TOPSOIL HORIZON

Usually darker colour due to good organic matter content; Has good worm and bacterial activity, drawing down organic matter and creating drainage holes; Zone of leaching and biological activity; Levels of nutrients are highest in this zone due to the breakdown of organic matter/minerals by micro-organisms (good aeration) and the addition of fertilizer to the topsoil by gardeners. As water moves down through the zone it leaches soluble nutrients and also tends to draw down the fine particles of clay and Humus into the subsoil. The presence of a good supply of organic matter aids the build-up of a good soil structure which in itself gives good pore spaces (Macro 0.06 mm up – good for drainage; Meso 0.06 mm down – good for holding onto capillary water; Micro holds water not available to plants) so the soil has a good balance of water retention/drainage. `

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