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Soil Science
Horticulture/Natural ResourcesSutherlin High School AST
September 15, 2015
What is Soil?
• Dynamic, living interface between the atmosphere and rock
Functions of Soil
• Anchor and nutrients for plants• Habitat for animals• Recycle waste through decomposition• Cleanse and store water• Engineering uses
Components of Soil
• Solids– Mineral– Organic Matter
• Pore Space– Water– Air
Soil Forming Factors
• Climate - temperature and precipitation• Organisms - type of biology present • Relief/ Topography – where is the water,
where are the people
Soil Forming Factors
• Parent Material - soil minerals and particle size impact drainage and filtration
• Time - influences ability of soil to extract pollutants physically and tie up nutrients biologically
• Climate• Organisms• Topography/relief• Parent Material• Time
Which one can we change?
Soil = f(cl,o,r,p,t)
Passive Factors
Active Factors
Mineral and Texture
• Minerals in soil:– Sand– Silt– Clay
Mineral and Texture
Mineral and Texture
1. Sand/Loamy Sand (Coarse)2. Sandy Loam (Moderately Coarse)3. Loam/Silt Loam (Medium)4. Clay Loam/Sandy Clay Loam/Silty Clay Loam
(Moderately Fine)5. Clay/Sandy Clay/Silty Clay (Fine)
Mineral and Texture
• Surface area per unit volume–1 g sand ~ 0.1 m2
–1 g silt ~ 1 m2
–1 g clay ~ 10-1000 m2
Mineral and TextureCoarse textured soils larger pores
Fine textured soils greater total pore space
SandClay
Mineral and Texture
Sand Silt Clay
Water-holding capacity
Aeration
Drainage
Nutrient retention
Low Medium High
Good PoorMedium
Slow Very slowHigh
HighLow Medium
Mineral and Texture
• Clay
Mineral and Texture
Root zone
Horizons
• Master Horizons• Special Horizons
Soil Color
• Result of soil elements, organic matter, wetness
Soil Color
• Described using the Munsell Color System
Soil Color
• Listed as a number system– hue (a specific color)– value (lightness and darkness)– chroma (color intensity)
Soil Color
• Color Characteristics– Black/dark brown: high organic
matter– Brown: well-drained, aerated– Grey: wet, color-less– Red: old, well established
(oxidized)– Red or Yellow: presence of iron
oxides– White: leached
Soil Color
• Color Categories1. Black/Dark Brown2. Brown/Light Brown/Yellowish Brown3. Reddish Brown/Red4. Grey/Light Grey/White
Soil Structure
• Soil breaks down to units called peds– Particles bound together
Soil Structure
• Peds come in multiple structure shapes– Blocky– Prismatic– Platy– Columnar– Granular
Soil Structure
• Soil without ped structure is considered structureless– Single-grained: sands– Massive: clay layers
• No natural breaks into peds
Soil Structure
• Structure Grade– Ability of peds to hold together– Stronger structure grade=peds easier to see and
separate from one another (clear breaks)
Soil Structure
• Structure Grade Categories– Strong (very easy to
see/separate)– Moderate– Weak (difficult to
see/separate)– Structureless (no
structure)
Mottles
• Redox (reduction-oxidation) reactions• Caused by periodic or seasonal saturation of
soil• Indication of wetness
Mottles
• Mottles used to determine internal drainage of soil– Excessively drained soil: 40”+ of coarse/ moderately
coarse– Well-Drained: No mottles in the top 40”– Moderately-Well Drained: No mottles in the top 24”– Somewhat Poorly Drained: No mottles in the top 8”– Poorly Drained: Mottles in the top 8”
Mottles
Coarse Fragments
• Non-soil fragments over 2mm in diameter• Coarse fragments decrease water holding
capacity• Percentage
coarsefragments vsPercentage soil
Special Features
• Unique characteristics of the soil• Tillage Pan
– Ap horizon caused by multiple years of plowing– Creates hard layer that limits water passage/roots
Special Features
• Duripan– Layer of calcium and other minerals that have
collected into a concrete-like layer below the surface horizon(s)
– Bkqm horizon
Special Features
• Fragipan– Layer
Special Features
• Cr– Weathered bedrock– Rock that can be dug
with a spade
Special Features
• Slickensides– Formations of
shrink-swell clays– Leaves shiny
patches from pressure of swelled clay
Soil Orders and Naming
• Master horizons• Transition horizons• Special horizons
Properties of the Whole Soil
Effective Depth
• Ability for roots to penetrate soil depth• Inhibited by impermeable layers
– Bedrock– Massive clay layer?– Durapan?– Cr?
Effective Depth
• Available water calculations only matter where roots can reach
• Look for root depths
Available Water Holding Capacity
• Amount of water available for plants• Measured in inches water/inch of soil
Available Water Holding Capacity
• A factor of texture– Values vary depending on clay content– Calculated by
= Inches of soil X texture value X % soil
Soil Permeability
• Speed of water’s ability to move through the soil
• Affected by texture and structure grade
Soil Permeability
• Surface permeability determined using the first mineral horizon (A)
• Subsoil permeability determined using the slowest permeable layer above 30 inches of depth
Erosion
• Erosion is a factor for the surface horizon• Wind Erosion
– Only a factor in Eastern Oregon• Water Erosion
– Factor of texture and slope
Erosion
• Management practices affecting erosion– Vegetation– Water flow management (ditches/diversions)– Tilling vs no-till
Internal Drainage
• Indicator of how often the site is saturated, and at what level
• Determined by mottles• Use mottle rules
Parent Material
• How did the soil form/arrive there• Residuum – resides in place• Colluvium – moved by gravity
Parent Material
• Alluvium – moved by water– Old: older than 100 years– Recent: within last 100 years
Parent Material
• Lacustrine – old lake bed• Wind-blown sand (eolian)/
silts (loess)• Volcanic ash
Relief/Site Position
• Uplands (Residuum)• Footslope (Colluvium)• Fan (Recent alluvium)• Stream Terrace (Old alluvium)• Floodplain (Recent alluvium)
Slope
Stoniness/Rockiness
• Amount of large surface rocks greater than 10” in diameter
Stoniness/Rockiness
• Inhibits surface tillage– None– Stony/Rocky (1 every 30 to 100 feet)– Very stony/rocky (1 every 5 to 30 feet)– Extremely stony/rocky (more than 3% of the
surface)
Drainage Feasibility
• Ability to remove water from the soil site– Limited by textures,
permeability• Involves adding drainage
tile– Perforated pipe, drains soil
water to an outlet
Drainage Feasibility
• Not needed if soil is well-drained• http://
www.youtube.com/watch?v=G2t6JYzuExw
Irrigation Suitability
• Can irrigation be used on the site?• Factor of water holding, slope, permeability• Whether water is available or not does not
matter
Land Class
• Categorization of land based on its usability for agriculture
• Class I thru VIII• Class I-IV are arable• Class V-VIII are livestock/
forestry
Most Intensive Crop
• Crop with most food value that can be produced on land
• Does not consider economics of each crop
Erosion Control
• Method of limiting soil loss based upon the utilization of the land
• Practices– Water-control/cover crop: diversions, planting off-
season crops after harvest
Erosion Control
• Practices– No-till/stubble mulch: leaves root stalk after
harvest, does not disturb surface horizon– Controlled grazing: timing of livestock/numbers
Soil Amendments
• Additions to the soil to promote plant growth• Fertilizers
– Nitrogen: added annually (spring)– Phosphorous: recommended 60#/acre– Potassium: recommended 300#/acre
Soil Amendments
• Soil pH– Optimal for plant growth: 6.2-8.4
• Soils below 6.2: correct acidity by adding lime• Soils above 8.4: correct alkalinity by adding gypsum,
sulfur (tiger yellow)
Soil Amendments
• Soil pH– Not all soils are amended
• Forestry sites: fertilizers not practical• Cannot correct alkalinity if irrigation water not available
Septic Feasibility
• Ability to install septic drain fields for waste management
• Affected by texture, slope