Tag Archives: thermal compost

The Microbes Version of the Thermal Compost

March 13, 2020

The Essence of A Thermal Compost
as told by the microbes, in community

Material Variety

Amy Amoeba begins the compost story, “Wow. I just got thrown onto a big pile with critters I have never seen before.”

“Yes indeed”, echos Belinda Bacteria ecstatically, “Look at all the nitrogen choices: one bucket beer mash – very hot commodity, and three buckets of finely chopped fresh plants, coffee grounds and seeds. Yum. Yum.”

“As for me”, responded Henry (fungal) Hyphae, “I prefer the six buckets of carbon a la carte: sieved wood chips, hardwood bark and brown leaves. Plenty of carbon here for me to put away in the soil. I can break down lignin and even plastic!”

Belinda again. “I just got a text from my cousin Armando Bacteria. He’s in a pile with only manure and straw.

“Oh no!,” the microbes chanted, “Borrring. With so little diversity, that compost might not have enough nitrogen-metabolizing bacteria. And will it be the best pathogen suppressant?”

Sun, Mar 15, 2-4, Work Party
Mon, Mar 30, 6:30-8:30pm, Fig Pruning Class
Mon, Apr 6, 6-8pm, Work Party
Sun, Apr 19, 2-4, Work Party

The Mesophilic Stage

“It’s getting cozy now.” Pretina (predatory) Nematode was delighted. “At 125F, and with 50% moisture, we can feast without worrying about whether we’ll use up the oxygen or water.”

But Henry sounded the alarm. “Well let’s not spoil it Pretty Pretina. Let’s just keep the temperature right where it is. Slow down. Chew each bite 20 times.”

Amy Amoeba, transformed in her naked form, moved closer. “But wait Henry. We won’t get rid of those nasty plant pathogens until it feels like an oven in here.”

The Thermophilic Stage

“Whoa”, cried Nemar, the young bacterial-feeding nematode. “We have been pigging out, using the moisture and oxygen. We may end up in a dray sauna! I think I will lay an egg and then get outta here.”

“Belinda Bacteria choked out a few words. ” I am only so mobile and I can’t get to that bamboo pole with air holes in it. I’m writing my will.”

“Oh no you’re not,” exhorted Amy, “I insist that you encyst! If the temperature is above 131F, we only have to hang on for three days or, at 150F – just two days and, if we can handle 165F – just one day. Those times and temperatures will take care of the pathogens. Look over there. Silly Ciliate is spinning into a dormant cyst right now. Maybe we will get through this. It’s necessary that everybody take a turn in the hot center.”

“Well now”, slurred Baxter the nasty (pathogenic) bacteria. “150F this morning. Pretty hot but I found a completely dry pocket in some oversized chips. I can weather the storm tucked in here. Feng Farmer better do a thorough job of watering and turning if he wants to eliminate me and my weed seed pals.

“Oh my. What is going on?” Baxter’s adrenaline soared. “Someone just tossed me from the middle of the pile to the outside and the outside of the pile is going into the middle. And a splash of water everywhere. This farmer knows how to rid the compost of pathogens.”

“Oh. Yes. Feng is a pro!” Pretina confirmed, “I have been on this farm for years and I know they turn and water the pile. But they only turn as many times as needed to ensure all parts roast for the required amount of time, per Amy’s outline above.”

The Cooling Stage (Second Mesophilic Stage)

The alarm clock of Nemar’s protected egg sounded and he broke out from his dormant state. “Hello everyone.” He panned the abundant new microbial mix, searching nervously for any hyphae that might be constructing nematode-trapping loops. He twisted toward an unknown amoeba. “Can you tell me where the nearest Starbucks is? I just woke up.”

The amoeba responded kindly. “There may still be some remnants of the coffee grounds but most of us drink compost tea. It’s cheap.”

The young nematode sipped some tea and observed how fast the numbers and types of microbes were increasing. They were coming out of dormancy, hatching from eggs,  joining from the surrounding soil, or being dispersed by a larger organism. It seemed they were falling from the sky. So many different microbes! Tens of thousands per gram of soil. “Time to eat!”

The Maturation Stage

In six month’s time Nemar’s nematode egg grew to be a reproductive adult. She knew the compost had been stable enough for the garden for a couple of months; microbial respiration had slowed and the pile had reached ambient temperature. She also knew, however, that the diversity of the pile kept increasing for about six months and right now the compost was mature for one of its main uses – as a pathogen suppressant. The proof, of course, will be in the pudding: the successful seed germination and hearty plant growth.

“We are in the zone!” She shouted to the others. “The volume of fungal hyphae have finally caught up and we now have a fungal to bacteria ratio of 4:1, perfect for the apple trees. The color of our pile is dark brown and doesn’t smell like rotten eggs. I hope Feng is not thinking to wait until we look like soil because at that point, we won’t be compost anymore. Feng! Liberate us. Use us or lose us!”

“Feng is so smart. Here he comes with his wheelbarrow”, smiled the amoeba. “We can keep the soil food web going.  Those of you who aren’t coming along in this ride, you’ll be comfortable because Feng will maintain the pile at about 35% moisture.”

Feng looks closely into the pile. Belinda Bacteria has the energy and divides. But here comes the nematode to snarf up her new sister. A clever fungal hyphae squeezes Nemar’s offspring, and it’s not love. Then Amy Amoeba sits and sucks on the hyphae, but then soon becomes lunch for a Springtail (Collembola).

I acknowledge Dr. Elaine Ingham, with Soil Food Web, who makes science very accessible. And to Seattle’s Sound Bio Lab, a non-profit science lab that turns no one away.

The photos are from my microscope, sent to ClipppingPathIndia where they make line drawings from photos.

Watch the freewayestates.org calendar for a thermal compost class in May.

© 2020 Ruth Callard

Pathogen-Reducing Compost

January 14, 2020
© 2020

Benefits of compost are widely known: 1) enhances water holding capacity, soil structure, organic matter, drainage, and nutrient holding capacity of soil, 2) provides a source of beneficial microbes, 3) decreases both inputs (to your garden) and outputs (from your garden), a plus for sustainability, and, 4) reduces fertilizer and pesticide use.

However, did you know that well-made compost has the ability to reduce pathogens and enhance plant growth?

An extensive research study of 120 bioassays, involving 18 composts and seven pathogens, found positive disease suppression in 54 percent of the treatment combinations, a disease stimulating effect only rarely (3%), and no effect in 43 percent of the treatment combinations (Termorshuizen et al., 2006).

Other studies have shown that “backyard” compost is superior to the commercial product, possibly due largely to richer and varied starting materials, plus a more relaxed thermophillic phase (wherein temperatures are sanitizing but lower than those recorded in commercial composts). Backyard composting presented higher counts of bacteria, actinomycetes, and fungi. It also shows higher percentages of isolates producing extracellular enzymes which allow the breakdown of tough substrates, including polyethylene!

Although the studies show the efficacy of compost, no one has come up with the perfect recipe or management strategy to combat a particular soil pathogen. This is because the soil microbial community is so dynamic and complex. Quality control tools are also lacking.

Still, we know from research that microbial organisms in compost are able to reduce pathogens my means of: direct antagonism (antibiotic production and direct parasitism), predation, competition for resources, enzyme production, and, induced resistance in plants – through signaling networks and hormones.

Sun, Jan 19, 2-4. work party
Sat, Feb 1, 10-12, Work Party
Sat, Feb 1, 1-3, PRUNING CLASS
Sun, Feb 16, 2-4, Work Party
Sat, Mar 7, 10-12, work party

Note, compost is more effective as a pathogen prevention method than when used as a management strategy for some existing soil or plant pathogen. Elaine Ingham, veteran soil scientist, points out that compost and soil should be colonized with a sizeable and diverse body of microbes. “There are only so many seats at the table. If the good guys are already there, the bad guys are turned away.”

Image Credit: Zosia Rostomian & Jill Banfield, Creative Services, Berkeley Lab

Who are these microbial actors who play such a beneficial role in a garden? It’s bacteria, fungi, protozoa, and nematodes, none of which can be seen with the naked eye. There are millions of microbes in a gram of compost and hundreds of thousands different species. In fact, it’s the diversity of players that makes good compost a pathogen suppressor.

Commercial composts can differ widely in their suppressive effects and can vary as to which pathogens are diminished. However, commercial composts can meet the objective of adding organic matter to the soil. In contrast, the special compost that you can produce with backyard composting, using correct temperature, moisture, aeration and curing processes, will yield a compost that you can use sparingly as an inoculum throughout your garden. It will jump-start good soil biology and maintain nutrient cycling, creating an environment fostering pathogen-suppressive soil.

Next up – A template on making a thermal compost.
Also, watch the FreewayEstates.org calendar for a hands-on thermal composting class, coming in early May, 2020

Ruth

References:

Hadar & Papadopoulou, 2012 – Suppressive Composts: Microbial Ecology Links Between Abiotic Environments and Healthy Plants DOI: 10.1146/annurev-phyto-081211-172914

Vaz Moreira et al., 2008 – Diversity of Bacterial Isolates from Commercial and Homemade Composts. DOI: 10.1007/s00248-007-9314-2

Welgarz et al., 2018 – Microbial diversity and nitrogen-metabolizing gene abundance in backyard food waste composting systems DOI: 10.1111/jam.13945

Fayolle , L., 2006 –  Eradication of Plasmodiophora brassicae during composting of wastes
https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/

Cangelos, G, 2014, Dead or Alive: Molecular Assessment of Microbial Viability
https://aem.asm.org/content/80/19/5884 DOI: 10.1128/AEM.01763-14

Plant Pathogens – Pasteurize? Sterilize? Sanitize? Boil Everything!

March 26, 2019

Recently, I was watching someone rinse a plastic polyethylene plant-potting container in a Brown Rotbleach solution for reuse. I was pretty sure that pot needed to be thoroughly rinsed of organic matter prior to the bleach rinse.

The observation made me think of several reasons why a gardener needs to know how kill plant pathogenic microbes, e.g., effectiveness of our thermal composting process, best product to spray on our pruning shears or, preparation of a previously purposed plastic pot for propagation.

I tried and failed to make a helpful chart. It proved far too difficult, due to so many factors to consider:

varied expressions of quantities
different types of substrates and their porosity
amount of contact time needed
type of organism and state of organism
health hazards
the level of disinfectant desired
shelf life of product
humidity in relation to temperature
corrosiveness
cost of product
where the organism lies and whether you can even get at the bugger

Method

 

Botrytis cinerea (gray mold-fungal) Nectria galligena (apple canker) Weed seed

(sow thistle)

Verticillium dahliae (Verticillium wilt)

 

Pseudomonas syringae pv. tomato (Bacterial speck)
0°F yawn
165°F Dead 1 hr Dead 1 hr
5% sodium hypochlorite (bleach) sol. 2g/liter 20 hr LD90
4%v/v iso. alcohol effective
.3% iodine solution 93% dead 93% dead
Quaternary ammonium 4g/liter 20 hr LD90

Heat destroys microbes best and heat with humidity is even better. However, except during our thermal composting process, heating to 149F for two hours is not practical. As such, I tried to get some answers about products that are available and familiar.

Sat, Apr 6, 10-12, Work Party
Sun Apr 21, 2-4, Work Party
Sat May 4, 10-12, Work Party
Sun May 19, 2-4, Work Party

Let’s start with bleach. Sodium hypochlorite is very reactive, affected by surface contamination from organic matter and it’s irritating to use. It’s difficult to know what dose to use and, at the concentrations that many people use, it leaves a residue on the surface. (1000 ppm will destroy all microbial pathogens but for the tough resting spores. Using household bleach (5.25% sodium hypochlorite), the dilution would be 1:50 or 5T per gallon.)

Ethanol (think Everclear) can kill most organisms but it is highly flammable and evaporates quickly. It dries out the organism (which is why the similar product, isopropyl alcohol, is better as a disinfectant for the skin). Alcohols reportedly won’t kill some spores and they harden rubber and some plastics on tools.

I could not get a clear idea whether hydrogen peroxide is a good pathogen hunter. Articles refer to its effectiveness, especially on inanimate surfaces, but indicate that hydrogen dioxide is a superior disinfectant on plant production surfaces.

Quaternary ammonium chloride. Hmm. There is a lot of controversy about Quats and they are reported to be not always effective against the tough customer – the fungal resting spores.

This brings me to a possible unsung hero – iodine. Remember when you went camping where the water was bad. You mixed the two tablets in water and waited. That second tablet helps with the discoloring and the taste and also is a solubilizing agent. One potential downside is shelf life – about five years.

A flameless loop sterilizer might be the ultimate tool but not readily available and you would need a power source. (We will leave out solarization, which, for the time being anyway, might be challenging in Western Washington.)

This study is way more complex that I could have ever imagined. There is no one size fits all solution. Shown here is a popular chart from two State of Washington professors (who are also fine authors of plant pathology books).

Good reads:
Investigation on the fungitoxic effect of an iodine solution on three plant pathogens in vitro. Bengt Boysen.
Bachelor project in the Danish-Swedish Horticulture programme
2004-1 (ISSN 1652-1579)

Time and Temperature Requirements for Weed Seed Thermal Death
Ruth M. Dahlquist, Timothy S. Prather, and James J. Stapleton
Weed Science 2007 55:619–625

Soil Solarization and Thermal Death: A Logarithmic Relationship Between Time and Temperature for Four Soilborne Plant Pathogens.
G.S. Pullman, J.E. DeVay and R.H. Garber
American Phytopathological Society, Vol 71, No. 9, 1981 p 959

Temperatures Necessary to Kill Fungi in Wood
USDA Technical Note 259, Forest Products Lab Feb 1956

Safe Procurement and Production Manual A Systems Approach for the Production of Healthy Nursery Stock
Griesbach J., Parke, J.L., Oregon Association of Nurseries, January 2012
https://www.researchgate.net/publication/282649506

Dose Curves of Disinfectants Applied to Plant Production Surfaces to Control Botrytis cinerea
W.E. Copes, Plant Disease-American Phytopathological Society, May 2004

Chemical Disinfectants
https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html

Quaternary Ammonium Compounds
Quaternary ammonium compounds are the most commonly employed broad-spectrum hard surface disinfectants employed in animal research facilities.
From: Laboratory Animal Medicine (Third Edition), 2015
https://www.sciencedirect.com/topics/neuroscience/quaternary-ammonium-compounds

EPA Hard Surface Disinfectants
https://www.education.nh.gov/instruction/school_health/documents/disinfectants.pdf

Ruth