Compost Microbiology and the Soil Food Web (1)

Introduction

Compost is the product of an aerobic* process during which microorganisms* decompose organic matter into a stable amendment for improving soil quality and fertility. During composting, microorganisms use the organic matter as a food source, producing heat, carbon dioxide, water vapor, and humus* as a result of their furious growth and activity. When applied to and mixed into the soil, humus can promote good soil structure, improve water- and nutrient-holding capacity, and help to control erosion. Humus makes up approximately 60 percent of finished compost.

A wide range of organic materials such as yard trimmings, manures, and food processing discards go into producing composts. Materials used to feed compost microorganisms are referred to as compost feedstocks.*

Part I of this fact sheet addresses the composting process and associated microorganisms. Part II then addresses how compost contributes to the soil food web and overall plant health.