State EnvirothonSoils Dennis Brezina USDA-Natural Resources Conservation Service Resource Soil Scientist – Bryan Area Helping People Help the Land
What is Soil? Soil: The combination of air, water, and organic and mineral matter on the earth’s surface that is distinguishable from its parent material and can support rooted vegetation.
What is Soil? It is a product of the effects of CLIMATE, BIOTIC ACTIVITY, acting on PARENT MATERIAL as conditioned by TOPOGRAPHY over TIME.
Four Components of a Typical Soil 1% 25% 49% 25% Pore space remains about the same If the soil is wet>>>it contains more water As the soil dries>>>air takes its place
FIVE SOIL-FORMING FACTORS • Climate • Biotic Activity (Living Organisms) • Parent Material • Topography • Time
CLIMATE • MOST INFLUENTIAL FACTOR • Weather over time • Temperature and precipitation in particular • Determines the nature and speed of formation and development • High Heat, High humidity, abundant rain generally produces more development • For every 10 degrees C rise in temperature, the rate of chemical reactions doubles • Also micro-climates created because of topography
BIOTIC ACTIVITY • Plants and manipulation by animals • Especially Native Vegetation - Grasses vs. trees • Microorganisms Soils under forest vegetation generally hold less moisture, have lower pH and organic matter, and thus are generally lighter in color, and have lower fertility Soils under prairie vegetation hold more moisture, have higher pH and organic matter, and thus are generally darker in color, and have higher fertility
PARENT MATERIAL • Weathered fragments of Organic or Mineral material from which soils form • Related to Geology • Most of the eastern half of Texas was influenced by the Gulf Coast as Coastal Plain Sediments ( At least 85% of Texas was under water at one time) • Soils are derived from sandy, loamy and clayey sediments
TOPOGRAPHY Slope or configuration of the land • Nearly level vs. sloping – - Water shedding vs. water receiving - Flat areas are generally wetter than steeper, sloping areas • Different soils will occur on the ridge, side slope and foot slope of a hill - Soils on backslopes and shoulder slopes are generally thinner than those on summits, footslopes and toeslopes
TIME • Soils on flood plains and along the coast are “younger” or less-well developed • Stable landscapes have “older” more developed soils Takes about 500 years to form an inch of soil from hard parent material Geologic Yardstick of Time
SOIL TEXTURE • The relative proportion of SAND, SILT and CLAY. • The MOST IMPORTANT PHYSICAL PROPERTY of the soil because it determines the capacity of a soil to retain moisture and air. • Essentially impossible to change unless you remove it, or add large amounts to it.
The Three SOIL Particle Sizes • Sand size particles are the largest of the soil particles - feels gritty - compare it to the size of a baseball • Silt size particles are intermediate in size - has a smooth, talcum powder feel - compare it to the size of a marble • Clay size particles the smallest - feels sticky and plastic when wet - compare it to the size of a BB
Clayey Soils • High Shrink-Swell – clay minerals expand when wet and shrink when dry - Cause cracks in building foundations, sidewalks, etc. • Many are called VERTISOLS • High Organic Content • High Water Holding Capacity (High clay=high water) • Slower permeability • Agriculturally productive • Difficult to work with More Water
Sandy Soil • Larger pore spaces • Low organic matter • Low fertility • Low water holding capacity • Rapid infiltration and permeability • Generally better drained • Easy to work with More Air This doesn’t mean that sandy soils are not as “good” as clayey soils. Sandy soils are just good for different things (peanuts, timber production, etc.).
Loamy Soil • Somewhere in between • Wide array of soils • Low to High Fertility • Low to High Organic content • Low to High Water Holding Content • Moderate to work with • Often have an Argillic Horizon
Argillic Horizon • Generally have a Sandy or Loamy surface • Increase in Clay from the surface to the Subsoil • This horizon is called an ARGILLIC horizon • Sometimes called a “Claypan” • Water often perches on top of the Argillic horizon
SOIL COLOR Most visible soil property Soil color is written as: Hue Value/Chroma (10YR 6/3) HUE CHROMA VALUE
Soil Color 1. HUE Most visible soil property • Dark=high organic content Humus/Organic Matter is generally black or brown; thus soils that are high in organic matter are generally darker in color • Light=low organic content • Red, yellow, brown is well drained Generally due to iron compounds. Reds are highly oxidized. Compare to rust on iron=metal gets wet, as it dries (oxidizes) it turns a reddish-yellow color • Gray could mean excessive wetness Iron is either removed or reduced due to the removal of oxygen 3. CHROMA 2. VALUE
Two Basic Soil Epipedons or Surface Horizons • 1. Mollic Epipedon • Thick, Dark Surface • Color Value of 5 or less (3 or less moist) • Color Chroma of 3 or less (moist) • Dark=high organic content • Soil Order is either Mollisols or Vertisols
Two Basic Soil Epipedons or Surface Horizons • 2. Ochric Epipedon • Basically any other surface horizon • Light Colored Surface • Light=low organic content • Soil Order is generally Entisols, Alfisols or Inceptisols
Mottles/Redoximorphic Features • Mottles or redoximorphic features are caused by oxidized or reduced iron • Red, orange and yellow colors are iron accumulations (oxidized iron) • Grays are iron depletions (reduced iron)
Gray Could mean Wet • Gray surface • Contains mottles (oxidized or reduced iron) • Mottles indicate alternate wetting and drying • Concave or Flat landscape! The water cannot drain off the area • Wet soils could be associated with wetlands!
3 Requirements for a Wetland • Hydric Soil • More than 50 percent Hydrophytic Vegetation • Hydrology indicating seasonal inundation, ponding or saturation by water
Hydric Soil • Soils that formed under conditions of saturation • Soils developed under sufficiently wet conditions to support the growth and regeneration of hydrophytic vegetation • Essentially a “gray” soil
Hydrology Water Marks
Soil pH • Ideal pH range is 5.5 to 7.5 • Most U.S. soils have pH range of 4 to 8.5 • pH >8.5 could mean high salt content • pH<4 Aluminum and Iron toxicity • pH meters best tool for testing • Add lime for soils less than 5.5 and sulfur for soils above 7.5
Three Main Plant Nutrients N-P-K • Nitrogen (N) encourages above ground vegetative growth (makes the grass greener) • Phosphorous (P) important for seed germination, disease resistance, root development and plant maturation (flowering, fruiting, seed formation) • Potassium (K) important for root development and photosynthesis (especially root crops and for starch formation) ACME FERTILIZER N-P-K
How can the Nutrients be put back when used up? • Organic Fertilizer - lawn clippings, mulch, cottonseed meal, guano, manure, poultry litter, ash, peat • Inorganic Fertilizer - chemically produced. Broad range of types. Easy to use, but easy to over-fertilize--and with higher fuel costs, expensive $$ • On lawns, Rule of Thumb is to put: 1 pound of Nitrogen per 1000 square feet. More is NOT always better.
How much do you use? • N-P-K is expressed as a percentage of Nitrogen, Phosphorous and Potassium • Rule of thumb: 1 pound of nitrogen per 1000 square feet • Question??? • How many pounds of this fertilizer (25-10-5) should you use on a yard that is 6000 square feet ? ACME FERTILIZER N-P-K 25-10-5
How much Fertilizer for 6000 square feet? • 25-10-5 25 percent N 0.25 pounds (lbs) of N per pound of Fertilizer • 0.25 lbs N x ? lbs Fert = 1 lb N per 1000 sq ft • 0.25 lbs N x ? lbs Fert = 1 lb N per 1000 sq ft = 0.25 lbs N 0.25 lbs N • 4 lbs Fert per 1000 sq ft = 4lbs Fert/1000 sq ft • 4 lbs Fert X 6000 sq ft = 1000 sq ft 24 lbs Fertilizer
How big is 1000 square feet? • Square root of 1000 is 31.6 or • About 32 feet x 32 feet 32 ft x 32 ft = 1024 sq ft
Salinity • Causes soil to become hard • Modifies and degrades soil structure over time • Damages roots and stunts plants • Reduces the water that is available to plants (moisture can be in the soil, but the sodium “ties” it up to where it is not available to plants) • Damages steel
Remember our Argillic Horizon? • Sodium makes a special type of Argillic horizon called a NATRIC horizon • The salts and sodium (especially Na, Ca and Mg) leaches through the surface and collects at the Argillic horizon (remember how water perches on top of the Claypan?) • This modifies the soil structure over time • The argillic horizon becomes hard
Natric Horizon • The Sodium starts to coat and seal off the natural soil structure and water starts to perculate only through larger structure cracks called COLUMNS or PRISMS • Damages roots and stunts plants • Reduces the water that is available to plants (moisture can be in the soil, but the sodium “ties” it up to where it is not available to plants)
Soil Structure Blocky Structure Columnar Structure Platy structure is associated with water lain sediments. Single Grain is generally your sands. Columnar structure is associated with high sodium. Massive is associated with compact, heavy clay soils.
Erosion • Wearing away or removal of the earth’s soil or land surface • Soil moved by wind, water, ice or gravity • Especially occurs on bare soil • Areas with more than 3 percent slope are susceptible to water erosion
Why is Soil Conservation Important? What do we get from soil? • Food (Fruits, vegetables, cereal grains, beef, chicken, pork, etc.) • Cotton (clothes) • Leather (shoes, jackets) • Rubber (comes from trees) • Lumber • Paper • Paints, color dyes
Why is Soil Conservation Important? Imagine the Earth as an Apple… • Only 1/4 of the Earth is land, the rest water. • 1/2 of that is mountains, deserts, or covered with ice (non-livable). • Cut remaining 1/8 that is livable into fourths (Cities, too dry or too wet, too hot or too cold) . • Only 1/32 of the Earth is farmable. • Now, peel the skin off this 1/32 slice of the apple, and that is our soil that we are farming on. http://www.flickr.com/photos/
Types of Erosion • Raindrop Splash • Sheet and Rill Erosion • Gully Erosion • Wind Erosion
Stubble Mulch or Ridge-Till No-Till Conservation Practices Preventing Erosion Contour Farming Strip Cropping Terracing Planting Wind Breaks
Preventing Raindrop Splash • Stubble Mulch or Ridge Till • No-Till • Pasture or Rangeland • Some type of vegetative cover • Cover Crops • No-Till intercepts Raindrop Splash almost like having grass cover. • Soil structure improves with time, and more water infiltrates and percolates through the soil.
Comparison of No-Till to Conventional Tillage The clear water from the no-till side of the field is transporting less topsoil, nutrients and pesticides. Runoff from no-till field on the left and Conventional tilled field on the right. Milan Experiment Station-Milan, Tennessee
Preventing Sheet and Rill Erosion • Contour Farming • Terracing • No-Till, Stubble Mulch or Ridge-Till • Grassed Waterways • Slow the speed of surface water flow • Contour farming and terracing intercept and slow down the speed of surface water flow. • Some crops do not leave enough residue and cover to use No-Till. • Clayey soils also do not accept No-Till as well as loamy soils (hard to work).
Preventing Gully Erosion • Grassed Waterways • No-Till • Vegetative cover • Contour Farming • Strip Cropping • Terracing • Grassed Waterways are used a lot all over the country to prevent all four types of erosion. • Terraces are used on steeper land to intercept and slow down the downhill flow of water.
Preventing Wind Erosion • Planting Wind Breaks • Rotary Hoe-adds surface roughness • Strip Cropping • The perfect time to Break Wind http://www.ewrs.org/pwc/rotary.htm
Secondary Benefits of Preventing Erosion • Moisture Conservation leads to Increased Yields (especially in drier years). • Improved Soil Structure leads to Moisture Conservation (see above). • Preventing Fertilizer Loss leads to Increased Yields and saves money. • Takes less horse power to use a spray rig than tillage (saves Fuel and money).
Soil Quality Indicators • Soil organic matter: soil fertility, structure, stability, nutrient retention; soil erosion • Physical: soil structure, depth of soil, infiltration and bulk density; water holding capacityChemical: pH; electrical conductivity (salinity); plant available nutrients • Biological: microbial biomass C and N; potential for mineralization of N; soil respiration.
Soil Surveys • An inventory of soils that includes maps, soil descriptions, photos and tables of soil properties and features • Used by farmers, real estate agents, land use planners, engineers and others who desire information about the soil resources for use in general land use planning
The major parts of a soil survey publication... • How to Use this Soil Survey • Table of Contents • Introduction and General Nature of the County • General Soil Map & Block Diagrams • Detailed soil map units • Use and management and interpretive tables • Classification of soils • References • Glossary • Index to map sheets • Soil maps