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Garden Soil

Soil Health

Soil as a Living Ecosystem

Our crops and forage grow in the soil, but it is more than just a medium to hold plants. It is a living ecosystem, capable of providing the essentials of life to plants and animals.

Soil Health is defined by the USDA Natural Resources Conservation Service as "the continued capacity of soil to function as a vital living ecosystem." Soil function is the ability of soil to cycle nutrients and water. 85%-90% of nutrient cycling is through biology, so without a robust living component, soil is unable to function properly. 


A non-functioning soil increases the need for purchased inputs such as fertilizers, pesticides, and additional infrastructure such as irrigation or drainage tile.  Well functioning soil increases plant and animal health, purifies water and restores landscape hydrology, and supports local farm economies.  

Soil Health Principles

Implementing basic soil health principles is essential to having a healthy, thriving agricultural system.  Building the health of your soil is not an all or nothing game.  The tools to implement the soil health principles are varied and there is no cookie cutter approach.  However, by religiously following two or more of the soil health principles you will see positive changes in your farm operation.

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Minimize soil disturbance such as tilling, disking, and plowing. All  break soil aggregates into smaller particles and limit the soil organisms ability to move. Applying synthetic fertilizers and pesticides also disrupts the soil food web, often in ways we don’t fully understand.

Keep soil covered with mulch or living plants to stabilize soil temperatures, preserve soil moisture and prevent erosion. A diverse soil microbial community needs a stable environment, armor your soil! 

Plants exude 30% or more of the plant sap they produce out through the roots to feed the base of the soil food chain, mostly bacteria, which in turn are eaten by larger organisms. This process builds soil health. Without living roots in the soil year around these organisms cannot survive.

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Build diversity in your system. Different species of plants emit different types of plant exudate. These different types of exudate support different species of organisms making the soil food web more diverse.

Livestock integration. Our most fertile soils, the prairies and savannas,  developed with large herds of migratory grazing animals. They are the biological driver of soil health when managed using a few basic grazing principles. 

Manage within the ecological and human context of your operation and adapt the soil health principles to fit into your system.

Testing Soil Health

Testing or predicting soil fertility in a biological system is extremely complex.  Scientifically acceptable methods to test the chemical component of soil are well advanced, despite the vast number of chemical reactions happening in the soil. These processes are well documented and are what we have based soil amendments on for decades. It is recommended that a chemical soil test is done every three to five years in most situations.


Testing soil health is much more complex.  In a healthy soil, the microbial interactions seem incalculable.  But fear not, science and nature have your back.  


One way scientists have been testing the health of soil is by using mass assay genomic testing to study soil microbial biomass in the soil food chain; the exudate from plant roots, the microbes that feed on the exudate, the predators higher up the food chain, and the organic matter left behind by all this life, to serve as energy for robust plant growth.  A few decades ago this testing was slow and expensive, but that has changed. There are now test kits that will assess soil microbial biomass, as well as fungal/ bacterial relationships, for as low as $13.50 per test.


Another soil test that helps determine the biological fertility of soil includes the soil respiration test.  The carbon dioxide / oxygen exchange, or respiration of the soil organisms has been studied since the mid 1800s, but until the last couple of decades was slow and expensive.  There are now do it yourself kits that can determine soil respiration rates in 24 hours for under $20.


Phospholipid fatty acid (PFLA) tests measure fatty acids in cell membranes of soil organisms and can give an accurate measure of microbial biomass in the soil.  It is particularly useful as a tool to measure the effectiveness of different management practices.  By identifying “signature” fatty acids this test can also determine various functional groups such as bacteria, fungal, protozoa, etc.  This gives a snapshot of the microbial community and structure at the time it was taken.    


There are other soil health tests available, and likely many more in development, but maybe the simplest and most effective test to determine soil health is the shovel test.  Dig in the soil, feel the soil texture and observe the root structure. Is there good aggregation and root development?  Are there living soil organisms present? Give it a good sniff.  Does it smell fresh and earthy? Or does it smell stagnant, sour, or metallic? A healthy soil will show life, it will have the texture of chocolate cake. Healthy soil balances out nutrients. It stores them in forms that don’t leach or offgas, but are available to plants.  As Ray Archuletta would say, “By digging a little, you can learn a lot.”. 

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