One of the first steps in improving problem soils such as sands and heavy clays is to mix in plenty of organic matter and thus build up the population of microorganisms. Whether this applied material is compost, rotted manure, spent mushroom manure or dried sheep manure bought in bags from the garden center, it will help "seed"
the soil with essential bacteria at the same time that it creates an environment in which they can thrive.
Organic matter is the "intermediary" that keeps all soil functions in harmony. It is made up of dead plant and animal tissues (plus minerals), and provides, in turn, the essential environment for the growth of plants that give food and pleasure to man. The ideal soil, "Gardener's Loam," is basically one that is high in organic content. The processes involved in the production of humus are complex, but the gardener's chief concern is with how to use the humus.