Soil Is Not Dirt

Why do We Study Soil? Essential natural resource Snapshot of geologic, climatic, biological, and human history Medium of crop production Great integrator: all parts of ecosystem Producer and absorber of gases Waste decomposer Source material for construction, medicine, art, etc. Medium for plant growth Home to organisms (plants, animals and others) Essential natural resource Filter of water and wastes

Soil Forming Factors

What is Soil? Each DISCIPLINE defines soil in a different way, depending on how soil affects it. Wiki says soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics.

About ½ of the soil volume is solid particles What’s In Soil? About ½ of the soil volume is solid particles About ½ of the soil volume is pore space

Physical and Chemical Characteristics of Soil Physical Characteristics Soil Texture, Consistency, & Structure Soil Compaction (Bulk Density) Soil Moisture Nutrient Characteristics (Soil Chemistry) Chemical bonding pH Cation Exchange Capacity (CEC) Nutrient Availability

Physical Characteristics Physical Characteristics of Soil: Texture: the mineral components Consistency & Structure: How the mineral components are put together Bulk Density Soil Moisture

The way the soil “feels” is called the soil texture. Soil texture depends on the amount of each size of mineral particles in the soil. 9 9

Sand, silt, and clay are names that describe the size of individual mineral particles in the soil. Sand are the largest particles and they fell “gritty” Silt are medium sized, and they feel soft, silky or “floury” Clay are the smallest sized particles, and they feel “sticky”

Soil Texture: Relative Size Comparison of Soil Particles beachball Sand (feels gritty) (2.00 - 0.05 mm, USDA) (2.00 - 0.02 mm, ISSS) frisbee dime Clay (feels sticky) Silt (feels floury) (< 0.002 mm, USDA) (< 0.002 mm, ISSS)  The way a soil “feels” is called the soil texture.  Soil texture depends on the amount 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are the largest particles and they feel “gritty.” 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. (0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS)

Clay percentages are read from left to right across the triangle Soil Texture Triangle Clay percentages are read from left to right across the triangle  Record the percentages of each grain size or name of soil  Sand from lower right towards the upper left portion of the triangle  Silt is read from the upper right to lower left 

40 % clay, 50 % silt, 10% sand Soil Texture Triangle What kind of soil do we have?

Again

Effects of Texture on Soil Soils are more cohesive when they have more fine particles (Clays). Soils are more loose when the have more coarse particles (Sand). Different combinations of coarse and fine contents produce different soil textures. A loam is a mixture of sand, silt and clay: sandy clay loam is best in landscapes - best for agriculture. Many other inclusions, such as cobbles, boulders.

Soil Consistency Describes the general organization of the soil. Hold a moist sample between the thumb and forefinger, and gently squeeze it until it falls apart.

The soil is classified by the following categories Loose: You have trouble picking out a single sample and the structure falls apart before you handle it. Friable: The sample breaks with a small amount of pressure. Firm: The sample breaks when you apply a good amount of pressure and dents your fingers before it breaks. Extremely Firm: The sample can't be crushed with your fingers (you need a hammer!).

* Soils with “single grained” structure always have loose consistence. Soil Consistency Soil Consistence Loose* Extremely Firm Firm Friable * Soils with “single grained” structure always have loose consistence.

Soil Structure Soil Structure: the shape that the soil takes based on its physical and chemical properties. Possible choices of soil structure are: With structure Without structure 2 2

Soil Structure: with Structure Soil w Structure Soil Structure: with Structure Granular Blocky Prismatic Columnar Platy

Soil Structure: without Structure Soil w/o Structure Soil Structure: without Structure Single Grained Massive

Bulk Density Bulk Density: a measure of soil compaction Sample is made of Solids and Pore Spaces 1 cm. (so, there is 1 cubic centimeter of soil) 1.33 gms.

Basic Soil Components Basic Soil Components Soil Particles: mineral and organic Pore Spaces: location of air and water

Porosity and Permeability Porosity: percentage of void spaces between grains in soil - effects how much water soil can hold AND how fast water can flow through layer Permeability - measure of the ability of a porous material to allow fluids to pass through it http://techalive.mtu.edu/meec/module06/Permeability.htm

Permeability Granular Blocky Platy

Movement of Fluid Through Soil Rate depends on: pore space (structure) and consistency particle sizes (texture) and particle size distribution. compaction

Run-off Angle and length of slopes Soil or surface type Presence or absence of vegetation

Soil Horizons Soil Horizons: Horizon “C” Horizon “O” = leaf litter Unconsolidated leaf (forest) litter Some decomposed material Horizon “A” = topsoil High in minerals and nutrients High in rich organic material called humus Dark black material Horizon “B” = leached zone, subsoil, zone of illuviation Much lighter in color Lower in minerals and nutrients Horizon “C” Little or no soil development Big chunky rocks Sits atop bed (parent) rock

Soil Horizons O A B C R

Soil Profiles

Soil Chemistry Cation Exchange Capacity (CEC) Nutrient Availability pH

Plant Nutrients Macronutrients: Micronutrients: (needed in large amounts) Nitrogen (N) Phosphorus (P) Potassium (K) Calcium (Ca) Magnesium (Mg) Sulfur (S) Micronutrients: (needed in small amounts) Chlorine (Cl) Cobalt (Co) Copper (Cu) Iron (Fe) Manganese (Mn) Molybdenum (Mo) Nickel (Ni) Zinc (Zn)

Where Do the Nutrients Come From? P K

Where Do The Nutrients Come From? Water Acid Zn Ca K Ni Cu Mg

Where Do the Nutrients Come From? Human introduction Fertilizer Manure and sludge

Absorption and Nutrients Absorption refers to the ability of an object to attract and hold particles on its surface. Solid particles in soil have the ability to adsorb Water Nutrients and other chemicals The most important absorbers in soil are Clays Organic matter

Anions and Cations Chlorine: Cl- Sodium: Na+ What happens when an anion meets a cation? Anions have a negative charge (-): Cations have a positive charge (+): When they meet, they combine to become a molecule, the simplest compound: NaCl (sodium chloride = table salt) Chlorine: Cl- Sodium: Na+

Common Soil Cat+ and An-ions Common soil cations and anions, their chemical symbols and ionic forms

Clay Clay ¼ cup of clay has more surface area than a football field The large surface area of clay allows it to Absorb a lot of water Retain nutrients Stick to other soil particles ¼ cup

- - - - - - - - - - - - - - - - - - - - - - - - - - Chemistry of Clay The Chemistry of Clay: - - - - - - - - - - - - - Clay Particle - - - - - - - - - - - - - Clay particles carry negative charges

- - + + - + - + What’s This Mean? With Magnets In Soil CLAY NH4+ Ammonium CLAY K+ Potasium Unlikes Attract - - + + CLAY NO3- Nitrate Likes Repel - + - +

Cation Retention on Clay Calcium, +2 Magnesium, +2 Potassium, +1 Ammonium, +1 Sodium, +1 Copper, +2 Aluminum, +3 Hydrogen, +1

Cation Retention on Organic Material Hydrogen Nutrients Increasing pH increases cation exchange capacity of organic matter Low pH, 4 - 5 (acidic soil) Neutral pH, 7 (“sweet” soil)

Cation Exchange Capacity (CEC) Cation exchange capacity (CEC) is the total amount of cations that a soil can retain The higher the soil CEC the greater ability it has to store plant nutrients Soil CEC increases as: The amount of clay increases The amount of organic matter increases The soil pH increases (becomes more basic)

Negatively Charged Nutrients Some very important plant nutrients are anions. Soils are able to retain some of these nutrient anions. Retention of nutrient anions varies from one anion to another 1- 2- 2- 1- Nitrate Phosphate Sulfate Chloride

Phosphate Retention in Soil 1. Formation of a new solid material + Aluminum phosphate solid Phosphate Aluminum 2. Anion exchange + 2- Phosphate +

Phosphate Retention in Soil Con’t. 3. Adsorption on oxide surfaces Phosphate anions - Each held by two chemical bonds to the iron oxide surface Iron oxide surface

Nitrate Retention in Soil Unlike phosphate, nitrate is very weakly held by soils Nitrate does not react to form new solids Nitrate is not held by oxide surfaces NO3- If nitrate is not taken up by plants it is very likely to be lost from the soil

Moving Nutrients from Soil to Plants Nutrients in soil solution Plant Root Nutrients on soil clay and organic matter

Soil pH pH of the soil solution is very important because soil solution carries nutrients Ex: If the pH of the soil solution is increased above 5.5, in the form of nitrate is made available to plants. Phosphorus is available to plants when soil pH is between 6.0 and 7.0 Can change pH by adding lime

What Should We Title This Slide? Absorbed nutrients are not prone to loss in drainage water Soil absorption capacity can be exceeded leading to greater nutrient loss Soil consists of mineral and organic matter, air and water Soils are able to adsorb nutrients and other chemicals The most important absorbers are clay and organic matter Absorbed nutrients are available to plants