Soil Organisms - The Recyclers and Soil Builders

Soil organisms - many are microscopic workers spending lifetimes endlessly recycling dead plant materials and maintaining the fertility of the soil.

In areas where their life cycles are not damaged soils naturally conserve themselves or actually build. These include uncut forests, soils under ponds and lakes, prairies and meadows with permanent plant cover and to some extent no till and mulched fields and gardens.

"We know more about the movement of celestial bodies than about the soil underfoot." - Leonardo Da Vinci, circa 1500's

We've managed to figure out how to measure aspects of the soil's chemistry - so we think we know all about the soil. I know when I do a little test and find out my soil's pH is 8 I figure I know a whole bunch. But, equally, if not more important, are the soil organisms living within the mineral stew.

The problem with soil organisms is that most of them are invisible to us. The most important, the bacteria and fungi, are microscopic and we think that they might be a problem. I mean have you ever considered loving your bacteria - or your fungi.

Plus they just aren't all that cute. They're blind - which makes absolute sense given that they live in the dark - so they don't have eyes. They aren't pretty colors - most variations on the black and white theme. Basically you have to be someone like Grissom (from CSI) to love them.

Who are These Soil Organisms?

Even the smallest amount of information about soil organisms can threaten your world view - and with luck entice you to love and care for these small beings. Or at least it has done so for me.

I'm a committed organic type gardener and have been for some time, but, I have to admit I didn't really understand what was going on in that soil underfoot my feet touch everyday. I still don't really - it's too complex and brilliant for me to totally fathom. But thanks to a few soil nerds who've been kind enough to share their work with the world in books I've been partly enlightened.

My Favorite book for this is James Nardi's Life in the Soil.

Here is the information in a nutshell. Soil, or at least healthy soil, is teeming with life. This life lives in an extremely symbiotic and mutualistic way unfailing offering their services to help the whole system work.

In a thimble full of soil - about a gram weight - you can expect to find

  • 100 million to 1 billion bacteria
  • Several yards to several miles of fungi depending on whether you have agricultural or forest soil
  • Several thousand protozoa and up to several hundred thousand in forest soils
  • From ten to several hundred nematodes

This is all in a thimble full of soil. And this doesn't begin to count the larger mites, spiders and earthworms who together form a complex called the Soil Food Web.

I suspect that we would love soil organisms a lot more if we could see them. But the fact is we can't see most of them and to a large extent out of sight is out of mind.

What Do Soil Organisms Do?

Remember, in a natural system you don't need to be adding a bunch of fertilizers, pesticides, herbicides and fungicides every year to keep things growing and healthy. Natural systems maintain themselves thank you very much and they do this with the work of the soil food web.

First the Bacteria and Fungi - foundations of the web

  • Hold nutrients in the root zone for your plants
  • Build soil structure so that water both drains and holds better
  • Help prevent soil erosion
  • Produces plant stimulating hormones
  • Fixes nitrogen from nitrogen gas to plant usable nitrogen
  • Makes phosphorus available in a plant usable form
  • Open the soil so that plant roots can penetrate more deeply
  • Compete with bad guy bacteria and fungi thus keeping them in check and helping plants fight disease or stay disease free

The other soil organisms, the protozoa, nematodes and other larger members of the soil food web eat the bacteria and fungi and in doing so release the nutrients the plants need when they need them. Pretty amazing really.

Care and Feeding of Your Soil Organisms

For a moment think of your soil organisms as very cute and lovable puppies. Naturally you want to give them a comfortable and safe home, good food, and the air and water they need. Guess what - soil organisms have similar needs. Unfortunately they aren't cuddly and you can't play with them, for the most part you can't even see them, so you might not notice that you're killing them with either your gardening or farming methods or sheer neglect.

Habitat - most of the soil creatures live in the top few inches of the soil. When we turn the soil over with a rototiller or a shovel we can bury our babies in a place where they no longer can function. Fungi have the worst time with our cultivating methods. Their filaments get chopped up and the long straws they were forming to siphon nutrients to their plant partners get severed and big parts cease to function. Many farmers have adopted no till methods in their fields to improve soils. This serves to give the soil food web a chance to recover.

Air - when we walk on our gardens we compact the soil under our feet. This is many times worse when we drive over land with a tractor. What it does is eliminate some of the pores that were holding oxygen - always handy for the beneficial soil organism. As oxygen goes down the anaerobic bacteria and fungi go up and the bad news is these are the guys that cause plant diseases.

Feed Good Food - like us the soil organisms need good food. Bacteria tend to like the green foods and sugars and fungi the brown foods like woods and tough leaves. Compost, being a blend of green and brown foods, is the perfect solution - and it has the added benefit of increasing the numbers of bacteria, fungi, protozoa and nematodes at the same time.

Avoid Bad Food - In the past - and even now - we tend to feed the garden chemical fertilizer. This changes the habitat fast - too fast for our soil pets to move or adapt so they can die. Essentially we then put our plants on life support - something akin to an IV drip instead of real food. In doing so we kill the chance of real food coming their way through the network of the soil food web. Plus we of course have bills to pay - fertilizer bills.

Safety - here is where the -cides come in. When the biology of the soil gets out of whack we tend to have a bunch of problems crop up - insect pests run amuck, fungi and bacteria shift from help mode to destroy mode and weeds take over. So naturally we reach for pesticides, herbicides and fungicides. They are effective killers but like big bombs they tend to kill a lot more than we intended. We lose our soil food web and all it's benefits once again.

Want More Details... Check Out These Pages

Soil Bacteria - There is huge diversity in the bacteria found in the soil. This page introduces these guys. The following go into more details with some important bacteria roles.

  • Nitrogen Fixing Bacteria - The most well known are the ones that love legumes but if you have green plants new methods of gene sequencing show many species of nitrogen fixing bacteria live in the soil... we didn't know about them because they aren't crazy about petri dishes in the lab.
  • Decomposer Bacteria - These are the ones getting the compost going and without whom nutrients couldn't cycle and life as we know it would cease.
  • Actinobacteria - Another class found in compost and a source of many of our antibiotics.

Soil Fungi - These are essential decomposers. They are especially helpful in the curing stage of your compost.

Mycorrhizal Fungi - I have several pages about this type of fungi. Given how important it looks like they are I find it hard to believe I somehow missed them in the first few decades of my life as a gardener.


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