Soil is a heterogeneous mix of water, minerals and
anorganic particles (by size)
- Rocks break down and wash away very slowly, improve drainage and aeration, disturb the growth of root vegetables
- Sand breaks down very slowly and wash away slowly, improves drainage and aeration
- Silt breaks down slowly washes away and is blown away by wind easily, fair to good drainage and aeration
- Clay microscopical particles in suspension, sticky, bad drainage and aeration, nutrient rich
- Decomposing material dead plant and animal matter, manures
- Living organic matter soil bacteria and fungi, worms, nematodes and other soil dwelling animals
The content of organic matter in the soil strongly changes the soils properties.
It improves aeration, has an effect on soil acidity, improves drainage and water retention, keeps nutrients in the soil offers the necessary environment for soil bacteria and fungi that plants need to grow in symbiosis with.
The layer of undecomposed and decomposed organic material on the soil is called the humus layer, it is this layer and the next 5 cm of soil, where the maximum of biological activity and leaching of nutrients can be found. In the next 20 cm we find the maximum of chemical accumulation.
In a natural environment organic matter is constantly fed back to the soil by dying plants and animals that decompose and become compost. In our gardens we take produce out of the system and need to ‘pay’ organic matter back. We can do this by adding
- grass clippings
- leaf litter
- worm castings and -juice
- coconut coir
small amounts of ash
- rotten mushroom compost and well rotten cow or sheep manure is also great, but be aware that this is also a nitrogen rich fertiliser, so don’t go over the top with this
the most fertile soil
The most fertile soil in the world is called loess. Loess shows a loamy texture and is composed of about 20% clay, and 40% each of sand and silt intermixed with some chalk. Only 10% of the earth’s surface is covered with loess. But even loess is only really fertile if covered in a thick humus layer.