Introduction to Agriculture Soil Science Unit 2 Physical Properties Physical properties or characteristics of the soil determine to a large degree how useable and productive soil will be Productivity of soil is affected by the physical properties of soil ID: 642573
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Physical Properties of Soil
Introduction to Agriculture
Soil Science
Unit 2Slide2
Physical Properties
Physical properties or characteristics of the soil determine to a large degree how useable and productive soil will beSlide3
Productivity of soil is affected by the physical properties of soil
Factors of productivity
How quickly water penetrates
How well water stays in the soil
How well soil holds up under machinery
The ease of root penetration
The aeration of the soil
Important because influences:
Plant and root growth
Microorganism population and activity
Growth of toxins
Water and nutrient absorption
Disease developmentSlide4
Physical Characteristics Include
Texture
Structure
Consistency
pHSlide5
Soil Texture
Texture refers to the size of the individual soil particles called SOIL SEPARATES
The larger the size of the separates, the coarser the soil feels
Largest of the soil particles is sand
Silt particles are smaller than sand
Smallest particles are referred to as clay
Can compare the separates to a basketball, golf ball, and BB for relative size differenceSlide6
Soil TextureSlide7
Soil Texture
Soils rarely are composed of pure sand, pure silt, or pure clay… rather a combination of all three
Ideal soil
Loam Soil: nearly ideal for growing most crops
Soil that is <52% sand, 28-50% silt, and 7-27% claySlide8
Soil Texture
Sandy soils
Coarse
Does not hold water well…particles are so large, water from rain or irrigation pass through the soil and little is retained for plants
Coarser soil results in fewer soil nutrients that will be in the soil and available for plants
Coarse or sandy soils are less productive because they do not hold water or nutrients as well as finer soils
When particles are large, water moves out of the pores taking water-soluble plant nutrients with it
LEACHING Slide9
Soil Texture
Clay soil
May not let enough water through
Cause the water to run off or hold the water too long Slide10
Soil Texture
Mixture of finer textured silts and clay
Typically more productive
Slow water down and hold a portion of water for plants to use
Make nutrients available longer for plants
Have more nutrients adhere to the greater surface area of claySlide11
Soil pH
The pH of the soil has to do with how acid the soil is
Acid – a substance containing hydrogen that forms hydrogen ions when dissolved in water
Hydrogen ion – a hydrogen atom with a single proton (+)
Hydroxide ion – a hydrogen atom with two electrons (-)
pH scale – a measure of the relative strength of the hydrogen ion or hydroxide ion activity in a substance
Neutral substance – has as many hydrogen as hydroxide ions; ranks 7.0 on the scale
Hydrogen ions > hydroxide ions = acid; score lower than 7 on the scale
Hydrogen ions < hydroxide ions = alkaline; score higher than 7 on the scaleSlide12
Soil pH
Soils that are either too acidic (higher _________ ion concentration), or too alkaline (higher ___________ ion concentration) may not be ideal for production of certain crops
Examples:
Potatoes, tomatoes, peppers, beans, onions
Cabbage, Brussels sprouts, mustard, Slide13
Soil Structure
Water flow through soil is greatly influenced by the structure of the soil
Factors that cause soil particles to clump together are:
Affected by freezing/thawing
Root movement
Earthworms/other life forms
Variation of moisture contentSlide14
Soil Structure
Group of clinging soil particles are called
peds
, or soil aggregates
Peds are held together by the clay and humus in the soil
Peds categorized by
Type (shape)
Spherical
Plate-like (flat and thin)
Block-like (cubic)
Prism-like (long with several sides)Slide15
Soil Structure
Class (size)
Very fine
Fine
Medium
Coarse
Very coarse
Grade
Strength, how stable, not changing or fluctuating – permanent
Structureless soils – no real structure… either single grains (sand in a dune) or massive (clays stuck together with no distinguished peds)
Weak structure – peds are hard to distinguish and only a few can be separated in moist soil
Moderate structure – peds are visible and can be handled without breaking up
Strong structure – most of the soil is formed into peds and can be handled without breaking up