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Class 1: Introduction to Soil Formation, Texture and Structure Chris Thoreau February 11, 2012 Slide 2 Soil is a dynamic composition of: Minerals Water and its solutions Water Organic matter (detritus) Organic matter Air and other gas mixtures... Air...which, through interacting with each other and with plant roots, allows for the growth of photosynthesizing terrestrial plantsinteracting with each other and acts as a habitat for micro- and macro- organismsmicro- and macro- organisms which also interact with plants and plant roots Or Slide 3 Physical Aspects: Minerals (from rocks) Sand Silt Clay and Colloids Organic Matter Plants and Roots Detritus (decaying organic matter) Animal waste (including microbes) Pore Space Air/Gases Water Slide 4 Soil is the Mother of All Terrestrial Life Slide 5 Conceptual Aspects: Habitat Micro-organisms Bacteria, Fungi both good and bad Viruses Macro-organisms Worms, Arthropods, Detrivores and Predators Plants Small Mammals Birds Slide 6 Conceptual Aspects: Provider to plant life Rooting substrate Water holding and release Nutrient supply and reserve Heat sink and release Soil gases Symbionts Bacterial and fungal Insects Slide 7 Habitat What happens when we disturb this habitat? At micro and macro level? What happens when we make additions to, or removals from, this habitat? Carbon:Nitrogen ratio? How do soil organisms and plants respond? Nutrient loss or gain? Providing for plant life What are the short-term and long-term results? Are we providing for the soil as well as the plants? What is the difference? Slide 8 As a habitat we need to treat soil like a living organism, which requires: Food Organic Matter and Minerals Water Irrigation and Natural Air Shelter Cover crops, Cash Crops, Mulches General tender loving care Slide 9 Questions? Slide 10 Where does soil come from? Soil comes (mostly) from the weathering of rocks over long periods of time a process highly influenced by biological organisms, topography, aspect and human activity Slide 11 1. Parent Material 2. Climate 3. Biota 4. Topography 5. Time Slide 12 1. Parent Material Transported Gravity - ColluvialColluvial Water Alluvial, Marine, and LacustrineAlluvialMarineLacustrine Wind EolianEolian Ice GlacialGlacial Cumulose Due to plant life and anaerobic conditions High water table Peat and muck soils Residual In situ; long periods of weathering Slide 13 2. Climate Temperature and rainfall are major factors Affect intensity of weathering Increased T and precipitation accelerate weathering 3. Biota Plants influence organic matter Arthropods and worms mix soil; add to OM Small mammals also mix soil Slide 14 4. Topography Slope influences soil development Water infiltration rate Surface runoff Vegetation Aspect North and South slopes develop differently Elevation Climate changes with altitude Slide 15 5. Time Often noted as most important soil formation factor Our soils in Lower Mainland are relatively young Since last ice age 10-12,000 years ago Slide 16 Primary Minerals Sand and Silt Primary Minerals Formed at high T and P (at depth); anaerobic conditions Formed at high T and P Physically and chemically formed Quartz, Feldspars, Micas, Secondary Minerals Clay Secondary Minerals Come from primary minerals Formed at low T and P (at surface) with Oxygen present Mostly chemically formed Silicate Clays Slide 17 Weathering of Rocks Physical Chemical 1 Chemical 2 Slide 18 Additions Losses Transformations Translocations Slide 19 Slide 20 Organic (O) Horizon High in organic residue from plant drop A Horizon Mineral component plus OM Most fertile part of soil; location of much root activity B Horizon Subsoil A horizon leaches here C Horizon Little influence by soil-forming processes Slide 21 In a given area, over the period of soil formation, environmental conditions cause a certain set of soil processes to occur, which leads to a distinctive set of soil horizons at the time we observe the soil. These soil horizons are the basis for classifying the soil in the Canadian System of Soil Classification. Canadian System of Soil Classification Slide 22 Slide 23 Podzol Gleysol Chernozem Brunisol Luvisol Organic Solonetzic Vertisol Regosol Cryosol Slide 24 Video here Slide 25 Any questions? Check follow up readings and websites for more detailed information UBC Virtual Soil Science Soil Orders of Canada Videos Canadian System of Soil Classification Slide 26 Soil texture refers to the relative amount of sand, silt, and clay found in a soil The mixture of these components affects the feel of the soil as well as water, nutrient, and pore space interactions Slide 27 Mineral Components Sand Silt Clay Slide 28 Mineral ratios determine soil texture Slide 29 Sand Largest soil mineral particles (.02 2 mm) Formed greatly from physical processes Spherical/erratic in shape Sand = little rocks Larger pore spaces Good drainage Does not hold a charge Difficult to compact Slide 30 Silt Size between sand and clay (.002 -.02 mm) Usually physically formed out of sand Hold and releases water well Flat or round in shape Holds very little charge Feels soapy Carried in moving water Slide 31 Clay Smallest soil mineral particle (