What is soil made of?
I didn't know much about what soil is made of until doing a Permaculture Design Course.
Most of the information below comes from my PDC handbook, so must be credited to Hazel Mugford and Avice Hindmarch (the PDC facilitators).
So, what is soil made of? Soil consists of small pieces of rock, air, water, and organic material (matter from dead plants and animals).
Soil is formed slowly as rock erodes into tiny pieces near the Earth's surface. The organic matter decays and mixes with inorganic material (rock particles, minerals and water) to form soil.
Plants help the development of soil by attracting animals, and when the animals die, their bodies decay, making the soil thicker and richer than before. The process continues until soil is fully formed, and can then support a wide diversity of plants.
The wonder that is humus
Humus soil is the dark organic material which is formed by the decomposition of plant and animal matter. Humus helps soil to hold water for longer, and water provides the means for plants to absorb nutrients.
Soil organisms also require humus for their own existence and will either die or migrate if humus levels are too low. What’s more, they also contribute to humus when they die.
Humus creates soils that can deal with erosion more effectively as porous soils will not lose precious topsoil due to water runoff.
Meanwhile, mulch can also be used to protect soil surfaces from erosion by wind and water, and protect plants from damage by rain splash.
Humus and mulch act as buffers to plants in adverse conditions, be it drought, heat, cold or water-logging. In turn, mulch suppresses weed growth, allowing plants to grow without competition.
The presence of humus in soils, and mulch on soils, regulates soil temp and allow for strong surface root formation. And lastly, humus can transform acid and alkaline soils so nutrients can be made available to plants. Isn’t humus wonderful?
All about crumbs
Organic matter also preserves soil structures together to form crumbs, which contain larger pores and channels where water and air can move freely or be stored. This creates a living space for plant roots (allowing roots to penetrate easily!).
Earthworms, microbes and fungi play an important role in producing the glues to hold soil particles together to make them resistant to wind and water erosion. When we dig or plough, we expose soil organisms to sun and air, culminating in their death.
The process begins with the destruction of the crumb structure, which causes the soil to compact, making it difficult for plants and organisms to function in these less aerated conditions. So the soil deteriorates, losing structure, animals and nutrients.
Healthy soil strategies
• Don’t dig as this creates aeration and disrupts life of soil
• Use mulch (it supplies organic matter for micro-organisms and moderates climate, humidity and temp)
• Never work clay soils while wet
• Leave areas of native vegetation as these will host the native species of bacteria, fungi and Mycorrhiza
• Use deep-rooted plants to mine and recycle nutrients leached into the subsoil layers
• Use green manures and cover crops to always keep the soil protected from erosion and to supply organic material
• Learn to work with the weeds present. Generally the native weed is the plant most adapted to that environment, those soil conditions; it is there to protect the soil and is the ideal species to correct any mineral or nutrient deficiencies
• Don’t over-fertilise. Even organic fertilisers can be overdone and cause nitrate poisoning
• Don’t overdo the use of legumes. Copy strategies used in your area, they are mostly pioneer phase and seldom in climax stage. When making changes (adding lime, rock dust etc.) use frequent small additions to avoid dramatic changes in the habitat of the bacteria, fungi and other organisms
• If watering, use deep soaks rather than shallow spurts
Simple soil testing
My PDC notes came in handy here! The following test is a simple, yet effective way to identify soil by its texture. Take a small portion (2 teaspoon full) and moisten, knead and roll it into the palm of the hand:
- If no ball can be rolled (or just rolled) – sand
- If a sausage can just be rolled – loamy sand
- If the sausage can be slightly bent – sandy loam
- If the sausage can be bent almost half-way round – sandy clay loam
- If the sausage can be bent more than half way round – sandy clay
- If the sausage forms a ring – clay
Another even simpler method comprises taking a small soil sample, moistening it and kneading it till it just marks the back of your hand.
- Feel texture: clay is sticky, silt is silky and sand is gritty
- Taste a small piece: acid is sour, alkaline is soapy
- Form a ribbon through the palm and thumb, the longer the ribbon before breaking, the more clay, 50 mm = 30 % clay
Loamy soil has a higher pH and calcium content because of previous organic matter. The perfect substrate consists of 20% sandy to loamy with some clay. However, soil without calcium becomes acidic, killing soil. The best way to change acidic soil is through creating humus to introduce calcium.
One can also buy a pH kit to test your soil’s acidity/alkalinity. It’s also possible to identify what a soil is like through what plants grow there, for instance, fynbos means that soil is usually very acid.
Use a pH test kit to test samples for various spots and various depths. If the ph is near 7 leave it to nature to do the work. If pH is very low add lime/dolomite/chalk in small amounts over a few years.
If pH is very high (rare in humid areas) add organic material, copper sulphate, sulphur, urine or bone.
Organic material (humus) helps moisture/air penetration, moisture retention and improves structure, especially in sandy to silt soils.
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