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Transcript
Soils Credits: Dr. E La Canada High School Soils: Formation • Soil horizons • Soil profile • Humus Immature soil O horizon Leaf litter A horizon Topsoil Regolith Bedrock B horizon Subsoil C horizon Young soil Parent material Fig. 10.12, p. 220 Mature soil Soil Properties Fig. 10.17, p. 224 Water Water • Infiltration • Leaching High permeability Low permeability • Porosity/permeability 100%clay • Texture • Structure • pH 0 80 Increasing percentage clay 60 40 20 20 Increasing percentage silt 40 60 80 Fig. 10.16, p. 224 0 100%sand 80 60 40 20 100%silt Increasing percentage sand Texture Nutrient Capacity Infiltration Water-Holding Aeration Capacity Tilth Clay Good Poor Good Poor Poor Sand Poor Good Poor Good Good Loam Medium Medium Medium Medium Medium Soil Chemistry Acidity / Alkalinity – pH Major Nutrients – Nitrogen – Phosphorus (phosphates) – Potassium (potash) Acidity / Alkalinity – pH Soil is best if between pH 6 – 8 (except for certain acid loving plants) – ‘Sour’ if too acidic – ‘Sweet’ if too basic If soil is too acidic, add limestone If soil is too basic, add organic material like cow manure Nitrogen Content Importance – Stimulates above ground growth – Produces rich green color – Influences quality of fruit One source is fertilizer from cow manure. Phosphorus for Growth Needed for: – Strong root systems – Increases seed yield and fruit development – Parts of root involved in water uptake (hair) Fertilizer is made from rock phosphate Potassium Content Potash Important in vigor and vitality of plant – – – – Carries carbohydrates through the plant Improves color of flowers Improves quality of fruit Promotes vigorous root systems Found naturally in feldspar and micas Soil Formation Soils develop in response to 1. Climate 2. Living organisms 3. Parent Material 4. Topography 5. Time Climate Two most important factors that determine climate are Temperature and Moisture. These factors affect: 1. Weathering processes 2. Conditions for soil organisms 3. Plant growth 4. Decomposition rates 5. Soil pH 6. Chemical reactions in the soil Parent Material Refers to the rock and minerals from which the soil comes from. The nature of the parent rock has a direct effect on the soil texture. Parent material may be native or transported to area by wind , water or glacier. Topography Physical characteristics of location where soil is formed. 1. Drainage 2. Slope direction 3. Elevation 4. Wind exposure Time After enough time, the soil may reach maturity. – Depends on previous factors – Feedback of biotic and abiotic factors may preserve or erode mature profile. Soil Destruction -Weathering Landscapes broken down by chemical & Physical physical processes & erosion 1. Temperature changes (freezing and thawing) 2. Crystal growth 3. Burrowing animals Chemical 1. Always in water Destructional - Mass wasting Gravitational movement of weathered rock down slope without aid of water or wind often set off by man’s activity can involve very small to immense volumes of material Sliding or slumping Soil Destruction - Erosion most significantly by running water Sheet erosion – by water flowing down valley sides – severe when vegetation removed Stream erosion – materials brought down slope by mass wasting and sheet erosion are transported by streams Soil Destruction - Karsts Forms by dissolving of limestone limestone is the only common rock soluble in water - dissolved carbon dioxide in rain water formation of sink holes - when buried leads to surface subsidence (ground sinks)