Diversity - Intensity of Cover Crop Systems: Managing Weed Seed Bank - Soil Health

Diversity - Intensity of Cover Crop Systems: Managing Weed Seed Bank - Soil Health

Summary

This project is addressing two related issues on low-input and organic small-scale diversified vegetable farms: recurrent and ubiquitous weed problems, and the need for long term soil improvement. Cover crop species and the frequency, timing, and depth of soil disturbance can affect soil quality and contribute to weed management by imposing stresses at multiple points in weed life cycles. Different cover cropping strategies are being investigated with simultaneous goals being the depletion of the weed seed bank and the maintenance or improvement in soil health. Cover cropping practices that can address these issues are critical to sustain production without herbicides, and are needed if reliance on cultivation is to be reduced or eliminated.

Objectives/Performance Targets

1) Experiment Station and on-farm research will yield a decision-aid matrix including weed species or functional groups, timing and intensity of disturbances, and diversity of cover crops deployed; management strategies will be identified based on their ability to reduce the germinable portion of the weed seed bank while maintaining or improving soil health.

2) Fifteen farmers will implement intensified/diversified cover cropping strategies on particular fields to reduce the seed bank of problematic weed species.

Accomplishments/Milestones

The main research component of this grant is a three acre field study at the University of Maine Rogers Farm which was established in 2001 to compare the following four vegetable/cover cropping systems: (1) Conventional system is a conventionally-managed 2-year rotation of broccoli and winter squash; (2) Beech Hill system is an organic, “land limited” system, also a 2-year rotation of broccoli and winter squash, but with winter cover crops (e.g. rye/hairy vetch) planted following harvest of the cash crops; (3) New Leaf system is an organic, 4-year rotation of broccoli, winter squash, cereal/red clover, red clover sod; and (4) Nordell system is an organic, 4-year rotation of broccoli, cover crop/summer fallow/cover crop, winter squash, cover crop/summer fallow/cover crop.

After the first season the density of germinable Chenopodium album seeds, the most dominant species at the site, was greater following winter squash in each system (4060 m-2 to 10 cm depth) compared to following broccoli (1100 m-2 to 10 cm depth). The decline in the seedbank due to the disturbance-intensive cover cropping practices (4, above) was also evident in comparison to the sod-based cover cropping system (3, above), with mean densities of 1200 and 4600 germinable C. album seeds m-2, respectively.

Beginning in 2002 we initiated sampling in the systems trial described above to characterize one of the several mechanisms which affect seed bank dynamics, seed predation. The predominant invertebrate seed predator found in the plots was a carabid beetle, Harpalus rufipes. Pitfall trap counts of H. rufipes collected in August averaged over 2002 and 2003 revealed considerable greater density-activity of H. rufipes in the Newleaf system (30.8 H. rufipes per plot) then compared to the other three systems, Nordell System (20.5 H. rufipes per plot), Beech Hill System (19.3 H. rufipes per plot) and Conventional System (19.4 H. rufipes per plot). To determine the rate of seed predation caused by resident invertebrates, we conducted a typical “feeding” trial in which 25 seeds of each of six weed species were placed in the field. Averaged over weed species (interaction P = 0.441), seed recovery was 89% with the vertebrate + invertebrate exclosures, intermediate at 55% with the vertebrate exclosures, and least at 43% with no exclosure (P < 0.001). Predators preferred Galinsoga ciliata with Abutilon theophrasti being the least preferred and the other species lying in preference between these extremes. This systems comparison highlights the challenge offered by crops likely to have high levels of seed rain and promises to refine our ability to recommend cover cropping practices based on weed management requirements.

Outreach activities related to this project continued this year with several talks given covering many aspects of cover cropping including the effects on weed control and soil quality. A cover cropping demonstration trial was also established at the Maine Organic Farmers and Gardeners Association’s Common Ground Fair site in Unity. This cover cropping demonstration trial was the focus of several talks given at the Small Farm Field Day and at the Common Ground Fair.

Collaborators: