We All Want Food that is

PlentifulPlentifulNutritiousNutritious

SafeSafe

To Your Good Health (Soil)• Keep pH near neutral

• Avoid Compaction

• Maintain Good Moisture

• Promote Drainage

• Good Temperature

• Organic Matter

Purpose of Soil Health

• Promote Plant and Animal Systems

• Promote Clean Water

• Prevent Soil Erosion

• Promote Good food + Human Health

• Promote Life !

Topography begins the story

Parent MaterialParent Material

Materials from volcanoes, sediment

transported by wind, water, or

glaciers are some examples.

Parent Bedrock affects Soil typesLimestone + CaCO3

Igneous Rocks + minerals

Soil Formation takes Time

Soil Begins to Develop on a Columbia River Lava Flow

Gotta’ start somewhere!

TimeTime

It takes hundreds of years to form one inch of soil from parent material.

Soil Profile : thin soil layers shown

Soil, on average, consists of 45% mineral, 25% water, 25% air

and 5% organic matter.

How does soil form? = weathering product of minerals/rocks

• 5 factors influencing soil formation:Parent materials (volcanic, limestone?)Climate (temp, rainfall)Topography (slope, landform)Vegetation (inputs)Time

• Soil Profile: understanding soil “layers”O, A, B, C

ClimateClimate

Weathering processes like the cycles of

freezing and thawing, along with wetting and drying

vary with each region.

Soil Particle Size RelativityThis diagram demonstrates the difference in size between the various soil elements.

Soil Particle SizeSoil is composed of many particles of varying sizes. Soil scientists have classified soil particles into three major groups: Sand, Silt and Clay.

Sand particles are the largest and tend to hold little water (good drainage) and allow good aeration.

Clay particles are very small in size and tend to pack down so that water does not drain well and little or no air can penetrate. Can result in wetland type soils.

Silt particles are medium sized and have properties in between those of sand and clay.

Particle Size + Soil type = Soil Name

Soils get their names by what soil elements are found together and in what ratios.

A soil that is 55% Clay & 45% Silt would be a Silty Clay.

If the percentages were reversed, the soil would be a Clayey Silt.

LOAM SOILA loamy soil, is one that combines all three of these types of particles in relatively equal amounts. Loamy soil is ideal for most garden plants because it holds plenty of moisture but also drains well so that sufficient air can reach the roots.

Soil consists of:

•minerals and weathered rock fragments

•organic matter

•Gases

•water

•living organisms

Regolith are minerals and weathered rock fragments.

Humus is decayed organic matter.

Blue-green Algae inhabit soils and add nutrients

What Controls Rate of Decay• Temperature

• Moisture

• Food Supply

• Oxygen

• C:N Ratio

Fungi• Hundreds of Thousands per Gram

• Perform Functions Similar to Bacteria– Decomposition

• Important in Plant Nutrition– Mycorrhizae (fungus root)

Mycorrhizae• Mutualism

• Benefits Plant and Fungus– Ectomycorrhizal

• Hyphae do not penetrate root cells

– Endomycorrhizal• Hyphae do enter root cells

• Arbuscular

• Very Common– 90+ % of plant families

Roles of Bacteria• Nitrogen Fixation

• Mineralization

• Organic Matter Decomposition

• Soil Stabilization

• Aeration

Root Nodules with N-fixing symbiotic bacteria.

Experiments without/ with N-fixing bacteria

Soil Animals

• Earthworms

• Mites

• Nematodes

• Protozoa

• Beetles

• Termites

Earthworms are decomposers

Ameba attacks bacteria

Fungus attacks ameba

Bacteria attacks fungusFungus attacks nematode

Beetle grub attacks plant roots

Centipedes, Isopods, and Mites are predators

(Campbell and Reece, 2005)

Biologically important

Reservoirs: atmosphere++, soils & sediments, surface water, biomass

Key processes: nitrogen fixation

•Basic Soil Structure:

•Layers (horizons) that change with timeO = organics, at surfaceA = zone of leaching, (+) ions removed, organic rich (dark)B = zone of accumulation or ions and clays and metals (red, rusty, clay rich C = partially weathered bedrockBedrock = Parent Material

What is a soil profile?

A soil profile consists of several soil horizons.

•O horizon = This is the layer of humus on the ground surface.

•A horizon = Top soil; Rich in organic matter. Typically has dark color. Also called zone of leaching.

•B horizon = Subsoil; Also called zone of accumulation. May contain soluble minerals such as calcite in arid climates (caliche).

•C horizon = Weathered bedrock or saprolite (rotten rock).

•Bedrock lies below the soil profile.

A nutrient poor canopy adds does little to neutralize acidic soils

A nutrient rich canopy adds a lot of alkaline nutrients to the soils, neutralizing acidic soils

Water infiltration in Soils

A thin surface crust caused by raindrop impact on a bare soil of poor structure

Crusting and subsurface compaction can result in serious losses of water and soil

Erosion can create deep channels carrying away topsoils in Africa

Calcification of Soils – too

much irrigation

The white are calcium salts

Fight Against Soil Erosion

Contour Plowing to preserve soils

Soil erosion

•Soil may be eroded due to the action of water (runoff) or wind.

•(Please note that weathering and erosion are two different things).

•Soil is transported by streams, and most will eventually be deposited on a floodplain or at the mouth of the river in a delta.

•The Dust Bowl of the 1930's was due to wind erosion of soil following extended drought and over-tilling of the soil.