This document discusses humus, which refers to the stable fraction of soil organic matter that results from the decomposition of plant and animal materials. It defines humus and distinguishes it from total organic matter. Humus is composed of humic substances like fulvic acids, humic acids, and humin. The document outlines the key properties and benefits of humus, including its impact on soil structure, aeration, water retention, buffering capacity and support of biological life. It emphasizes the importance of maintaining or increasing humus levels through practices like adding organic matter, using low-till practices, and growing cover crops.