Defining & Achieving Healthy Soils

Definition of healthy soils

There is no universally accepted definition of healthy soil.  The  commonality of the existing definitions reference healthy soil as a living ecosystem.  

1.  https://rodaleinstitute.org/why-organic/organic-farming-practices/soil-health/     
2. https://www.ecofarmingdaily.com/build-soil/humus/healthy-soil-defined/

 The word “healthy” can only be used to refer to living things.  Therefore, in reference to soil health, soil must be considered a living ecosystem full of life, like any other living complex system.   

A preferred hybrid definition of healthy follows:  Healthy soil exhibits sustainable productivity, promoting plant growth with optimal  efficiency with little to no  disease or pests and without a need for major soil disturbances (like plowing and tillage) and without a need for off-farm supplements.

The upper six inches of healthy soil over a one-acre surface area typically contains 10-20 tons or more of soil organic matter of which up to about 1 ton consists of living microorganisms.  https://ohioline.osu.edu/factsheet/SAG-16   

 Since this soil life is crucial for nurturing the next generation of plants, it becomes important for all working landowners to understand the factors that promote increased levels of soil organisms and organic matter.  These soil organisms are commonly referred to as the soil food web of life. According to the U.S. Department of Agriculture, the soil food web is the community of organisms living all or part of their lives in the soil. https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/soils/health/biology/?cid=nrcs142p2_053868#:~:text=The%20soil%20food%20web%20is%20the%20community%20of%20organisms%20living,as%20one%20organism%20eats%20another. 

 It consists of a complex array of microbes (bacteria, fungi, protozoa), arthropods, ants, spiders, worms, and some higher animals. Organic matter in the soil fuels this soil food web of life. “Climate smart agriculture” are those working land practices that lead to healthy soil conditions which means increasing the soil organic matter (SOM)

Soil Organic Matter (SOM)

SOM is derived from all the living and dead forms of the soil food web organisms plus fresh or dead and decaying plant components in and on the soil surface and the substances excreted from growing roots. Soil organic matter is crucial to produce healthy soils.   Soil organic matter is highly complex and is derived from all the materials (including minerals) found within living plants, insects, animals, microbial cells, and tissues. 

 SOM is the fuel that drives the health of soils and brings all the measurable co-benefits to healthy soil ecosystems. Farmers can increase soil organic matter using specific agronomic practices. A major percentage (about 58%) of SOM consists of carbon derived from atmospheric carbon dioxide through photosynthesis. Therefore, increasing SOM may lead to sequestering or binding of carbon for long periods of time within the soil ecosystem.

Healthy Soils & Carbon Sequestration

Increased SOM leads to healthy soil conditions with increased populations of the soil food web organisms. SOM contains about 58% carbon that originates from atmospheric carbon dioxide.  This Greenhouse Gas (GHG) is converted to SOM through the processes of photosynthesis.

About 20-40% of the carbon contained within the SOM becomes sequestered soil carbon.  Agronomic practices that decrease SOM content decrease soil health and release sequestered carbon from the soil in the form of carbon dioxide gas. Practices that decrease sequestered soil carbon (and reduce SOM) include aggressive plowing, tillage, and use of chemicals, including pesticides, herbicides, and synthetic  fertilizers.

Long Term Strategic Importance of Healthy Soils

There have been numerous studies that illustrate the agronomic benefits associated with healthy soil conditions long term. A comprehensive perspective from the Natural Resources Conservation Service of the USDA are presented here:   https://www.nrcs.usda.gov/wps/portal/nrcs/main/national/soils/health/   

 The benefits of storing SOM are summarized here:    https://www.cultivateoregon.org/granges can_become_part_of regenerative_agriculture_movement

 It should not be surprising therefore that farmers everywhere are using conservation agricultural practices that increase soil health with organic matter and carbon in their soils.

Sequestering carbon requires practices that bring long-term additions of soil organic matter (SOM) to the soil.  When plants die, they decompose and 60-80% of the residues undergo short term decomposition (within a year or two) and this plant carbon re-enters the atmosphere.  The rest (some 20-40% of the plant residues along with other dead or decaying matter) enter the soil and persist for years, decades, to hundreds of years becoming sequestered carbon. https://ohioline.osu.edu/factsheet/SAG-16  

Once there is SOM, one wants to keep it to maintain soil health. Maintaining SOM is achieved  by reducing the frequency and aggressiveness of tillage and adopting  other agronomic practices such as growing cover crops, keeping the soil surface green/covered as long as possible each year, etc. The value of sequestered carbon ranges from about $15-20/ton.  See Section V, “The carbon marketplace”. 

In order to create healthy soil, no-till was practiced on 104 million acres of U.S. lands in 2017. The number of farms practicing no-till totaled 279,370.  Cover crops were seeded on 153,402 farms in 2017. https://www.no-tillfarmer.com/articles/8929-no-till-cover-crop-acres-continue-upward-trend?v=preview#:~:text=In%20the%20U.S.%2C%20no%2Dtill,slightly%20from%20278%2C290%20in%202012. 

Farming practices that use no till, minimal till, no plowing and/or cover crops are collectively referred to as conservation or regenerative agriculture. So, overall, some 140 million acres of farmland in the U.S. are currently enrolled in  one of several conservation-related financial and technical assistance opportunities from the federal government to install resource and wildlife preservation practices. https://www.fb.org/market-intel/more-than-140-million-acres-in-federal-farm-conservation-programs

The many benefits of healthy soil include “Saving Mone.” According to an August 2021 article by the USDA/NRCS entitled, “Saving Money, Time and Soil: The Economics of No-Till Farming,   https://www.usda.gov/media/blog/2017/11/30/saving-money-time-and-soil-economics-no-till-farming, on average, farmers practicing continuous conventional tillage use just over six gallons of diesel fuel per acre each year. Continuous no-till requires less than two gallons per acre. That difference leads to nearly 282 million gallons of diesel fuel saved annually by U.S.  farmers who practice continuous no-till instead of continuous conventional till. The savings for individual farmers may be substantial.  For example, assuming an average off-road diesel fuel price of $2.50 per gallon, a farmer farming 100 acres of crops who switches from continuous conventional till to continuous no-till, saves about 400 gallons of diesel fuel – more than $1,000  – each year. https://www.usda.gov/media/blog/2017/11/30/saving-money-time-and-soil-economics-no-till-farming   

 Furthermore, a farmer who plows 15 acres per hour, for instance, would save roughly 7 hours of work with each eliminated pass over a 100-acre field by adopting no-till. Depending on labor costs and equipment maintenance, that’s an additional several hundred dollars saved each year. 

There are other economic and environmental co-benefits associated with reduced or no-till operations, especially when coupled with seeding of cover crops. For example, healthy soil reduces erosion, loss of precious fertile topsoil, and increases water infiltration into the soil instead of creating runoff and soil loss. SOM holds about 10 times its weight in water  https://www.nrdc.org/experts/lara-bryant/organic-matter-can-improve-your-soils-water-holding-capacity).

According to USDA scientists, each 1% of SOM holds some 20,000 gallons of additional water   https://edis.ifas.ufl.edu/publication/SS661.    This is particularly valuable in drought-prone areas, where lack of water is a major concern tied to crop loss.   (https://www.usda.gov/media/blog/2016/12/19/seeing-believing-soil-health-practices-and-no-till-farming-transform)  

Collectively these healthy soil practices lead to healthier air and water quality conditions, an obvious co-benefit for land owners and those who live in agricultural areas where healthy soil practices are employed. https://www.cultivateoregon.org/granges_can_become_part_of_regenerative_agriculture_movement