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

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

Summary

Although two key personnel graduated or left for permanent employment, tissue sample processing from field experiments was completed. Data aggregation and preliminary analyses were inititated. A search was also initiated to replace personnel after we received permission for a “no-cost” extension of grant funds. The last position is expected to be filled in early 2008.

Objectives/Performance Targets

1. Critically evaluate the role of N transfer in the development of weed patches.
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 transfer on weed competitiveness and reproduction.
c. Determine the impact of N transfer on the N nutritional status of weed seeds and the competitiveness of offspring.

2. Compare weed growth, competitiveness, and seed production in traditional organic production systems with the new, modified system that uses a “low N transfer” soybean variety in rotation with a sweetpotato variety that has a lower N requirement.

Accomplishments/Milestones

15N analysis has been completed for all experiments addressing our objectives.
A job search was initiated to refill vacant research associate position.

Impacts and Contributions/Outcomes

Preliminary data analysis suggests that nitrogen transfer is occurring from soybeans to prickly sida (a mycorrhizal host species) but not to pigweed species (non-mycorrhizal host species). This is encouraging as it suggests that mycorrhizal host weed species might be further limited in their competitiveness with N conserving genotypes of N-fixing leguminous crops. Effects on non-mycorrhizal host weed species are not yet clear.

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