Opportunity Deep in the Dirt of Cover Crops

Part 3 of our “Advanced Farming Opportunities” Series with Bill Brandon

By Bill Brandon

In this series’ previous installment, I discussed the above ground significance of cover crops. In this part I will review the below ground significance.  

This is all about microbial ecology.  Without soil microbes, plants would not grow.  Over the years of following ‘industrial’ methods recommended by large agricultural suppliers and agricultural schools and extension services, post WWII farming practices have disrupted ‘good’ microbial ecology.  Chemical fertilizers and accompanying methods created the ‘first green revolution’ that greatly increased productivity. After many years, we are learning that it also had a down side.

Radical, and often uninformed, activists have blamed famers for a linty of transgressions, lumping them in with the institutional and corporate interests that gave farmers the template for ‘modern farming’.  

The ‘new modern farming’ will need to take what has been learned to build a system that better serves our whole population and the environment which plants, animals and people must live in.  Here we must start with understanding soil organic material (SOM).

SOM is composed of:

  1. The ‘living’, all microbes, fungi, nematodes, protozoa, etc. that live in the soil and carry out metabolism, taking in ‘food’ and giving off CO2 or methane.
  2. The ‘recently dead’, plant material that has recently died and animal excrement that exist primarily near the surface.  If this material, provided to us by the sun through photosynthesis, were not broken down into energy and ‘recycled’, we would be in compost from here to the stratosphere.
  3. The ‘long term dead’, organic materials that resist decomposition and remain sequestered in the soil for long periods of time. Some small amount of these materials are man made and are often called ‘forever chemicals’ and are often toxic.

Bacteria and fungi are the two primary ‘decomposers’ of the ‘recently dead’.  They are in competition for food and some fungi are somewhat antibiotic to give themselves an advantage.  You might ask what difference it makes whether bacteria or fungi provide the decomposition of SOM and recycling of nutrients. It is generally thought that fungi dominate forests while bacteria dominate tilled farmland for very good reasons.

BacteriaFungus
SOM RoleNematodes and protozoa eat the bacteria and excrete ‘chelated’ nutrients that can be taken up and used by plants.  Fungi, however, are multi-celled structures that directly deliver chelated nutrients to the plant root, which it has surrounded.  
Nutrient RequirementsBacteria are very resilient, going for long periods of time without food.  They exist dormant and then come ‘alive’ when conditions change.  Fungi need a continuous source of food.  When a field is plowed or tilled the structure of the fungi is torn apart and they have a hard time regenerating, while the oxygen supplied to bacteria makes them eat and multiply like crazy.  In the winter, food becomes scarce for fungi if their entire neighborhood is an annual plant.  
Carbon Conversion PerformanceBacteria are poor ‘carbon converters’, using only 20 – 30% of the carbon of the ‘recently dead’ to produce more cells, while 70-80% is released as CO2 into the soil and then into the atmosphere.  Mycorrhizal fungi convert 40 – 55% of their food source into new cells, thereby increasing living SOM faster.  
Nox Conversion PerformanceBacteria contain more nitrogen than fungi but when converted by nematodes and protozoa not all is converted into a form the plant can use; some is converted into Nox. Fungi use different chemical routs to make nitrogen available to plants and little or none is converted into Nox.

A well developed microbial ecology adds to soil fertility and larger amounts of SOM’s living components promote water retention in all the micro passageways created by the microbial community that is also used for oxygen access to the plant root.  Ecological offset credits will strongly focus on the amount of converted and stored CO2 in the soil and how much Nox (CO2 equivalent) is reduced. Restoring fungi to soils will greatly enhance this ‘carbon storage and offset’ component of the offset credit.

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