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

Final Report for GNE14-072

Project Type: Graduate Student
Funds awarded in 2014: $13,147.00
Projected End Date: 12/31/2015
Grant Recipient: University of Maine
Region: Northeast
State: Maine
Graduate Student:
Faculty Advisor:
Dr. Eric Gallandt
University of Maine
Faculty Advisor:
Dr. Jianjun Hao
University of Maine
Dr. Aaron Hoshide
University of Maine
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Project Information

Summary:

This project aimed to characterize several weed management strategies to help farmers determine which best matches their management goals. The strategies included cultivation only during the crop’s “Critical Period,” season-long cultivation with the goal of “Zero Seed Rain,” and use of mulches such as black plastic mulch, straw mulch, or hay mulch to suppress weed emergence. Field experiments compared these strategies using yellow onion (Allium cepa) as a test crop. Many results were as expected: The Critical Period strategy resulted in the greatest end-of-season weed biomass, Zero Seed Rain required the most weeding labor, plastic mulch warmed the soil, and natural mulches had the most favorable effects on soil health. The most unexpected result was that the Zero Seed Rain and hay mulching strategies had the greatest onion yields, and were the most profitable, even though they were the most expensive to implement and are typically thought of as investment strategies. Seed production from the Critical Period strategy caused a yield loss in the subsequent crop. Case studies generally validated our field results. For example, a farmer who often uses the Critical Period strategy does so to reduce weeding labor, but has found that high weed seed production perpetuates their weed problem. Conversely, a farmer with a Zero Seed Rain approach now has such low weed emergence that he can manage a 4-ha farm with only two additional workers. A farmer that makes frequent use of plastic mulch has found that it allows him keep up with his early-season planting schedule. A farmer who applies natural mulch to many of his crops appreciates its water retention and soil building properties. A decision aid was completed using the results of our field experiments with the Analytic Hierarchy Process that takes farmer management goals and graphs the probability of each strategy to satisfy those goals. The decision aid, along with results of the field experiments and case studies were promoted in outreach, which included ten presentations, two poster presentations, three non-journal publications, and four expected peer-reviewed publications.

Introduction:

Organic farmers use many different practices to manage weeds, generally aiming to control weed seedlings, manage their weed seedbank, or aiming to prevent weeds with mulch.  There are successful farmers who rely on each of these strategies. While each strategy may work to control weeds, each also has distinct costs and benefits. For example, “Critical Period weed management,” i.e., control of weed seedlings early in the crop growth cycle, requires only minimum amount of weed control to avoid crop yield loss (Nieto et al. 1968; Knezevic et al. 2002), thus, farmers may be initially attracted to potential reductions in weeding labor. However, critical period weed management may result in abundant weed seed production, which will likely cause a dramatic increase in required weeding labor. A “Zero Seed Rain” strategy aims to prevent weed seed production so that less weeding labor will be required over time (Norris 1999; Gallandt 2014). Mulching strategies have their own distinct trade-offs. Black plastic mulch is commonly used for its soil-warming benefits but natural mulches such as straw or hay may also be used. Mulches involve an early season investment in labor to apply the mulch, however, they may reduce weeding labor requirements later in the season. Mulches may also benefit soil health (Schonbeck and Evanylo 1998) and reduce occurrence of certain diseases and arthropod pests (Larentzaki et al. 2008). In determining which strategy is best for their farm, growers are faced with a complex decision in which multiple contrasting criteria need to be weighed in the context of their management goals. Our aim was to characterize selected benefits and drawbacks of each strategy so that growers may make a more informed decision.

Gallandt ER (2014) Weed management in organic farming. Pages 63-86 in Chauhan BS, Mahajan G, eds. Recent Advances in Weed Management. New York: Springer

Knezevic SZ, Evans SP, Blankenship EE, Van Acker RC, Lindquist JL (2002) Critical period for weed control: The concept and data analysis. Weed Sci 50:773–786

Larentzaki E, Plate J, Nault BA, Shelton AM (2008) Impact of straw mulch on populations of onion thrips (Thysanoptera: Thripidae) in onion. J Econ Entomol. 101:1317-1324  

Nieto HJ, Brondo MA, Gonzales JT (1968) Critical periods of the crop growth cycle for competition from weeds. PANS (C) 14: 159–166

Norris R (1999) Ecological implications of using thresholds for weed management. J Crop Prod 2:31–58

Schonbeck MW, Evanylo GK (1998) Effects of mulches on soil properties and tomato production II. Plant-available nitrogen, organic matter input, and tilth-related properties. J Sustain Agr 13:83–100

Project Objectives:

Objective 1. Investigate the hypothesis that four weed control systems (critical weed free period control, zero seed rain, plastic mulch, and natural mulch) have varying short- and long-term effects on yield, soil quality, weed/pest suppression, and profitability. This objective was achieved with field experiments in 2014 and 2015.

Objective 2. Determine the factors that motivate farmers to adopt these contrasting weed management strategies. This objective was achieved with in-depth case studies of four farmers that have made specialized use of each of the weed management strategies. In the case studies we evaluated the factors that influenced the creation of their current weed management philosophy.

Objective 3. Develop a decision aid that determines the optimum weed control strategy based on a farmer’s current resources and management goals. A decision aid was created with an Excel-based model using the Analytic Hierarchy Process, which was uploaded to our blog. (https://gallandt.wordpress.com/)

Objective 4. 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. This objective has been achieved by dissemination of results in 4 expected peer-reviewed publications, 3 non-journal publications, 10 presentations, and 2 poster presentations. Outreach was intended to engage an initial 600 people; however, we estimate that around 1215 people were reached in presentations alone, most of whom were directed to use the online decision aid.

Cooperators

Click linked name(s) to expand
  • Dr. Eric Gallandt
  • Mark Guzzi
  • Dr. Jianjun Hao
  • Tom Honigford
  • Dr. Aaron Hoshide
  • Tom Roberts

Research

Materials and methods:

A field experiment was designed to compare prominent organic weed management systems. These systems were implemented in six treatments: 1) cultivation only during the “Critical Period” of the crop, 2) cultivation throughout the entire season, with a goal of “Zero Seed Rain,” 3) black plastic mulch with cultivated paths, 4) black plastic mulch with straw mulched paths, 5) straw mulch covering the beds and paths, and 6) hay mulch covering the beds and paths.

The experiment was conducted at the University of Maine Rogers Farm in Old Town, ME (44.93°N, 68.70°W) in 2014 and on a different field in 2015, both fields were Nicholville very fine sandy loam. The experiment was setup in a randomized complete block design with four replicates. Plots were 6.1 m by 1.7 m. Yellow onion (Allium cepa cv Cortland) was used as a test crop. Onions were bare-root transplanted by bed with three onion rows per bed, with rows spaced 30 cm apart, planting holes 15 cm apart, and two onions per hole. Primary and secondary tillage were achieved with a rototiller and field cultivator, respectively. Fertility was applied prior to secondary tillage at rates suggested by a soil test, using soybean meal, dehydrated poultry manure, bone char, and fish emulsion. Drip irrigation was controlled by plot, so that each system could be optimally irrigated. Irrigation quantity was determined using weekly soil moisture meter readings to find the amount of water necessary to recharge the soil’s water holding capacity.

Aside from tillage and application of the plastic, all labor was done by hand. We recorded the time required to complete daily tasks such as planting, weeding, mulching, and harvesting. Cultivation was achieved using wheel hoes for the paths, long-handled hoes closer to the crop, and short-handled hoes in the crop row. In 2014, cultivation only occurred for an 8 wk period following transplanting in the Critical Period system (Menges and Tamez 1981; Wicks et al. 1973; reviewed by Brewster 2008), but due to yield loss, this was lengthened to an 11 wk period in 2015 (Knezevic et al. 2002). Hand-pulling was necessary for mulched plots. However, straw and hay mulched systems were cultivated for about one month after transplanting to allow for soil warming before applying the mulch.

Measurements intended to capture differences between weed management systems included end-of-season aboveground weed biomass and evaluation of seed production, onion yield, onion storability, soil temperature, soil nitrate, soil organic matter, and assessments of carabid beetles, earthworms, invertebrate pests, and disease.

Following the 2014 onion crop, sweet corn was planted in 2015 and managed uniformly in order to assess potential legacy effects of the different weed management strategies, such as weed emergence resulting from prior seed rain, or effects on soil quality that may affect yield.

Statistical analyses were completed using JMP 10 (SAS Institute Inc., Cary, NC). Analysis of variance (ANOVA) was used to determine effects of weed management strategy on dependent variables. Years were analyzed separately due to interactions between Year and Treatment. Fisher’s Protected LSD was used for most means comparisons. Data failing to meet assumptions was transformed as necessary or analyzed with the nonparametric Krusgal Wallis test (Krusgal and Wallis 1952) and pairwise Wilcoxon signed-rank tests (Wilcoxon 1945).

Economic analysis was achieved with a small-farm enterprise budget, created with assistance of Dr. Aaron Hoshide. Most of the budget was informed by our labor and expenses data, other assumptions of the budget were determined based on previous work (Lazarus 2015). Net profitability was evaluated with risk and sensitivity analyses.

Case studies were conducted by visiting and interviewing four farmers; each having specialized in Critical Period management, Zero Seed Rain management, plastic mulching, or natural mulching. Interviews were conducted after obtaining IRB approval to work with Human Subjects and questions aimed to highlight difference in motivations and risks associated with each strategy. Soil samples were also collected from each farm to evaluate their weed seedbank and soil organic matter.

An Excel-based online decision aid was created for farmers to use as a heuristic tool to think about how different weed control strategies might help them achieve multiple management goals. The decision aid allows farmers to rate their management goals using slider bars and using the Analytical Hierarchy Process, it immediately adjusts a graph of the probability of each strategy fulfilling those goals. This was designed to be a simple tool, thus much of our data was amalgamated into single categories. For example, a generalized criterion was calculated for “soil health” for each strategy, which was calculated by averaging normalized data for soil compaction, soil organic matter, soil nitrate conservation, water infiltration rate, and earthworm populations. Such broad categories as “soil health” allowed for a quick comparison between strategies but ignored nuance in favor of simplicity since farmers our publications are available for more details.

Brewster JL (2008) Onions and Other Vegetable Alliums. 2nd edn. Wallingford, UK. CAB international. Pg 173–176

Knezevic SZ, Evans SP, Blankenship EE, Van Acker RC, Lindquist JL (2002) Critical period for weed control: The concept and data analysis. Weed Sci 50:773–786

Kruskal WH, Wallis WA (1952) Use of ranks in one-criterion variance analysis. J Am Stat Assoc. 47 (260): 583–621 

Lazarus, W. F. (2015). Machinery Cost Estimates. University of Minnesota Extension.

Menges RM, Tamez S (1981) Common sunflower (Helianthus annuus L) interference in onions. Weed Sci 29:641-647

Wicks GA, Johnston DN, Nuland DS, Kinbacher EJ (1973) Competition between annual weeds and sweet Spanish onions. Weed Sci 21:436–9

Wilcoxon F (1945) Individual comparisons by ranking methods. Biometrics Bull 1:80–83

Research results and discussion:

Overall, the project progressed as planned and many of the results were as expected. For example, end-of-season weed biomass and weed seed production were greatest in the Critical Period system while the Zero Seed Rain and hay mulch treatments had nearly zero end-of-season weed biomass (Brown and Gallandt in review, a). It was surprising that weeds were able to successfully emerge through the planting holes of the plastic mulch, even after several weeding events. Another unexpected outcome was that the high-quality oat straw mulch contained oat seed that was able to emerge through the mulch and require hand-pulling. The hay mulch system required the least weeding labor while the Zero Seed Rain system required the most (Brown et al. in prep.). The Critical Period system required the least amount of overall labor while the hay mulch system required the most. Yield differed by system in one year of two, with the Critical Period system showing a yield loss, likely due to weeds, and the plastic mulch systems also showed a yield loss, likely due to premature senescence caused by increased soil temperatures. Onion storability varied by treatment in 2014, with onions in cultivated systems remaining firmer and onions in the highest yielding systems maintaining the highest soluble solids levels after cold storage. Related to yield, a whole-farm enterprise budget revealed that the Zero Seed Rain and hay mulch systems were the two most profitable strategies, which was unexpected result because those were the two most expensive strategies to implement (Brown et al. in prep.). Furthermore, Zero Seed Rain and hay mulch are usually thought of as investments that will pay dividends in subsequent years in terms of reduced weed emergence or increased soil organic matter, respectively, thus their profitability in the first year was surprising. A sensitivity analysis revealed that onion yield was one of the most important parameters affecting profitability, which reflects the strong profitability of the high-yielding Zero Seed Rain and hay mulch systems.

Additional measures of farm ecology were largely driven by the presence or absence of mulch. For example, all mulched systems required less irrigation than cultivated systems (Brown and Gallandt in review, a). Additionally, plastic mulch warmed the top 5 cm of soil by an average of 2.8 C, while natural mulches decreased temperature by 2.7 C compared to the cultivated treatments. Mulched treatments were also less compacted than cultivated treatments in one year of two. Soil nitrate (NO3-N) was conserved in the plastic mulched systems, reflecting less leaching during rainfall events. In one year of two, soil microbial biomass was elevated in the Critical Period and hay mulch systems, reflecting reduced late-season disturbance, but surprisingly the same effect was not seen in the plastic mulch systems. Earthworms, which are generally beneficial for soil health (Hopp and Hopkins 1946; Edwards and Lofty 1977), were the most abundant in natural mulch systems. Granivorous beetles in the Carabid family were most abundant in Critical Period plots, possibly due to the habitat provided by the weeds (Birthisel et al. 2015; Shearin et al. 2008). Incidence of disease and invertebrate pests was low and sporadic. The year after each system was implemented, soil organic matter measurements that included residue were greatest in natural mulched systems. However, in a crop of sweet corn managed in weed-free conditions, yield was not affected by the system implemented the previous year. Conversely, in plots managed with only early-season cultivation, the abundant weed seed rain from the Critical Period system the prior year resulted in weed competition that reduced sweet corn yield.

Case studies of four farmers whose approaches reflect the systems compared in my field experiments were used to highlight farmer perspectives of the motivations and risks behind each weed management strategy (Brown and Gallandt in review, b). A farmer who often utilizes Critical Period management began doing so because his farm already had a high weed seedbank when he arrived, so he learned how to tolerate weeds and continued to expand his markets, but now he is unlikely to scale back and focus on depleting the weed seedbank, even though his weed sensitive crops have high weeding labor requirements due to abundant weed emergence. A farmer with a Zero Seed Rain approach initially simply admired the appearance of a weed-free field, but soon found that his approach offered a great benefit in that weed emergence was greatly reduced in subsequent years, however, he is concerned that his frequent cultivation may negatively impact soil health. A farmer who utilizes plastic mulch on most of his transplanted crops has found that it has reduced early-summer weeding labor so that he can devote time to planting, but he laments about the environmental cost of using a petroleum-based product. A farmer who applies natural mulches appreciates that in addition to weed suppression it also greatly reduces his need for irrigation, and it has increased his soil organic matter to over 20%, but it requires a large amount of labor to collect and apply the mulch. In conclusion, while each of these farmers differ in their approach, and each approach offers unique benefits and drawbacks, each of these farmers is successful and well-respected. Furthermore, our field experiments show that each system has the potential to be successful but they range widely in effects on economics, seedbank dynamics, and soil health (Brown and Gallandt in review, b). Therefore, while there may not be a single “best” weed management strategy, growers should understand the motivations and risks of each strategy in order to select the most appropriate strategy for their situation.

Birthisel SK, Gallandt ER, Jabbour R, Drummond FA (2015) Habitat and time are more important predictors of weed seed predation than space in a Maine USA mixed vegetable agroecosystem. Weed Sci 63:916–927

Brown B and Gallandt ER (in review) A systems comparison of contrasting organic weed management strategies. Weed Science.

Brown B and Gallandt ER (in review) To each their own: Case studies of four successful, small-scale organic vegetable farmers with distinct weed management strategies. Renewable Agriculture and Food Systems.

Brown B, Gallandt ER, Hoshide AK (in preparation) An economic analysis of organic weed management strategies in onion. Organic Agriculture.

Edwards CA, Lofty JR (1977) Biology of earthworms. 2nd ed. Rothamsted Experiment Station, Chapman & Hall, London. Pp 118–119

Hopp H, Hopkins HT (1946) Earthworms as a factor in the formation of water-stable soil aggregates. J Soil Water Cons 1:11-13

Shearin AF, Reberg-Horton CS, Gallandt ER (2008) Cover crop effects on the activity-density of the weed seed predator Harpalus rufipes (Coleoptera: Carabidae). Weed Sci. 56:442–450

 

Research conclusions:

This project effectively quantified the benefits and drawbacks of several distinct organic weed management strategies and has made that information available to farmers so that it may guide their management decisions. One of the greatest impacts of this project is likely the altered perception of farmers. Two weed management approaches – Zero Seed Rain and hay mulching – that are often thought of as “too labor intensive to be successful,” were actually the two most profitable. Furthermore, these strategies likely reduced weed seedbank and improved soil organic matter, respectively, indicating that with continued management, their success may improve over time. These results have increased the feasibility of Zero Seed Rain and natural mulching in the eyes of farmers. Possibly related to our results, there seems to be an increase in these practices in New England. Both of these practices have the potential to improve agricultural sustainability. For example, a depleted weed seedbank resulting from a Zero Seed Rain approach may allow for indirect, ecologically based weed management practices such as cover cropping to be more effective. Furthermore, the increased soil organic matter provided by natural mulching now provides most the fertility for one of our case study farmers.

Related to our changing climate, natural mulches are often grown on-farm or obtained locally, thereby reducing the carbon emissions associated with transportation of fertility. Furthermore, both plastic and natural mulches reduced the amount of irrigation required, which would be a benefit in drought conditions, and they increased water infiltration rates in 2014, which may allow them to more quickly soak up extreme rainfall events and reduce the risk of erosion. Additionally, the soil temperature profile that we observed indicates that black plastic may be best used in cool springs, while natural mulches may be used to moderate soil temperature in the heat of summer.

Our case studies (Brown and Gallandt, in review) will also benefit farmers by providing technical know-how related to each weed management strategy. Since farmers learn well from other farmers, these case studies should be very effective in highlighting successful practices. These case studies will be published in a scientific journal but have been written for a broad audience using clear language so that they may also be used for extension purposes. Real-life examples from the case studies include anecdotes about “disastrously” weedy years using a Critical Period strategy, from which the farmer was able to recover by avoiding weed sensitive crops and using cover cropping to bring the seedbank down to a manageable level. Conversely, a farmer who made an early-career investment in reducing their weed seedbank and now has greatly reduced weeding labor, such that he can now manage a 4 ha mixed-vegetable farm with only two other workers.

Another product of this project that may continue to be used by farmers and extension personnel is our online decision aid, which brings all of our ecological and economic data together into one user-friendly heuristic tool. Finally, the results and experience gained in this project were leveraged in a grant application to USDA NIFA regarding use of mulches as an Integrated Pest Management strategy.

Brown B and Gallandt ER (in review) To each their own: Case studies of four successful, small-scale organic vegetable farmers with distinct weed management strategies. Renewable Agriculture and Food Systems.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

Results were disseminated in a variety of ways, as listed below. Presentations were especially well-received and several of the presentations were invited by conference organizers. Journal publications have been submitted in addition to several more user-friendly non-journal publications. Additionally, a decision aid was created to simplify the complexity of our results into a heuristic tool for farmers (https://gallandt.wordpress.com).

Submitted Publications

Gallandt ER, Birthisel S, Brown B, McCollough M, and Pickoff M (in review) Organic Farming and Sustainable Weed Control. In Korres, N.E., Burgos, N.R., and Duke, S.O. (eds) Weed Control: Sustainability, Hazards and Risks in Cropping Systems Worldwide. CRC Press. (submitted 02/03/17).

Brown B. and Gallandt ER (in review) A systems comparison of contrasting organic weed management strategies. Weed Science (submitted 01/17/17).

Brown B and Gallandt ER (in review) To each their own: Case studies of four successful, small-scale organic vegetable farmers with distinct weed management strategies. Renewable Agriculture and Food Systems (submitted 11/19/16).

Expected Submissions

Brown B, Gallandt ER, Hoshide AK (in preparation) An economic analysis of organic weed management strategies in onion. Organic Agriculture (to be submitted 03/17).

Non-journal Publications

Brown B and Gallandt ER (2016) A simple tool to explore alternative weed management strategies. UMaine Weed Ecology Group. Available online at https://gallandt.wordpress.com/  

Noble D (2016) Weed management: To mulch or to cultivate? Onion World Magazine. July/August. Available online at http://reader.mediawiremobile.com/ColumbiaPublishing/issues/103934/viewer?page=17 

Brown B and Gallandt ER (2015) A comparison of organic weed management strategies in onions. UMaine Weed Ecology Group. Available online at https://gallandt.wordpress.com/

Presentations

Brown B (02/16/17) Non-chemical weed management in a changing climate. Maine Climate and Agriculture Network Mini-Symposium. Orono, ME. 30 Attendees.

Gallandt ER, Birthisel S, and Brown B (01/12/17) Ecologically based weed management: Targeting the weed seedbank. 2017 Long Island Agriculture Forum, Sustainable Ag and Vegetable Session. Riverhead, NY. 50 Attendees.

Gallandt ER, Birthisel S, and Brown B (12/08/16) Ecological weed management in organic vegetables. Great Lakes Fruit, Vegetable & Farm Market EXPO. Grand Rapids, MI. 100 Attendees.

Brown B (11/22/16) Successful alternative weed management strategies. New York State Integrated Pest Management Program. Geneva, NY. 30 Attendees.

Brown B and Gallandt ER (11/06/16) Tradeoffs between controlling weed seedlings, preventing weed seeds, and mulching. MOFGA Farmer to Farmer Conference. Northport, ME. 60 Attendees.

Gallandt ER, Birthisel S, and Brown B (11/06/16) Mulching and weed management. Maine Organic Farmers and Gardeners Association (MOFGA) 2016 Farmer to Farmer Conference. Northport, ME. 30 Attendees.

Gallandt ER and Brown B (10/26/16) Mechanical weed control for small scale operations.  North Country Fruit & Vegetable Seminar and Trade Show. Whitefield, NH. 30 Attendees.

Brown B (09/15/16) Weed research results to aid small farms. Purdue Extension Farm Tour. University of Maine Rogers Farm. Old Town, ME. 35 Attendees.

Brown B (02/02/16) Weed control in organic onion. Mid-Atlantic Fruit and Vegetable Convention. Hershey, PA. 200 Attendees.

Gallandt ER, Birthisel S, and Brown B (12/16/15) Mulching and weed management. New England Vegetable and Fruit Conference. Manchester, NH. 100 Attendees.

Brown B and Gallandt ER (07/26/15) Organic weed management strategies for onions. University of Maine Rogers Farm Field Day. Old Town, ME. 40 Attendees.   

Brown B and Gallandt ER (06/16/15) An overview of ecological weed management techniques for beginning farmers. MOFGA Farm Training. Dover-Foxcroft, ME. 35 Attendees.     

Brown B and Gallandt ER (05/12/15) A Presentation of Hand Tools Used in Organic Gardening. Cooperative Extension Master Gardener Program. Old Town, ME. 40 Attendees.

Brown B and Gallandt ER (01/16/15) First year results of a comparison of prominent organic weed management strategies for yellow onion (Allium cepa). State Legislators Tour. Orono, ME. 35 Attendees.

Poster Presentations

Brown B and Gallandt ER (02/09/16) Improve soil quality, decrease costs, or reduce the weed seedbank? Insights from a systems comparison of prominent organic weed management strategies. Weed Science Society of America Annual Meeting. San Juan, PR. 200 Viewers.

Brown B and Gallandt ER (01/06/15) A systems comparison of cultivation-based versus mulch-based weed control for yellow onion (Allium cepa). NorthEastern Weed Science Society (NEWSS), Williamsburg, VA. 100 Viewers.

Project Outcomes

Project outcomes:

This project has demonstrated the potential for improved farm economic viability through weed management practices that improve yield and profitability while providing additional farm benefits. All weed management strategies yielded similarly in 2015. However, in 2014, the Zero Seed Rain and hay mulching strategies demonstrated a 59% increase in yield compared to the Critical Period system. Indeed, the excellent weed control provided by the Zero Seed Rain and hay mulching approaches had a profound effect on onion yield. Furthermore, these systems demonstrated clear benefits to the weed seedbank and soil health, as previously discussed.

The yield loss in the Critical Period system (compared to the highest yielding systems) was likely due to weeds. Since sensitivity analyses showed that profitability was most highly affected by yield, the risk of a costly yield loss should be safeguarded against by a lengthened Critical Period (we adjusted from 8 wk in 2014 to 11 wk in 2015). Furthermore, in both 2014 and 2015, weeds in the Critical Period plots produced over 20,000 seeds m-2 – a result that contributed to a yield loss in the subsequent crop.

The plastic mulch systems did not perform as well as expected – demonstrating an 18% loss compared to the highest yielding systems in 2014 – likely due to higher soil temperatures, which likely promoted the one-month-premature senescence of onions in this system.

Anecdotally, each of our case study farmers are successful and well-respected, but the farmer with a Zero Seed Rain approach was the only one to mention the high profitability of their operation, likely related to the greatly reduced weed emergence. Conversely, the farmer utilizing a Critical Period approach seems restricted by the paradox of his high weed seedbank. He attempts to decrease weeding labor through use of Critical Period management, but such management often results in abundant weed seed production and perpetuates the problem. Furthermore, with a high weed seedbank the incentive is to grow crops such as winter squash or corn, which can tolerate weeds. But again, since yield of these crops is minimally affected by late season weeds, the incentive to control weeds in the late season (when they are producing seed) is low, thus the problem is perpetuated. Hopefully our presentation of alternative approaches will prevent farmers from entering this trap.

Farmer Adoption

Farmer response to the project was overwhelmingly positive. One farmer commented, “Great work! I’m glad to see research being done in this area.” Another expressed that this type of combined ecological and economic analysis has not been done previously and that it will be a great help. For new farmers, this project clearly outlines the benefits and drawbacks of several prominent weed management strategies, which has helped them make more informed decisions about how to invest their often-limited startup capital related to weed management. For established farmers, this project provides the necessary knowledge for them to consider alternative practices that may be better suited to their management goals. It was surprising to hear that in some cases, growers had not heard of or considered other weed management options and it was encouraging that this project has broadened their options for weed management.

From the results of this project, it was expected by most farmers that the large amount of weed seed rain in the Critical Period strategy would cause a yield loss in the subsequent crop. However, this result serves to reinforce a seedbank management perspective. One of the biggest surprises to farmers from our results was that a Zero Seed Rain approach could be feasible, given the perception that it would require an extreme amount of weeding labor. In fact, the weeding labor required for the Zero Seed Rain approach was only 32% more than for the Critical Period approach. Furthermore, as one of our case study farmers has observed at his farm, there is a potential for dramatic labor savings in the long run by adopting a Zero Seed Rain approach. Another farmer who has adopted a Zero Seed Rain strategy remarked, “I’m glad to see that research is validating what I’ve been doing on my farm.” Our results also lend evidence to support the shift of some farmers in Maine from using black plastic to using silver plastic, which does not heat the soil as dramatically. Our result that natural mulching was very profitable, despite the large labor requirement to apply it, may serve to propel the already increasing number of farmers in New England that are growing their own hay mulch or utilizing their town’s municipal leaf collections as mulch. Finally, farmers really enjoyed hearing about the operational details of the farmers from our case studies – “it’s very interesting [to hear] what the other farmers are doing!” Details can be invaluable to farmers. For example, tips included following mechanical cultivation with hand weeding to control escaped weeds and rescue buried crop plants or using a flail mower to produce the best length mulch. This type of know-how can often have a large impact on farm success.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Overall, growers were pleased with the breadth and depth of this study but they did bring up several questions that could provide the basis for future research. They wondered if the quality of the mulch, for example, decaying hay versus clean, first-cutting hay, would affect crop yields. Other growers had heard of using a very small transplanting hole in plastic mulch so that crop growth would cause the plastic to stretch around the crop and prevent weeds from escaping and they wondered about the effects of this practice on crop quality. Growers using hand tools for cultivation had questions about the most efficient timing of weeding. For example, could repeated use of a lightweight rake be used to quickly kill emerging weeds more efficiently than less frequent hoeing of larger weeds? Each of these questions could be addressed in future component studies that may build off our previous results.

 

Information Products

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.