When incorporated into a soil, compost acts as a soil amendment. When applied to the soil surface and not incorporated, it serves as a mulch. In their soil amendment role, composts improve fertility and tilth, while as mulches they can reduce erosion, conserve water, control weeds, and manage pests.
Before you can evaluate the suitability of a compost for a particular application, you need to have an understanding of several compost properties—which differ significantly from soil qualities you may be familiar with. Parameters such as carbon-to-nitrogen (C:N) ratio, organic matter content, salinity, total nitrogen, total phosphorus, stability, phytotoxicity, pH, maturity, boron, chloride, sodium, particle sizes, heavy metal concentration, and pathogen concentrations are factors to evaluate when you are comparing available compost products.
This publication describes each of these measures and proposes reasonable limits for five common types of compost application.
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