Balancing economy and ecology: A systems comparison of leading organic weed management strategies

Balancing economy and ecology: A systems comparison of leading organic weed management strategies

Summary

In the second year of this project, we continued to quantify the benefits and drawbacks of the most prominent organic weed management strategies to ensure that farmers use the most appropriate strategy for their situation. The strategies investigated included 1) cultivation during the critical weed free period of the crop, 2) more extensive cultivation with the goal of zero seed rain, and 3) weed suppression with plastic mulch or 4) organic mulch. Strategies were implemented using yellow onion (Allium cepa, cv Cortland) as a test crop while labor, expenses, weed suppression, soil health, and yield were recorded. Results from the two field seasons indicate that the zero seed rain and organic mulch strategies were more profitable than the other strategies despite their high labor and/or materials costs. Zero seed rain and organic mulch were expected to be poorest performing in their first year but improve over time due to debits to the weed seedbank and benefits to soil quality, respectively. Sweet corn followed the onions in the second year and though the field was managed uniformly, yield was reduced in the plots managed with critical period weed control from the previous year due to weed germination ten times as high in those plots. Economic and simulation modeling will expand the results to other scales, crops, and durations. Results will inform the creation of a decision tool that will be used in outreach.

Objectives/Performance Targets

Objective 1 was to investigate the hypothesis that four weed control systems (critical weed free period control, zero seed rain, plastic mulch, and organic mulch) have varying short- and long-term effects on yield, soil quality, weed/pest suppression, and profitability. This has been completed for two field seasons using yellow onion as the test crop. Additionally, one field season of uniformly managed sweet corn was used to attain a measure of the carry-over effects of the strategies. Initial results were uploaded on our research blog (see attachment).

Objective 2 was to determine the factors that motivate farmers to adopt these contrasting weed management strategies. Preliminary case-study farm visits were completed in 2014 and follow-up interviews in 2015. Soil organic matter was tested and a germinable seedbank assay was completed for each farm. Results will soon be made available on our research blog.

Objective 3 was to develop a decision aid that determines the optimum weed control strategy based on a farmer’s current resources and management goals. This objective has been partially satisfied through a multi-institutional collaboration to develop an Excel-based organic decision support tool. Our own decision aid will be produced from our field results as well as the results of economic and simulation modeling that expand our results to other farm scales and crops.

Objective 4 was to publicize our results through presentations, publications, and extension events so that 100 New England farmers benefit by using our decision aid to inform their management strategy. Initial results were promoted this first year results at the NorthEastern Weed Science Society January 2015 meeting, the New England Fruit and Vegetable Conference, and the University of Maine Rogers Farm Summer Field Day. Results will also be presented at the 2016 Mid-Atlantic Fruit and Vegetable Convention and the 2016 Weed Science Society of America Annual Meeting.

• Research blog post

Accomplishments/Milestones

This past spring, case study farmers representative of each strategy were interviewed. Farmer perspectives and experiences related to their chosen weed management strategy were discussed. These interviews were transcribed and will soon be made available on our research blog. Soil organic matter was tested and a germinable weed seedbank assay of each farm was completed. As expected, the farmer that aims to not let any weeds go to seed had a very low weed seedbank and the farmer that utilizes organic mulch had very high soil organic matter. The case study results will also factor into our decision aid.

In 2015, we completed the second season of fieldwork comparing the various weed management systems. Thankfully, no major obstacles were encountered in the implementation of the fieldwork. The results of 2015 were similar to 2014 (see research blog post in Objectives); the more extensive weed management strategies controlled weeds better but required more labor and mulch-based strategies benefited the late-season soil quality. Also, the more intensive strategies continued to be more profitable than other strategies despite their high labor and materials costs. Sweet corn was grown following the first year’s onion crops and managed uniformly so that any differences in yield could be attributed to the previous year’s management. The yield was reduced in the critical period weed control plots. This was likely due to weed competition since germination was ten times as great in those plots and since weed-free subplots were maintained, which exhibited no differences in yield.

I have begun to work with one of the key individuals listed on the grant, Dr. Aaron Hoshide, to input our field results into an economic model that will extend the applicability of our results to farms of larger scale than what we implemented. I have also created a draft of an agent-based simulation that will evaluate the performance of the weed management systems in other crops and crop rotations. I have also drafted an Analytic Hierarchy Process in a program called SuperDecisions that will serve as the decision aid. The results of the modeling efforts will be be used to parameterize and validate this tool. This will allow farmers to interact with the tool to visualize how the economic and ecological aspects of their operation might affect the decision to pursue each of the strategies.

Impacts and Contributions/Outcomes

The main product of the project, the decision aid, has not yet been finalized but there are some results that may have begun to have an impact. The most surprising result – that the more intensive strategies were more profitable in their first year – may be particularly interesting to farmers. The fact that these strategies, were the most profitable in the first year will make adoption much more appealing to farmers. Aside from greater profitability allowing for increased sustainability of operations, these two strategies are expected to have cumulative benefits over time; great reductions to the weed seedbank in the zero seed rain approach should create an ever decreasing need for cultivation and the soil building aspects of the organic mulching strategy should enrich soil and possibly boost yield while reducing fertilizer and irrigation requirements. The carry-over effects of the strategies observed in the sweet corn crop following the onions showed that in most plots excellent weed control was achieved with a harrowing, two cultivations, and two hilling events. The exception was the critical period weed control strategy, which had a germination rate ten times the others and resulted in a yield loss. This result may encourage farmers to improve late-season weed control efforts in order to preclude a disastrous following year. 

Initial results were presented at the NorthEastern Weed Science Society January 2015 meeting, the 2015 New England Fruit and Vegetable Conference, and the 2015 University of Maine Rogers Farm Summer Field Day. I am also currently preparing to present at the 2016 Mid-Atlantic Fruit and Vegetable Convention and the 2016 Weed Science Society of America Annual Meeting. In addition to publications and presentations outlining the findings, the online decision aid will be the main thrust of the dissemination of results to farmers. Overall, it is expected that at least 100 New England farmers will use the decision support tool to inform their weed management strategy.

Collaborators: