Here I will give all the basic information on soil and how to improve your soil for gardening.
Soil Formation and Soil Horizons
Soil is formed by the erosion (breakdown by water and wind) of rocks and bedrock. The deposition of organic material increases the disintegration of the rock and allows an environment for microorganisms and plants to colonise the soil. This process continues until the soil can be distinguished into several layers (soil horizons) with different physical and chemical properties.
|General Soil Profile|
Keep in mind that the combination of horizons and their relative thickness varies between regions (even around the house). Each horizon is divided into more layers, where different processes contribute to the overall profile of the soil.
The topmost layer contains all the organic material (O-horizon) or humus, which is a dark brown complex organic component derived from the decomposition of plant and animal remains.
Humus improves the soil by:
ü Adding nutrients
ü Retains water
ü Improves mineral reservoirs
ü Reduces leaching
Nutrients, including clay, humus, minerals and water leach from horizon A to B (Subsoil). Leaching is a natural process whereby dissolved nutrients in the water moves into lower layers of the soil. Resulting in a greatly varying profile of horizon B and larger plants’ roots can reach into this layer. Leaching is good as it builds nutrient and water reservoirs in the soil for larger plants to access (for instance during drought when the top layers remain dry), but leaching can become a problem, diverting all nutrients away from plants during erosion.
The two lowest horizons (C and D) form part of the ‘parent material’ (calcium carbonate CaCO3 and magnesium carbonate MgCO3) of the soil. It is progressively breaking down into the top horizons of soil, due to the micro-organism, animal (worms, nematodes etc.) and plant root activity in the O-B horizons of the soil. Most of the mineral content (inorganic portion) of the soil is derived from these two horizons (C and D). There is no organic matter or plant roots within this area.
Interesting soil profiles
|Chernozem Soil Profile|
- Latosol -Another interesting soil system is that of tropical rain forests. Latosol soils have thick O, A and B-horizons due to the large amount of organic matter deposited into the soil from the forest leaf litter. The soil is maintained by the forest roots and their removal results in the breakdown of this system. Thus these soils are not suitable for agriculture.
- Podzol -
- Savannah -
Savannah grasslands have ferruginous (iron containing) soils. There is a thin organic layer followed by a hard cemented layer of laterite in the top part of the A-horizon. The laterite is formed by the leaching and capillary action of minerals between seasons. This is the type of soil I have, and it is ideal for grass cultivation for grazing, but not ideal for gardening. Later in the article I will provide the details on how I am slowly converting this red soil into a more vegetable friendly soil.
|Savannah Soil Profile|
The ideal soil is quite obvious in terms of its properties:
ü Retains water and does not dry out quickly
ü Contain a large amount of nutrients
ü Large air pockets for plant roots and soil organisms
ü Soil community (soil animals)
To identify this ideal soil, is to look for soil with the consistency and appearance of ground filter coffee you put in you filter coffee machine each morning J This means as gardeners, we need to work towards a Chernozem soil profile in our vegetable beds, which is the ideal soil type for growing vegetables and fruits.
My Sad Soil Story…J
Then we got compost to just kick-start the process. The problem was that the commercially produced compost contained high amounts of manure that was not properly decomposed. Only after planting I realised this as some plants got chemical burn (browning and die-back of large parts of the plant). The lettuces were first to signal this, starting to die within 2-3 hours. We dug the compost in well with the red soil in a 40:60 (compost: soil), which prevented further chemical burn.
The best soil status ‘indicators’ are your root vegetables, such as beet and carrots. Mine had a lot of roots (hairy appearance) and almost no carrot or beet set. This indicated the huge lack of potassium in my garden. So we searched for cheap yet ‘bio-available’ potassium to add to the soil. After some research we came upon good ol’ wood ash. We burned a whole lot of acacia branches (so basically untreated, raw wood) that were dried and not in use and had a braai (barbecue) at the same time J. Then I had 7L of wood ash and another bucket full of burned wood pieces. I added this each time I planted new vegies, and now I am getting lovely big and sweet carrots and beets (no more hairs J). - Sprinkling the ash in top of the soil before watering and burying the bigger pieces around the veg roots.
It took a year of working in kitchen waste, adding wormery-liquid fertiliser and wood ash to the soil to get healthy and happily producing veggies. So that is basically my strategy for soil maintenance and it is easy and inexpensive way to improve what you have instead of buying large amounts of compost (that would essentially be cheaper to buy the veggies from the market than plant in the expensive soil J) and working my way to establishing a Chernozem type soil in my garden J.
- Update 2013 -
We started some home composting, basically dug a big hole into the soil and add your garden/kitchen waste. We don't follow any specific strategy such as 'hot or cold' composting, it gets turned when we have time and the chickens scratch through it every day. Adding about a year's worth of compost to your soil (about 3-5 wheelbarrows) gives it a good kick. Matured home made compost is super high in nutrients and helps a tremendous amount with the overall soil structure- the chickens keep it clean from critters, but unfortunately due to it not going through 'hot composting' we do get weeds.
Green manures are very good to incorporate into your soil rehabilitation program as well (especially during the winter months here in SA when most of the garden remains unused). Green manures grow and break up the hard soil structure and add nutrients to the soil while they grow. Afterwards the plants themselves are added to the soil to provide additional nutrients and organic matter. Please refer to the links below for details on each method of soil rehabilitation.
Good soil is essential for plant health, resistance and production, please refer to Composting (including Instant Compost), Vermicomposting, Green Manure and Comfrey for some hints and tips on adding nutrients to your soil from your kitchen.
|Home made compost|
|Cover-crops & Green forage|
|Comfrey: Organic fertiliser|
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