Thursday, January 26, 2012

Soil Health: Level 1 - Introduction of Terms

Level 1 - This post is intended to introduce terms which describe the essential components of a healthy soil. This discussion is complicated, so we will provide increasingly detailed levels of information, at the risk of oversimplifying in the beginning.

All plants, found on earth today, evolved to thrive in a soil system filled with variety. Ancestral soils teamed with organisms and carbon compounds, which supplied abundant nutrients and water. What does a varied soil system look like when compared to a conventionally managed soil system?

A varied, or healthy, soil system contains the following essential components:
  • Carbon Compounds:  
    • Labile Carbon: 
      • Carbons which easily decay, such as those present in microorganisms, compost, crop residues, manures, and mulches.
      • These materials release mineral nutrients back into the soil.
    • Recalcitrant Carbon:
      • Contains Humic Acids which are essential to a healthy and productive soil, Humic Acids are known commonly as Humus.
      • Humic Acids endure the stress of time and will remain in an undisturbed soil for thousands of years.
      • Humic Acids improve soil structure, for as long as they remain in the soil.
      • Humic Acids increase a soils capacity to hold water more than any other soil component.
    • Both Labile and Recalcitrant Carbon levels are often very low in conventionally managed soils systems, because the pipeline of their formation has been compromised. 
  • A Diversity of Organisms:
    • Soil organisms, such as Mycorrhizal fungi, beneficial bacteria and earth worms, are absolutely essential in soil heatlh management.
      • Mycorrhizal fungi greatly improve soil structure and nutrient uptake.
      • Beneficial bacteria provide a wide range of benefits, including Nitrogen fixation.
      • Earth worms contribute enzymes and decompose labile carbons.
    • The diversity of microorganisms increases as vegetation types increase.
    • The redwood forest soils of California, with their incredible diversity of vegetation, provide abundant  fertilization as a result of this biodiversity. 
    • The lack of biodiversity, in conventionally managed soil systems, contributes to unhealthy and unproductive crops.
  • Nutrient Availability:
    • Mycorrhizal fungi increase plant root mass and solubilize mineral nutrients. 
    • Humic Acids increase Cation Exchange Capacity (CEC), thereby storing mineral nutrients.
    • Nutrient availability is greatly decreased when Mycorrhizal fungi and humus are not present.
    • Please see our blog for more information: Understanding the Importance of Cation Exchange Capacity .
  • Macroaggregates
    • Macroaggregates result when Mycorrhizal Fungi bind soil particulates together.
    • Humic Acids have been shown to increase macroaggregate formation.
    • Tilling of soil will destroy these structures, increase erosion and create soil compaction.
    • Please follow this link for more detailed information: NRCS Water Stable Soil Aggregate Handbook .
  • Increased Moisture: 
    • Moisture must first be absorbed -  water will  penetrate soils when macroaggregates are present. 
    • Humic Acids and decomposing surface organic matter will then retain water which has penetrated an uncompacted soil.
    • Water in conventionally managed soil systems frequently runs off without being absorbed.
  • Decomposing Surface Organic Matter:
    • Mulches can be described as a decomposing surface layer which insulates and protects the soil from environmental stresses. 
    • This organic matter will eventually become part of the labile carbon fraction of the soil.
    • Conventionally managed soil systems often lack even thin layers of surface organic matter.
    • Please see Got Mulch? for more information.
Our most precious natural resource, healthy top soil, is disappearing at alarming rates. For generations modern soil management practices have systematically reduced the diversity of soils, resulting in reduced yields. To compensate chemical fertilizers have been added, a costly and increasingly ineffective solution.
Stay tuned for Level 2.
Written by:
Aurora Fabry-Wood
Staff Biologist