Soil Properties

• Physical

• Chemical

• Biological

Different soil properties

- Texture

- Structure

- Soil Depth

- Topography

Physical properties

Texture

Size and relative proportions of various

size groups in a given soil

Structure

Arrangement of soil particles into

groups or aggregates

Soil Depth

Top and sub-soil

Topography

Physical configuration of the soil

surface (drainage, run-off, erosion)

- Clay

- Silt

- Sand

Textural group

Clay

< 0.002 mm

Silt

0.002 - 0.05 mm

Sand

0.05-2.00 mm

Gravel

> 2.00 mm

Soil Textural Triangle

The percent (by weight) of the sand, silt and clay

fraction determines the texture of the soil

45, 35, 20

Loam soil that has __%

sand, __% silt and __%

clay content.

Soil Structure

It refers to the grouping of particles of sand, silt,

and clay into larger aggregates of various sizes and shapes

Structural aggregates resistant to physical stress

Important to the maintenance of soil tilth and productivity

Decreased Aggregate Stability

Excessive cultivation or tillage of wet soils disrupt aggregates and accelerate the loss of organic matter, causing decreased aggregate stability

Soil Structure

Movement of air, water, and plant roots through a soil is affected by this

Stable aggregates

Result in a network of soil pores that allow rapid exchange of air and water with plant roots. Plant growth depends on rapid rates of exchange.

- Crop rotation

- Organic matter addition

- Timely tillage practices

How to maintain Good Soil Structure

Sandy Soils

Difficult to maintain aggregate stability due to low organic matter, clay content and resistance of sand particles to cementing processes

Soil Depth

It refers to the thickness of soil materials which provide structural support, nutrients, and water for plants

Soil permeability

It is a measure of the ability of air and water to move through it

- Permeability

- Moisture content

- Plant Cover

Factors that Affect the Infiltration Rate

Topography

"Lay of the land" or physical configuration of soil surface

Topography

Impact on whether a field can be irrigated

Relief

Component of topography that refers to the difference in height between the hills and depressions in the field

Relief

Affects the type of irrigation system to be used, the water conveyance system (ditches or pipes),

drainage requirements and water erosion control practices

Slope

Incline or gradient of a surface (%)

- pH

- Salinity (EC)

- Cation Exchange Capacity

- Organic Matter

- C:N ratio (Carbon to Nitrogen)

Chemical Properties

Soil pH

A measure of the acidity or alkalinity of a

soil

Low pH Soils

It results in an increase in Al Aluminum is toxic to plants

Increasing Soil pH

Liming materials (pure calcium carbonate or

dolomitic lime) increase soil pH

Wood Ashes

Use also to raise soil pH

Wood Ashes

They also are a source of K, Ca, and Mg

Wood Ashes

Some composts also can increase soil pH.

Decreasing Soil pH

Some plants thrive under acidic conditions

Cation

It is a positively charged ion

Cation-Exchange Capacity (CEC)

It is a measure of the quantity of cations that can be adsorbed and held by a soil

Cation-Exchange Capacity (CEC)

It is dependent upon the amount of organic

matter and clay in soils and on the types of clay

Higher, higher

In general, the ______ the OM and clay content, the ______ is the CEC

Physical

Stabilizes soil structure, improves water holding characteristics, lowers bulk density, dark color may alter thermal properties

Chemical

Higher CEC, acts as a pH buffer, ties up metals

Biological

Supplies energy and body-building constituents for soil organisms, increases microbial populations and their activities, source and sink for nutrients, ecosystem resilience, affects soil enzymes

Soil Organic Matter

Release is highest under warm, moist conditions and slowest in cool dry climates

Soil Organic Matter

Microorganisms are the driving force for nutrient release to plants.

Soil Microorganisms

It constitute < 0.5% (w/w) of the soil mass yet they

have a major impact on soil properties and processes

Microflora

60-80 % of total soil metabolism is due to the what

Soil Microorganism

Responsible for cycling of C, N and other nutrients

Soil Microorganism

Enhance soil structure

Soil Microorganism

Relocate and decompose organic materials

Soil Microorganism

Maintain soil quality and health

Soil Microorganism

Increase soil aeration and penetrability

Soil Microorganism

Involved in disease transmission and control

Macrofauna

Mice, moles, etc.; Earthworms and other worms; Ants, beetles, termites, spiders

Mesofauna

Nematodes, arthropods (mites, centipedes, and springtails), mollusks

Microfauna

Protozoa

Bacteria

Most numerous in soil

Bacteria

Most diverse metabolism

Bacteria

Can be aerobic or anaerobic

Bacteria

Optimal growth at pH 6-8