Soils and Soil Minerals Remember, most things can be too little or too much. 1
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Source of essential elements CO 2, O 2 from atmosphere H 2 0, O 2, minerals from soil NH 4, SO 4 can volatilize and be transported dry deposition can be critical in nutrient poor areas or near the coast rainfall can bring materials from the atmosphere, from smoke, volatilization, volcanoes, pollution, etc 4
Soils are critical for Support and anchorage Supplies mineral nutrients Supplies water Allows gas exchange (especially O2 and CO2, also ethylene and other gasses) Soil Soil is a dynamic feature of systems containing organisms Soil results from the interaction of climate. substrate and organisms (principally plants) Shifts in any one of these 3 inter-actors can change the dynamics and characteristics of soil 5
Soil results from Plants Dynamic, constantly evolving process Geological Substrate Climate Rock Residual Soil Forming Factors - Substrate Transport water gravity ice wind Deposition lakes streams oceans downslope ice water wind wind Parent Material Lacustrine Alluvial Marine Colluvial Till, Moraine Outwash Lacustrine Alluvial Marine Eolian 6
Soil Forming Factors - Climate Temperature Warmer -> faster soil development Cooler -> slower soil development Precipitation Higher rainfall -> greater leaching in profile Leaching zone determined by CaCO3 in soil profile (caliche layer in arid zones) Soil Forming Factors Biotic Plants Add organic matter Leach and deposit considerable chemicals (especially organic acids ph determinate) Animals & micro-organisms Mix horizons Modify and transform organic matter 7
Soils are not created equal Strong variation among soils in their mineral content, water holding ability, depth, and other characteristics. Strong determinant of plant (community) distribution patterns Critical Features of Soil Source of resources (minerals, water) and support Resources adsorb to surfaces of soil particles. Surface Area per Volume Relationships as a quantitative dimension for resource availability Soil Texture (proportions of particle size classes) Soil Structure (% of soil organics that bind soil together into larger particles) 8
1. Soil Texture Texture refers to the proportions of different size classes of particles decomposed from rock. 3 classes are recognized that can make up soil clay (<0.002 mm) silt (0.02-0.002 mm) sand (2.0-0.02 mm) Different types of rocks yield different soil materials 9
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Water adsorbed to surfaces Silt or Sand particles PORE Clay crystals Proportions of clay vs. silt vs. sand modify the size and frequency of soil pores, and consequently influence characteristics of water and mineral retention. Available water varies greatly by soil type. 11
Characteristics of soils Depend on soil texture Clay has high surface area and negative charges in its crystalline structure which can readily adsorb minerals and water At the other extreme, sand is a large particle with relatively little surface area, but it can create large soil pores (spaces), which are critical for gas and water movement Clay soils can hold more cations because of clay s negative charges and high surface area. 12
Clay is classified into different types depending on its chemistry, structure and other characteristics. Montmorillonite, for example, holds more minerals and water because of its charges and the larger distance between its crystal lattice layers 13
2. Soil Structure Structure refers to the ability of organic matter to bind particles into larger soil aggregates dissolved organics react with each other forming large carbon compounds that can glue particles together into larger aggregates Aggregates act as if they were larger particles, creating large soil pores, but also having high surface area Soil Structure Soil Aggregate - soil particles bound together into larger structures High Surface Area due to small particles High Soil Porosity due to large aggregates yielding large pores 14
Generalized Soil Profile Soils vary with distance from source of organic matter (litter) and depending on ability (amount) of rainfall to leach materials to depth. Generalized soil profile associated with a northern forest. 15
Soil development Dependent on climate, vegetation and substrate, topography Key aspect is soil organic matter Addition of organic matter modifies soil characters due to acidity, ability to adsorb minerals, tendency of organic matter to bind and react. 16
Topography, location and texture: As water empties from a mountain stream, its velocity starts to decrease. The largest size particles, like sand, are the first to drop out of suspension (Site A). Fine, clay size particles can be carried further away from the base of the slope before they are deposited. As a result, coarse textured soils tend to be found near the base of a mountain and fine textured soils are located farther away (Site C). In the context of soils: Vegetation responds to Variation in texture (e.g., sandy vs clayey soils (NE Pine Barrens; chaparral-clay interfaces in coast ranges) Variation in geological substrate serpentine (low in N, P, high in heavy metals) granites (low nutrients, degrade to acidic soils) limestones (very high in Ca) 17
Unusual geology often results in unusual plant communities Toxic or imbalanced mineral content restricts plant communities to those that can adapt or tolerate conditions Significant shift in soil texture will shift communities Soils above the yellow line made from uplifted crust high in magnesium, coarse textured. Below, clay soils with fine soils covered by grassland. White Mountains Bristlecone pine on dolomite outcrops Dolomite is a Calcium & Magnesium rich substrate. Like limestone, it is a carbonate based mineral. Often contain restricted or rare species. 18
Serpentine Soil the state rock Sargent s cypress and Mt. Tam manzanita Frog-footed Jewel Flower Serpentine Soils contain large numbers of endemic species. Low in N, high in heavy metals. N. Calif. Pismo Beach Vegetation of Sandy Substrates Many places in California experience the deposition of sand as a major process. Some of these areas are active, like beaches and desert dunes; others more historic, like the ancient dunes at Bonny Doon. Bonny Doon area Death Valley Kelso Dunes Anzo-Borrego 19
Sierran Granites The percentage composition of feldspar varies between 65-90%, quartz can range from 10 to 60% and that of biotite lies between 10 to 15%. Feldspar breaks down into clays Quartz into sand Biotite (mica) into clays Sierran Soils: Mostly Granitics and Volcanics 20