Soil is the mixture of minerals, organic matter, gases, liquids, and the countless organisms that together support life on Earth. Soil composition is an important aspect of nutrient management. While soil minerals and organic matter hold and store nutrients, soil water is what readily provides nutrients for plant uptake. Soil air, too, plays an integral role since many of the microorganisms that live in the soil need air to undergo the biological processes that release additional nutrients into the soil. Soil is composed of both organic and inorganic matter, and it is essential for life on earth to exist.

soil composition

 Soil is composed of:

Mineral Particles: Mineral particles are the largest ingredient and make up approx 45% of soils . They are the original rock that got broken down by weathering and erosion to form the basis of soil. The type of rock that was broken down to form it is called the parent rock. The broken down rock produces minerals such as calcium, phosphorus, and potassium in the soil on which the plants feed. The parent material influences the soil color, depth, texture and pH value.

Organic Matter: Organic matter is decayed vegetation that is broken down by
micro organisms in the soil to form humus . Humus is a dark jelly like substance that binds the soil together and improves its texture. It increases the soils ability to retain moisture. . The color of the soil is an indication of the amount of organic material it contains with darker soils having more organic content.

Soil organic matter includes:

  • Living organisms (soil biomass) 
  • The remains of microorganisms that once inhabited the soil  
  • The remains of plants and animals  
  • Organic compounds that have been decomposed within the soil and, over thousands of years, reduced to complex and relatively stable substances commonly called humus.

As organic matter decomposes in the soil, it may be lost through several avenues. Since organic matter performs many functions in the soil, it is important to maintain soil organic matter by adding fresh sources of animal and plant residues, especially in the tropics where the decomposition of organic residues is continuous throughout the year.

Air and Water: Air is vital for the survival of micro- organisms and without theses, there would be a shortage of humus.Plants cannot survive without water present in the soil .Mineral particles are soluble in water and the roots of plants can only absorb the nutrients of them after they have been dissolved.

In nutrient management, a proper balance between soil water and soil air is critical since both water and air are required by most processes that release nutrients into the soil. Soil water is particularly important in nutrient management. In addition to sustaining all life on Earth, soil water provides a pool of dissolved nutrients that are readily available for plant uptake. Therefore, it is important to maintain proper levels of soil moisture.

Soil water is important for three special reasons:

  • The presence of water is essential for all life on Earth, including the lives of plants and organisms in the soil. 
  • Water is a necessity for the weathering of soil. Areas with high rainfall typically have highly weathered soils. Since soils vary in their degree of weathering, it is expected that soils have been affected by different amounts of water.  
  • Soil water is the medium from which all plant nutrients are assimilated by plants. Soil water, sometimes referred to as the soil solution, contains dissolved organic and inorganic substances and transports dissolved nutrients, such as nitrogen, phosphorus, potassium, and calcium, to the plant roots for absorption.