What is soil, functions, Study notes of Environmental Science

Download What is soil, functions and more Study notes Environmental Science in PDF only on Docsity! What is soil? Soil is the loose surface material that covers most land. It consists of inorganic particles and organic matter. Soil provides the structural support to plants used in agriculture and is also their source of water and nutrients. Soils vary greatly in their chemical and physical properties. Processes such as leaching, weathering and microbial activity combine to make a whole range of different soil types. Each type has particular strengths and weaknesses for agricultural production. The basic components of soil are minerals, organic matter, water and air. The typical soil consists of approximately 45% mineral, 5% organic matter, 20-30% water, and 20-30% air. These percentages are only generalizations at best. In reality, the soil is very complex and dynamic. Physical characteristics of soil The physical characteristics of soils include all the aspects that you can see and touch such as:  texture  colour  depth  structure  porosity (the space between the particles)  stone content. Good soil structure contributes to soil and plant health allowing water and air movement into and through the soil profile. Soil stores water for plant growth. Soil texture, structure, drainage characteristics Figure 1. Soil aggregate The combination of mineral fractions (gravel, sand, silt and clay particles) and organic matter fraction give soil its texture. Texture grades depend upon the amount of clay, sand, silt and organic matter present. The solid part of the soil is made up of particles such as organic matter, silt, sand and clay which form aggregates. Aggregates are held together by clay particles and organic matter. Organic matter is one of the major cementing agents for soil aggregates. The size and shape of aggregates give soil a characteristic called soil structure. Soil structure influences plant growth by affecting the movement of water, air and nutrients to plants. Inorganic component of soils Inorganic material is the major component of most soils. It consists largely of mineral particles with specific physical and chemical properties which vary depending on the parent material and conditions under which the soil was formed. It is the inorganic fraction of soils which determines soil physical properties such as texture. This has a large effect on structure, density and water retention. Soil texture The texture of soil is a property which is determined largely by the relative proportions of inorganic particles of different sizes. the inorganic fraction of soils:  Gravel — particles greater than 2mm in diameter  Coarse sand — particles less than 2mm and greater than 0.2mm in diameter  Fine sand — particles between 0.2mm and 0.02mm in diameter  Silt — particles between 0.02mm and 0.002mm in diameter  Clay — particles less than 0.002mm in diameter. The inorganic minerals of soils consist primarily of silicon, iron and aluminium which do not contribute greatly to the nutritional needs of plants. Those in the clay fraction have the capacity to retain nutrients in forms which are potentially available for plants to use. Organic component of soil The organic matter of soil usually makes up less than 10% of the soil. It can be subdivided into living and the non-living fractions. The non-living fraction contributes to the soil's ability to retain water and some nutrients and to the formation of stable aggregates. Organic matter fraction of soils The organic matter fraction of soils comes from the decomposition of animal or plant products such as faeces and leaves. Soil organic matter contributes to stable soil aggregates by binding soil particles together.