Weed Management in Organic Conservation Tillage/No Tillage

Project Overview

Project Type: Research and Education
Funds awarded in 2004: $146,314.00
Projected End Date: 12/31/2008
Region: North Central
State: Ohio
Project Coordinator:
John Cardina
Ohio State University

Annual Reports


  • Agronomic: corn, rapeseed, rye, soybeans, wheat


  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, participatory research
  • Pest Management: allelopathy, biorational pesticides, botanical pesticides, mulches - killed, weed ecology
  • Production Systems: agroecosystems
  • Soil Management: green manures, organic matter, soil quality/health


    Field experiments showed that the soil conservation advantages of no-till agriculture can be used in organic systems where soybeans are planted into standing residue of small grain cover crops planted the previous fall.

    Three years of studies on various extracts from seeds of many crop plants show little potential for an easily-extracted plant-derived product that could provide residual weed suppression and substitute for synthetic herbicides in a no-till organic system.

    Soybean yields were more affected by late planting in the no-till plots than by weeds or possible allelopathy from rye cover crops.


    The ideas for this project came from a group of organic farmers who attended a farm tour and initiated a discussion on how less tillage-intensive practices might be adopted on organic farms to gain some of the benefits that were apparent in conservation tillage systems. The main obstacle that was quickly identified was weed management: how to manage weeds without the amount of soil disturbance used in standard organic systems or the amount of herbicide used in conventional reduced-tillage systems, and thereby get the benefits of organic farming and conservation tillage in a single system.

    Long-term working relationships between the Ohio State University researchers and the core group of organic farmers who initiated this discussion were established through our Organic Food and Farming Education and Research (OFFER) interdisciplinary program. It became clear in our discussions that there are opportunities to take advantage of the benefits of both organic and conventional no-till or reduced tillage systems in order to protect and improve soil resources while attaining a level of weed control that does not interfere with crop production or quality.
    The collaboration developed through semi-formal meetings quickly led to a set of objectives that are of interest to the farmers and scientists whose ideas are represented in this proposal.

    Topsoil is the resource base of every farm. Any crop or soil management practice that enhances soil quality, by adding organic matter or protecting the surface from erosion, adds to the long-term productivity and sustainability of that farm. Organic farming and no-tillage are two approaches that farmers are using to help build and protect their soil resource base. Both approaches are effective and economical for different groups of farmers. However, management practices in both approaches often jeopardize soil quality for the sake of controlling weeds.

    Weed control is a major concern of organic and conventional farmers. Weed problems are a significant obstacle hindering adoption of either organic farming or no-tillage conservation practices by many conventional farmers. Respondents to the Organic Farming Research Foundation’s recent national survey of organic growers ranked weed management as their number one research priority. In an Ohio survey, 74.3% of organic growers ranked weed control as a major concern or barrier to productivity. Surveys have also indicated that inadequate weed control has been an obstacle to adoption of soil conserving practices (no-till and reduced-till) among conventional farmers.

    Both organic and conventional conservation tillage systems have benefits for building biologically active soils. In organic systems, growers add manure and compost to improve soil organic matter and humus, while tillage is used to incorporate cover crops into the soil to add organic matter, recycle nutrients. No-till systems let soil organisms to take over the job of residue incorporation. These systems benefit soil by maintaining surface residue to conserve moisture, reduce water runoff, build up organic matter, and increase water infiltration.

    The down side of organic systems is that they rely heavily on energy-intensive, soil-disturbing mechanical weeding: up to four pre-planting field cultivations, two or three blind rotary hoe or tine weedings, and at least one row cultivation. The down side of no-till systems is the reliance on herbicides to control weeds, and potential for soil compaction from the traffic of heavy equipment. A typical conventional no-till corn farmer in Ohio applies about 3 lb of herbicides annually for ‘burndown’ of existing plant growth, residual control of summer annuals, and postemergence control of escaped weeds.

    Cover crops with allelopathic (weed-inhibiting) chemicals have been studied as natural substitutes for inorganic herbicides. These cover crops also suppress weeds by competing for water, nutrients, light, and space, as well as by physically smothering weeds before they emerge. Plants in the Brassicaceae family produce chemicals called glucosinolates, which are the precursors to allelopathic metabolites that can inhibit weed seed germination and seedling growth. Isothiocyanate, the most effective brassica-derived allelochemical for controlling weeds, was recovered from the soil in which Brassica napus was being grown, suggesting that some release is occurring in the environment without the need for cutting or tillage. Two students in our labs completed dissertations evaluating the use of brassica cover crops for biological weed control, and found that the best cover crop for biological weed control was a spring yellow mustard (Sinapis alba, family Brassicaceae, cv. Ida Gold). It provides abundant biomass as a cover crop when planted in the autumn of the year, it has the right spectrum of allelochemical properties for weed control, and it is a spring variety that is killed naturally (without use of herbicides) as a result of the cold winter weather. Almost all of the work, to date, on use of brassica cover crops for biological weed control have been done in the greenhouse or in field plots where the brassica residues have been incorporated into the soil. Spring oat (Avena sativa) and winter rye (Hordeum vulgare) have been found to be a low cost and reliable fall cover crops in Ohio. They provide benefits such as abundant biomass, a nutrient catch crop, and also acts as an allelopathic smother crop for weed control

    Since cover crops have many soil-building benefits, the use of a cover crop that also helps control weeds is a ‘win-win’ situation for organic growers. For example, cover crops cut fertilizer costs, prevent soil erosion, conserve soil moisture, protect water quality, improve yields by enhancing soil health, help safeguard personal health and introduce large amounts of biomass to the soil. Although cover crop residues are effective in suppressing winter and spring germinating weeds, they have not eliminated the need for control of summer weed species.

    The identification of phytotoxic, natural products that can be applied to summer annuals would provide organic farmers with additional means to manage summer weeds without sacrificing soil quality. Many natural plant extracts (phenolics, coumarines, tannins, flavonoids, terpenoids, alkaloids, steroids, and quinines) can suppress germination and/or growth of weeds The interest in reducing tillage to conserve soil quality among the organic farmers who initiated this project reflects a compelling need for more sustainable crop, soil, and weed management practices. In this project, we made an effort to develop the basis for integrating allelopathic cover crops with plant-derived natural products that suppress weeds. The eventual adoption of these approaches to weed management in no-tillage systems will help growers maintain and enhance soil quality.

    Project objectives:

    The specific objectives of the project were as follows:
    1) Develop agronomic practices for managing allelopathic cover crops to control weeds while enhancing soil quality.
    a. Evaluate planting time and methods for establishment.
    b. Determine optimum proportions of mixed cover crop species for weed suppression.
    c. Evaluate grower experience using cover crops for weed suppression.

    2) Evaluate the effectiveness of various natural products for suppressing weeds;
    a. Screen essential oils, vinegar products, organic soaps, etc. against typical grass and broadleaf weeds in greenhouse studies.
    b. Evaluate effectiveness of promising natural materials for suppressing weeds that appear in a cover crop system.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.