Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Soils Soils • Products of weathering Soil Characteristics • Regolith – Loose material covering solid rock • Dust, sediment, broken rock – Soil is the only part that supports the growth of plants Soil Characteristics • Composition • Texture • Structure Soil Composition • Mineral matter – Broken rocks • Organic matter (humus) – – – – Remains of dead organisms Source of nutrients Increases ability to retain water Percentage varies • Bogs are almost all humus, deserts have very little Soil Composition • Water – Provides moisture for chemical reactions – Provides nutrients in a form that plants can use • Air – Source of CO2 Soil Texture • The proportions of particle sizes • Influences ability to support plant life • Based on % of clay, sand and silt Soils SAND: • Drains quickly; dries out Soils LOAMY SAND: • falls apart when handled. Soils LOAM: • feels spongy • Drains well without drying out • Contains more nutrients Soils SANDY LOAM: Soils SANDY CLAY: Soils SILT LOAM: Soils CLAY: • Drains slowly • Hard for plant roots to grow Soils SILTY CLAY: Soils SILTY CLAY LOAM: Soils CLAY LOAM: Good Quality Soils • Typically consist of 50 % organic and mineral matter • Other 50 % consists of pore spaces – Air and water circulation Soil Structure • Soil particles form clumps that give soils a particular structure – Determines: • How easily it will erode • How easily it can be cultivated • Water infiltration Soil Formation Parent Material • Source of the mineral matter • Bedrock – Residual soil • Unconsolidated material – Transported soil Parent Material • Affects: – Rate of weathering and soil formation • Unconsolidated material forms soils more quickly than residual – Plant fertility • Determines types of plants that can grow Soil Formation • Climate: – Temperature, humidity, precipitation – Most important factor • Time: – Older soils are thicker Soil Formation • Organisms – When living things die, decomposers break them down • They become part of the soil • Add nutrients to soils • Plant acids speed up weathering – Burrowing • leaves holes for air and water circulation Soil Formation • Topography/Slope – Steeper slopes have more erosion, less water Soil Profiles • Soil forms top down • At different depths, soil varies in: – Composition, texture, structure and color Soil Profiles • Mature soils tend to have 3 distinct horizons Soil Horizons • O – Humus, typically considered part of A • A – Topsoil, mostly organic matter • B – Subsoil, lower limit of roots and burrowing, – Hardpan – clay that forms a compact layer • C – Partially weathered parent material Pedalfer • Forms in temperate areas with more than 63 cm of rain each year – Much of the eastern US – B horizon • Large amts. of iron oxides (reddish brown) Pedocal • Forms in drier western US – Less clay (b/c weathering is slower) – Contain calcium carbonate – light brown Laterite • Hot, humid, tropical areas • Lots of water – Distinctive orange-red • Almost no organic material (quickly used)