IB ESS - Topic 5 (Soil & Terrestrial Food Production Systems) Full Notes

IB ESS - Topic 5 (Soil & Terrestrial Food Production Systems) Full Notes. The soil system may be illustrated by a soil profile that has a layered structure (horizons). 2. Soil system storages include organic matter, organisms, nutrients, minerals, air and water. 3. Transfers of material within the soil, including biological mixing and leaching (minerals dissolved water moving through soil), contribute to the organization of the soil. 4. There are inputs of organic material including leaf litter and inorganic matter from parent material,precipitation and energy. Outputs include uptake by plants and soil erosion. 5. Transformations include decomposition, weathering and nutrient cycling. 6. The structure and properties of sand , clay and loam soils differ in many ways, including mineral and nutrient content, drainage, water-holding capacity, air spaces, biota and potential to hold organic matter. Each of these variables is linked to the ability of the soil to promote primary productiv7. A soil texture triangle illustrates the differences in the composition of soils. The exact mix of these four portions give soil its character: ● mineral particles mainly from the underlying rock. ● organic remains that have come from the plants and animals. ● water within spaces between soil grains. ● air also within the soil grains. It is also a habitat for plants and animals. Soil is a highly porous medium typically with a 50:50 mix pore spaces. The pore spaces contain variable amounts of water and air. Soil profile A record of the processes that have created the soil, its mineral composition, organic content, and chephysical characteristics such as pH and moisture. Horizons Soil cross-section profile is changed over time as organic material leaches downwards and mineral matermove upwards. ● top layer is often rich in organic material while the lower layers consist of inorganic material. ● inorganic material is derived from the weathering of rocks. ● materials are sorted and layers are formed by water carrying particles either up or down – translocation . ● in hot, dry climates (P<E) water is evaporating at the soil surface and water from lower soil lamoves upwards. ○ it dissolves minerals and takes them to the surface, where the minerals are left behind wwater evaporates. ○ this also happens in irrigation and is called salinisation . ● in colder and wetter climates (P>E) water flows down in the soil. ○ it dissolves minerals and transports them downwards, causing leaching to occur. P: precipitation E: evaporation O Horizon ● uppermost layer of newly added organic material – comes from organisms that die on top of th● fungi, bacteria and other animals will start to decompose the dead material. A Horizon: ● upper layer where humus builds up. ● humus forms from partially decomposed organic matter and is often mixed with fine mineral partic● incomplete decomposition forming a layer of dark brown/black organic material – the humus layer.● in normal conditions, organic matter decomposes rapidly, releasing soluble minerals that are then up by plant roots. ● waterlogging reduces the number of soil organisms, resulting in a build-up of organic matter and lead to peat formation. B Horizon: ● where soluble minerals and organic matter tends to be deposited from the layer above. ● in particular, clay and iron salts can be deposited in this horizon. C Horizon: ● mainly weathered rock from which the soil forms. R horizon: ● parent material (bedrock or other medium). Variation: ● not all soils contain all three A, B and C horizons. ● sometimes only two horizons can be distinguished. ● in some soils, there may not be distinct layering. ● in some cases, we cannot dig deep enough to find the C layer. Soil structure Soil texture depends on the relative proportions of sand, silt and clay particles. ● most soils also contain > 2mm pebbles and stones, but these are not considered in a descriptiotexture. ● Sandy soils are gritty and fall apart easily. ● Silty soils feel slippery like wet talcum powder and hold together better than sandy soils. ● Clay soils feel sticky and can be rolled up into a ball easily. Ways to separate particles: ● dry out a soil sample, pass it through a series of sieves of decreasing mesh size to separate diameter. ● place a sample of soil in a jar, fill it with water, shake it then leave it to settle out to separProductivity Soil texture determines the soil’s fertility and primary productivity. Loam soils are ideal for agriculture. ● sand particles ensure good drainage and a good air supply to the roots. ● clay retains water and supplies nutrients – so they are fertile. ● silt particles help to hold the sand and clay particles together and they can be worked easily