N2-fixation and weed competition: breaking the connection between crops and weeds

Project Overview

Project Type: Research and Education
Funds awarded in 2004: $248,000.00
Projected End Date: 12/31/2008
Region: Southern
State: North Carolina
Principal Investigator:
Michael Burton
NCSU -- Crop Science Department

Annual Reports


  • Agronomic: barley, corn, peanuts, sorghum (milo), soybeans
  • Vegetables: sweet potatoes


  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, on-farm/ranch research
  • Farm Business Management: budgets/cost and returns
  • Pest Management: competition, integrated pest management, mulches - killed, mulches - living, physical control, prevention, weed ecology
  • Soil Management: green manures, soil analysis
  • Sustainable Communities: sustainability measures


    Weed control is one of the biggest problems with low input sustainable systems and organic systems. In this project, we explore the possibility of controlling weeds through limiting N transfer from N2-fixing soybean plants. Soybean varieties have different capabilities for N transfer, but this does not appear related to differences in mycorrhizal colonization – mycorrhizae act as the ‘bridge’ for N transfer into weeds plants. Low transfer seems to be an inherent trait of individual soybean genotypes. The results show that weed competitiveness and reproduction decrease greatly when N availability is limited.

    Project objectives:

    1. Critically evaluate the role of N transfer in the development of weed populations.
    a. Determine N transfer distances and penetration into weed patches, and the impact of transfer on weed population dynamics.
    b. Determine the influence of N on weed competitiveness and reproduction.
    c. Determine the impact of N on the N nutritional status of weed seeds and the competitiveness of offspring.
    2. Compare weed growth, patch development, and seed production in a traditional organic production system with the new, modified system that uses a “low N transfer” soybean variety in rotation with crops that have low N requirements and high N use efficiencies.

    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.