Soils Mr. Gust
Soil Definition • A layer of natural materials on the earth’s surface containing both organic and inorganic materials and capable of supporting plant life.
Why is Soil Important? • Gives plants something to grow in • Holds nutrients • Home to microorganisms • Holds water • Provide us with a food source
Soil Formation Factors Five factors control soil formation: • Parent material-Source of mineral matter • Limestone, sandstone, shale, basalt • Time-longer forming, thicker soil • Climate-greatest effect on rate. Hot wet climate goes fastest • Vegetation- More vegetation, increased soil forming • Topography-slope. Erosion elevated, less soil formed
Physical properties of soil: • Soils are made up of four substances: • Small mineral particles – from the breakdown of rocks – about 45% • Organic matter – plant and animal material, both dead and living, microbes – about 5% • Water • Air • Percentages of water and air can vary greatly
Ideal soil growing media: Air 25% Solid 50% Water 25%
Soil textures: • Large particles: stones, cobbles, gravel • Mineral particles in soil: • Sand (largest particles) • Silt (smaller) • Clay (smallest) • Soil texture refers to the amount of sand, silt and clay in the soil.
Particle sizes: (diagram) Texture Sand Silt Clay Sand compares to barrel Silt compares to a plate Clay compares to a coin
How can you tell what soil texture you have? • Sand can be seen with the naked eye. Feels gritty. • Silt is intermediate in size. Visible under microscope. Feels like talcum powder. • Clay is smallest particle. Feels slick and sticky when wet, firm when moist and hard when dry. Size of particles affects moisture-holding ability, plowing, which crops can be grown.
Hydrometer Method • Largest particles fall out first • Measure amount (mm) of each particle size • Use chart to determine soil type
Pores • Spaces in soil between the mineral material (sand, silt, clay), organic matter • Micro Pores • Water filled at field capacity • Macro Pores • Air filled at field capacity • Field capacity=amount of moisture in soil after excess water has drained away
Soil/water relationships: • Water drainage depends on soil pore size • Large pores in the soil can take in water more rapidly than fine pores. • Sandy soils drain fastest • Clay soils retain water longer
Soil/Water Relationships • Saturation • Can take no more water, water starts to puddle on top • Field Capacity • Moist • Wilting Point • Plant can not uptake any more water, starts to wilt
Soil profile (horizon) is … • The arrangement and properties of the various soil layers • Topsoil (A Horizon) • Organic material, dead plant/animals, roots, humus • Subsoil (B Horizon) • Clay that has moved (leached) down over time • Parent material (C Horizon) • Rock
More about topsoil: • Surface, top layer of soil • From a few inches to several feet thick • Darker, contains organic material • Softer, more easily worked than underlying areas. • Also called the A horizon • Farmland
More about subsoil: • Layer just under topsoil • Lighter in color – may be red, brown, yellow or gray in color • Little or no organic material • Usually higher in clay content than topsoil • Firmer, more difficult to penetrate • Also called the B horizon
More about parent material: • Lower soil layer • Material from which topsoil and subsoil developed • Very firm and difficult for roots to penetrate • Also called the C horizon
What does soil color indicate? • Drainage • Brown or dark brown surface soil layers indicate the presence of organic matter. • Subsoils are often reddish brown, red, yellowish brown, yellow or gray, indicating how wet the soil is at certain times. • Gray means poorly drained and clay • Red, brown or yellow colors means well drained • Light/dark color can affect heat too
Soil depth is: • The total depth of topsoil, subsoil and parent material for plants to grow. • Can cause the yield of a crop to be high or low. Deep rooted plants, such as alfalfa, will not grow well when planted on a shallow soil. • Deep soil= 35 inches plus • Moderately deep soil=20 to 34 inches deep • Shallow soil= 10 to 20 inches deep. • Very shallow soil is 10 inches or less.
Soil pH: • Water in soil contains dissolved mineral salts – the “soil solution.” • Numbers from 1 to 14 measured with a pH meter • Some materials added to soil change the pH (peat moss is acidic, limestone is alkaline) Alkaline Acidic Neutral 5 7 1 2 3 4 6 8 9 10 11 12 13 14
Cation exchange capacity (CEC): • The total number of exchangeable cations a soil can hold (the amount of its negative charge) is called its cation exchange capacity or CEC. • The higher a soil's CEC, the more cations it can retain. • Cations include Phosphorus, Potassium • CEC increases as organic matter/clay increases.
Organic matter improves the soil: • Soil organic matter consists of plant and animal residues in various stages of decay. • The 4 benefits of organic matter: • Improves physical condition and structure • Increases water infiltration • Decreases erosion losses • Supplies plant nutrients (increased CEC)
Soil Erosion • Erosion is the process of wearing away or removing • Water • Splash • Sheet • Rill • Gully • Stream bank • Wind • Surface creep • Saltation • Suspension
1965 soil taxonomy system for the United States: • Gelisols - soils with permafrost within 6 feetof thesurface • Histosols - organic soils NRCS photos
1965 soil taxonomy system for the United States: • Spodosols - acid soils with a subsurface accumulationof metal-humuscomplexes • Andisols - soils formed in volcanic ash NRCS photos
1965 soil taxonomy system for the United States: • Oxisols - intensely weathered soils of tropical and subtropicalenviron-ments • Vertisols - clayey soils NRCS photos
1965 soil taxonomy system for the United States: • Aridisols - calcium carbonate-containing soilsin aridenviron-ments • Ultisols - soils with a subsurface zone of silicate clay accumu-lation NRCS photos
1965 soil taxonomy system for the United States: • Mollisols - grassland soils • Alfisols - another type of soil with a subsurfacezone ofsilicateclayaccumu-lation NRCS photos
1965 soil taxonomy system for the United States: • Inceptisols - soils with weakly developed subsurfacehorizons • Entisols - soils with little or no morphological develop-ment NRCS photos
Wrapping it all up: • Soil is the soft outer covering of the earth. • One of our most importantnatural resources • Necessary for plants to grow • Provides food for plants, which in turn furnish food for humans and animals • Stores much of the water that plants use