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

Tissue sample processing from the 2005 and 2006 field experiment continued throughout the year. Pigweed species continued to be problematic, flowering in mid to late June (necessitating early weed harvest to comply with agreements to prevent seed rain). Samples of pigweed, prickly sida and soybean roots were evaluated for percent mycorrhizal colonization. The statistical analysis and sample repeats continue. Variation within these data is high, which is typical with 15N natural abundance analysis, but preliminary data analysis suggests that nitrogen transfer is occurring from soybeans to prickly sida but not to pigweed species (which is consistent with our original hypothesis).

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

Planted, maintained, harvested, processed and submitted samples for 15N analysis for all experiments addressing our objectives.
Completed root sample preparation for all root samples to be analyzed for estimation of the percent of mycorrhizal colonization.
An additional year of work field season and comprehensive analyses remain to be completed.

Impacts and Contributions/Outcomes

Identified methods that allow for more efficiency at all levels of data collection, harvesting and processing.

Collaborators: