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?”

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