main zone of planty growth`
Topsoil is the outermost layer of soil, varying in depth. It has the highest concentration of organic matter and micro-organisms and is where most of the earth’s biological soil activity occurs. Plants generally concentrate their roots in and obtain most of their nutrients from this layer. The actual depth of the topsoil layer can be measured as the depth from the surface to the first densely packed soil layer known as the subsoil.
Soil is made up of: Partials 45% (sands, silts and clay partials); Humus/organic matter 5%; Air 20/30%; Water 20/30%. In the air and water you have the living zone.
For the growth of plants its properties are:
Nature according to its texture (read notes on texture);
Has a good structure ( notes on soil structure);
Good levels of organic matter creating soil structure, providing nutrients and holding moisture;
A natural openness giving a balance of air and water;
Good supply of plant nutrients (clay particles have a buffering effect, i.e., hold onto molecules of plant foods by a chemical reaction);
Stable structure to anchor roots;
Good biological activity, bacteria to worms and moles all contributing to soil structure, nutrition and aeration.