Solarization and the Soil Microbiome

Grace Smith, Undergraduate in Molecular and Cellular Biology

Sonja Birthisel, PhD Student in Ecology and Environmental Sciences

Eric R. Gallandt, Professor of Weed Ecology and Management

A soil microbiome consists of tiny organisms such as bacteria, archaea, fungi, and protists that impact plant life. Beneficial microbes decompose organic molecules, rendering them usable by plants and protect against harmful microbes. Conversely, pathogenic microbes can have major detrimental effects on crops.


In June through August  of 2016, we expanded our study of solarization (see previous blog posts about solarization for weed control) to examine the effect of solarization on soil respiration and specific populations of beneficial microorganisms: general bacteria, general fungi, Bacilli, and fluorescent pseudomonads.

A picture of a rose bengal agar plate which was used to select for the growth of general fungi in our experiment.


The Experiment:

Solarization was performed for two and four weeks in a field and closed hoop house at Umaine Greens, located on the campus of the University of Maine, Orono.

Plots were rototilled and irrigated prior to application of previously used clear polyethylene mulch. Temperature was recorded throughout and soil samples were collected at the beginning of the experiment, at plastic removal, and 5 & 14 days after plastic removal for microbial analyses.


Solarization caused average temperature increases of 4 and 7℉ in the field  and  hoop house, respectively; furthermore, maximum temperatures increased by 10 and 15℉. The maximum temperature increase is of interest because prior research indicates that maximum temperature may be more important than average temperature in pathogen control. The dip in soil temperature between July 6th and 13th (labeled “A” in the figure below) corresponds with cool air temperatures during those days (Bangor International Airport, NOAA).


Temperatures over the course of four weeks of treatment in the field and hoop house. CON = control ; SOL = solarized.


Soil Respiration:

Soil respiration was measured to serve as an estimate for total microbial biomass, an indicator of soil health. We found that solarization decreased soil respiration to a minor extent in the field, and more significantly in the hoop house. We originally predicted that soil respiration would be reduced while plastic was in place, but would bounce back to normal levels by two weeks after plastic removal. Since this was not the case, it would be valuable in the future to test how long it takes for soil respiration to fully return to control levels. 


Soil respiration in the field and greenhouse at treatment termination (time of plastic removal) and 14 days after termination. * = significant difference.


Populations of Specific Beneficial Microbes:

In this experiment, we measured populations of four beneficial microbe groups: general bacteria, general fungi, and rhizobacteria Bacilli and fluorescent pseudomonads.  Many general bacteria and fungi decompose large indigestible organic molecules into smaller, plant-useable nutrients. Fungi increase soil water holding capacity by growing hyphae: long, threadlike filaments. Some Bacilli convert atmospheric nitrogen into ammonia making it available to plants, and some fluorescent pseudomonads release antibiotics that decrease populations of plant pathogens.

The good news first: field solarization did not harm any of these four groups of beneficial microbes we were able to grow in the lab.  Under the hotter temperatures in the hoop house, there was a slight decrease in these microbes overall due to a decrease in fluorescent pseudomonads; the other groups of microbes were not significantly impacted.


Number of soil microbe colonies grown from soil collected 5 days after treatment termination in the field and hoop house. * = significant difference.


Literature Review of Expected Pathogen Response to Solarization:

Measuring the effects of solarization on plant pathogens was beyond what we could accomplish in this experiment.  However, to get an idea whether pathogen control with solarization is theoretically possible in Maine, we reviewed papers of known pathogen responses to temperature, and compared this to the maximum temperatures measured in our experiments.  Nearly half of the pathogens we investigated are predicted to decrease in number under temperatures we measured in our field, and over three-quarters are predicted to decrease with temperatures achieved in our hoop house. The only included pathogen that we predicted might increase in response to solarization is noble rot, also known as gray mold, a fungus that affects grapes and other horticultural crops.  These theoretical results need to be backed up with real-world experiments in Maine, but provide a preliminary indication that solarization could contribute to not only weed management (see past blog posts), but pathogen control as well.



Potential effect of solarization on some pathogens of vegetable and horticultural crops in Maine, based on temperatures measured in our experiments and known temperature tolerance of these pathogens. 🠋: pathogens that may decrease in response to solarization; 🠉: pathogens that may increase in response to solarization; Ø: pathogens that are expected to be unaffected by solarization.  



This study suggests that solarization did little harm to beneficial soil microbes in an open field, but in a hoop house soil respiration and populations of the beneficial fluorescent pseudomonads bacteria were significantly reduced, at least in the short term.   Further research is needed to see if these effects  are long lasting and have subsequent  impacts to crop growth. Based on the soil temperatures we measured, it is possible that solarization could contribute to plant pathogen control in Maine, though more research on this topic is needed to confirm this.  



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!

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:


Prologue to the Weed Master Project


Weed Master Field Trial:  Fisher Farm


Weed Master Field Trial:  Fail Better Farm

Weed Seedbanks: 2009 On-farm Sampling

“Credits” to the weed seedbank occur when weeds shed seed, i.e., seed rain, and “debits” when seeds are removed from the soil by germination, predation, or decay/death, in this declining order of importance.
Seedbanks on the Beech Grove, New Leaf and Peacemeal Farms
During the 2009 field season we visited Eric and Anne Nordell of the Beech Grove Farm in Trout Run, PA, Dave and Christine Colson of New Leaf Farm in Durham, ME, and Mark Guzzie and Marcia Ferry of Peacemeal Farm in Dixmont, ME, to collect soil samples from selected fields.  At each sampled location on each farm we collected ten soil cores (6.5 cm diam. x 10 cm deep) from a 25 square meter area.  Soil samples were sieved to remove stones and spread over a layer of vermiculite and placed in a greenhouse.  Weed seedlings were identified, recorded and removed weekly.  The soil was allowed to dry and was then mixed and replaced in the flats once a month for four months.
Weed communities were comprised of an average 8 to 10 species on each farm (see Table, below).  The three most abundant species at the Peacemeal Farm are troublesome in most vegetable crops and are a widespread problem among northeastern vegetable growers.  At the New Leaf Farm, smooth crabgrass was the top-ranked species, primarily because of a large infestation in a field where pigs had been pastured.  Low cudweed and corn spurry, while a problem in salad mix, are not particularly troublesome in most other vegetable crops.  At the Beech Grove Farm, typically pernicious summer annual weeds were rare and not among the top ranked species.

Typical samples are shown below.  These photos were taken after approximately 4 weeks in the greenhouse.  They offer a visual representation of the “low,” “medium,” and “high” seedbanks measured on these farms.

Seedbank Management

Managing weeds with a focus on the seedbank looks at the farming system with an eye first towards opportunities for preempting seed rain with short-season cash or cover crops that are harvested or terminated before troublesome weed species produce mature seeds.  Next, opportunities for shallow soil disturbance, strategically-timed to be coincident with weed species-specific peak emergence potential, will encourage germination.  Subsequent disturbance events can kill these “flushes” of weeds.  When seed rain occurs, opportunities for predation are greater if seeds remain on the soil surface.  This hypothesis, that fall tillage should be delayed to encourage seed predation is the focus of current field studies.

For more information see:

Managing weeds with crop rotation

and these eXtension articles:

Manage the Weed Seed Bank—Minimize “Deposits” and Maximize “Withdrawals”

Manipulating Weed Seed Banks to Promote their Decline

Managing weeds with crop rotation

“Rotation of crops…is the most effective means yet devised for keeping land free of weeds.  No other method of weed control, mechanical, chemical, or biological, is so economical or so easily practiced as a well-arranged sequence of tillage and cropping.”

— C.E. Leighty.  1938 Yearbook of Agriculture

Diversity is key.  Dissimilar crop species with disparate management practices impose a wide range of stresses and mortality factors, creating an unpredictable environment to which the weed community is continually adjusting (Liebman and Staver, 2001).  Diversity, however, may also establish and/or perpetuate weed problems.  Fall cucurbits, for example, may permit considerable weed growth after vines run, causing abundant seed rain (see, Figure 1, below).  Cover crops, while frequently noted for their ability to reduce weed biomass, often contain weeds going to seed.  Perennial legumes or sod crops favor perennial weeds such as quackgrass, and do not include timely soil disturbance events that promote germination losses of annual weeds.  Thus, while diversity is key, successful weed management requires cropping sequences that feature practices that minimize, or better, eliminate, “credits” to the weed seedbank, while maximizing seed “debits.”

Short-season cash or cover crops, whose growth is terminated before weeds set seed, are the most useful elements in preventing weed seed credits (Figure 1).  The tillage events necessary for these crops are often well-timed to preempt seed rain of winter annual weeds.  Ideally, the crops are then terminated before their associated summer annual weeds set seed.  In considering longer-season crops, good weed control, a competitive canopy, and opportunity for hand roguing surviving weeds are key attributes.

We measured common lambsquarters weed seed rain in a broccoli, winter squash rotation, managed without cover crops (control), with fall cover crops, two consecutive years of red clover (2-Yr. CC), or alternate years of vegetables and cover crops with summer fallowing (e.g., after strategies described by Nordell and Nordell, 2007; Figure 1).  The alternate year cover crop system consistently had the lowest common lambsquarters seed rain (see Alt.-Yr. CC, solid boxes, below).  This, combined with the seedbank depleting fallowing periods during the cover crop years, prevented this species from increasing over the four years of the experiment (data not shown).


Figure 1.  Effect of cover crop systems on common lambsquarters seed rain in 2001 through 2004.  Within a year means labeled with different lowercase letters are significantly different based on Tukey’s HSD (P < 0.05).

Debiting strategies require consideration of weed seedbank ecology (Gallandt, 2006).  Because germination is the most effective way to deplete the seedbank, it may be useful to consider primary tillage practices that maintain seeds at or near the soil surface, in the “active seedbank,” where seeds are most likely to experience environmental conditions that encourage germination.  Seed predation is also an important source of loss from the seedbank, and a further reason to keep seeds at the soil surface.  Avoiding fall tillage and rapid weed seed burial maintains seed at the soil surface where they are more readily consumed by predators.

Initial conditions of the seedbank should be carefully considered in short-term crop sequence planning.  Where the starting weed pressure is very high, a clean fallow period is the best strategy for drawing down the seedbank (Mohler, 2009; Nordell and Nordell, 2007).  Because weed species vary in their seasonal patterns of emergence, the timing of fallow periods should target the most problematic species or group of weeds.  Winter annuals, for example, exhibit peak emergence in the late fall and early spring—summer annuals, in the warmer periods of June and July.  Shallow tillage coincident with this emergence periodicity will stimulate germination of the targeted group of weeds, and subsequent tillage kills these seedlings.

If the seedbank is at a moderate level, cropping options may be expanded to include crops that are both amenable to effective cultivation, and are sufficiently competitive that abundant weed seed rain is unlikely.  These so-called “cleaning crops,” seem to vary from farm to farm.  Onions, for example, are a cleaning crop for some growers.  A long-season and uncompetitive crop, growers know onions must be nearly weed free, so they make frequent cultivation a priority for this crop.  This frequent, shallow cultivation offers benefits similar to fallowing strategies, encouraging successive flushes of weeds that are removed by subsequent cultivation events.  While the need for repeated cultivation may be viewed negatively in the short-term, the long term effect is depletion of the seedbank. Potato and sweet corn are cleaning crops for some growers.  These crops can be aggressively cultivated and weeds kept at a minimum.  Slow to establish, uncompetitive species, e.g., carrot and parsnip, onion and leek, are ideally planted in the cleanest of fields.

Given the importance of the relative size of the weed seedbank to the success of subsequent weed management practices, it seems counterproductive for an otherwise clean rotation sequence to include a crop likely to result in abundant weed seed rain (e.g., my problem with winter cucurbits).  Rotation blocks could consider likelihood of seed rain as a first separating criterion.  “Weed-free” blocks could be managed with a long-term vision for improving weed management conditions.  Elsewhere, the commonly used “critical period” for weed control can continue to guide management, focusing on control of weed seedlings in the early to mid-period of crop growth.  Before the start of this period, weeds are too small to reduce crop yield; after this period crop competition alone will avoid weed-related yield losses.  In other words, “beat the weeds back” early to ensure a good crop and don’t worry about weedy crops late in the season.  There are many successful farmers who rely on this approach to weed management.  They focus on repeated cultivation and hand weeding until crops are judged to be sufficiently weed-free.  However, seed rain from weeds surviving the critical period means that weed pressure is likely to increase over time.  In response, the frequency of cultivation and hours of hand weeding will have to increase to simply maintain a given level of weed control.  The alternative, managing for improving weed conditions, requires careful deployment of diversity, minimizing credits and maximizing debits to the seedbank (Gallandt, 2006).


Gallandt, E. R. (2006). “How can we target the weed seedbank?” Weed Science 54: 588-596.

Leighty, C.E.  1938.  “Crop Rotation.”  in Soils and Men, U.S.D.A Yearbook of Agriculture.  pgs. 406-430

Liebman, M. and C. P. Staver (2001). Crop diversification for weed management. Ecological Management of Agricultural Weeds. M. Liebman, C. L. Mohler and C. P. Staver. Cambridge, UK, Cambridge University Press: 322-374.

Mohler, C. L. (2009). The role of crop rotation in weed management. Crop Rotation on Organic Farms.  A Planning Manual. C. L. Mohler and S. E. Johnson. Ithaca, NY, Natural Resource, Agriculture, an dEngineering Service (NRAES): 44-46.

Nordell, A. and E. Nordell (2007). Weed the Soil, Not the Crop.  A Whole Farm Approach to Weed Management. Trout Run, PA: 42.

Prepared for the 2009 Proceedings of the New England Vegetable & Berry Conference.

Farm Training Project Workshop

June 16, 2009

Peacemeal Farm, Dixmont, Maine

There was an impressive turnout Tuesday evening for the Weed Management workshop at the Peacemeal farm.  Part of the Farm Training Project Workshop program organized for farm apprentices, and others, by MOFGA, the Maine Organic Farmers and Gardeners Association, the presentations, demonstrations and field tour for this session were focused on weeds.  After some introductory comments related to the ecology of weeds in organic farming systems, the seventy five participants moved to the field for a demonstration of hand tools, including the Weed Master.

Clayton Carter, Fail Better Farm, Montville, Maine, demonstrates the Weed Master to MOFGA Apprentices at the June 16 evening Farm Training Project Workshop on weeds.  Photo Credit: Mike Mardosa, University of Maine

Clayton Carter, Fail Better Farm, Montville, Maine, demonstrates the Weed Master to MOFGA Apprentices at the June 16 evening Farm Training Project Workshop on weeds. Photo Credit: Mike Mardosa, University of Maine

Mark Guzzie, Peacemeal Farm, Dixmont, Maine, offers Russell Libby, Executive Director of MOFGA a turn at the helm of the Weed Master.  Photo Credit: Mike Mardosa, University of Maine.

Mark Guzzie, Peacemeal Farm, Dixmont, Maine, offers Russell Libby, Executive Director of MOFGA a turn at the helm of the Weed Master. Photo Credit: Mike Mardosa, University of Maine.

Fail Better Farm, Montville

June 2 and 3, 2009

We visited Clayton Carter, Fail Better Farm, Montville, Maine, this week to test the Weed Master in several crops on his diverse organic vegetable farm.

Here are some images from these tests; I’ll update the post further next week.

Cultivating garlic with the Weed Master and sweeps

Cultivating garlic with the Weed Master and sweeps

Sweeps attached to parallel linkage units entering a 3-row bed of garlic

Sweeps attached to parallel linkage units entering a 3-row bed of garlic

Sweeps even controlled some large horsetail weeds in fava beans

Sweeps even controlled some large horsetail weeds in fava beans

Fava beans cultivated with disk hillers and then sweeps

Fava beans cultivated with disk hillers and then sweeps

Using the depth control wheels as row markers

Using the depth control wheels as row markers

Finger-weeding Onions at Fisher Farm

22 May 2009

We headed to the Fisher Farm in Winterport, Maine, Friday morning to meet Beth Haines, Dennis and Joe Fisher, and found perfect conditions for cultivating onions.  Hot, dry weather, level beds, and straight rows of onions.   Particularly convenient was the fact that there were two-rows per bed so it was not necessary to adjust the Weed Master for a center row and then outside rows as we had to at Peacemeal.  Weeds included crabgrass, common lambsquarters, chickweed, some larger than would be optimal, but mostly in the cotyledon to 1-leaf stage.

Beth Haines, Joe and Dennis Fisher of Fisher Farm in Winterport, ME, prepare to cultivate onions.

Beth Haines, Joe and Dennis Fisher of Fisher Farm in Winterport, ME, prepare to cultivate onions.

Dennis and Joe Fisher testing the finger weeders on onions.

Dennis and Joe Fisher testing the finger weeders on onions.

Finger weeders get close within the row and dislodge some, but certainly not all, larger weeds (e.g., 2 to 4-leaf).

Finger weeders get close within the row and dislodge some, but certainly not all, larger weeds (e.g., 2 to 4-leaf).

Long-handled, colinear hoes are the favored precision cultivating tools at the Fisher Farm.  They are sharpened to a fine edge before each use.

Long-handled, colinear hoes are the favored precision cultivating tools at the Fisher Farm. They are sharpened to a fine edge before each use.

Well-sharpened colinear hoes provide the "standard practice," that the finger weeders were matched against.

Well-sharpened colinear hoes provide the "standard practice," that the finger weeders were matched against.

Before cultivation, weed counts were made in 1/16 square meter quadrats at six locations within each bed. Post cultivation weed counts in these flagged areas were made the following day. The colinear hoe bed had an average of 45 weed seedlings per quadrat before hoeing, and 12 afterwords, a reduction of 73% in the 12 minutes it took to weed this bed (seed bar graph below). Five other beds were cultivated with the Weed Master and finger weeders, taking an average of 2 min 30 seconds per bed. Weed control efficacy for these treatments ranged from 44 to 62% (avg. 55%).

Thus, the standard practice of precision colinear hoeing was more effective, but the improved weed control was not proportional to the additional time input.

The very high working speed of the finger weeders was impressive and, combined with subsequent hand weeding, could improve overall weed control with out additional labor, or maintain a similar level of weed control with less time commitment.

Weed density in onions before and after cultivation

Weed density in onions before and after cultivation

Fisher Farm, Winterport Maine

Fisher Farm, Winterport Maine

Disk Hilling Peas

May 20, 2009

Peacemeal Farm, Dixmont, Maine

Peas are nearly ready for trellising at Peacemeal, and thus the last opportunity for cultivating.  The disk hillers were quite simple to attach to the tool bar, and relatively simple to adjust.  We found the pushing bar/handle adjustment to have a noticable affect on the aggressivity of the disks.  If the handle was low for a shorter operator, the frame was not horizontal to the ground, and the disks moved less soil.  We adjusted the handle lower to ensure the tool bars were parallel to the soil surface, and the disks were more aggressive.

A brief video clip of the disk hillers in action has been posted to YouTube:

Overall the disk hillers were quite impressive.  Conditions were optimal, including the fact that Tim had “Pigged” the inter-row space the day before, leaving loose soil easily moved by the disks.

Peas, post-hilling, Peacemeal Farm, 22 May 2009

Peas, post-hilling, Peacemeal Farm, 22 May 2009

The disks rolled over coarse residues in the field; efficacy was likely reduced in these areas, but the unit rolled on.  Performance was best on the flatter, more uniform beds, with increasing inconsistency in places where peas were on the edge of a ridge or other irregular soil feature.

Most observing the field following hilling were impressed.  Mike’s first comment was “Fantastic.”  I think we were all impressed with the consistency of the action of the disks.  Each pass of the 277 ft. bed took 2 min. 30 sec.  The disks were relatively easy to control at a comfortable walking pace, simply by focusing on the area where the disks attached to the tool bar, and ensuring that the crop row was centered here enabled a good working speed.  In places where the crop was short it was possible to slow considerably to reduce soil movement into the row.

As in the previous trials we conducted pre-cultivation weed censuses.  Post-cultivation censuses were conducted Friday, 22 May.  Counts were made in 15 quadrats, and by subtracting the number surviving from the starting number we calculate efficacy, i.e., proportion of weeds killed, which can range from zero, no weeds killed, to 1.0, all killed.  Mean efficacy of the disk hillers was 0.59, ranging from 0.32 to 0.86.  We did not separate our censuses to distinguish the intra-row region from the inter-row (between rows), but the lower efficacy values likely reflect areas where weeds were outsize the zone of working for the disks.

Cultivation efficacy, total weeds, intra- and inter-row following disk hilling.

Cultivation efficacy, total weeds, intra- and inter-row following disk hilling.

Peas, two days post disk-hilling at Peacemeal Farm, 22 May 2009.

Peas, two days post disk-hilling at Peacemeal Farm, 22 May 2009.

Carrot Bed Flaming, Pre-emergence

May 13, 2009

Peacemeal Farm, Dixmont, Maine

In addition to the tests in onion, we used the bed flamer to preemergence flame two beds of carrots.  Six quadrates were placed in each bed and all weeds counted prior to flaming; post-flaming weed density was measured the following day (14 May).  Efficacy was greater in the ‘Nelson’ carrots, 82% compared to ‘Mokum’ carrots, 66%.  Both beds contained predominately broadleaf weeds; very few grass weeds were counted.  The working speed of the unit was 2 min. 30 sec. to cover the length of the 320 ft. beds.  Two passes were used to cover the entire width of the bed, with some overlap at the center row.  There were no problems with the tank or lines freezing up during these tests.

David Merrill films the Weed Master bed flamer in action.  May 13, 2009

David Merrill films the Weed Master bed flamer in action. May 13, 2009

Two flaming units attached to the shroud of the Weed Master bed flamer.

Two flaming units attached to the shroud of the Weed Master bed flamer.