Soil Project: The Haney Test
Soil health is at the core of regenerative farming. When soil is healthy, it sequesters carbon into the ground, alleviates stormwater runoff, creates the growing medium for nutrient dense food, and helps balance the climate.
The best way to build up healthy soil is to avoid disturbance and encourage microbial activity. At our farm, we attempt this in a few ways:
To avoid disturbance, we practice cover cropping - meaning we plant grasses and legumes to “cover” the soil in between crop plantings, which helps protect the soil from erosion. We also practice no-till farming as much as possible. Rather than churning up the soil between crop plantings, we leave old root systems intact.
To encourage microbial activity, we practice crop rotation - meaning we don’t plant the same kind of crops in the same place within a three year period. We don’t spray chemical pesticides or herbicides, which kill off not only the weeds, but also the microbes in the soil.
We have anecdotal evidence that these methods make our soil healthier - happy plants, lots of earthworms, and high amounts of biodiversity are clear indicators that this approach is working. But we’ve started a project to gather more quantitative data about the soil health of our farm to help us define and evolve our farming methods even further. As we learn, we’ll be sharing our findings here.
The Haney Soil Test
Since 2017, we’ve been testing our soil annually through the North Carolina Department of Agriculture’s free testing services. The agency uses a test called the Mehlich-3 extraction, which gives a solid snapshot of the makeup of our soil each year, including details like pH, and levels of core nutrients.
This year, in addition to our standard testing protocol, we also sent off soil samples to be tested using the Haney Soil Test. Developed by Dr. Rick Haney, a USDA-ARS researcher at the Grassland, Soil and Water Research Laboratory in Temple, Texas, this test goes beyond the conventional nutrient analysis of traditional soil tests (like the Mehlich-3 we’ve been doing annually), which measure the availability of nutrients like phosphorus, potassium, and nitrogen, which are crucial for plant growth. The Haney Soil Test gives more insight into microbial activity, organic matter content, and the soil's ability to sustain biological activity over time.
For our first run with the Haney Test, we gathered soil samples, and sent them off to Ward Labs in Kearney, Nebraska. Now, the results are in.
Where Did We Test
We selected samples from nine different sites on our farm:
Our hoop house (HH)
Garden 2 (G2)
Garden 3 - which we broke up into the top six rows (G3A) and the bottom six rows (G3B)
Garden 4 (G4)
Garden 5 - which we broke up into the top six rows (G5A) and the bottom six rows (G5B)
Our grape vineyard (GRP)
Our pollinator garden, which is a bed full of native perennial plants (POLL)
The Results
Overall Soil Health Calculation
Looking for the TL;DR takeaway from this test? It’s this metric right here.
The soil health score integrates various indicators, including soil respiration, water-extractable organic carbon, and water-extractable organic nitrogen, to provide an overall assessment of soil health. The score can range anywhere from 0 to 50, but most soils do not score higher than 30. Higher scores indicate better soil health, with scores above 7 generally considered good.
Here’s a line-by-line break down of the rest of our test results, by location:
Soil Respiration
The soil respiration levels are indicated by the CO2-C ppm values, which show how much the soil "breathes" indicating microbial activity. Higher values indicate more microbial activity and better soil health. 0-50: below average; 50-100: above average; 100-200: high; >200: very high.
Water Extractable Organic Carbon (WEOC)
WEOC indicates the amount of organic carbon readily available for microbial use. The ideal range is between 100 and 300 ppm, representing a healthy balance for microbial activity.
Water Extractable Organic Nitrogen (WEON)
WEON reflects the organic nitrogen available to microbes, essential for soil fertility and health. Most soils fall between 10 and 30 ppm of WEON, which would be ideal for supporting microbial processes and plant growth.
Microbially Active Carbon (%MAC)
%MAC shows the percentage of WEOC that is actively utilized by microbes. Ideal values range from 50 to 75%, indicating a healthy microbial activity level and balance in soil organic matter. A high %MAC value suggests a large and active microbial population in the soil, as these microbes are actively consuming the available organic carbon. But it also might indicate that the available WEOC is becoming a limiting factor for microbial respiration. In such cases, adding more organic carbon to the soil might be necessary to sustain microbial activity and soil health.
Organic Carbon to Nitrogen Ratio (C:N)
The Organic C:N ratio measures the balance between carbon and nitrogen, key elements for microbial life and soil health. This ratio is crucial for optimizing microbial efficiency and nutrient cycling in the soil.
Simply put: carbon is responsible for energy, while nitrogen offer nutrition. High organic carbon with low nitrogen suggests abundant energy but poor nutritional quality for microbes, akin to an energy drink. Conversely, low organic carbon with high nitrogen indicates good nutrition but insufficient energy.
An optimal C:N ratio falls between 10:1 and 12:1, providing a balanced environment for microbial activity and soil health.
It’s important to note that the Haney Test's C:N ratio, based on water extract, differs from the total soil C:N ratio or that of organic matter, focusing on the available nutrients for microbes.
Organic Nitrogen Release (N Credit)
A nitrogen credit (N credit) refers to the amount of nitrogen in the soil that is available for plant use and can be counted toward the total nitrogen requirement for a crop, reducing the amount of additional nitrogen fertilizer that needs to be applied. N credits are typically built up by planting nitrogen-fixing crops like legumes.
The amount of organic N release credit is influenced by the soil respiration score and the size of the water extractable organic nitrogen (WEON) pool. Higher soil respiration indicates more microbial presence and activity, which enhances the potential for nitrogen mineralization. A larger WEON pool means more nitrogen is accessible for microbial utilization, increasing the potential for organic N release.
What Now?
Armed with this dizzying amount of new data, our next steps involve setting some goals for the health of our soil, and pinpointing specific actions that make sense within the context of our farm. In a future post, we’ll share our takeaways and analysis of these results, and how we plan to incorporate them into our land management strategies.
Resources:
The version of the Haney Test that we used was through Ward Labs “Soil Health Assessment” package
NC Agronomic Services Soil Testing (for free annual Mehlich-3 Extraction test)
Noble Research Institute, “How To Measure Soil Health with The Haney Test”