Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/12/2005
Publication Date: 4/12/2005
Citation: Millner, P.D. 2005. Bio-based Plant Nutrients: Stability, Maturity, and Microbial Activity. Compost Science and Utilization. In: Reynnells, R. (Ed). Proc. Bio-based Plant Nutrient Products: Quality Assurance, Marketing, and Regulations, Conference, Oct. 31, 2004, Seattle, Washington. USDA, CSREES, PAS, Washington, D.C. 162. pp. 48-53.
Interpretive Summary: This report presents a current overview and evaluation of testing and assay approaches used to determine the stability and maturity of bio-based plant nutrient products. Several approaches and multiple technical options are currently available to assess the stability and maturity of composts. Those that address stability involve some measure of respirometry relative to some characteristic of the organic carbon content. In some cases, organic carbon is detected simply with by scaling a colorimetric change in dye-impregnated gel incubated in a closed chamber with the compost. In other cases, determination of carbon may require more extensive extractions and measurements. Other measures of stability rely on reheat potential without directly measuring gases, but using temperature rise as the indicator of residual microbial activity driven by consumption of available carbon. Maturity is based on some form of whole plant response, either germination or root elongation, to detect the presence of phytotoxins. This may require several days, so techniques that can reduce the time required for these evaluations are desirable. Both the stability and maturity tests are unique to bio-based plant nutrients and would not be applicable to mineral-based plant fertilizers because they are designed to measure the biological/biochemical attributes and properties of bio-based products. The development of new techniques, tests, and protocols for standardized measurement of stability and maturity is expected to continue to evolve until the cost and time per unit analysis reaches a point that allows compost producers to integrate the sampling and analysis frequency to a level that provides sufficient but not excessive information to guide the composting process to desired and targeted endpoint quality. Similarities and distinctions among test approaches as they have evolved currently are highlighted. Need for validation, precision and accurancy, and quality controls are noted. This information will help inform compost producers, customers, and private and public compost testing laboratories, state officials who deal with compost, solid waste recycling, and soil amendment and fertilizers rules, scientists, and environmentalists in gaining a contemporary perspective of the state-of-the-knowledge of tests and their use in determining stability and maturity attributes of organic residuals used in agriculture and horticulture.
Technical Abstract: The primary feature distinguishing bio-based plant nutrient products from strictly mineral-based counterparts is their complex carbon composition. This carbon basis and its inherent biological and biochemical components, which include either intact microbes or their by-products, i.e., enzymes and metabolites, impart unique properties and characteristics that make these products more than an assemblage of strictly physical and chemical components. These same biological and biochemical properties vary widely in accordance with the type and range of biodegradable materials and process characteristics This report highlights the relevant terminology, principles, factors, and tests for stability and maturity. In addition, this report describes why such data and information are essential for producers, growers, and regulators to use in production and quality control and assurance programs.