Dr. Michelle M. Wander, University of Illinois
Some content and the structure of the article is based on the consensus about indicators compiled by the North Central Regional Committee (59) on Soil Organic Matter: Formation, Function and Management. Members of the committee will play an ongoing role in the update of information.
Organic management focuses on soil management with the intent to maintain and enhance soil biological activity. There are a variety of ways that biological activity is measured in soils. Few, if any, of these measures are used routinely to test soils in the way that standard chemical assays are used. The various methods of assessing soil biology and biological activity differ in their accuracy, difficulty, and suitability for use. The following table is a summary of measures prepared by the Soil Organic Matter, Formation, Function and Management Committee (NCERA-59) describing the characteristics of widely used measures.
|Soil Respiration Rate (CO2 efflux)||Microbial community||Microbial community||Microbial Biomass|
|What's measured||Proxy for decay rates; can include root respiration when done in field||Phospholipids in cell membranes||Physiological profiles; BIOLOG plates or other assays that measure increased decay after substrate addition||C and N released by fumigation and determined after extraction or through incubation|
|Sensitivity||High, maybe too high||High||Low to medium||Medium|
|Expertise of user||Medium||Very high||Runs low||Low to medium|
|Cost||Variable||Very high||Medium to low||High|
|Difficulty||Low||Very high||Low to medium||Low to medium|
|Special equipment requirements||Variable||Yes||No||Some, variable|
|Accepted interpretation for soil test application||No||No||When used to identify specific organisms grown in pure culture||As a proportion of total soil organic matter or indicator of response to management|
|Scope and/or relevance|| |
Low unless done at high spatial and temporal resolution and with appropriate controls
Microbial community composition, mostly for research applications
Use in lab is basis for Solvita® soil test
Metabolic diversity research application
Biomarkers for broad functional groups, e.g., fungi, bacteria, gram+ and gram- bacteria, actinomycetes, protozoa
Used for bacterial id by BBC lab
Used by some alternative testing labs
High variability in-the-field; seasonal, spatial variability
Useful for controlled incubations
Repeatable; seasonal and spatial variability
Used for compost tea and compost assays
|Useful for treatment comparisons and assessing influence of management on function||Useful for treatment comparisons and possibly to set a benchmark as a proportion of SOC|
|Bacterial/Fungal ratios (B/F)||Mycorrhizae||Microbial abundance||Nematodes|
|What's measured||Direct counts of active or total biomass using staining and microscopy||Plant associated fungi that assist with nutrient and water uptake||Direct counts of bacteria and fungi grown on media||abundance, diversity, and/or community structure|
|Sensitivity||Low||High||Low||High, functional level types|
|Expertise of user||High||Medium to high||Low||High for speciation|
|Cost||Medium to high; labor-intensive||Medium||Labor costs high||Labor costs medium|
|Requires special equipment||Microscope||Microscope||Colony counter||Microscope|
|Accepted interpretation for soil test application||No; there is considerable interest in developing F/B ratios as an index but weaknesses in the method make many sceptical about its utility||Some||High||High; food web integrator; reflects nutrient enrichment|
|Scope and/or relevance|| |
Proposed as an index of disturbance and nutrient enrichment; inconsistency in methods has made some conclude that the method has little-to-no practical relevance
Used by Soil Foodweb, Inc.
|BBC Labs offers 3 commercial tests: root colonization, spore enumeration, and infectivity potential||Limited; used by some testing labs for fungi||Now offered by Soil Foodweb, Inc.|
Limited agreement between this method and other techniques is problematic
Popular interest reflects the importance of this conceptualization
|Varies with season and cropping phase||High variability||Seasonally variable|
|Earthworms||Cellulose decomposition, paper disk||Cotton strip or buried bag||Smell|
|What's measured||Abundance and diversity||Mass loss||fiber strength||subjective|
|Sensitivity||High||Very high||Very high||High|
|Expertise of user||High for speciation, low for total numbers||None||None||None|
|Cost||Labor costs medium||Low||Low||Low|
|Requires special equipment||No||No||No||No|
|Accepted interpretation for soil test application||Low||Low|
|Scope and/or relevance||Useful for demonstration purposes|
|Other||Sensitive to environment|
|Expertise of user||Need technical experience|
|Requires special equipment||Spectrometer|
|Accepted interpretation for soil test application||Not yet; needs correlating with other properties||Biological activity index||Not yet; needs correlating with other properties|
|Scope and/or relevance||General||General||General||General; must use fresh soil samples||General; P cycle||General; S cycle||General; urea fertilizer use negates results||General|
|Other||Best enzyme for index; low coefficient of variability (CV)||Moderate CV||Moderate to low CV||Higher CV||Low CV||Low CV||Moderate CV||Moderate CV|
References and Citations
- Microbiological identification [Online]. BBC Laboratories. Available at: http://www.bbclabs.com/english/mic_id.html (10 March 2010).
- Mycorrhizae (VAM or AMF) [Online]. BBC Laboratories. Available at: http://www.bbclabs.com/english/mycorrhizae.html (10 March 2010).
- Soil Foodweb, Inc. [Online]. Available at: http://www.soilfoodweb.com/ (10 March 2010).
- Soil Organic Matter, Formation, Function and Management. North Central Research and Extension Committee 59 (NCERA-59). (Available online at: http://www.nimss.org/lgu_v2/homepages/outline.cfm?trackID=13316) (verified 8 Nov 2015).
- Solvita®: Respiration Test for Soil [Online]. Woods End Laboratories, Inc. Available at: https://solvita.com/soil/ (verified 16 May 2019).