Soil Analysis Methods used in the USA: a summary
“To be a successful farmer one must first know the nature of the soil.”– Leonardo da Vinci
Albrecht/Base Cation Saturation Ratio
All the farms (organic) that I visited in New York, Pennsylvania and Wisconsin are using Albrecht analysis, although it is reported that organic farms in California use different analysis. Albrecht analysis is provided by a number of laboratories, the best known being Mid West Laboratories. https://www.midwestlabs.com/test/s3c-soil-testing-package-agriculture/
For a cost of $25.50 their S3C Package includes:
Organic Matter, Available Phosphorus (P1 Weak Bray and P2 Strong Bray), Exchangeable Potassium, Magnesium, Calcium and Hydrogen, Soil pH, Buffer Index, Cation Exchange Capacity, Percent Base Saturation of Cations Sodium, Nitrate Nitrogen, Sulphur, Zinc, Manganese, Iron, Copper, and Boron.
There is a useful interpretation guide here https://www.midwestlabs.com/resource/interpreting-soil-analysis
As in the UK, where Rothamsted soil scientists have roundly dismissed the science behind it, Albrecht analysis is not generally supported by the establishment soil scientists in the US; most of the criticism stems from the emphasis put on cation ratios i.e. the ratio between Calcium, Potassium and Magnesium. See the following for more information: https://www.sare.org/Learning-Center/Books/Building-Soils-for-Better-Crops-3rd-Edition/Text-Version/Getting-the-Most-From-Routine-Soil-Tests/The-Basic-Cation-Saturation-Ratio-System
What I found was that advisers and farmers enthusiastically supported Albrecht analysis; they tended to place much less emphasis on ratios than the critics claimed and it seems that the real value of the analysis lies in the fact that a wide range of elements is analysed, including trace elements, there is some assessment of the reserves as well as available forms of phosphate and the fact that organic matter is included.
Tim Reinbott of Minnesota University has finally started to challenge the critics with some very useful field scale research and answer the question whether Albrecht analysis and management works, or not. Replicated medium term trials have clearly shown that it does.
Soil Health Analysis
There is now widespread interest in "soil health" assessment amongst farmers, advisers and academics, however I only met one farmer who is using such a service, and then primarily as a check every few years or to help diagnose a field which has problems. It is not being use on a routine basis.
The analysis undertaken varies between labs; it generally includes the Solvita carbon dioxide burst (respiration) test, organic matter and in some cases the Active Carbon test using potassium permanganate. A Soil Health service is offered by
Cornell https://soilhealth.cals.cornell.edu/testing-services/comprehensive-soil-health-assessment/ I have reported in more detail elsewhere on the Cornell service.
Woodsend https://woodsend.org/wp-content/uploads/2017/09/Soil-Health-Quick-Guide.pdf
The Haney Soil Health test is also a soil health analysis which includes the Solvita respiration carbon dioxide burst as an indication of microbial activity, available nitrogen, phosphorus and potassium, water extractable carbon, C:N ration and aluminium, iron, calcium, sodium and magnesium. It is offered by a number of labs.
Standard Analysis
While none of the commercial farms that I visited used a standard analysis, as used by conventional farms, it is reported from California that many farmers are in fact using a standard analysis, as indeed is Rodale on their commercial farm and in the Farming Systems Trial.
Cornell offers a service which seems to be widely used, http://css.cornell.edu/cnal-forms/CNAL-S-tests.pdf
including a much wider range of nutrients than is typical for the UK:
Cornell Soil Fertility Test Package [Modified Morgan, Mehlich I, or Mehlich III extractable) Includes: Al , As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sr, Zn, pH, buffer pH (Modified Mehlich) and organic matter. Cost is $25
Soil Biology analysis
It is of course apparent to everyone working with organic and biological systems that analysis of the soil chemical content, or minerals, is only half the story, probably not even that. Our reliance on making nutrients more available through biological solubilisation, the importance of mycorrhiza for accessing nutrients and the role of free living and rhizobial nitrogen fixing bacteria all mean that soil biological activity is central. And that is apart from the role of larger creatures including earthworms and insects in soil processing.
The fact that we have no reliable means of assessing biological activity, let alone know how to manage it predictably has always been a fundamental gap in our ability to manage soils more effectively.
I have in the past experimented with the Soil Food Web service offered by Elaine Ingham, and briefly by Laverstock Park, and travelled to Oregon to discuss it in more detail. At that time there was evidence to support the technique of counting fungal and bacterial populations but little to demonstrate that the highly variable populations and relative numbers were useful in informing soil management in field cropping conditions.
Science has moved on and now there are reliable gene screening methods that allow rapid analysis of the whole soil genome.
Poornima Parameswaran’s Trace Genomics company https://www.tracegenomics.com/#/products is a new lab in San Francisco offering a unique service over the last two and half years.
By using DNA analysis it is possible to assess the soil microbial species, populations and level of activity, providing the following principle information:
Identification of plant pathogens such as nematodes and fusarium which can be used to decide whether to grow a certain crop or whether remedial action is needed, such as use of bio-fumigants.
Soil biological metrics, which can be used to identify the cause of poor areas in a field and to guide future management. It includes bacterial and fungal diversity, fungal to bacterial ratio, aerobicity, plant growth promoting bacteria, arbuscular mycorrhiza, and the root disease suppressiveness of the soil. Further detailed analysis provides information on the ability of microbial action to improve nutrient availability; nitrogen, phosphorus, and potassium and the availability of labile carbon, which serves as both food for the microbes cycling nutrients, and a source of the nutrients.
Trace Genomics do not do mineral analysis but their analysis of soil biology and function is expected to be used in conjunction with mineral analysis. The service is relatively expensive at $199 for pathogen analysis and $349 for the Health test, which includes fungi, bacteria and pathogen analysis, but it is a quite different service to that provided by other labs offering soil health analysis.