Recommended Measurements for Evaluating Soil Health
In an Aug. 12, 2022 press release, the Soil Health Institute (SHI) announced its recommended measurements for assessing soil health. These recommendations are based on results from a 3-year project that was conducted across North America where conventional management systems were compared to soil health-improving systems.
Based on the results from this project, the SHI recommends a minimal suite of three measurements that can be widely applied. These measurements were selected based on cost, practicality, availability, redundancy, and other filters. The three measurements and details about each, plus links to SHI’s standard operating procedures for their measurement, are listed below.
Soil Organic Carbon Concentration. Soil organic carbon (SOC) is a measureable component of soil organic matter (SOM), and refers to the carbon component of SOM. Since SOM is difficult to measure directly, labs tend to measure and report SOC. Soils with a high SOC are likely to be more productive, will hold more available water, and have better biological, chemical, and physical properties. Sequestering carbon in SOC has been suggested as one way to mitigate climate change by reducing the amount of CO2 that is released to the atmosphere. SOM can be reasonably estimated from the SOC% that is measured. Changes in stable SOC generally occur very slowly–i.e. generally take more than 10 years–but more rapid changes are most likely to occur in the top 4-6 in. of soil. SHI’s standard protocol for measurement of this trait can be found here.
Carbon Mineralization Potential. Carbon mineralization (conversion of carbonaceous material in soil to CO2) is mainly a function of the soil microbial population. Changes in carbon mineralization are usually determined by measuring the basal respiration of soil. SHI’s standard protocol for measurement of the amount of CO2 that is produced over a 24-hour period after the rewetting of dry soil can be accessed here.
Aggregate Stability. Soil aggregate stability is the ability of a soil to regulate the movement and storage of air and water throughout the soil profile. It is generally accepted that the more stable a soil’s aggregates, the more productive the soil. Soils are composed of a matrix of aggregated sand, silt, and clay particles that is held together by mycorrhizae, fine plant roots, earthworm slime, and residues of dead soil microbes; this matrix regulates air and water movement. Soils which have stable aggregates–i.e. aggregates that resist external forces from raindrops and traffic–are usually more productive. Aggregate stability is widely accepted as an indirect indicator of a soil’s biological activity, water-holding capacity, and the presence of mycorrhizae. In essence, it is the measured ability of a soil to hold together and maintain structure even when encountering disruptive forces from raindrops, water and/or wind erosion events, and tillage. SHI’s standard protocol for measurement of a soil’s wet aggregate stability, or its ability to resist breakdown or degradation, can be found here.
Understanding soil health involves assessing and managing a soil’s inherent properties of fertility, structure, microbial activity, etc. so that it functions to support optimal plant growth and provide beneficial ecosystem services. This means that changes in soil health must be constantly monitored so that soil is not degraded but rather is maintained in or improved to a healthy status. The above three measurements should allow producers to determine just how healthy their soils are so that they can institute and/or continue practices that will maintain soils that are deemed healthy, or adopt practices that will improve the health of a soil that is deemed less than healthy.
Composed by Larry G. Heatherly, Aug. 2022, larryh91746@gmail.com