Essential Question- What is soil made of Essential Question- What is soil made of? How do soils differ in structure?

Introduction to Soil

What do these words make you think of? Earth Dirt Soil http://www.flickclip.com/flicks/Wall-E.html

What is Soil? Soil: Unconsolidated mineral or material on the surface of the earth resulting from and influenced by time, parent material, climate, organisms, and topography. The soil vs. a soil- If "the soil" is thought of like a forest, "a soil" would be an individual tree in that forest. The same applies to soil.

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

What ‘stands out’ about the landscape? COLOR! Soil color is the most obvious characteristic of soil. Soil color is used unconsciously as a quality indicator or as a diagnostic tool.

Soil Color RED YELLOW BROWN GRAY BLUE Color is the most obvious characteristic of soil. Soil color is influenced by the oxidation state of iron and manganese. What are some colors encouraged by well aerated conditions? Soil color is important because it is an indirect measure of important characteristics such as aeration and drainage. RED YELLOW BROWN What are some colors encouraged by poorly aerated conditions? GRAY BLUE

Soil Color, Soil Aeration or Drainage, and the Oxidation State of Iron POOR AERATION GOOD AERATION 1. Iron is reduced 2. Fe++ 3. dull colors (grays, blue) 4. poorly drained 1. Iron is oxidized 2. Fe+++ 3. bright colors (yellows, browns) 4. well drained Soil color is influenced by iron compounds in various states of oxidation. Bright red or brown colors are indicative of well aerated soils; conversely, dull grey and blue colors indicate poorly aerated soils. Iron in the reduced (Fe++) state is referred to as ferrous. Iron in the oxidized state (Fe+++) is referred to as ferric.

Soil Color Tells A Story Drainage on this farm? This slide illustrates a basic point: Soil color gives us a tremendous amount of information. By looking at the profile of the same soil taken from two different locations in a field, we readily know what the drainage is like in that field without having the need to ever step foot on that farm. The soil profile on the left has the tan and brown colors that are derived from oxidized iron, a key indicator of a well drained soil. The soil profile on the left has dull grey colors as a result of reduced iron, which means this soil is poorly drained. Well Drained Poorly Drained

Soil Horizons Zone of highest organic matter content. The ‘p’ denotes that this soil has been plowed. Ap A layer of accumulation of iron and clays. Blocky structure is readily seen in this layer. B To describe soils, horizons are used and identified along with their characteristics. The A horizon is the zone of maximum biological activity and is usually the highest in organic matter content. The B horizon is commonly referred to as the subsoil. This horizon usually has the highest accumulation of clay and iron oxides. The C horizon is the naturally occurring unweathered parent material. The A and B horizons are the most important from an agricultural viewpoint. Regolith- unconsolidated layer above hard, unweathered, bedrock Solum- upper portion of the regolith that has been altered through biochemical and physical processes. The material between the solum and bedrock is referred to as the C horizon. It is slowly changing into solum. Unconsolidated material. Outside the zone of major biological activity and is not affected by soil forming processes. C

Soil Profile What do we see? organic matter - surface soil is darker due to organic matter iron oxides - subsoil has brighter browns and tans due to iron oxides drainage horizons - layers of different color or texture; formed from the top down

. . . more on Soil Horizons Ap A B C Mollisols: *characterized by a thick, dark profile *predominant soils under grassland or prairie native vegetation *considered to be some of the most naturally fertile soils in the world *~25% of land in the U.S. is classified as mollisol (most in the world) *mollisols are dominant Illinois and Iowa; but they also dominate northern Argentina and southern Brazil. *the former USSR has vast amounts of soil classified as mollisols Alfisols: *characterized by an argillic (overlaying layer has deposited clays) Bt horizon *~14% of soils in the U.S. are classified as alfisols *dominates Ohio C

Average Soil Composition 45% Inorganic (mineral materials) 25% Water                                                                                                    { } Pore space 50% Solids 50% An average soil is composed of mineral matter, organic matter, and pore space, which may be occupied by air and/or water. The percentage of these four components can vary depending on how and where the soils were formed. 50% solids and 50% pore space; obviously, these are mixed in a natural environment and fluctuate greatly throughout the year. 25% Air 5% Organic Matter

Soil Texture Determined by the relative proportion of sand, silt and clay Surface Area Charge Sand 50 cm2/g none Silt 500 cm2/g none Clay 5,000,000 cm2/g negative Soil is made up of different particle sizes: sand, silt and clay. The texture of a soil is determined by the relative proportion of sand, silt and clay. Soil structure is the arrangement of sand, silt and clay. 5,000,000 cm2/gram of soil = 5382 ft2 in one gram of soil !!! Don’t believe me? Here are the calculations: 5,000,000 cm2/g x 1 in2/6.45 cm2 x 1 ft2/144 in2 = 5382 ft2/gram of soil 5382 ft2 also equals 0.13 acres. Wow! It is clay’s incredible surface area (and negative charge) that makes it an extremely important component of nutrient exchange and ultimately, soil fertility.

Relative Size Comparison of Soil Particles barrel plate coin Clay - feels sticky Silt - feels floury (< 0.002 mm) (0.05 - 0.002 mm) Sand - feels gritty (2.00 - 0.05 mm) USDA system for determining soil separates

UEQ: How can you determine the texture of a soil sample? WARM UP: Which soil particle is the smallest? The largest? Which one falls in-between? LEQ: What qualitative method is used for identifying your soil type? VOCAB: texture triangle, sand, silt, clay, particles, loam, coarse, fine

Soil Triangle Coarse Medium Fine Percent Clay Percent Silt Silty Clay Percent Silt Sandy Clay Clay Loam Silty Clay Loam Sandy Clay Loam There are 12 basic textural classes found on the texture triangle. Each class can determine fertility, ease of tillage, droughtiness, and general productivity. There are two widely acceptable ways to determine soil texture. The first is determining texture by feel. The second method requires some laboratory equipment, and is referred to the hydrometer method. The hydrometer method separates particles by their rate of settling in water. The texture of a soil can be found by knowing (or estimating) the percentage of two of the three components, usually clay and sand in the hydrometer method. Loam Silt Loam Sandy Loam Silt Sand Loamy Sand Percent Sand

Plant Available Water Available Water Inches water/ft soil 4 Field Capacity 3 Available Water Inches water/ft soil 2 Plant available water is influenced by texture, and is important from an agricultural viewpoint. Clay textures retain the most water due to the many small pores, while sand retains the least amount of water. However, the medium textures like loam or silt loam have the most plant available water since the soil water is not as tightly bound compared to clay soils. Clay holds the most water, sand holds the least; but silt loam offers the best combination of macro and micropores for plant available water. Field Capacity is defined as -0.3 bar (or -30kPa). Wilting Point is defined as -15 bars (-150 kPa). Wilting Point 1 Sand Sandy loam Silt loam Clay loam Clay

Available Water Holding Capacity Storage capacity Texture (in./ft.) Silty clay loam 1.8 Clay loam 1.8 Silt loam 2.0 Silty clay 1.6 Sandy loam 1.4 Rhoads and Yonts, 1984.

Of the Available Water Holding Capacity, which soil from the chart in the previous slide “holds” the most water? Which type would “hold” the least?

… and the answer is… Silt loam would be able to “hold” the most water, whereas sandy loam would “hold” the least. Why?

Less porespace but more macropores Texture and Pore Space Comparison of Coarse Textured and Fine Textured Soils Coarse Textured Soil Fine Textured Soil Soils with a high proportion of pore space to solids have lower bulk densities than those that are more compact and have less pore space. Sandy soils have bulk densities that are commonly higher than in the finer-textured soils such as clay loams and clays. This fact may seem counterintuitive at first because sandy soils are commonly referred to as ‘light’ soils, while clays are commonly referred to as ‘heavy’ soils. In this case, ‘light’ and ‘heavy’ do not refer to bulk density, but rather the amount of effort required for tillage. Less porespace but more macropores More total porespace

Exit ticket Fill in the graphic organizer of each soil horizon and the characteristics of each.