Soil Health

Soil Health Test:


The soil health test is an integrated approach to soil testing using chemical and biological soil test data; it is designed to mimic nature’s approach to soil nutrient availability as best we can in the lab. This tool is the culmination of nearly 20 years of research in soil fertility and many believe that it represents the next step in soil testing for the 21st century. This tool is designed to answer some simple questions about the soil:

  1. What is your soil’s condition?
  2. Is your soil in balance?
  3. What can you do to help your soil?

The soil health test is designed to work with any soil under any management scenario because the program asks simple, universally applicable questions. The methods use nature’s biology and chemistry by using a soil microbial activity indicator, a soil water extract (nature’s solvent), and the organic acid extractant H3A, which mimics the production of organic acids by living plant roots to temporarily change the pH in the area around the roots thereby increasing nutrient availability. These organic acids are then broken down by soil microbes since they are an excellent source of carbon, which returns the soil’s pH to its natural, ambient level. The test uses an integrated approach to soil testing, reflecting the complex ecosystem of soil, instead of depending upon the narrow measurement of inorganic N, P, and K. The integrated approach is naturally controlled so that N and P will not exceed what is available from the organic N and organic P pools. In addition, micronutrient availabilities can be assessed along with a lime determination using an extraction that is much less “harsh” that current soil testing methodology. However, with that being said we do not have 50 years of research backing this information like we do with current soil testing methodology. We have approximately 2 years of data and will continue to refine and update this information as we move forward. How can the soil test be used?

  1. It can be used to compare the condition of two farms that are being considered for purchase or rent. If purchase/rent price are the same then the farm with the best soil health indicators will have more “bang for the buck.”
  2. It can be used to assess a management practice (i.e. tillage versus no-tillage, cover crops versus no cover crops, manure versus no manure, etc…).
  3. The test can be used for trouble shooting “problem” areas within a field because it provides both biological and chemical information.
  4. The soil health test can be used to make N, P, K, and lime recommendations (it can do micronutrients too, but since the methodology is so new we are still learning the exact “critical” levels).


Respiration (Solvita CO2-C):

This number is ppm CO2-C released in 24 hrs by soil microbes after soil has been dried and rewetted. This is a measure of microbial activity in the soil and is highly related to the fertility of the soil.

Extractable Organic Carbon:

This number in ppm is the amount of organic C extracted from the soil with water. This pool of carbon is roughly 80 times smaller than total soil organic C pool (% organic matter) and reflects the energy/food source that is driving your soil microbes.

Extractable Organic Nitrogen:

The total water extractable N from your soil expressed in ppm.

% Microbially Active Carbon:

This number is the percent of water extractable organic C that the soil microbes broke down is 24 hrs. It is the Solvita 1-day CO2-C divided by the organic C times 100. We like to see the number above 20.

Total Available Nitrogen:

The total amount of plant available nitrogen in your soil expressed in pounds of N per acre.

Available Inorganic Nitrogen:

The amount of ammonium and nitrate nitrogen in pounds of N per acre.

Available Organic N:

The amount of N being released through mineralization in pounds of N per acre. While the ratio of microbially active carbon to extractable organic nitrogen tells us how much nitrogen is being acted upon by the microbes, the Nmin estimates how much N will be immediately available. The amount of Nmin relies heavily on the organic C:N value.

Extra Nitrogen Credited for Active/Healthy Soils:

This value is included in the organic N release when it is greater than zero. The value was used to adjust the potential organic N release in relatively active and healthy soils. Soils that are “healthier” are more efficient at mineralizing nitrogen.

Organic C:N:

This is the ratio of organic C to organic N in soil based on a water extraction. This number is used in conjunction with the Solvita CO2-C number to estimate potential N and P mineralization. It is also used in the soil health calculation. This number is a very sensitive indicator of the health of your soil and has a significant impact on the activity of soil microbes. We like to see number below 20.

Organic N:P:

This number is the ratio of organic N to organic P. Since plants take up nitrogen and phosphate in a roughly 3:1 ratio, respectively, we like to see this number around 5 or lower. A higher number indicates a soil system that may be out of balance and needs some adjustment.

Soil Health Calculation:

This number is calculated as 1-day CO2-C divided by organic C:N ratio plus a weighted organic carbon and organic N addition. It represents the overall health of your system. We like to see this number above 7, but that is just an average. There are soils where 7 may never be achievable (i.e. sandy soils), while on other soils it may be much higher. Taking a sample from an undisturbed or native area can help you gauge what this value should be on the soils that you work on. In addition, keeping track of this value will allow you to gauge the effects of your management practice changes over the years.

Cover Crop Mix:

This is a suggested cover crop planting mix recommendation based on your soil test data, the soil health score, and the organic C:N ratio. It is designed to provide your soil with a mixed species cover crop to help you improve or sustain your soil health.

Total Available P:

Total plant available P in lbs P2O5 per acre.

Available Inorganic P:

Inorganic P is soil extracted with H3A and analyzed for orthophosphate in pounds of P2O5 per acre.

Available Organic P:

Organic P release is the P that will be released through mineralization of organic P by soil microbes depending on their activity and the organic C:N ratio in pounds of P2O5 per acre..

% P Saturation Iron + Aluminum:

% P saturation is the amount of P divided by the amount of iron and aluminum extracted from your soil. Values below 5 typically indicate the need for P fertilizer.

% P Saturation Calcium:

% P saturation is the amount of P divided by the amount of calcium extracted from your soil. Values below 5 typically indicate the need for P fertilizer.

K2O lbs per acre:

Pounds of plant available K2O per acre.

Calcium + Magnesium / Aluminum:

This value in conjunction with the Ca:Mg ratio can be used to determine if an application of lime or gypsum is needed. See table A for explanation.

Calcium:Magnesium ratio:

We want these values to range between 5 and 8 for a balanced soil. What we have found is that to keep Mg% above 8% then the Ca:Mg has to be roughly less than 8 and to keep Mg% below 20% the Ca:Mg has to be roughly above 5. See table A below to help with recommendations.

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