Soil Composition

Soil is formed by the gradual breaking up of rock into small pieces. It consists of soil particles, organic matter of humus, water , air , mineral salts and soil organisms

Soil particles : these are the products of weathering. They form a basic Skeletal structure with uneven pore spaces. Their sizes and chemical nature largely determine the properties of soil.

Humus : The decomposition of plant and animal remains form a layer of black, jelly like organic material called humus on the top is the soil. This is drawn into the soil by soil organisms like the earth worm. Decomposers continuously break down humus to release inorganic substances such as nitrates and phosphate, and so enrich the  soil nutrient content.

    Humus darkens, as well as , increases the water retaining ability of the soil. It also  improves soil structure as it helps to stick soil particles together in crumbs, hence increasing the pore spaces. Thus humans, a good crumb structure helps to keep the soil well drained and aerated.

Water :  Soil water contains mineral salts dissolved in it. It is usually restricted to  thin film around the soil particles or crumbs. Some types of soil can hold more water than others, I.e. they have a higher water retaining capacity. When soil contains too much water, they are said to be water logged. Certain soils allow water to drain through them more quickly than others, i.e. their porosity is greater.

• Air : Soil usually contains air in the pores spaces. Plant roots and soil organisms take in the oxygen from this air for cellular respiration. Nitrogen in the air is used by the bacteria in the root nodules of legumes to produce nitrogenous compounds. A good crumb structure is essential for the circulation of soil air. Water logged soils are poorly aerated as the pore spaces are filled with water.

• Mineral salts : These include salts of potassium, iron, magnesium, phosphates, sulphates and nitrates. They are present in solution in soil water. They come from the soil particles and form the break down of dead organic matter by decomposers in the soil. Mineral salts are absorbed By the roots of plants and used to build up cell material.

Soil organisms : These include organisms such as termites and earthworms. They improve the circulation of air In the soil by their tunneling activities. Decomposers like bacteria and fungi break down dead organic matter to form humus and soluble inorganic salts. These processes in crease the nutrient content of soil, thus improving its fertility.