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