Andy KleinschmidtDon McClureExtension EducatorSoil ScientistVan Wert CountyNRCS-USDA

What is Soil?A logical place to begin today is with a definition of soil.Soil: Unconsolidated mineral or material on the surface of the earth resulting from and influenced by time, parent material, climate, organisms, and topography.Not all soil is created equal, the soil vs. a soil.

Why are soils important?

ObjectivesSoil colorSoil textureSoil structureSoil pHCECMicroorganismsNutrient movement

What stands out about the landscape?

Soil ColorColor is the most obvious characteristic of soil.What are some colors encouraged by well aerated conditions?What are some colors encouraged by poorly aerated conditions?Soil color is influenced by the oxidation state of iron and manganese.

Soil Color, Soil Aeration or Drainage, and the Oxidation State of Iron1. Iron is reduced2. Fe++3. dull colors (grays, blue)4. poorly drained1. Iron is oxidized2. Fe+++3. bright colors (yellows, browns)4. well drainedPOOR AERATIONGOOD AERATION

Soil Color Tells A StoryWell DrainedPoorly DrainedDrainage on this farm?

Soil HorizonsBCApZone of highest organic matter content. The p denotes that this soil has been plowed. A layer of accumulation of iron and clays. Blocky structure is readily seen in this layer.Unconsolidated material. Outside the zone of major biological activity and is not affected by soil forming processes.

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

. . . more on Soil HorizonsMollisolAlfisolBCApA

USDA-NRCS National Soil Survey Center

Average Soil Composition{}Pore space 50%Solids 50%25% Water25% Air5% Organic Matter45% Inorganic (mineral materials)

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Soil TextureDetermined by the relative proportion of sand, silt and clay Surface Area ChargeSand50 cm2/gnoneSilt500 cm2/gnoneClay5,000,000 cm2/gnegative

Relative Size Comparison of Soil ParticlesSand - feels grittySilt- feels floury(2.00 - 0.05 mm) (0.05 - 0.002 mm)(< 0.002 mm)barrelplatecoinClay- feels stickyUSDA system for determining soil separates

ClaySilty ClaySilty Clay LoamClay LoamSandy ClaySandy Clay LoamLoamSilt LoamSiltSandy LoamSandPercent ClayPercent SiltPercent SandFineMediumCoarseLoamy Sand

SandSandyloamSiltloamClayloamClay1234Inches water/ft soilPlant Available Water

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

Comparison of Coarse Textured and Fine Textured Soils Coarse Textured SoilLess porespace but more macroporesFine Textured SoilMore total porespaceTexture and Pore Space

Soil StructureSoil structure is the combination or arrangement of primary soil particles into secondary unitsThe way soil particles are arranged to form stable aggregatesCompare this to clods, which are caused by disturbance (plowing or digging)Compaction results from implement traffic, stable soil aggregates are broken down

Common Types of Soil StructureGranularPlatyPrismaticColumnarBlockySingle GrainMassive

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CBEAGranularPlatyBlockyMassive

Bulk Density DeterminationFor our example, lets assume we have 1 cubic centimeter of soil that weighs 1.33 gramsSoil is made of solids andpore spaces1.33 grams{}

Bulk Density (cont.) Bulk density (g/cm3)Soil Cropped Uncropped

Hagerstown loam (PA) 1.25

Marshall silt loam (IA) 1.13

Nappanese silt loam (OH) 1.31Data from Lyon et al.

Some Common Bulk DensitiesUncultivated/undisturbed woodlots 1.0 to 1.2 g/cm3Cultivated clay and silt loams1.1 to 1.5 g/cm3Cultivated sandy loams1.3 to 1.7 g/cm3Compacted glacial till1.9 to 2.2 g/cm3Concrete2.4 g/cm3

Bulk Density and Compaction8 inches1.430 inches7 inches9 inches10 inchesBulk Density (g/cm3)1.901.871.841.801.60Plow layerCompacted zoneUncompacted subsoilDepthData from Camp and LundTill2.20

Influences of Soil Texture, Soil Structure and DensityWater movementWater retentionSoil temperatureGas exchangeErosion potentialFertility

Hydrologic Cycle and SoilColorStructureBulk DensityTexturepHTemperatureMoistureHorizonDepthsSoil properties that are part of the hydrologic cycle.

Soil pH - a master variableAcid (pH=1.0)Neutral (pH=7.0)Alkaline (pH=14.0)A measure of the hydrogen (H+) ion activityOne pH unit change = a ten fold change in acidity or alkalinity

Why called master variable?soil pH controls:soil microbe activitynutrient exchangesnutrient availabilitygaseous exchangeschemical degradationCEC

pH value{{Too alkaline for most plantsToo acidic for most plantsRange of alkalinity soils of arid and semiarid regions have pH greater than 8.0Range of acidity weathered soils of the southeastern US coastal plains typically have pH less than 5.0

Soil pHMethods for soil pH determination can vary widelyMeasure of the direct concentration of H+ ions in the soil solutionBuffer pH measures both H+ ions in the soil solution and the reserve H+ ions bound on cation exchange sitesIt is used to express the acidity or alkalinity of the soil solution, not lime requirementpH represents the equation -log[H+]

Factors Affecting Soil pHParent Soil MaterialPrecipitationNitrogen ApplicationsCropping SequenceOrganic Matter Breakdown

Making Acid Rainacid rain a concernair has carbon dioxide (CO2)acid produced by nitrogen applications

Clay MineralsClay structure magnified 1,600 times

Clays are layered minerals made of . . .. . . together they form . . .

Organic Matter

Factors Influencing Organic Matter AccumulationTopographyNative VegetationClimateTimeOrganisms

Forest Soil0481216202428320246804812162024283202468101214Percent Organic Matter in SoilWell DrainedPoorly DrainedSoil Depth in InchesSoil Depth in Inches

Prairie vs. Forest SoilPrairieForestEffect of Native VegetationA horizon = 14 inchesA horizon = 4 inches

Importance of Soil Organic Matter Physical and Chemical PropertiesImproves physical conditionAllows for good aggregation of soil particles because of the plant and animal residues in the surfaceIncreased water infiltrationAllows water saturation by acting as an absorbentImproves Soil TilthAllows for more uniformity of the soil aggregates in proportion to the plant, animal and mineral residues present

Cation Exchange Capacity (CEC)Ability of a soil to hold and exchange cationsIons are atoms with an electrical chargeNegatively charged colloids (organic matter and clay) attract and hold cations

CEC of a soil is due to:Organic Matter ContentClay ContentType of ClayMontmorillonite high CECIllite mod. CECKaolinite low CEC

NRCS STATSGO Database

CEC (cont.)Most soils are negatively charged and hold cations.Cations held on exchange sites may move into the soil solution & be taken up by roots.Anions are not held on soil and are subject to leaching (P is exception).

SOIL COLLOIDN SN SS NN S+ -- ++ -+ -Like poles (charges) repelOpposite poles (charges) attractCa2+K+Na+Mg2+SO42-NO3-Cl-NH4+

Common CEC RangeHeavy Clay50 CECSand2 CECCEC 25More Clay, More Positions to Hold CationsCEC 5Less Clay, Fewer Positions to Hold CationsK+Ca2+Mg2+NH4+Na+K+Ca2+K+SandClayAnother Schematic Look at CEC

Some practical applications Soil CEC 11-50Soil CEC 1-10

Microorganisms* in the SoilMicrobes live in small clumps In fact, less than 1% of the soil surface will support the growth of microbesDo not migrate muchTheir goal: maintain species7,000 different species in one gram of soil!4.5 x 1016 bacteria/acre, 3 inches deep*Excludes nonarthropod and arthropod animals, as well as vertebrates

One final thought . . . What do you notice about this soil core?

Preferential Flow Calculated from Kladivco, et al. (1999); models from Cornell

SoilsENJOY THE REMAINDER OF THE TRAINING.

WERE GLAD YOU ARE HERE.

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.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 is important because it is an indirect measure of important characteristics such as aeration and drainage. 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.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.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.

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 OhioAqualf = high water table, very productive when drainedCryalf = cold, northern temperatureUdalf = humid moisture regimeUstalf = limited water for plantsXeralf = mediterranean climate, cool winters and hot/dry summersAn 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.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 !!!

Dont 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 clays incredible surface area (and negative charge) that makes it an extremely important component of nutrient exchange and ultimately, soil fertility.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.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).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.

There are many different types of soil structure, but the most common are granular, platy, blocky, prismatic, and massive. Granular is normally found in the A horizon. Platy is sometimes found at the base of the A horizon, or near the top of the B horizon. Blocky and prismatic are most common in the B horizon and massive is usually associated with the C horizon.

A common question to consider for agricultural interests is How is structure formed? The largest component is microbial exudates. Therefore, additions of organic matter from residue or manure will in theory lead to formation of stable peds.

Granular, platy, prismatic, columnar, and block are all generically referred to as peds.

Single grain and massive are understood to be structureless. Bulk density is simply dry weight of soil divided by total volume of soil. Soil texture, soil structure, and density work together to influences many other soil properties. Water movement, water retention, soil temperature, gaseous exchanges, erosion potential, and fertility are all influenced by texture, structure and density..Moisture and color relate to temperature.Soil pH is a measure of the hydrogen ion activity and is expressed on a scale of 1 to 14. Soil pH can sometimes be confusing the way it is expressed. Many growers associate a one unit change in pH with very little change in soil acidity. They fail to recognize that soil pH is expressed on a logarithmic scale, and that a one unit change in pH is actually a 10X change in hydrogen ion concentration.Many factors affect soil pH.Parent material of the soil can make a soil either acidic or alkaline.Precipitation can leach Ca and Mg through the soil, lowering pH.Nitrogen applications can lower pH through H+ ion production during nitrification.Cropping sequence can affect Ca and Mg removal.Organic matter breakdown can release organic acids lowering pH.Acid rain has been a major environmental concern. Its detrimental affect on streams and lakes and on fish populations within those waters is well documented. One would expect pure water to have a pH of 7. However, since air is approx. 0.03% CO2, some CO2 becomes absorbed into rain water and the pH drops due to the formation of weak carbonic acid.

Atmospheric CO2 in equilibrium with rain water gives rain a natural pH of 5.6. But today, sulfur oxides and nitrogen oxides in the air from use of fossil fuels make rain slightly more acidic, as low as 4.2 in some areas. Yet, there is still very little acid in rain. The H2SO4 and HNO3 amount to only 1/2 lb. of H+ per acre per year, which requires less than 25 lbs. of limestone per acre to neutralize.

The real acidity problem is most soils comes from the H+ produced by the microbial oxidation of nitrogen compounds, and from the natural leaching of alkaline cations from the soil.

from: Graveel and Fulk-Bringman, Demonstrations in Soil Science, Purdue University.

Soil organic matter is an important component of soils. Arguably, it can be the single most important component for soil fertility consideration. Most mineral soils have an organic matter content between one and six percent.

Organic matter is a highly complex substance, as shown in the structure by Frank Stevenson, a pioneer in soil organic structure research.Topography (landscape position), native vegetation, and climate are three major factors that influence organic matter accumulation.

Higher levels of organic matter are normally found in the lower areas of a field or landscape. Decomposition of plant residue is slower under cool, wet conditions that are associated with the low areas of a field.

Native vegetation impacts organic matter content. Example, forest soils contribute less organic matter than prairie soils.

The climatic effect on organic matter accumulation relates to temperature and moisture. Warm and moist climates increase organic matter decomposition by microbes, often resulting in less organic matter content in soil.The effect of drainage on organic matter accumulation for a forest soil.Organic matter influences many important physical and chemical properties.Cation exchange capacity (CEC) is very important in regards to soil fertility. CEC is simply the ability of a soil to hold and exchange cations. A cation is an element with a positive electrical charge, while an anion is an element with a negative electrical charge. Negatively charged colloids (clay and organic material) attract and hold cations. The cation exchange capacity of a soil is influenced by organic matter and clay content. Clay type can also influence CEC with montmorillonite contributing more than illite or kaolinite to a soils charge. The type of clay is determined by the original parent material from which the clay was derived. Regardless of clay type, organic matter is the greatest contributor to a soils CEC.Iowa has some of the highest CEC soils in the U.S. Remember from a few slides back that mollisols dominate Iowa soils. Get the connection?The negative sites of CEC hold positive ions (cations) allowing those cations to avoid being leached through the soil profile. Anions are not held on the exchange sites and are subject to leaching (except P).

Phosphorus is not prone to leaching in the PO43- (phosphate) form, even though it is clearly an anion. CEC functions on electrostatic attraction. Phosphate chemically binds to soil. This diagram illustrates the principle of CEC. Just like the magnet, where opposite charges attract, negatively charged soil attracts positively charged cations. These cations can be exchanged and replaced in the soil by another cation.

This is a great photograph of a soil core loaded with macropores. Use this slide to build up to Preferential flow.

It has also been noted that in some cases nutrients, pesticides, and biosolids (manure, etc.) can move through a soil profile much more quickly than what may be expected. These materials are carried down rapidly by rain (or their own water carrier as in the case of liquid biosolid waste) that moves through large macropores, cracks and other such pathways, often before the bulk of the soil is thoroughly wetted. This phenomenon is referred to as preferential flow. Research suggests that most of the water flowing through large macropores in soil does not come into contact with the bulk of the soil. Such flow catalyzes downward leaching of nutrients, pesticides, and/or biosolids applied to the soil surface.