic ingredients) Check for vigorous nodulation of legume cover crops
Nitrogen fixation
Nitrogen fixation May contain biopesticides, growth promoters, stickers
Irradiated Nitrogen fixation
Contains sticking agents Nitrogen fixation
Nitrogen fixation Only Vault NP is listed for use in organic production by the Organic Materials Review Institute (OMRI)
Nitrogen fixation Inoculate legume seed with correct strain of Rhizobium or Bradyrhizobium (not genetically modified, irradiated, or containing synthetic ingredients) Check for vigorous nodulation of legume cover crops
Prohibited ingredients in formulation? Irradiated Dormal Plus was one of first transgenic products on market. Hard to distinguish from Dormal, so caught some organic farmers off guard. No longer available. All have same active ingredient, and trade name, but only one product is OMRI-listed Contains sticking agents
Resources SARE, 2007. Managing Cover Crops Profitably, 3 rd Edition, 245 pp. Free Download: http://www.sare.org (click Learning Center then Books ) extension.org: http://www.extension.org/pages/59454/ cover-cropping-in-organic-farmingsystems
Thanks! Tony Silvernail Jon Cambron Joni Nelson Eddie Reed KSU Farm Crew Kirk Pomper Teferi Tsegaye