SOIL 101



The San Juan Islands Conservation District provides one free soil analysis for everyone who has taken advantage of our Farm Planning or Cost Share program. A soil survey is an inventory of the distribution of different types of soils in a given area. Through a soil survey, soil scientists create a map that characterizes soil types to provide useful information about their suitability for various land uses. Soil surveys help us to determine such characteristics as water infiltration, root penetration, acidity, alkalinity, erosion susceptibility and suitability for various types of plants.  If you have not taken advantage of these programs, you still qualify as a San Juan County resident for a reduced fee.

Call us at 360-378-6621 or email us today with your soil analysis needs.


Soil Health – We All Love It, But What Is It Worth?

Click here to read Full ARticle by By Rachel Gilker 



Soil Health Committee – WA State

Soil Health

Soil Interpretation Guide (OSU)

Soil Testing: A Guide for Farms with Diverse Vegetable Crops (WSU Extension)

USDA Natural Resources Conservation Service Soils



  1. It is possible to build carbon-rich, water-holding soil organic matter by working with the natural processes of photosynthesis and decay.
  2. Change in soil carbon can be measured affordably and accurately via small, fixed plots.


Today we understand as never before the crucial role that soil carbon plays in biosphere function, soil fertility, flooding and drought, biodiversity, and the carbon content of the atmosphere.

There’s been tons of talk about soil carbon. It’s time for action to show with good data what is possible – and to recognize those land managers who know how to increase the carbon content of their soil.

A competition such as the Carbon Challenge will demonstrate land management practices that increase soil carbon, improve the soil and its water holding capacity. It will supply creative and unconventional solutions within the reach of any landowner. A competition has the potential to leapfrog decades of research, pilot projects, legislation, and incentives. It will showcase leadership based on on-the-ground knowhow and performance. A competition such as this can tell the stories of soil carbon to citizens, governments, and farmers better than anything else. The Soil Carbon Challenge can shift the question from Can it be done? To how well, and how fast?

Who is it for?

The Soil Carbon Challenge is for:

Land managers who are, or will be, working to increase carbon (and water) in their soils and enhanced ecological function, and who want feedback and accountability relative to this goal, The land involved may be a garden plot, an urban lot, or 100,000 acres.

This is a 10-year monitoring program for those who commit to the process.


The Soil Carbon Challenge will measure soil carbon change with permanent plots, field sampling, and elemental analysis (CN analyzer). Baseline plots will be resampled at years 3, 6, and 10.

The Soil Carbon Challenge recognizes that the biological carbon cycle in a landscape has wide variability over time – and that human land management decisions impact the functioning of the carbon cycle. The Carbon Challenge will document this variability, measure it accurately, and attempt to learn from it on a site-specific, case-by-case basis.

The Soil Carbon Challenge is based on the understanding that soil carbon has value as the keystone of ecological function and health. Increasing carbon levels in the soil, therefore, does more than offset fossil fuel consumption. The Challenge is not an offset market scheme. It is a platform for monitoring, experimentation, and recognition of success in increasing carbon content of the soil, where land managers choose the strategies they will implement. The Challenge will increase exposure and highlight the importance and role of soil carbon.

Work Underway

  • Establish 3-5 baseline plots on San Juan, Lopez and Orcas in the summer and fall of 2015.
  • Promote and educate the public about the Carbon Challenge, the importance of soil carbon and how to increase soil carbon through good management practices.



What is soil carbon?

Living organisms contain a fair proportion of the element carbon. So do the remains of living organisms. Some of these remains end up in the soil, processed and decomposed in various ways by fungi, microorganisms, insects, and worms. This soil organic matter can be 50 to 58% carbon by dry weight, and some of it can remain stable in the soil for generations or centuries. The vast majority of carbon in the top layers of soil is in soil organic matter. Darwin called it vegetable mould (though he recognized the important role of animals such as earthworms in its formation), and it is also called humus.

Some soil carbon is inorganic, such as calcium carbonate or caliche. Carbonates are typically more prevalent in arid environments, where soil pH is above 7.5. They do not have the water-holding properties of organic soil carbon, but are a significant sink for atmospheric carbon.

What is the difference between soil organic matter and biochar?

Biochar is a product of fire. It is plant matter that has been burned in a low-oxygen environment. Another word for it is charcoal. It is mostly carbon, and fairly resistant to decay and oxidation, although there are some losses through leaching into water. Soil organic matter, by contrast, is the product of biological decay processes. These processes are often slow, and require the participation of millions of self-motivated microorganisms.

What removes soil carbon from the soil?

Microorganisms can combine the carbon in soil organic matter with oxygen, creating carbon dioxide. In the soil, oxygen is often limited, especially deep down. When soil is plowed or turned over and exposed to air, these microbes can turn much of the carbon into atmospheric carbon dioxide. William Albrecht, who was soils professor at the University of Missouri during the 1920s and 1930s, wrote in the 1938 Yearbook of Agriculture:

“But with the removal of water through furrows, ditches, and tiles, and the aeration of the soil by cultivation, what the pioneers did in effect was to fan the former simmering fires of acidification and preservation into a blaze of bacterial oxidation and more complete combustion. The combustion of the accumulated organic matter began to take place at a rate far greater than its annual accumulation. Along with the increased rate of destruction of the supply accumulated from the past, the removal of crops lessened the chance for annual additions. The age-old process was reversed and the supply of organic matter in the soil began to decrease instead of accumulating.”

How does carbon get stored in the soil?

For atmospheric carbon dioxide to become soil carbon, it first needs to be captured by green plants in photosynthesis. Much of this carbon is released right back into the air by respiration or decay of plant material, or fire. But some of it can become soil organic matter. Perennial grasses, for example, periodically shed their roots into the soil. These dead roots feed complex soil foodwebs, and soil organic matter and humus can be the stable result. Also, these grasses exude carbohydrates into the rooting zone, typically at night, which feed complex food webs.

To summarize, growing soil carbon usually involves:

  • Soils covered at all seasons with living or dead plant material (no bare exposed ground).
  • Healthy, productive, diverse plants, which require animals to function as a whole system.
  • Perennials, because of their greater investment in root mass, have advantages in growing soil carbon. But annuals, particularly with diversity and long seasons, can do well.

How much of the biosphere’s carbon is in the soil?

Estimates vary. Rocks, such as limestone and chalk, contain enormous tonnages of carbon. Much of the biosphere’s carbon is in the ocean, and most of that is in the deep layers that may take thousands of years to be exposed to the atmosphere. Fossil fuels are significant, and so are soils, followed by the atmosphere, and then biomass (vegetation, bacteria, fungi, animals). Usually, living bacteria in the soil are considered part of soil organic carbon.

  • Oceans: 38,000 gigatons C (stable, average turnover of a C atom is about 100 years)
  • Fossil fuels: 4,000 gigatons C (estimate)
  • Soils: 1600 – 2,400 gigatons C (average turnover about 35 years); recent new estimates of soil organic matter in peat and in polar regions have increased these estimates
  • Atmosphere: 800 gigatons C (average turnover 5 years)
  • Biomass: 600 gigatons C (average turnover 10 years)



© San Juan Islands Conservation District 2016