Dimesions and Interpretation of Soil Health

Dimensions of 𝐒𝐎𝐈𝐋 Health (Credit: Jagdish Patel https://youtu.be/8D3CfRi4f-k).

For optimal soil and crop growth, we can assess and test a complete package of soil health parameters, indicators, and indices to quantify the effectiveness of adopting best management practices as a beneficial agricultural practice toward meeting the main objectives of your project. These indicators measure soil functionality and integrate them into informative soil-health parameters. 

Recently, we have seen the introduction of soil tests with greater emphasis on the organic pools of plant nutrients like N and P, along with other biological indicators beyond soil organic matter. One such test was developed by Dr. Rick Haney (formally USDA-ARS, Temple, TX), known as the Haney Test. 

The Haney Test employs a multifaceted approach to measure various aspects of a living soil system. First, the test uses organic chemistry to mimic natural soil solutions to extract commonly measured nutrients such as N, P, K, etc. Second, the test includes a measure of soil respiration as an indicator of microbial biomass and potential activity related to nutrient cycling. The third part of the test uses a water extract to measure the available pools of organic carbon (food) and nitrogen (protein) available to the microbes to drive their growth and function. All three of these independent processes collectively help track advancements in soil health and provide a more holistic picture of soil fertility management. 

SOIL HEALTH ANALYSIS 

The soil health analysis is based on the Soil Health Tool, an integrative soil testing procedure that uses the ratio of water-extractable organic carbon to nitrogen (C: N) (not the total soil C: N). A C:N ratio above 20:1 generally indicates that no net N and phosphorus (P) mineralization will occur, meaning the N and P are “tied up” within the microbial cell until the ratio drops below 20:1. As the ratio decreases, more N and P are released to the soil solution which can be taken up by growing plants (Haney et al., 2018).

As we know, the soil carbon pool is large and mostly inactive, providing little information related to soil nutrient cycling. Therefore, using a water-extractable organic C:N ratio is a more sensitive and preferred indicator because it better represents active soil pools related to nutrient cycling. The water-extractable organic C (WEOC) used for our soil testing reflects the quality of soil organic C and the energy source feeding soil microbes (Haney et al., 2012). In other words, the N pool is highly related to the WEOC pool and will be easily broken down by soil microbes and released to the soil in inorganic N forms that are readily available to plants. This provided a good indication of soil health functions with respect to nutrient and carbon cycling and estimation of plant available N, P, and potassium (K).

Please, read more about the Science and Economics of Soil Health, presented by the author of this web, in:

https://www.no-tillfarmer.com/articles/8689-understanding-the-science-and-economics-of-soil-health.