It is essential to amend the soil in many parts of Africa where there are the following soil types:
black cotton soil
These soils have too much clay and/or have little organic humus resulting in:
poor growth and low crop yields
poor water retention or flooding
root destruction when soil is dry
With no winters to destroy unwanted pests and diseases, soil bound insects will eat the roots
of western vegetables and multiply unchecked and attack the valuable crop.
This can be solved by mixing different types of earth using clay, sandy and silty soils and then steam cleaning the mixture.
Mixing can be done by hand or mixer (photo - top)
The picture below shows the steamer and a liquid fertilizer distiller with a compost chamber in the rear.
showing: the Mixing and Steaming of Soils
showing: the Production of Liquid Fertilizer
Like macronutrients, micronutrients or trace elements are essential for plant growth, but they are needed in much smaller quantities.
There are eight micronutrients which are mostly metallic or semi-metallic elements that plants obtain from the soil.
These micronutrients are mainly from weathering of parent rock materials, but small amounts are added from organic materials such as manure.
Iron is essential for the synthesis of chlorophyll, so a deficiency causes yellowing between leaf veins.
It’s rare for soils to be lacking iron, but plants may be unable to absorb it in alkaline soils and soils with high
levels of available phosphorus, manganese and zinc.
Boron is important for strengthening plant cell walls, and strongly affects plant metabolism and fruiting.
Boron deficiency is one of the most common micronutrient deficiencies with symptoms including stunting, dying growing tips,
and lack of fruit set. Boron is mostly present in soil in a soluble form which is prone to leaching; this means sandy soils
are prone to boron deficiency.
Chlorine is the only non-metallic or semi-metallic micronutrient, and the most recent to be discovered.
It is important in photosynthesis and regulating internal moisture by opening and closing gas exchange pores (stomata).
Chlorine occurs in the soil as negatively charged ions, which like boron and molybdenum is prone to leaching. Deficiency
symptoms include wilting due to a stunted root system. In brassicas, lack of chlorine causes an absence of the distinctive
cabbage smell – the reason is a mystery.
Manganese is another metallic element essential for photosynthesis, and deficiency symptoms are similar to iron.
It can be distinguished from iron deficiency as younger leaves are affected first since manganese is not mobile in the plant and
cannot be moved from older to younger parts. Like many micronutrients, manganese availability is related to soil pH and iron content.
Zinc is essential for DNA replication and is the most common plant micronutrient deficiency.
Almost half the world’s cereal crops are grown on zinc-deficient soils - resulting in loss of yield and
widespread zinc deficiency in humans. Plant zinc deficiency symptoms include yellowing and stunting of the
leaves (‘little leaf’).
Copper is required for photosynthesis, metabolism and strengthening plant cell walls. Deficiency
symptoms include yellowing leaves and dying growing tips. Like iron and manganese, the availability of copper
to plants depends on soil pH. Copper is also more difficult for plants to take up when phosphorus and iron soil
levels are high.
Molybdenum is involved in nitrogen metabolism, and a shortage causes nitrate to build up in plant
tissues, resulting in yellowing. Molybdenum is also essential for nitrogen fixation in legume root nodules, so a
deficiency in these plants causes nitrogen deficiency. Unlike most micronutrients, molybdenum is easier for plants
to absorb from alkaline than acid soils.
Nickel is also involved in nitrogen metabolism. Specifically, it is essential for the enzyme that converts
urea from animal waste into non-toxic forms of nitrogen which plants can use. Nickel deficiency causes a build-up of urea
in plants leading to yellowing and death of leaf tips.
Reading through this section, you may have noticed that many micronutrients are influenced by the pH and concentration
of other nutrients in the soil. This is explored further in the next step.