SOILS

What is Soil?? Soils are the transition between the biotic and abiotic worlds. Soil is a mixture of: 1. Minerals 2. Water 3. Gases 4. HUMUS-Dead “things” that have broken down and become organic material—decayed plant and animal remains (thanks to decomposing fungi and bacteria)

Soil Composition (idealized)

Why are soils important? Soils are important: As a habitat for growing crops As a habitat for growing crops Food Food Fabrics/Dyes Fabrics/Dyes Rubber/Building Materials Rubber/Building Materials Medium for photosynthetic organisms Medium for photosynthetic organisms Medium for decomposers Medium for decomposers As foundations of buildings As foundations of buildings As beds for roads and highways As beds for roads and highways As an absorbent of domestic wastes in rural areas as well as a depository for other wastes As an absorbent of domestic wastes in rural areas as well as a depository for other wastes As a filter for pollution that comes from rain and water runoff As a filter for pollution that comes from rain and water runoff

What determines how soil forms? There are THREE main contributing factors 1. Length of time soils have been developing—the AGE of the soils 2. The materials (rocks) from which they form- these are called PARENT MATERIAL 3. The ENVIRONMENT in which they developed (climate, vegetation, soil life, topography) Good rule of thumb: yrs per inch of topsoil

How do parent materials get into soils?? WEATHERING: Any process where rock breaks down (changes chemically and physically) There are two types of weathering: Physical or Mechanical Weathering: Large rock mass is broken into smaller fragments of the same type-NO CHEMICAL CHANGE Chemical Weathering: mass of rock is decomposed by chemical reactions

What is happening in these photos?

Let’s take a closer look at frost wedging… 1.Water collects in cracks in rock 2.Water expands when it freezes 3.Water melts; Pieces of rock break off Rock

Chemical Weathering Most chemical weathering involves gases in the atmosphere (oxygen, carbon dioxide, Most chemical weathering involves gases in the atmosphere (oxygen, carbon dioxide, acid gases) and/or water Example: Think about metal rusting You go from metal to rust—a chemical reaction has taken place You go from metal to rust—a chemical reaction has taken place Contrast with EROSION ( movement! ) by wind, water, ice

Topsoil Formation

Detritus-based Soil Ecosystem All these happy little critters break down dead plant and animal material and aerate the soil—they make topsoil!

What is a soil profile?

Soil Profiles Soil Profiles - the sequence of layers (horizons) from the surface downward to rock or other underlying material Soil Profiles - the sequence of layers (horizons) from the surface downward to rock or other underlying material Soil Layers - “O”- organic horizons, litter derived from dead plants and animals - A- TOPSOIL horizons which lie at or near the surface [Eluvial- Characterized as zones of maximum leaching, E = Exit] - B- SUBSOIL [sometimes illuvial I = Into] - C- unconsolidated parent material under A&B layers - Bedrock

Soil profile example Maryland Soil Profile

What are some soil properties? Texture Texture pH pH Porosity Porosity Permeability Permeability Nutrient Levels—Nitrogen/Phosphorus Nutrient Levels—Nitrogen/Phosphorus Color Color

SOIL TEXTURE Soil texture: The way a soil "feels" Soil texture: The way a soil "feels" Depends on the fraction of each size of particle in the soil Sand, silt, and clay are names that describe the size of individual particles in the soil. Sand, silt, and clay are names that describe the size of individual particles in the soil. SAND are the largest particles and they feel "gritty.“ SAND are the largest particles and they feel "gritty.“ SILT are medium sized, and they feel soft, silky or "floury" SILT are medium sized, and they feel soft, silky or "floury" CLAY are the smallest sized particles, and they feel "sticky" and they are hard to squeeze. CLAY are the smallest sized particles, and they feel "sticky" and they are hard to squeeze.

Why care about soil texture? Predicts soil properties-fertility, drainage, etc. Sandy soils Sandy soils low organic matter low organic matter Poor retention water and nutrients (it flows through) Poor retention water and nutrients (it flows through) As silt and clay fractions increase, As silt and clay fractions increase, More organic matter More organic matter Better buffered Better buffered Better retention of water and nutrients Better retention of water and nutrients But you can have TOO much clay But you can have TOO much clay Hard to cultivate-too sticky when wet; too hard when dry Hard to cultivate-too sticky when wet; too hard when dry Shrinks and swells Shrinks and swells The best soils are a mix of all three (20% clay, 40% sand, 40% silt) and are called LOAM

Soil pH What does pH measure? It’s a measure of how acidic or basic of a solution is on a 0 to 14 scale (REM: inverse log of [H+]?) It’s a measure of how acidic or basic of a solution is on a 0 to 14 scale (REM: inverse log of [H+]?) We actually measure pH of soil SOLUTION We actually measure pH of soil SOLUTION The pH of the soil solution affects how much of soil nutrients are available to plants. The pH of the soil solution affects how much of soil nutrients are available to plants. TOO ACID or TOO BASIC, can cause important nutrients (like nitrogen and phosphorus) to be unavailable. At these extremes (too acid and too basic), METALS also released into soil, causing TOXIC effects in plants At these extremes (too acid and too basic), METALS also released into soil, causing TOXIC effects in plants PESTICIDE TIE-IN: If soil is too acidic, applied pesticides, herbicides, and fungicides will not be absorbed (held in the soil) and they will end up in runoff PESTICIDE TIE-IN: If soil is too acidic, applied pesticides, herbicides, and fungicides will not be absorbed (held in the soil) and they will end up in runoff

Plant pH Preferences Plants the like strongly acid soil (pH 4.0 to 5.0) Plants that prefer slightly acid soil (pH 5.0 to 6.5) Plants that prefer neutral soil (pH ) Sundew Pitcher Plants Venus flytrap Azalea Rhododendron Camellia American holly Orchids Many evergreen trees and shrubs Strawberries Potatoes Carrots Fescue grasses Alfalfa Bluegrass Most vegetables (lettuce, tomato) Grains (corn, wheat)

Soil Porosity and Permeability Porosity- volume of pores (spaces) per volume of soil—sometimes referred to as “aeration” Porosity- volume of pores (spaces) per volume of soil—sometimes referred to as “aeration” Permeability- rate of flow of materials through soil Permeability- rate of flow of materials through soil Infiltration—water getting into soil Infiltration—water getting into soil

Soil Nutrients Nitrogen Nitrogen Phosphorus Phosphorus Nutrients: essential chemical elements needed for the growth of healthy plants Plants get nutrients from soil after the nutrients have dissolved in the soil solution (the water around soil particles) Each nutrient has specific roles in producing healthy plants

 Needed for chlorophyll, growth Low nitrogen causes yellowy leaves  Needed for chlorophyll, growth Low nitrogen causes yellowy leaves Needed for roots, energy  Low phosphorus causes purply leaves, poor roots poor roots

Sources of Images GLOBE Program- Agricultural Soils GLOBE Program- Agricultural Soils ures/Soils.pdf ures/Soils.pdf ures/Soils.pdf ures/Soils.pdf EnvironPowerPts/Agriculture%5B1%5D.ppt EnvironPowerPts/Agriculture%5B1%5D.ppt EnvironPowerPts/Agriculture%5B1%5D.ppt EnvironPowerPts/Agriculture%5B1%5D.ppt