Soil Health Goal Setting

The “regeneration” in regenerative agriculture refers to the transformations that take place when soil is managed as a living ecosystem. For example, a soil that is undisturbed and has more continuous living roots will begin to show improvements in structure, as organic residues from plants and microbes glue mineral particles together into aggregates. Well-structured soils feature a wide range of micro-habitats and, consequently, can support a greater diversity of soil organisms. These organisms’ life cycles improve conditions for plant growth (e.g., aeration by earthworms and enhanced nutrient availability due to microbial decomposition of organic matter), leading to further improvements in soil structure and biological activity.

“A question worth asking early in the regenerative agriculture journey is: how far can these transformations go? Or, in other words, how much healthier can a soil get?”

Given that these transformations can be gradual and different management strategies can be used to achieve desired changes, a question worth asking early in the regenerative agriculture journey is: How far can these transformations go? Or, in other words, how much healthier can a soil get? To explain how the Soil Health Institute is helping farmers and their advisors answer this question, we’ll look at how we quantify both current and potential soil health.

Vital Signs of Soil Health

The concept of soil health refers to a soil’s ability to perform the multiple jobs it is expected to do, including providing crops with water and nutrients, reducing runoff and erosion, and storing atmospheric carbon fixed by plants through photosynthesis. These different functions depend on soil physical, chemical, and biological properties, so assessing soil health is a fundamentally multifaceted task.

Soil scientists often measure soil health indicators to make a comprehensive assessment of soil functioning. Understanding how much organic matter is present in the soil is particularly important, as organic matter plays a central role in multiple soil functions. Organic carbon measurements provide a direct indicator of organic matter content because organic matter is >50% carbon by weight. Measuring soil organic carbon content also makes it possible to estimate organic carbon storage per unit area if bulk density, sample depth, and rock content are also known. Aggregate stability, or the ability of soil aggregates to withstand applied disruptive forces, is a reliable metric for soil structure and resistance to erosion. Additional insights into soil structure can be gained by measuring soil water-holding capacity, saturated hydraulic conductivity, and compressive strength. The biological dimensions of soil health can be assessed using proxies for microbial activity, including enzyme activities, permanganate-oxidizable carbon (“active carbon”), and respiration during laboratory incubation (“potential carbon mineralization”). When evaluated together, soil health indicators give a snapshot of soil health status for integrated assessment of management outcomes. Diagnosing specific soil properties limiting crop growth may require additional measurements.

Bulk density measurements are on soil health indicator.

Your Soil on a Scale: Setting a Target

Interpretation of each soil health indicator requires defining what values are ideal. Soils can exhibit different ranges of indicator values depending on site characteristics, including precipitation, temperature, soil types, and topographic position. An organic carbon concentration of 1.5% may be very high for a soil on a sandy hilltop, but relatively low for a neighboring soil in a clay-rich depression, both under the same management. Differences in inherent properties (i.e., texture and topographic position) give these soils different capacities to store organic carbon.

How can we determine different soils’ potential soil health? First, we need to clarify what we mean by “different soils.” Soils are incredibly diverse due to processes that occur over hundreds to thousands of years; if no two snowflakes are identical, then certainly no two soils are. However, soils can be grouped based on natural variation in the properties that are most relevant to soil health, including texture (i.e., sand, silt, and clay content), drainage, and mineralogy. Spatial trends in these properties can be evaluated using publicly available data (e.g., USDA National Cooperative Soil Survey maps) in conjunction with in-field interpretation. These properties allow us to group soils based on potential soil health, so that soil health indicators measured on one soil can be interpreted using data for soils with similar inherent properties and site characteristics. Grouping soils according to the inherent properties relevant to soil health makes it possible to link soil health indicator values to differences in management, rather than natural variation across sampling locations.

“Soil health indicator values under optimal management for soil health are referred to as Soil Health Targets.”

The potential soil health of each group of soils can be established by measuring soil health indicators under management conditions that exemplify the soil health principles, including minimal soil disturbance, continuous living roots, and physical protection of the soil surface. In many landscapes, perennial vegetation may provide the best reference for the capabilities of a soil health group after long-term implementation of the soil health principles. Soil health indicator values under optimal management for soil health are referred to as Soil Health Targets. Soils under row crops are not expected to achieve 100% of target values, as some degree of disturbance is unavoidable in crop production. However, standardizing soil health measurements relative to Soil Health Targets provides a consistent basis for comparing soils with different inherent properties.

Unlocking Your Soil’s Potential

Once you’ve measured your current soil health and compared it to what your soil is capable of, you have the data you need to set achievable goals for management outcomes. Integrated assessment of physical, chemical, and biological soil health indicators, relative to Soil Health Targets, can point to the management changes that will most likely lead to the greatest improvements in soil functioning. For example, if aggregate stability is high but biological activity (e.g., active carbon or carbon mineralization) is low, disturbance may be minimized enough to develop soil structure, but greater organic matter inputs may be necessary to stimulate the soil microbial community. The experiences of farmers with similar soils and the advice of trusted local advisors are invaluable resources for developing the specific management strategies that will move you towards your Soil Health Targets.

“Once you’ve measured your current soil health and compared it to what your soil is capable of, you have the data you need to set achievable goals for management outcomes.”