Humus

humus - hands in soil with plant

Humus? Why in the world is he writing an article about a dip made of chickpeas? 

Well, I’m not.  Humus, as opposed to hummus, is vitally important to your garden and your plants as hummus might be to your next patio party.

What is it?

Humus is that dark stuff in healthy soil that forms when the organic matter reaches the final stages of decay.  Sounds a little yucky but, it is where everything eventually ends up.  It is the ultimate in recycling and nature has been doing it for millions of years.

Humus is the last stage of the composting process that renders the decomposed organic matter into the form of nutrients that plants can absorb.  This process is called mineralization and has to occur for plants to have access to the nutrients that are locked up in the cell structures of the material we put into our compost piles.  Whether this happens in the compost pile or the soil after the application of the compost to your landscapes and garden beds is immaterial.  Mineralization must occur for the nutrients to reach the inorganic forms that plants can absorb.

Mineralization

Microorganisms perform this mineralization with bacteria being the chief operators, but all of the other thousands of microscopic and macroscopic life in the soil contribute to the process.   The chemical and mechanical means of producing humus are complex and, as yet, not fully understood.  What is known is that humus is a complex substance and has a carbon to nitrogen ratio of 10 to 1.  That means that for every 1 Nitrogen atom locked up in humus, there are ten carbon atoms collected.  That is a hugely significant number for several reasons.

humus - worms in soil

Research tells us that most of the humus in our soil is more than 100 years old.  The humus is locked up in soil aggregates that protect the carbon to nitrogen bonds from degradation into CO2.  The natural collection and storage of carbon is called carbon sequestration.  Some of you may have heard that term used with climate change.

Now for the interesting part.

The soil has been the natural storage place for carbon for millennia.  It is what makes healthy soil work.  But there is a problem.

At the end of World War I, the huge and profitable chemical industry had developed a huge capability to produce nitrates, an essential ingredient in making gunpowder.  Not wanting to put thousands of people out of work (and not lose their profits) the industry had to find a market for all that nitrate in a hurry.  It turns out nitrate is a very potent fertilizer.  Put it close to plant roots, and the plants experience a surge of growth.  Keep doing it, and the plants keep growing and producing.  It seemed a perfect situation.  With millions of hungry people in the world, here was a solution to feeding them.

row crop spraying

There is one downside to this seemingly perfect solution. The application of the nitrogen also stimulates the soil microorganisms to go into high gear and start consuming all the nitrogen that is available in the soil. Thus releasing all that carbon which has to go somewhere and that somewhere happens to be the atmosphere in the form of carbon dioxide.

Our problem

compacted soil

Once most of the available humus is gone from the soil, the plants become dependent on the synthetic nitrogen provided by the readily available fertilizers.  With no humus on which to feed, the soil organisms rapidly dwindle.  This leaves the soil in a state that I call dead.  There is no life in the soil.  With no life, the soil begins to deteriorate.  It is the microorganisms that provide the “glue” substance, called glomalin, that bind the soil particles together to form the aggregates.  Aggregated soil has as much air space as solid material.  These air spaces are the routes that air and water infiltrate into the soil, allowing places for bacteria and other organisms to exist and helping retain that moisture and dissolved nutrients where the plants can access them.

Without the microorganisms, the soil cannot create aggregates and begins to break down and compact.  Compacted soil drives the larger organisms away and leaves “dead” soil.

A self-feeding cycle of destruction

The effect over the last 80 or so years in the agriculture industry is the slow and consistent poisoning of our soil.  In much of the industrially farmed areas, the soil is so depleted of humus that plants can no longer produce crops with the same nutritive values as were common 100 years ago.  These practices create a vicious cycle requiring the application of more and more synthetic fertilizers to keep plants growing.  The condition of the soil is an open invitation to noxious weeds which must be controlled with synthetic herbicides.  Weakened crop plants are more susceptible to insect pest invasion, which required wider spread use of synthetic herbicides, which also contribute to the further degradation of the soil biome.  What is toxic to insects is almost always toxic to the creatures that live in the soil.

The mechanical effects

soil erosion

Erosion also becomes a problem in humus depleted soil.  Compacted soil breaks down into its parts and is easily washed away or blown away.  Topsoil erosion is still a major concern in large parts of the agriculturally based central US.

So, we are left with a few very important facts about the destruction of humus in the soil.

  • Destroying the humus content of the soil releases large amounts of carbon into the atmosphere.
  • Without humus in the soil, the organisms that create healthy soil don’t hang around.
  • Lacking the organisms in the soil, plants cannot get the required nutrients to remain healthy and productive
  • Soil erosion and nutrient depletion become huge problems without humus.

Is there a solution?

There is always a solution.  Stop the practices that have destroyed the humus content of the soil.  Stop the application of synthetic toxic chemicals to the soil.  Let nature do the work.  Use natural fertilizers such as manure and compost.  Concentrate on feeding the soil rather than feeding the plant. 

Allow nature to regenerate the soil.  Nature has an amazing ability to heal itself given time and the right conditions.  With a little help, these “regenerative” practices can be highly successful.  You can do this on a small scale in your urban landscape or on a large scale on a farm or ranch.  There are hundreds if not thousands of success stories to be found.

To read more about soil regeneration and regenerative agriculture, you can find links and sources on our website at West Texas Organic Gardening.

Other links and websites

Kiss the Ground

Green America

A Soil Owner’s Manual: How to Restore and Maintain Soil Health by Jon Stika

The Hidden Half of Nature: The Microbial Roots of Life and Health by David R. Montgomery and Anne Bikle