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Head to www.savemyexams.com for more awesome resources SL IB Environmental Systems & Your notes Societies (ESS) 5.1 Introduction to Soil Systems Contents 5.1.1 Soil Profiles 5.1.2 Soil S...

Head to www.savemyexams.com for more awesome resources SL IB Environmental Systems & Your notes Societies (ESS) 5.1 Introduction to Soil Systems Contents 5.1.1 Soil Profiles 5.1.2 Soil Systems 5.1.3 Soil Structures & Properties Page 1 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 5.1.1 Soil Profiles Your notes Soil Profiles Soil profiles provide a visual representation of the different layers or horizons present in a soil system These horizons reflect the processes and materials that have shaped the soil over time There are six main horizons A soil profile is a visual representation of the different horizons present in a soil system O horizon The O horizon, also known as the organic horizon, is the uppermost layer It is composed mainly of organic matter such as leaf litter, decaying plant material, and organic debris It is rich in nutrients and serves as a site for nutrient cycling and organic material decomposition A horizon Page 2 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The A horizon, also called the topsoil, is a mixed mineral and organic horizon It is usually darker in colour due to the accumulation of organic matter This layer is important for plant growth as it contains nutrients and provides a favourable Your notes environment for root development E horizon The E horizon, also known as the eluvial or leached horizon, is characterised by the leaching or removal of minerals and nutrients due to downward movement of water It often appears lighter in colour than the surrounding horizons B horizon The B horizon, also called the illuvial or deposited horizon, is the layer where minerals and nutrients leached from the upper horizons accumulate It often exhibits different colours, textures, or chemical properties compared to the horizons above and below it C horizon The C horizon represents the weathered parent material from which the soil has formed It is typically composed of partially weathered rock fragments and may contain limited organic matter The properties of the C horizon influence the development and characteristics of the upper horizons R horizon The R horizon, also known as bedrock, is the underlying solid rock that forms the base of the soil profile It is often unweathered It is relatively unaffected by biological activity and represents the original geological material from which the soil formed These layered horizons in a soil profile provide information about the soil's composition, nutrient content, water-holding capacity, and drainage characteristics They help scientists, farmers, and land managers understand the properties and fertility of soils, enabling them to make informed decisions regarding land use, crop selection, and soil conservation practices Page 3 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 5.1.2 Soil Systems Your notes Soil Systems As with any system, soil systems can be simplified by breaking them down into the following components: Storages Flows (inputs and outputs) Transfers (change in location) and transformations (change in chemical nature, state or energy) Soils are highly complex, dynamic systems made up of various storages, flows, transfers and transformations Page 4 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Soil System Storages Your notes Storage Description Refers to the accumulation of plant and animal matter in various stages of Organic matter decomposition - provides nutrients, improves soil structure, and enhances water- holding capacity Includes microorganisms, fungi, bacteria, insects, and other living organisms Organisms present in the soil - they play essential roles in nutrient cycling, organic matter decomposition, and soil structure formation Refers to elements necessary for plant growth, such as nitrogen, phosphorus, Nutrients potassium - nutrients are stored in the soil and are made available to plants through various biological and chemical processes Refers to the inorganic components of the soil derived from weathering of rocks Minerals and minerals - they contribute to the physical properties and fertility of the soil The pore spaces within the soil are filled with air, allowing oxygen to be available for Air root respiration and microbial activities Soil acts as a reservoir for water, holding it for plant uptake and providing a suitably Water moist habitat for soil organisms Soil System Inputs Page 5 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Input Description Includes inputs of plant material (e.g. leaf litter) and other organic materials (e.g. Organic matter animal faeces) that contribute to the organic matter content in the soil Inorganic matter Represents the mineral composition derived from parent materials (e.g. bedrock) from rock material and the weathering of exposed rock at the soil surface Precipitation Rainfall or snowfall that provides water to the soil system Infiltration The process by which water enters the soil from the surface Energy Solar radiation and heat influence soil temperature and biological activities Soil System Outputs Output Description Page 6 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The loss of dissolved minerals and nutrients from the soil into streams, rivers, lakes Leaching and oceans through water movement Uptake by plants The absorption of nutrients and water by plant roots for growth and development The downslope movement of soil particles due to gravity, such as landslides or soil Mass movement creep The removal of soil particles by water or wind, leading to the loss of topsoil and Soil erosion degradation of soil quality Soil System Transfers Transfer Description Page 7 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The movement of soil particles and materials by soil organisms, including burrowing Biological mixing animals, earthworms, and root growth - it contributes to the mixing of organic matter and minerals, enhancing soil structure and nutrient distribution The process in which minerals dissolved in water are moved downwards or Leaching horizontally through the soil profile - it can result in the loss of nutrients from the root zone, particularly in areas with high rainfall or excessive irrigation The removal of fine particles, such as clay and dissolved organic matter, from the Eluviation upper layers of the soil by the downward movement of water The deposition of materials, including minerals and organic matter, in lower soil Illuviation layers - it occurs as a result of leaching and eluviation processes, leading to the accumulation of materials in specific horizons Soil System Transformations Transformation Description Page 8 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The process of organic matter breakdown by microorganisms, resulting in the Your notes Decomposition release of carbon dioxide, water, and nutrients - it involves the conversion of complex organic compounds into simpler forms The physical and chemical processes that break down rocks and minerals into smaller particles, contributing to soil formation - it includes physical weathering Weathering (mechanical breakdown) and chemical weathering (alteration of minerals through chemical reactions) The cycling of nutrients within the soil-plant system, involving uptake, assimilation, Nutrient cycling release, and recycling of elements like nitrogen, phosphorus, potassium - ensures the availability and redistribution of essential nutrients for plant growth The process of organic matter transformation into stable humus - it involves the Humification accumulation of complex organic compounds, leading to the dark colouration and improved water-holding capacity of soil - contributes to soil fertility and structure The decomposition (i.e. oxidation) of the chemical compounds in organic matter, by which the nutrients in those compounds are released in soluble inorganic forms that may be available to plants e.g. the conversion of organic nitrogen compounds Mineralisation into inorganic forms, particularly ammonium (NH4+) and nitrate (NO3-) - it occurs through microbial activity, releasing nitrogen for plant uptake and contributing to the nutrient pool in the soil Page 9 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 5.1.3 Soil Structures & Properties Your notes Soil Structures & Properties Soils vary greatly in their structure and properties, with distinct characteristics that influence their ability to promote primary productivity Sand, clay, and loam soils differ in their mineral and nutritional content, drainage, water holding capacity, air spaces, biota, and their potential to hold organic matter Understanding these soil properties is crucial for comprehending their impact on plant growth, nutrient cycling, and the overall health and functioning of ecosystems Photo by Dylan de Jonge on Unsplash Soil is a fundamental component of terrestrial ecosystems, serving as a vital medium for plant growth and supporting the intricate web of life in the natural world Sand Soils Mineral content: Dominated by large particles of sand, primarily composed of silica and other minerals Nutritional content: Typically low in organic matter and nutrients, as sand particles do not have a high capacity for nutrient retention Drainage: Excellent drainage due to the large pore spaces between sand particles, allowing water to move quickly through the soil Water holding capacity: Low water holding capacity as sand particles have limited ability to retain water Page 10 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Air spaces: Sand soils have ample air spaces due to the large particle size, facilitating oxygen availability for plant roots and soil organisms Biota: Generally lower microbial activity and lower diversity of soil organisms compared to other Your notes soil types Potential to hold organic matter: Low potential to hold organic matter, as sand particles do not have strong binding capacity Clay Soils Mineral content: Dominated by small clay particles, composed of various minerals such as silicates and aluminum oxides Nutritional content: Clay soils often have higher nutrient content and cation exchange capacity, allowing them to retain and supply nutrients to plants Drainage: Poor drainage due to the small particle size and compactness, which limits water movement through the soil Water holding capacity: High water holding capacity as clay particles have the ability to hold water tightly Air spaces: Clay soils have fewer air spaces due to the compactness of the particles, leading to limited oxygen availability for roots and soil organisms Biota: Clay soils can support a diverse range of soil organisms due to their ability to retain water and nutrients Potential to hold organic matter: High potential to hold organic matter, as clay particles have strong binding capacity and can retain organic compounds. Loam Soils Mineral content: Loam soils have a balanced mixture of sand, silt, and clay particles, providing a combination of different mineral compositions Nutritional content: Loam soils generally have a moderate nutrient content and cation exchange capacity, allowing for adequate nutrient retention and availability Drainage: Moderate drainage characteristics, providing a balance between water movement and retention Water holding capacity: Loam soils have a moderate water holding capacity, retaining enough water for plant use while allowing excess water to drain Air spaces: Loam soils have a balanced structure, with sufficient air spaces for root respiration and soil organism activity Biota: Loam soils support diverse soil biota, including microorganisms, earthworms, and other soil organisms Potential to hold organic matter: Loam soils have a moderate potential to hold organic matter, as they provide a suitable environment for organic material decomposition and nutrient cycling Soil Properties Summary Table Property Sand Loam Clay Page 11 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Nutrient status Poor Moderate Good Your notes Water infiltration rate High Medium Low Water holding capacity Low Medium High Aeration Good Moderate Poor Potential to hold organic Low Medium High matter Ease of working (ease with which soil can be Good Moderate Poor manipulated) Primary Productivity of Different Soils The structure and properties of soils directly influence their ability to promote primary productivity: Nutrient content affects the availability of essential elements for plant growth Water holding capacity and drainage characteristics determine the availability of water to plants (water being essential for photosynthesis), whilst preventing waterlogging (which can be damaging for some plants and therefore lower primary productivity) Air spaces ensure oxygen availability for root respiration and soil organisms Biota, including microorganisms, play crucial roles in nutrient cycling, organic matter decomposition, and symbiotic relationships with plants (e.g. nitrogen-fixing bacteria) The potential to hold organic matter influences soil fertility, as organic matter provides essential nutrients and improves soil structure The combination of these factors in different soil types determines their suitability for supporting primary productivity, influencing the growth and health of plants and consequently the overall functioning of ecosystems Soil Structure and Texture Page 12 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Soil structure refers to the arrangement or shape of soil particles and has a direct impact on primary productivity Soil texture, on the other hand, refers to the size of soil particles, with sand particles being less than 2 Your notes mm in diameter, silt particles less than 0.02 mm, and clay particles less than 0.002 mm Soil texture is an important characteristic as it influences various soil properties, including moisture content, aeration, nutrient retention, and ease of cultivation and root penetration Clay soils have a high potential for nutrient exchange due to their large surface area relative to volume However, they tend to become waterlogged and are often described as "cold" or "heavy" In periods of drought, clay soils can shrink, leading to structural damage (e.g. cracking) Sandy soils have excellent drainage capabilities and are commonly referred to as "light" soils Silt soils are particularly prone to compaction if ploughed when wet, which can negatively affect soil structure and plant growth A loam soil, which is a balanced combination of sand, silt, and clay, is often considered the most favourable for cultivation It is easy to work with, drains well, retains moisture and nutrients, and provides good aeration As a result, loam soils have the highest potential for primary productivity (plant growth) Soil Texture Triangles Page 13 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Soil texture triangles are used to classify soil types based on their relative proportions of sand, silt, and clay A soil texture triangle is a graphical tool used to classify soil types based on their relative proportions of sand, silt, and clay The triangle is divided into three sections representing the different soil particle sizes: sand, silt, and clay The soil texture triangle allows for easy visualisation and classification of soil types based on their particle size distribution Page 14 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources By locating a soil sample's percentage of sand, silt, and clay on the triangle, it is possible to determine its textural class (e.g. sandy loam, silty clay, etc.) Your notes The soil texture triangle illustrates the differences in composition of soils by showing how the varying proportions of sand, silt, and clay affect soil properties such as moisture retention, drainage, nutrient holding capacity, and workability Soils with higher percentages of sand have larger particles, resulting in good drainage but lower water and nutrient holding capacity Soils with higher percentages of clay have smaller particles, which leads to higher water and nutrient retention but slower drainage Soils with higher percentages of silt have intermediate properties, offering a balance between drainage and water-holding capacity The soil texture triangle provides a practical tool for understanding and classifying soils, aiding in agricultural and environmental management decisions, such as irrigation practices, fertiliser application, and crop selection Page 15 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes A soil sample is found to contain 50% sand, 20% silt and 30% clay. Using the soil texture triangle, determine the textural class of the soil that the sample was taken from. Answer The textural class of the soil that this sample was taken from is sandy clay loam. Page 16 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Exam Tip Triangular soil texture graphs are often read incorrectly. Remember - the sum of the percentages must add up to 100%, so always check this. The diagram above shows how to correctly read off percentages for clay, silt and sand from each of the three axes. Page 17 of 17 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers