How To Choose The Right Indicators For Soil Health Testing

Mud Valley Institute defined its Monitoring and Evaluation (M&E) plan for soil health testing in April 2024 in collaboration with Ecosystem Restoration Communities (ERC), an organization supporting restoration hubs globally.

In this blog post, we will share with you more about the soil health testing plan we developed, including the choice of indicators we are using in the Soil Lab at Mud Valley Institute, their definition, and relevance to our ecosystem restoration work.

To learn why creating a Monitoring and Evaluation plan is important, you can read our first blog post in this series. In future posts we will focus more on some of the specific soil health assessment indicators, including our first and ongoing observations and results.

We leverage the ERC Soil Framework in order to share and communicate our results with other ERC hubs and local communities that use similar soil health testing methodologies. The plan includes numerous indicators and cost-effective methodologies inspired in citizen science to assess soil health.

The main objective of having an M&E plan is to monitor the essential indicators, also known as metrics or measures, of soil health, and to use this data to allow comparisons over time and across different global locations while still accounting for local needs.

Types of Restoration Indicators

Key impact indicators are higher level metrics which facilitate aggregation and comparison of data globally capturing the progress and effectiveness of restoration initiatives across diverse ecosystems.

Context-specific impact indicators align with site- or project-level goals, taking into account local ecosystem complexity as well as resource considerations.

Since we align to the ERC Soil Framework, we consider the following as high importance key impact indicators which we collect at all the sites we are actively engaged with:

• Success rate 1 year after planting (perennial crops, shrubs and/or trees)
• Tree survival rate (% from logging tree counts, or using tree mapper)
• Soil organic matter and carbon content
• Soil compaction or water infiltration
• Before and after pictures
• Area under restoration (hectares)
• Biodiversity (flora and/or fauna, supported by anecdotal and observed evidence)

Indicators and collection methods specific to each location assure optimized data capture and relevance.

A baseline was established in April-May 2024 for our first chosen experimental site: an old fig orchard where the Hügelkultur method was implemented in order to improve soil fertility and water retention. We started monitoring in spring, as it is the best season for soil health testing because soils are full of water and biological activity.

The choice of indicators was made based on different parameters: indicator effectiveness, cost, level of effort in collection (based on resources available), and relevance to our context in southwestern Portugal. We have a strong focus on soil restoration strategies which increase water retention.

We chose to measure the following 12 context- and site-level indicators from the ERC Soil Framework to assess and categorize soil health. The chosen soil indicators cover the different soil property categories.

• Physical property indicators: Soil texture, Soil structure and aggregate stability, Topsoil depth, Decomposition rate, Soil compaction, Water infiltration;
• Chemical property indicators: Soil organic matter, Soil pH;
• Biological property indicators: Soil biological activity, Soil fauna, Moth trapping, Biodiversity quadrats.

The chemical and physical properties of soil impact its biological properties. Thus, optimal chemical and physical properties will lead to optimal biological properties and soil functions, such as nutrient and water cycling.

In order to better understand soil health, it is important to choose indicators from each of the three different soil properties, even though soil biology is often understudied because of its limitations (i.e. difficult access under-ground, specific skills needed and time-consuming).

We use a number of indicators that allow for data collection using citizen scientists, so that we can engage the local community and increase its knowledge of soil health.

Many of the previously listed indicators can easily be collected by anyone, no scientific training required, by either digging in the soil or using smartphone apps like iNaturalist to observe and catalog aboveground biodiversity indicators.

Soil category collection:

• Soil texture: The soil jar test establishes the proportion of clay, silt, and sand of soils, which is key to understanding the retention of water and nutrients.
• Soil structure and aggregate stability: As a physical indicator, soil structure and aggregate stability tend to be correlated with the ability of a soil to provide water and air for roots and soil organisms.
• Soil color: This is the indicator that shows how the organic matter and carbon content of soil changes over time, with particular land-use and/or restoration interventions. The most accurate way of measuring a soil’s organic matter content is a lab test (Loss of Ignition test). However, in the absence of access to a lab, the soil color test can give a general indication.
• Earthworm count: Establishing the number of earthworms present in soil is a proxy indicator for biological activity. Earthworms help with breakdown of organic residue and create channels that improve infiltration and aggregation due to earthworm burrowing.

Biodiversity category collection:

• Biodiversity quadrats: Measuring changes in biodiversity within specific areas assesses ecological health, biodiversity trends, and gauges the impact of human activities. In addition, biodiversity monitoring supports conservation planning and scientific research, and engages communities in nature stewardship.
• Vegetation surveys: Tracking changes in plant diversity over time can determine whether interventions (or the absence of them) are attracting species and increasing the overall resilience and complexity of these ecosystems. Ideally, a greater diversity of plants within the site will be found relative to the baseline survey.
• Moth trapping: As pollinators and significant components of the food web, moths support various ecological functions. Their presence, absence, or population changes can indicate shifts in environmental conditions, making them a proxy for assessing ecosystem health.

We believe it is important to collaborate with the local community so that we increase awareness about science, our natural world, and the impact of humans. We also want schools to have students participate in citizen science projects such as this one, so the next generation can gain critical knowledge and skills.

We need to learn more from our soil management practices to know how to better restore our ecosystems. Our monitoring and evaluation plan here at Quinta Vale da Lama is a necessary component of our work, as it allows us to measure the success of our soil regeneration efforts and adjust them accordingly. Our soil health testing methodology not only informs our work locally, it also provides usable insights to other ecosystem restoration projects around the world.

🌱 The Soil Lab at Mud Valley Institute is an onsite, field-based soil laboratory supporting research and education focused on improving soil health and agricultural production gains. Learn more about it.

👉 Learn more about our partner, Ecosystem Restoration Communities, by visiting their website.