Presentation on theme: "An Introduction to Soil"— Presentation transcript:
1An Introduction to Soil Bryan McElvanyResearch CoordinatorWarnell School of Forest ResourcesPatrick Davies
2This is the stuff under your fingernails DIRTThis is the stuff under your fingernails
3Why is soil science intimidating? Whole new vocabularyHard to visualizeSomewhat complex topics like chemistry and physics
4What is soil? Several different ways to define soil 1) Geologic definition: Loose surface of the earth as distinguished from solid bedrock (support of plant life not required).2) Traditional definition: Material which nourishes and supports growing plants (includes rocks, water, organic material, air).
5What is soil made of?Mineral MatterOrganic MatterAirWater
6What is the function of soil? Plant mediumRecycling system for nutrientsAnimal homeEngineering mediumSystem for water supply and purification
7The ability of soil to perform those functions is dependant upon: Soil TextureSoil StructureSoil ChemistrySoil AgeSite Factors (topography, water, etc)Etc.
8Soil Formation Factors There are five main factors that influence soil formation processes.Type of Parent MaterialClimateTopographyBiotic ComponentsTime
10Parent Material Two major divisions in type of parent material Residual-Formed in place (Residuum)Transported-Parent material was moved by:- wind (Eolian)- ice (Glacial)- gravity (Colluvial)- water:rivers (Alluvial)oceans (Marine)lakes (Lacustrine)
11Soil Formation Processes Transformations – modification of soil constituents. Mineral weathering, organic matter breakdown.Translocations – movement up, down, or laterally of soil constituents.Additions – movement of soil material in from outside sources. Organic material from leaves, dust from atmosphere.Losses – movement of soil material out of the soil. Transportation to groundwater, erosion of surface materials.
13Soil Formation in Action The soil formation processes, operating under the influence of the soil formation factors, is the driving force in soil genesis.Important questions to remember are:What transformations and translocations took place in the parent material to form this soil?What materials were removed?What was added?How did the climate and topography affect those processes over time?
14Soil Horizons As soils develop they form layers called Horizons. These horizons have distinct characteristics produced by soil forming processes.Master horizons include the O, A, E, B, and C horizons.Not every soil contains every horizon based on the level of development of the soil.Depth of each horizon varies between different soils.
15O HorizonLayer of accumulated organic matter such as leaves, grass, twigsMaterial can be in various states of decompositionGenerally dark in colorOAEBCR
16A HorizonZone of incorporation of organic matter into the mineral soilGenerally it’s the most productive horizonHigh biological activityGenerally dark in colorTopsoilOAEBCR
17E Horizon E Zone of Eluviation or leaching Eluviation is the movement of soil material out of a layer of soilSoluble minerals and organic material move out of this horizonGenerally a lighter “washed” appearance in colorOAEBCR
18B Horizon B Zone of illuviation or deposition Accumulation of materials “washed” from horizons aboveThis material is commonly clay, humus, sesquioxides, or a mixture of the threeVariable in color from reds and yellows to browns and graysOAEBCR
19C Horizon C Parent material The unconsolidated material that has been affected little by the soil forming processesOAEBCR
20Soil TextureSoil Texture is the relative proportion of the primary particles in the soil.Sand = 2mm – 0.05mmSilt = 0.05mm – 0.002mmClay = < 0.002mm
21Soil TextureThis proportion of sand, silt, and clay can be grouped into textural classes.Soil texture has a great deal to do with many other soil characteristics.
22Soil TextureCoarse textured soil – soil that has a higher proportion of larger particles. Sand, Loamy sand, Sandy loam.Fine textured soil – soil that has a higher proportion of smaller particles. Clay, Silty clay, sandy clay.
23Soil StructureSoil structure is the arrangement of soil particles into aggregates.Structureless soils do occur as either single grained or massive.
24Pore SpaceThe voids between soil particles are called pores. These can either be filled with water or air.Soil texture plays a major role in total pore space as well as size of pores.Coarse textured soils (sandy) have larger pores, but less total pore space.Fine textured soils (clayey) have smaller pores, but more total pore space.
25Soil PermeabilityPermeability is a measure of how fast air and water can move through a soil.Soil texture and soil structure both pay a role in soil permeability.
28Soil Water Saturated soil is when that soils pores are full of water. Gravitational water is that water that moves out of the soil due to gravity. This water is generally in the larger Macro-pores.Capillary water is that water that is held in the soil due to adhesion and cohesion against the pull of gravity. This water is generally held in the smaller Micro-pores and as a film around soil particles.
29Soil WaterAfter a major rain event, once the gravitational water has left the soil, the soil is at Field Moisture Capacity.The wilting point is reached when soil water levels decline to the point that all remaining water is held too tightly by soil particles to be removed by the plant.
31Available Water Capacity Available water capacity is a measure of the water available to plants.Commonly defined as the difference between the amount of water at field moisture capacity and the amount at the wilting point.This is the water a plant has a chance of utilizing.