module 1: nature, functions, and properties of soils

Module 1: Nature, Functions, and Properties of Soils OverviewEO1: What is Soil?

What is Soil?Unconsolidated (loose) naturally occurring material of mineral and organic composition at the surface of the earth that supports plant life

What is Soil?Unconsolidated (loose) naturally occurring material of mineral and organic composition at the surface of the earth that supports plant life

Unpacking that……..1. Loose2. Natural3. Mineral and organic material4. Supports plant life

Anything bigger than 2 mm (2 dimes

stacked on top of each other) and we

call it a rock.

Four Principal Components of Soil

Air (gases)

Water (liquids)

Organic matter

Minerals

Actual Microscopic Image

Very Coarse 2.0 – 1.0 mm

Coarse 1.0 – 0.5 mm

Medium 0.5 – 0.25 mm

Fine 0.25 – 0.1 mm

Very Fine 0.1 – 0.05 mm

SAND

SILT

CLAY

Soil Texture Diameter of Individual Particles

.05 - .002 mm

< .002 mm

Soil Textural Triangle Not every soil particle is the

same size

There is a ‘distribution’

of particle sizes

0

500

1000

1500

2000

2500

3000

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05

Surface area to volume ratio changes sharply as particles decrease in sizes below 0.005 mm diameter. This makes a difference

A single sand particle from a sandy soil (99 % sand, 1 % silt, 0 % clay).

A multitude of small particles associated together in a clay loam(30 % sand, 43 % silt, 27 % clay).

Soil Solid Water Air

Figure 1. Soil compaction causes a reduction in available space for soil air and water, and limits pathways for crop roots.

‘Ideal Soil’ (50% solid, 25% air, 25% water) Compacted Soil

soil organic matter - SOM

What soil organic matter is• Fresh plant matter (must be < 2mm!!!)• Freshly deceased micro-organisms, insects, and animals• Fresh products and wastes from living organisms (e.g. manure, sugars, enzymes.)• Decomposing organic material (any of the above somewhere along the decay

spectrum)• Stable organic material (e.g. humus, charcoal from prairie and forest fires)

Shredder organismsWood shavings




Animal waste




Protein breakdown in soil


What soil organic matter is• Fresh plant matter (must be < 2mm!!!)• Freshly deceased micro-organisms, insects, and animals• Fresh products and wastes from living organisms (e.g. manure, sugars, enzymes.)• Well decomposed organic material (any of the above somewhere along the decay



What soil organic matter is• Fresh plant matter • Freshly deceased micro-organisms, insects, and animals• Fresh products and wastes from living organisms (e.g. manure, sugars, enzymes.)• Decomposing organic material (any of the above somewhere along the decay


Soil humusLeonardite Humus Minerals


What soil organic matter is• Fresh plant matter • Freshly deceased micro-organisms, insects, and animals• Fresh products and wastes from living organisms (e.g. manure, sugars, enzymes.)• Decomposing organic material (any of the above somewhere along the decay


CharcoalPrairie fire

Organic matter serves several important functions in soil1. Increased nutrient storage through cycling 2. Increase in water holding capacity (improves infiltrations but also slows down hydraulic

conductivity) 3. Improves soil structure through aggregation of clay particles.4. Reduces erosion potential.

Humus is a special example of SOM. It is a class of SOM that is particularly stable. This means that it resists breakdown by microorganisms, providing longer lasting benefits than fresh sources of organic matter. Humus develops naturally over time in soils when they remain undisturbed.

Charcoal is formed from any of the types of organic matter exposed to high heat from prairie or forest fires. Charcoal is ‘burned’ organic matter without enough oxygen present to promote complete combustion. This is why blackland soils are the color they are.


What soil organic matter isn’t• Geologic materials• Living plants, bacteria, fungi, worms, beetles, moles, or pigs buried in mud. SOM

does not include living organisms. The soil is a habitat for life, but is not made of living things. Some sources of information may differ from this point of view.

Synthetic growth media Microbes that are still alive

A brief bit about soil as a microbiome

~1 billion microorganisms / gram soil

~1 million microorganisms / gram ocean water

Soil is a massive habitat for life


Soil is a massive habitat for life - Bacteria

• There may be a ton or more of bacterial living biomass per acre of soil• They fill all sorts of niches in the microbial ecology

• Predator• Heterotroph• Anaerobes/ facultative anaerobes• Nitrifiers• Scavengers

Symbiotic Rhizobia bacteria The ubiquitous Bacillus’ soil attachment

A brief bit about soil as a microbiomeSoil is a massive habitat for life - Fungi

• Fungi have a slower activity than bacteria but tolerate more limiting factors• They fill all sorts of niches in the microbial ecology

• Symbiotes• Heterotroph• Anaerobes/ facultative anaerobes• Scavengers

Figure 2: Vesicles (left) and hyphae (right) of AMF under microscope showing AMF colonization on corn root

hyphaevesicles


Soil is a massive habitat for life - Protozoa, Nematodes, and Arthropods

• Protozoa are larger than - and therefore predate upon -bacteria

• Soil aggregates create micro environments that afford protection



• Nematodes are non segmented worms

• ~50 um in diameter• Four groups based on diet

Bacterial-feeders consume bacteria.Fungal-feeders feed by puncturing the cell wall of fungi and sucking out the internal contents.Predatory nematodes eat all types of nematodes and protozoa. They eat smaller organisms whole, or attach themselves to the cuticle of larger nematodes, scraping away until the prey’s internal body parts can be extracted.Omnivores eat a variety of organisms or may have a different diet at each life stage. Root-feeders are plant parasites, and thus are not free-living in the soil.



• Mites are microscopic arthropods

• Related to spiders and scorpions and millipedes (among others)

Many bugs, known as arthropods, make their home in the soil. They get their name from their jointed (arthros) legs (podos). Arthropods are invertebrates, that is, they have no backbone, and rely instead on an external covering called an exoskeleton.

module 1: nature, functions, and properties of soils

Documents