Magnesium is a component of several primary and secondary minerals in the soil, which are essentially insoluble, for agricultural considerations. These materials are the original sources of the soluble or available forms of Mg. Magnesium is also present in relatively soluble forms, and is found in ionic form (Mg++) adhered to the soil colloidal complex. The ionic form is considered to be available to crops.

Sources of Magnesium

  • Volcanic ashes
  • Weathering or rocks
  • Agriculture lime
  • Crop residues and organic manure especially farm yard manure.
  • Artificial fertilizers e.g. magnesium sulphate.

Importance of magnesium

  • It is necessary for chlorophyll formation.
  • Encourages formation of fats and influences transfer of phosphorus (phosphates) by enzymes reaction.
  • It is involved in the making and transfer of proteins and
  • Promotes growth of soil bacteria and the ability of legumes to fix nitrogen.

Ways through which magnesium may be lost in the soil

  • Through crop removal by oil plants
  • Leaching
  • Erosion

Deficiency symptoms of magnesium

  1. The parts between the veins become yellow as chlorophyll is removed but the veins remain green.
  2. Maize grains may show stripped leaves.
  3. The plants develop weak stems and long branches of roots.
  4. Development of purple orange and red patterns in crops e.g. Horticulture crops



Calcium is an alkaline metal of Group II A on the periodic chart and is the fifth most abundant element in the earth’s crust while being widely distributed in nature.  The electronic structure of the calcium cation makes it a unique element that is ideally suited to assist in plant growth.

Source of calcium

  • Agriculture lime and other artificial fertilizers e.g. CAN
  • Weathering rocks e.g. rock phosphate.
  • Crop residues and organic manures.
  • Wood ash and bone mill

Importance of calcium

  • It modifies soil PH and so encourages activities of soil organisms e.g. the nitrifying bacteria.
  • It essential for growth of meri stems, root hairs and root tips.
  • It affects meability o cell membrane and influences the transportation of sugar and proteins in plants especially in seeds and tubers.
  • It improves on plant vigiour and stiff noss of the stem.
  • It governs the availability of other essential nutrients like Boron, phosphorus and potassium.

Ways through which calcium can be lost form the soil.

  • Leaching
  • Erosion
  • Crop removal

Deffiency symptoms of calcium

  • Terminal buds and root tip development is restricted leading to standed growth and poor development
  • Weak stems
  • Chlorosis in leaves along margins of young leaves they roll up and eventually die.



It is widely accepted that the carbon content of soil is a major factor in its overall health. Soil carbon improves the physical properties of soil. It increases the cation-exchange capacity (CEC) and water-holding capacity of sandy soil, and it contributes to the structural stability of clay soils by helping to bind particles into aggregates. SOM, of which carbon is a major part, holds a great proportion of nutrients cations and trace elements that are of importance to plant growth. It prevents nutrient leaching, and is integral to the organic acids that make minerals available to plants. It also bufferssoil from strong changes in pH.

Sources of carbon

From the atmosphere as carbondioxide carbonate and hydrogen carbonates when carbonic acid from rain reacts with soil minerals.

Importance of carbon.

  1. All living things have carbon in them.
  2. It is essential in photosynthesis to make carbohydrates which are used by plants / animals to make energy.
  3. Provides energy to soil micro organisms

Loss of Carbon

  • Leaching
  • In sewerage system that end up in rivers.


Carbon can not be deficient since there is a continas supply of carbondioxide to the atmosphere as shown in the carbon cycle


Plants are able to take in carbondioxide through their leaves from the atmosphere during sunshine and manufacturer carbohydrates in a process called photosynthesis.


Plants also absorb carbonates and hydrogen carbonates from the soil and use it to build complex carbon compound e.g. the woody tissue.

When animals feed on plants, they take in carbon compounds and use them fore energy as well as building a body tissue.

As plants and animals carry out different metabolic processes they use carbohydrates for energy and respire to give out carbondioxide which returns to the atmosphere.

When plants and animals die and decay as wells as animals excreting they produce humus, some animals excrete may be lost into the sewage and eventually into the water bodies.

Soil micro organisms break down complex carbon compounds from plant and animals residues in the presence of oxygen to get energy for their body use.  In the process, carbondioxide is released and simpler carbon compounds combine with mineral slats from rocks to form carbonates and hydrogen carbonates that can be absorbed by plant roots.

When it rains, rain water can absorb some carbondioxide from the atmosphere to form carbonic acid. This can later be oxidized in the soil to form carbon compounds usable by plants.

During burning of plant and animal products, and also during industrial processes, carbondioxide is released into the atmosphere so that there is released into the atmosphere so that there is unlimited supply then the cycle continues.



Sources of hydrogen

Soil moisture. In association with other nutrients soil is always available.



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