Soil formation Soil horizons Leaf litter Topsoil Subsoil

Soil formation

Soil horizons Leaf litter Topsoil Subsoil Parent rock (Kreado, 2003)

Parent rock • Parent rock – formed from varying mineral combinations (Rockgeology, 2008)

Physical weathering 1 Physical 2 Chemical 3 Biological http: //www. youtube. com/watch? v=t-Acasoi. FEo http: //www. bbc. co. uk/schools/ks 3 bitesize/scien ce/environment_earth_universe/rock_cycle/r evise 6. shtml

Physical weathering is caused by physical changes such as: changes in temperature, freezing and thawing, and the effects of wind, rain and waves Picture from http: //3. bp. blogspot. com

Chemical weathering • Chemical weathering – by water, acid rain, oxygen (0₂) and carbon dioxide (C 0₂)

Biological weathering • Biological weathering – lichen, plant roots. (TJFlex, 2008) (Galacticdream, 2008)

Sub soil Ø Soil formed from minerals. Ø Often large soil aggregates (lumps) Ø Contains some plant roots Ø Devoid of organic matter – therefore light in colour

Topsoil • Soil formed from mineral and organic matter • Usually dark in colour • Usually fine soil aggregates (lumps) • Contains most plant roots • Contains many microorganisms that are beneficial to plant growth

Leaf litter / organic layer • • Fallen and decomposing leaves Rich in fungi Rich in insect life Holds potential nutrient and organic matter for topsoil

Minerals • The main ingredient in soils in the SE of England • Gravel, sand silt are minerals worn down to different size by physical weathering • Clay is formed by dissolved minerals that are re-crystalised together • Varying combinations of these minerals form together to make loam!

How is soil formed? • Parent material-weathered and broken down • Transported soil • Characteristics - drainage • Texture – Sand, silt and clay - minerals • Component parts (e. g. % of organic matter, H 2 O and O 2)

Transported soils Deposited - ice & water and not from local bedrock. Sand can be deposited by retreating glaciers Mud after a flood Soils deposited by water are called ALLUVIAL soils

Alluvial Soils • Rarely stony • Usually level • Fine-grained • Often very deep