Soil is a dynamic ecosystem. It provides nutrients and habitat to the living organisms. The organic matter binds soil particle into aggregate and improves water and air movement through soil influencing the ability of soil to sustain life and perform soil function.
Soil structure is the arrangement of soil particle (sand, silt and clay) into an aggregate. It determines how each soil bind and forms soil pores. Decline in soil structure means breaking down of soil aggregate, this destruction of soil aggregate may be due to change in the chemical structure.
Arrangement of soil horizon is known as soil profile. Soil horizon make up distinct soil and differ in color, texture and thickness. The soil is composed of mineral which is the weathered parent rock and the decomposed organic matter. The soil horizon are categorized as O, A, B, C & R. Each soil type has a different soil profile.
- O horizon consists of organic matter which is mostly undecomposed
- A horizon is the surface soil and has most of the soil organisms. This horizon consists of minerals along with the organic matter
- B horizon is the sub soil constituting of weathered parent material like iron, silicate etc.
- C horizon may comprises of some unbroken rock along with soluble compounds
- R horizon is composed of hard bedrock
The activity of the soil biota is affected by the presence of organic matter. All living organisms are made up of cells and the chemical composition of the cell varies. The common cellular component of plant and animal cells are nucleus, ribosome, endoplasmic reticulum, mitochondria etc. whereas, chloroplast is present only in plant and algal cell. Different chemical component of cell make different organic matter substrate.
The chemical composition of cell wall are diverse depending upon the different growth stages of the cells. The cell wall of plant is made up of cellulose, hemicellulose and pectin besides some lipid and proteins whereas, algal cell wall comprises of glycoprotein and polysaccharides; bacterial cell wall is of peptidoglycan and the fungi cell wall is made up of chitin. Similarly different cell organelle are comprised of different chemical such as:
- Nucleus is made up of protein & nucleic acid
- Ribosome is made up of ribosomal RNA (rRNA) as well as number of distinctive ribosomal protein
- Endoplasmic reticulum contains high lipid content specifically phospholipids and protein
- Mitochondrial membrane is made up of phospholipid and protein
- Chloroplast contains protein, lipid, chlorophyll, carotenoid, RNA, DNA, cytochrome f and small proportion of carbohydrate
When these plant cell residues are added to the soil, the soil microorganisms such as bacteria, fungi, actinomycetes release enzymes that break these biomolecules into the simpler forms thus utilizing it as nutrient, structuring soil and improving the soil fertility.