PPT Slide
The breakdown of organic residues produces long-chain polysaccharides that are gummy and bind soil particles into stable aggregates. Aggregation is also promoted by networks of hyphal strands from fungi growing through the soil and the action of plant roots. Aggregation and the activity of earthworms, burrowing insects, and plant roots produce channels that improve water infiltration, aeration, and drainage. In sandy soils that are excessively drained, organic matter can increase soil water-holding capacity. Breakdown of organic matter releases essential nutrients for plant uptake, and assimilation of nutrients by microbes and other soil organisms retains them from leaching for future release and uptake. Organic matter provides buffering of soil pH and retention of nutrients through its contribution to cation exchange capacity. Plentiful organic matter provides an abundant food and energy source for soil organisms, and the resulting biological diversity and competition can significantly suppress some plant pests.