Cover crop mulches for no-till organic onion production

Project Overview

Project Type: Graduate Student
Funds awarded in 2007: $10,000.00
Projected End Date: 12/31/2008
Grant Recipient: North Carolina State University
Region: Southern
State: North Carolina
Graduate Student:
Major Professor:
Dr. Nancy Creamer
North Carolina State University

Annual Reports


  • Agronomic: millet
  • Vegetables: onions


  • Crop Production: conservation tillage
  • Farm Business Management: whole farm planning
  • Pest Management: flame, mulches - killed, mulching - vegetative, physical control
  • Production Systems: holistic management
  • Soil Management: green manures, nutrient mineralization, soil analysis


    The purpose of this project was to expand the knowledge base informing sustainable agricultural practices. This project addressed three key challenges for organic, reduced-tillage vegetable production. First, selecting summer cover crops that winter kill eliminates the challenge of mechanically killing the cover crop. Second, we evaluated quantity and timing of nitrogen release from both the cover crops and organic amendment nitrogen during over-wintered vegetable production. Third, we evaluated the weed control potential of the different cover crop residues.


    Bulb onions can be fall planted for over-wintered production in the southeastern U.S. In eastern North Carolina transplanting dates are from October through mid-November. The average fall frost date for eastern North Carolina is mid or late October, which would allow for frost kill of a susceptible cover crop to correspond with onion transplanting. Warm season annual cover crops include C4 grasses such as foxtail millet [Setaria italica (L.) Beauv.] and heat adapted legumes such as cowpea ‘Iron & Clay’ [Vigna unguiculata (L.) Walp.], both of which are killed by frost and cold weather.

    Onions pose a particular challenge for weed control due to their sparse vegetative structure which incurs greater weed competition than crops that produce a closed canopy. Organically grown onions in Georgia are most often produced by transplanting into plastic mulch for weed control. With in-situ cover crop mulch, no-till transplanting equipment can be used to cut through surface residue, create a narrow furrow for the transplant and close the furrow with weighted press wheels.

    Winter cropping with N and weed suppression from summer cover crop residue and surface applied organic amendment N have not been thoroughly studied. Cool winter temperatures slow residue decomposition, which could enhance mulch-based weed control during a season when weed pressure is generally less, and could contribute to a prolonged period of N mineralization for cash crop uptake. This study assessed the contributions of summer annual grass and legume cover crops in different mixture ratios or monocultures and rates of soybean meal as an N amendment on over-wintered, no-till, organic onion production.

    Project objectives:

    1. Summer annual cover crops in monocultures or different ratio bi-cultures for organic fall planted vegetable production.
    2. Soybean meal as a N fertility source in combination with cover crops for over-winter production.
    3. Cover crop and soybean meal management affects on onion yield.

    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.