Testing “Gray Area” Materials

Is it a soil? Is it a growing media? Is it a manure? Is it a compost? Is it a fertilizer?

Requests to analyze uncommon materials that cannot be completely classified as one of the above categories is becoming increasingly common. Some of these materials are industrial biproducts looking for a beneficial reuse. Some materials are novel products proposed to be used as “soil amendments”. Others are being evaluated to be a feedstock for composting or a component of a soilless or greenhouse media. To choose the correct testing methods, you need to be able answer a couple of questions about the material. What are your trying to learn about this product? How is this product intended to be used? Are there any regulatory testing requirements? If you can answer these questions, the following summarization of the different testing methods should help to select the appropriate analytical methods.

Soil testing methods for nutrients are done using different extracting solutions to estimate the fraction of the nutrients that are available or soon will be available for plant uptake to make fertilizer recommendations. These methods do not give any information about the total nutrient content and are generally intended to be used on soils that have not been heavily altered with other non-soil materials.

Growing media nutrient analysis is done through a process called a saturated media extraction. This process uses deionized water to extract the fraction of nutrients that a growing plant has immediate access to utilize. These methods are intended for materials with little or no natural soil in them and will be used to grow plants in directly.

Manure testing methods use a complete digestion to measure the total nutrient content of the material. Using the moisture content of the material, the nutrient levels can easily be converted into units of pounds per ton or pounds per 1000 gallons which is useful for calculating appropriate application rates. In addition to animal wastes, these methods can be utilized on many other materials that are being land applied for disposal.

Compost testing methods will produce very similar results to manure testing but are done using slightly different methods that are approved by the U.S. Composting Council. These methods are intended finished compost products that will be sold commercially. However, if a material is being evaluated as a potential feedstock for composting, it should also be analyzed using compost methods to allow for equal comparison to the final product.

Fertilizer testing utilizes many different methods depending on what nutrients or other components are requested. These methods are very accurate and intended to be used for products that require a Guaranteed Analysis for the sale of a product based on its nutrient content. Also, if a product is being tested as a potential liming material, it should be analyzed using fertilizer methods.

Please be aware that materials being tested as a beneficial reuse of a waste product, a liming material, or a fertilizer may fall under different state regulations and require additional testing such as heavy metals that are not included in ALGL’s routine test packages. If you have any questions regarding proper testing of a “gray area” material, contact your ALGL representative.


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