Unspecified Composting Parameters

NOTE: These narratives that provide a detailed description of the parameter, the rationale for its inclusion, specific test methods, and other information.

Unspecified parameters are compost parameters not classified as quantitative or qualitative parameters because of the inability to measure them by industry standard test methods. These parameters are important and should be included at a future date.

Growth Screening: The growth screening test is an indicator of the presence of phytotoxic substances, including volatile fatty acids, alcohol, soluble salts, heavy metals, or ammonia. These substances may cause delayed seed germination, seed or seedling damage or death, or plant damage or death. The growth-screening test is not intended to identify which of the growth inhibitors is the specific cause of poor growth response. Growth screening tests include germination, root elongation, and pot tests. It is important to note that product which passes initial growth screening tests may fail later if improperly stored. Specific growth inhibitors, such as volatile fatty acids and alcohol, may form in compost stored in anaerobic conditions.

Stability: Stability is a measure of the level of biological activity in compost under a given set of conditions. Unstable compost consumes nitrogen and oxygen in significant quantities to support biologic activity and generates heat, CO₂, and water vapor, but stable compost consumes almost no nitrogen and oxygen and generates almost no CO₂ or heat. Unstable compost demands nitrogen when applied to soil and growing media. It can cause nitrogen deficiency and be detrimental to plant growth, even causing death to plants in some cases. If stored, and left unaerated, unstable compost can become anaerobic and give rise to nuisance odors.

Until industry standards are developed, we recommend that the aforementioned test methods be used for process control and as a means to qualify these parameters. However, a great need exists to standardize test methods for maturity and stability, as well as developing industry standard definitions for the terms. Only then can a full and measurable understanding of their effects on specific crops be developed. We believe that this is a vital issue that must be addressed by the composting industry with greater vigor.