Written by Molly McIlquham, Extension Coordinator, Washington State University, 04/04/2023
With increased awareness comes pressure and incentive to measure soil health on farms, which is great! Researchers and farmers alike want to know where the soil stands in terms of soil health. But soil health tests can be expensive, typically about $50-$70 for a basic test with many options to add on. So, measuring a whole suite of indicators on many fields can add up fast. There are three main questions to ask before you start measuring soil health.
Let me first ask you why?
Soil health is a topic almost everyone is talking about, grocery store shoppers, policymakers, and obviously farmers. And soil health comes with different definitions from different agencies. But at its core, it’s the soil’s ability to provide key roles to humans and the environment.
And with increased awareness comes pressure and incentive to measure soil health on farms, which is great! Researchers and farmers alike want to know where the soil stands in terms of soil health. But soil health tests can be expensive, typically about $50-$70 for a basic test with many options to add on. So, measuring a whole suite of indicators on many fields can add up fast.
What if I said you could measure your soil health to improve soil functions that would serve you and the surrounding ecosystem instead of simply measuring as many things as possible? That would be great, right?
There are three main questions to ask before you start measuring for soil health:
First, what soil functions do you want to improve?
Soil has five main functions that support life (Figure 1).
Figure 1. The five soil functions
- Supporting water relations: Soils are crucial in regulating water flow and quality. They can store and release water for plant growth, filter pollutants, and reduce the risk of floods and droughts.
- Providing physical support: Soils provide physical support, water, and nutrients to plants, which are essential for their growth and development.
- Supporting biodiversity and habitat: Soils are home to many organisms, from tiny bacteria and fungi to earthworms and insects. These organisms are vital in maintaining soil health and supporting biodiversity above and below ground.
- Storing and cycling nutrients: Soils store and cycle nutrients such as nitrogen, phosphorus, and potassium, essential for plant growth and productivity.
- Filtering and Resilience: Soils act as natural filters, removing impurities and pollutants from water as it passes through the soil. Soils are subject to disturbances, such as erosion, compaction, and nutrient depletion, which can lead to the degradation of the soil structure and function. Resilient soils are better able to withstand these disturbances and recover quickly.
Then, what soil health indicators measure the soil functions you want to change?
Soil health indicators can measure the soil’s physical, chemical, or biological aspects and provide a snapshot of how well your soil is functioning. But some indicators can be related to multiple functions. Like aggregate stability, the measure of soil aggregates’ resistance to degradation (typically from wind or water) falls into four of the five function categories (Figure 2). Soils with higher aggregate stability typically have better water infiltration (water relations), are less likely to be compacted (physical support), have adequate macro and micro pores for microfauna habitat (biodiversity and habitat), and have a lower risk of erosion (filtering and resilience). As you can imagine, multiple indicators are related to multiple functions, and indicators can also be related to one another, which is why it is important to not just look at one indicator score but look at how related soil health indicators are increasing or decreasing together. Soil organic matter, coined as one of the most important soil health indicators, is related to nearly every measured soil health indicator.
Some soil health tests include up to 20 indicators, some as simple as five. Many allow you to choose ala carte which indicators to measure. This allows you to tailor your test to measure what you want to know.
Many soil test labs that provide soil fertility or nutrients tests now run many of these soil health tests but check the lab’s capabilities before deciding on a lab. There are a few other things to consider when starting to measure soil health:
- Try to use the same lab each time. Some labs run tests a bit differently or report using different units. Switching between labs can make things confusing pretty quickly.
- Take samples at the same time each year. Many indicators like β-glucosidase and permanganate oxidizable carbon can change drastically from season to season, so you may see false changes from year to year.
- Determine how variable the fields are. It may make sense to split fields into sections to find areas with higher or lower values.
- Not all indicators change at the same rate. Indicators like soil organic carbon and bulk density can take more than three years to change, but others like ACE soil protein and mineralizable carbon can detect changes in management within a year (see Table 1).
Table 1: which soil health indicator measures each function and how often to measure.
| Frequency | Water Relations | Physical Support | Biodiversity and Habitat | Nutrient Cycling | Filtering and Resilience |
|---|---|---|---|---|---|
| 1-3 Years | • Aggregate stability | • Aggregate stability • Electrical Conductivity |
• ACE soil protein • Aggregate stability • Mineral Carbon • Permanganate oxidizable carbon • Potentially mineralizable nitrogen • β-glucosidase (enzyme) |
• ACE soil protein • Electrical conductivity • Mineralizable carbon • Permanganate oxidizable carbon • Potentially mineralizable nitrogen • Soil pH • β-glucosidase (enzyme) |
• ACE soil protein • Aggregate stability • Electrical conductivity • Mineralizable carbon • Permanganate oxidizable carbon • Potentially mineralizable nitrogen • Soil pH • β-glucosidase (enzyme) |
| 5-10 Years | • Surface and subsurface hardness • Infiltration • Water holding capacity |
• Surface and subsurface hardness • Infiltration • Water holding capacity |
• Surface and subsurface hardness | • Cation exchange capacity • Total organic carbon |
• Surface and subsurface hardness • Cation exchange capacity • Total organic carbon |
For information on common soil health indicators and the functions they are related to, you can check out the Cornell Soil Health Manual and WSU Extension publications: Soil Health in Washington Vineyards and Soil Health in Orchards.
Finally, what soil health management practices can you adopt?
Once you determine what soil functions you want to improve, you can make management changes and track the changes in soil health over time.
There are four main principles for improving soil health:
- Minimize disturbance
- Maximize soil cover
- Maximize living roots
- Maximize biodiversity
There are a few common management practices that can improve soil health through these principles, many of which are covered in the WSU Extension publication Soil Health in Orchards.
Cover crops can reduce erosion and increase soil organic matter by increasing soil cover and maximizing living roots. Cover cropping can be as simple as planting a single species or as complicated as many species. Make things as simple as possible starting out. It is generally recommended to include a legume to provide nitrogen to aid in nutrient cycling in addition to protecting the soil and keeping living roots in the soil. The Sustainable Agriculture and Research Education program has great resources guiding you through the first steps in starting to cover crop. Or even more simple is allowing the alleyway vegetation to grow and cover the soil. No cultivation needed to maximize biodiversity.
Perennial crops, like orchards, typically fulfill the minimizing disturbance principle by practicing reduced tillage. By reducing tillage as much as possible, you are reducing the opportunity for soil organic matter to oxidize or leave the soil and maintain soil structure.
Now you are ready to start measuring
So, by answering three questions: 1. What soil functions do you want to improve, 2. What indicators measure the functions you want to change, and 3. What management practices can you adopt? You can improve soil health to benefit you and the surrounding environment, keeping the bottom line in mind.
Investing in soil health creates a more productive and sustainable agricultural system that supports healthy ecosystems and provides food, fiber, and fuel for future generations. So, to ensure your farm’s long-term health and productivity, get started measuring soil health.
Contact
Molly McIlquham
Washington State University
molly.mcilquham@wsu.edu
360-610-7353
Additional information:
Soil Health in Washington Vineyards
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