Solarization to Prepare a Stale Seedbed

Sonja Birthisel, PhD Student in Ecology and Environmental Sciences

Eric R. Gallandt, Professor of Weed Ecology and Management

Solarization is the practice of using clear plastic mulches to trap solar energy, heating soils to temperatures lethal to pests including weeds.  Solarization is nothing new; it has been researched and used by growers extensively since the 1970s in warm, sunny places like Israel and California, but the conventional wisdom has been that it is not consistently effective in cool, northern places like Maine.

We expected that two weeks of solarization during May-June in Maine would not achieve temperatures hot enough to kill weeds, but would rather lead to an early flush of increased weed emergence.  After solarization, we thought these weeds could be killed by flaming, resulting in creation of a better stale seedbed than a “control” created with flaming only.

Presentation1.jpg

Hypothesis: two weeks of spring solarization will encourage weed seeds to germinate so they can be killed, depleting the seedbank and creating a better stale seedbed. 

We tested this hypothesis through four experiments in May-June of 2015 and 2016.  At the start of each experiment, fields were rototilled, thoroughly irrigated, and solarization plots were covered with salvaged 6-mil clear polyethylene hoophouse plastic.  We secured the plastic edges by clipping them to metal pipe laid in a shallow (4” deep) trench around each plot.  Control plots were left fallow after rototilling and irrigating.  After two weeks, plastic was removed, and all plots (solarized and control) were flamed using a hand-held propane burner to create stale seedbeds.  Two weeks after flaming, we counted the number of weeds that had emerged in each plot.

Picture3.png

To our surprise, two weeks of springtime solarization actually suppressed weed emergence, both while plastic was in place and after plastic removal and flaming.  On average, solarization plus flaming resulted in stale seedbeds with 78% fewer weeds than control stale seedbeds created with flaming only.  Soil temperatures were higher in solarized plots, reaching a maximum of 117°F at 2” soil depth, as compared to a maximum of 100°F in controls.

Picture5.pngResults: two weeks after we removed plastic and created stale seedbeds, there were 78% fewer weeds in the solarized treatment than the flamed control.  The “*” indicates a statistically significant difference between solarized and control treatments.  

 The weed suppression following solarization was so visually apparent, we wondered whether flaming after plastic removal was necessary.  To address this question, during one of our experiments we kept half of each plot un-flamed for comparison.  We found that flaming significantly reduced weeds in the control plots, but not the solarized plots.  In short, solarization did a good enough job that flaming afterward was not necessary.

Picture6.pngSolarization with or without flaming created an excellent stale seedbed.  The “*” indicates that flaming significantly reduced weeds in the control treatment, the “ns” indicates that flaming did not have a significant effect in the solarized treatment. 

 

Overall these results suggest solarization is a very promising strategy for stale seedbed preparation in Maine.  Although laying the plastic is labor-intensive, the weed control benefits may be worth the extra effort, especially prior to planting high value direct seeded crops.  More blog posts about solarization coming soon!

Picture4.png

 

 

A simple tool to explore alternative weed management strategies

Bryan Brown, Ph.D. Candidate

Eric Gallandt, Professor of Weed Ecology and Management

 

Weed management philosophies and employed strategies have inherent tradeoffs.  A surprising result from our field studies conducted in organic onion was the impressive performance of zero seed rain and mulch-based strategies, which performed better than expected even in the first year of use.

 

Below is a screenshot from the Excel-based decision aid, which can be downloaded here.

Picture1.pngRequires Microsoft Excel. Runs with macros enabled or disabled.  Note:  This decision aid is for educational purposes only. Results should be interpreted with an understanding that each farm is unique and this decision aid may not accurately represent the conditions present at each farm. Downloading the decision aid represents an acceptance of these terms.

A Comparison of Organic Weed Management Strategies in Onions

Bryan Brown, Ph.D. Student, and Eric Gallandt, Associate Professor

 What’s your strategy for managing weeds? Cultivate until the crop is large enough to tolerate late-emerging weeds, sometimes returning to harvest from a dense patch of weeds? Cultivate season long and pull any mature weeds as part of a longer-term strategy to prevent weed seed rain and make weeding easier and less costly over time? Intensively mulch to prevent weeds, perhaps improve soil quality, and reduce labor demands for weeding later in the season?

There are successful organic farmers who rely on each of these strategies, some using different strategies for different crops, others with a singular focus. Clearly there is no “best” strategy, but rather, trade-offs and compromises associated with each. Our aim with this field study comparing weed management systems is to quantify multiple dimensions of each system so farmers can evaluate and choose a strategy that is best aligned with their own philosophy, priorities and infrastructure constraints.

which strategy

Using yellow storage onions as our test crop (planted with two onions per hole, spaced 6” apart within rows and 3 rows per bed) on a field with a moderate weed seedbank at the University of Maine Rogers Farm, we implemented several prominent strategies:

1) Critical Period Weed Control (CPWC) – Control weeds only during the crop’s sensitive adolescent stage. This is the minimum amount of weeding you can do and still get a viable crop. However, it allows late-season weeds to go to seed.

2) Zero Seed Rain (ZSR) – Frequent cultivation with the goal of not letting any weeds set seed so that none “rain” to the ground. A strategy expected to be initially costly, but with decreasing cost over time as weed pressure declines.

3) Black Plastic Mulch (BPM) – Suppresses weeds and warms soil. Requires cultivation for the paths.

4) Black Plastic Mulch with Straw-Mulched Paths (BPMSP) – Suppresses weeds in the path as well; added organic matter in the paths.

5) Straw Mulch – Suppresses weeds and adds organic matter to the soil. Applied by hand in June after soil has warmed and onions are approximately the diameter of a pencil.

6) Junk Hay Mulch – Similar to straw but less expensive.

  Aside from primary and secondary tillage and application of plastic mulch, all activities were done by hand. Cultivation was achieved by wheel hoeing the paths, scuffle hoeing the shoulders and between rows, and using short-handled hoes for within rows. Drip irrigation was used to keep soil moisture levels optimum for each plot.

labor by activity

Labor by Activity from our 2014 field season (above) demonstrates that CPWC plots required the least amount of labor. Although they were weeded clean through early July, by the end of the season these plots were a weedy mess, and resultantly, had the longest harvest times. In the spring of 2015 we will collect soil samples to see how much weed seed was added to the seedbank.

In ZSR plots, weeding events took place about every ten days in the early- and mid-season, depending on weather, and less often later in the season as weed germination slowed.

Plastic-mulched plots required three hand-weedings to control the crabgrass coming through the planting holes, suggesting that plastic might be better suited to crops with wider spacing. Also, transplanting by hand took longer in plastic mulch. Soil temperatures under the black plastic were consistently 5-10 degrees Fahrenheit higher than the others. Onions under black plastic matured several weeks earlier, which may have contributed to the decreased yield. The BPMSP required the lowest amount of weeding labor of all strategies.

We used high quality oat straw mulch that didn’t have any weed seed but it did bring in a lot of oat seed (112 seeds/lb) that germinated within the mulch and forced us to hand pull twice. The straw mulch was much easier to apply than the junk hay, which stuck together. The junk hay mulch brought in a lot of weed seed (170 seeds/lb) but few weeds emerged through the mulch.

Not surprisingly, at the end of the season, mulched plots had less compacted soil and better water infiltration than unmulched plots. Plots with organic mulch had more earthworms than the others.

After harvest, the onions were cured in a greenhouse and weighed to measure marketable yield. Insect damage and disease were minimal for all strategies.

Breakdown of Net Income

In the Breakdown of Net Income (above), labor costs were set at $10/hour. Materials costs included fertility, mulches, tractor use, and an estimate of curing, packing, and shipping costs. Sales were calculated by assuming that 90% of the cured marketable yield could be sold at the organic wholesale price of $0.75/lb. Net income was determined as the difference between sales and costs of labor and materials.

It was surprising that the strategies typically used for long-term aims of reducing the weed seedbank (ZSR) or building soil quality (organic mulches), were the most profitable in the first year of implementation. That these more expensive strategies were more profitable than the others demonstrates the importance of high yields.

The CPWC was the lowest yielding strategy, indicating that the weed control period was not long enough. Based on growing-degree-days we expect that the onions should have been weeded through late July to avoid yield loss. This highlights the sensitivity of onions to competition.

In 2015, soil samples will be collected to determine the effects of the contrasting weed management strategies on the weed seedbank and soil organic matter. The onion experiment will also be repeated on a new field to show which results are consistent and which results are subject to yearly variation, so stay tuned for this season’s results!

Innovations in Electric Weeders!

After years of searching for innovations in hand tools, my students informed me of two tools I had not seen previously.  We are hoping to acquire these for 2014 field testing, comparing efficacy and working rates to Glaser wheel hoes and the Weed Master.

First, from France, the Pellenc Cultivator.  A battery-powered scuffle hoe, that looks very intriguing:

The second, from the U.S., Tillie and Solus, the Electric Wheel Hoe, from Carts & Tools:

https://cartsandtools.com/

 

And, this is what I’m hoping to add to the Weed Master!

 

 

 

Weed Master Video Update!

We are wrapping up the final reports for our NE SARE-funded project that supported our on-farm trials of the Weed Master.  In addition to inspiring this blog, we used this project as a test case for using video to capture the on-farm trials and experiences of participating growers and our research group.  Tavi Merrill, who recently graduated from the University of Maine Sustainable Agriculture undergraduate program, has done a fine job of directing and editing these videos.

We are continuing our field research on hand tools and scale-appropriate weeding tools for the small farm.  Ben Costanzi is a new M.S. student who will focus on this topic for his thesis work.

You can view the most recent videos below, or go to our YouTube Channel:

http://www.youtube.com/user/zeroseedrain

 

Prologue to the Weed Master Project

 

Weed Master Field Trial:  Fisher Farm

 

Weed Master Field Trial:  Fail Better Farm