A Better Way To Test Horse Pasture Soils – An Introduction to the Haney Soil Health Test
The Haney Soil Health Test is one of several new tests designed to include soil biological health metrics in addition to nutrient concentrations. The test relies on 4 key metrics:
1) Microbial soil respiration informs overall microbial activity.
2) WEOC measures how much food there is available to feed soil microbes.
3) WEON is a measure of the organic nitrogen pool to feed plants
4) C:N ratio tells us if organic carbon and nitrogen levels are in balance.
This data can be used to inform better pasture management practices to improve overall soil health, which in turn, leads to healthier pasture forage for our horses.
Soil health has experienced a paradigm shift in recent years, with a greater emphasis towards soil biology. Such changes have been motivated by an improved understanding of the critical role soil microbes play in plant health. For example, microbes provide plants with key macro- and micro-nutrients more effectively than we can through fertilizer, improve overall plant resiliency (i.e., the ability of plants to withstand environmental stresses, including drought, grazing pressure, etc), and improve overall soil structure.
Motivated by this improved understanding of the key role microbes play in soil health, new tests have been developed to measure soil biological health. One of the most promising and widely used such tests is the Haney Soil Health Test, developed by Dr. Rick Haney (USDA, Agricultural Research Service) and associates.
The Haney Soil Health Test is designed to answer three key questions:
1) What is your soil’s condition?
2) Is your soil in balance?
3) What can you do to help your soil?
In this blog article, I provide an overview of the Haney Soil Health Test and discuss how it can be used to inform better pasture management practices for horse pastures. The lab I use to run this test is Brookside Labs (www.blinc.com), one of a handful of labs in the US that offers this particular test. The example data presented in this blog comes from a horse pasture in Florida (USA) where I recently ran the test.
THE FOUR KEY METRICS OF THE HANEY SOIL HEALTH TEST
The table above shows results of the four key data metrics analyzed from an example soil health test taken from a horse pasture in Florida, USA. I will spare you a long description of the numbers, but researchers have conveniently provided a ranking for each metric, from Very Low to Very High. The four metrics are summarized in more detail below:
1) Microbial respiration (IR Gas Analyzer): A measure of soil microbial activity based on CO2 respiration by soil microbes. At Brookside and other labs, microbial respiration is measured using an IR Gas Analyzer.
2) Water Extractable Organic Carbon (WEOC): A measure of the energy source (food) feeding microbes. Whereas percent soil organic matter (% SOM) can be thought of as the quantity of soil organic carbon, WEOC is the portion of that carbon that can be used by soil microbes as food. WEOC is approximately 80 times smaller than the total soil organic carbon pool, and is measured by shaking soil sample in water for 10 minutes, centrifuging, and analyzing carbon using a C:N analyzer.
3) Water Extractable Organic Nitrogen (WEON): A measure of the “potentially mineralizable” N in your soil that can be broken down by soil microbes and released in inorganic forms to feed growing plants. Like WEOC, WEON is measured by shaking soil sample in water for 10 minutes, centrifuging, and analyzing nitrogen using a C:N analyzer.
4) Carbon to Nitrogen (C:N) ratio: A key metric for proper nutrient cycling that informs the release of N and P to the soil solution where it can be taken up by growing plants. In soils where C:N ratios are too high (i.e., too much organic carbon relative to nitrogen), N and P become tied up in microbial cells, and no net mineralization of N and P can occur to feed plants. Conversely, if the C:N ratio is too low (i.e., too little carbon relative to nitrogen), microbes do not have the food they need to carry out nutrient mineralization.
OVERALL SOIL HEALTH SCORE
The Haney Soil Health Test combines the IR Gas Analyzer + WEOC + WEON values into a single soil health score, as shown in the image above. (note: the exact equation used to calculate the soil health score changes somewhat depending on IR Gas Analyzer and C/N ratio values).
As you can see in the image, the soil collected from the Florida horse pasture has a soil health score of 8.48. But what exactly does that mean?
Soil health scores are the product of several factors:
1) The “natural” (or background) conditions of your specific soil type(s)
2) Short term weather and longer term climate conditions
4) Human management practices
Generally speaking, we have no control over the first three factors. Sandy soils in hotter climates (like Florida) are, for the most part, going to have lower soil health scores than loamy soils in cooler climates. The real power of the Haney Test is that it allows us to evaluate the impact our pasture management practices have on overall soil health over time, not just in terms of soil nutrient levels, but also, and perhaps more importantly, in how our pasture management practices are affecting soil biology.
SOIL NUTRIENT MEASUREMENTS BASED ON ROOT EXUDATE CHEMISTRY
In addition to looking at soil biology metrics, the Haney Test also provides soil nutrient data, but not in the same way that traditional soil tests do. Rather, the Haney Test uses a novel extract designed to mimic the chemistry of root exudates.
Root exudates are a suite of organic acids, amino acids, sugars and vitamins secreted by living roots that serve as food for microbes and aid in extraction of nutrients from soil. Whereas traditional chemical soil tests rely on strong, low pH acids to extract nutrients from a soil sample, the Haney Test uses a mixture of weaker organic acids designed to mimic root exudate chemistry. The thinking here is that the strong acids used in traditional soil testing are not found in nature, so why would we use such acids to measure soil nutrient levels? Rather, an extract that mimics the chemistry of root exudates should provide a better measure of soil nutrient levels that are actually available to plants.
The table below summarizes macro-nutrient levels measured from the same soil sample collected from the Florida horse pasture using three different soil extracts. The first column provides nutrient data using a traditional strong acid, low pH extract (the Mehlich III extract). The second column provides the same nutrient concentrations extracted from the same soil sample, however, this time using the extract in the Haney Test designed to mimic root exudate chemistry (the extract used in this test is called the H3A extract after the last name of three of the developers of the test who all had last names that started with an H). The third column provides nutrient data using a deionized water extraction. I will discuss this third test in more detail in a future blog post, so stay tuned. For now, suffice it to say that water extractable nutrients can tell us what nutrients are available to plants when it rains, and is particularly helpful in informing nutrients available to plants when they are no longer in the root growing phase.
As you can see from the table below, generally speaking the nutrient concentration values go down as you move from the traditional, strong acid test to the root exudate extractable test and finally to the water extractable values. For now, let’s leave it at that. I will discuss what nutrient levels are considered “optimal” for these newer tests in a future post. For now, I just wanted to show you how nutrient levels can vary based on the type of solvent used to extract the nutrients from the soil.
TIPS ON USING THE HANEY SOIL HEALTH TEST EFFECTIVELY
First, If you have made it this far, I appreciate your time reading through the entire blog article along with your interest in better ways to manage horse pastures through better soil testing. I will end this blog post with some tips on how use the Haney Soil Health test most effectively, and also tell you a little about a pilot program I am running to gather more information on using this test to inform better pasture management practices that improve soil biology and overall soil health.
1. When running the test for the first time in your horse pastures, it is a good idea to collect a second composite sample from an undisturbed area on your property to act as a control sample. This could be an undisturbed area along a tree line, or, if no such area is available, directly under your pasture fence. This second sample acts a control to compare the results of your pasture soil test to levels considered “normal” for your particular soil. When collecting a second control sample, it is best if this sample is of the same soil type as that in the pasture. In the US, you can use the NRCS web soil survey to look up your specific soil types on your property.
The example below shows two such samples collected from a horse property in Florida, USA. The first sample (labeled control) was collected from an undisturbed area outside the pasture, whereas the second sample comes from inside the pasture itself.
Generally speaking, in this particular example the two samples provide similar results. However, that is not unexpected, as the property has only been used for pasture for about one year (changes in soil health can often be slow). That being said, notice the slight drop in WEOC (water extractable organic carbon) in the pasture sample. Loss of soil carbon over time is common in pasture systems due to the impacts of traditional grazing practices on soil structure and function. As time goes by, if organic carbon is not returned to the soils (by, for example, spreading compost), I would expect to see this trend continue.
2. Once you have baseline soil health data for your pasture soils, you can use the soil health test to monitor changes over time (typically every one to three years) based on your pasture management activities. Are practices like rotational grazing, spreading compost, mulching etc. maintaining or even improving soil biology over time? Conversely, if you use too many synthetic fertilizers or overgraze your pastures, are you seeing a reduction in soil biological health over time?
The Haney Test, and soil tests like it, are becoming increasingly popular in the regenerative agriculture movement, defined as a system of farm management principles and practices that increase biodiversity, enrich soils, improve watersheds, and enhance ecosystem services. This movement is centered around five principles.
1. Armor the soil (no bare spots)
2. Minimize soil disturbance (no-till)
3. Increase plant diversity
4. Always have living roots (via pasture grasses, cover crops, or forage crops)
5. Integrate livestock
The goal of the pilot study is to use the Haney Test as a way to measure the impact of pasture management practices specific to the equestrian community on overall soil health, with a focus on soil biology. How well do practices like spreading compost, rotational grazing of pastures, mulching, or increasing pasture forage diversity improve soil biology? I also hope we can explore how these practices influence things like laminitis risk (although I will need help on that one). Conversely, do continuous grazing practices and use of synthetic fertilizers negatively impact soil biology over time in horse pastures?
If you are interested in participating by having your pasture soil tested using this new soil health test, please contact Clay Nelson at clay@SustainableStables.com. Participants are only asked to cover the lab fees associated with testing, which is being offered at a reduced price. We currently have participants in the US, UK and Australia.