SoilsChapters 15Living in the Environment, 15th Edition, Miller Advanced Placement Environmental Science La Canada High School Dr. E
Soils: Formation Immature soil O horizon Leaf litter A horizon Topsoil Regolith B horizon Subsoil Bedrock C horizon Parent material Young soil Mature soil • Soil profile • Humus • Soil horizons Fig. 10.12, p. 220
Soil Properties Fig. 10.17, p. 224 Water Water 100%clay High permeability Low permeability 0 80 20 Increasing percentage clay Increasing percentage silt 60 40 40 60 20 80 0 80 60 40 20 100%sand 100%silt Increasing percentage sand • Infiltration • Leaching • Porosity/permeability • Texture • Structure • pH Fig. 10.16, p. 224
Texture Nutrient Infiltration Water-Holding Aeration Tilth Capacity Capacity 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 • Proper pH directly affects the availability of plant food nutrients • Soil is best if between pH 6 – 8 (except for certain acid loving plants) • ‘Sour’ if too acidic • ‘Sweet’ if too basic
Acidity / Alkalinity – pH • Too acidic or basic will not • Allow compounds to dissolve • Allow presence of certain ions • If soil is too acidic, add ground limestone • If soil is too basic, add organic material like steer manure
Nitrogen Content • Importance • Stimulates above ground growth • Produces rich green color • Influences quality and protein content of fruit • A plant’s use of other elements is stimulated by presence of N • Taken up by plant as NH4+ and NO3- • Replenished naturally by rhizobacteria on legume roots • Fertilizer from manure or Chemical rxn.
Phosphorus for Growth • Abundant in • Strong root system • Increases seed yield and fruit development • Parts of root involved in water uptake (hair) • Major role in transfer of energy • Taken up by plant as H2PO4- and HPO4-2 • 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 • Offsets too much N • Found naturally in feldspar and micas
Justus von Liebig’s Law of Minimum Plant production can be no greater than that level allowed by the growth factor present in the lowest amount relative to the optimum amount for that factor
Soil Formation Soils develop in response to • Climate • Living organisms • Parent Material • Topography • Time
Climate • Two most important factors that determine climate are Temperature and Moisture and they affect • Weathering processes • Microenvironmental conditions for soil organisms • Plant growth • Decomposition rates • Soil pH • Chemical reactions in the soil
Parent Material • Refers to the rock and minerals from which the soil derives. • The nature of the parent rock has a direct effect on the soil texture, chemistry and cycling pathways. • Parent material may be native or transported to area by wind , water or glacier.
Topography • Physical characteristics of location where soil is formed. • Drainage • Slope direction • Elevation • Wind exposure • Viewed on Macro-scale (valley) or microscale (soil type in field)
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.
Physical includes temperature changes (freezing and thawing, thermal expansion), crystal growth, pressure, plant roots, burrowing animals causes disintegration of parent material and facilitates chemical weathering Chemical always in water includes hydration, hydrolysis, oxidation, reduction, carbonation and exchange examples : oxidation of Fe to form limonite, deposited in joints, inhibits groundwater flow hydrolysis of feldspars to form clay (kaolin) - forms infill for joints Destructional -WeatheringLandscapes broken down by chemical & physical processes & erosion
Destructional - Mass wasting • Gravitational movement of weathered rock down slope without aid of water or wind (landslips) • transported material is called colluvium • often set off by man’s activity • can involve very small to immense volumes of material • sliding, toppling, unravelling, slumping • controlled by discontinuities (joints, bedding, schistocity, faults etc)
Destructional - Erosionmost significantly by running water • Sheet erosion • by water flowing down valley sides • severe when vegetation removed and geological materials uncemented • Stream erosion • materials brought downslope by mass wasting and sheet erosion are transported by streams • erosion by the streams - meanders etc
Destructional - Karsts • Forms by dissolution of limestone - limestone is only common rock soluble in water - dissolved carbon dioxide in rain water • form highly variable ground conditions • formation of sink holes - when buried leads to surface subsidence