E7 and E12: Soil (UNMODIFIED)

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What

What is soil?

It is a complex mixture of inorganic and organic matter

Composition: Air (25%), Mineral Particles (45%), Organic Matter (5%), Water (25%)

TN: In terms of the 5% Organic Matter:

Humus (80%), Roots (10%) and Organisms (10%)

Importance:

Source of plant nutrients (e.g. N, P, K, Mg and S)

Provides anchorage for plants

Habitat for diverse community

Soil Degration:|| The result of human activities that reduce the ability of soil to support life.||

Causes:

Salinization

Nutrient Depletion

Soil Pollution

Salinization:

Refers to the accumulation of salts in soil

Causes:

Continual Irrigation of Crop Land

Water used for irrigation = often taken from lakes, rivers and groundwater supplies (contains variety of salts)

When water evaporates, the additional ionic compounds remain in the soil

Effects:

May cause the water table to rise up

Increased risk of variety of pollutants to enter water supplies

When concentration of salts build up, water will NOT be able to move up the roots of plants

Plants may be dehydrated

Plants may die when ions reach toxic levels

Nutrient Depletion

What's suppose to happen

Natural or well managed ecosystem, plant matters are left to decay

Nutrients released into soil --> left to grow

Human Interaction:

Crop harvesting clears the land of plants (esp. for intensive farming)

Much less plant matter left for decomposition

Nutrient cycle - disrupted (as the plant matter and nutrients are NOT returned to the soil) [e.g. K+, NO3+, POV 3-)

Artificial fertilizers are then required to promote plant growth, contributing to water pollution

Inorganic VS Organic Pollutants:

Inorganic:

not based on carbon-containing compounds

Organic:

based on carbon-containing compounds

Pesticide Use:

Pros:

Improve Crop Yields

Cons:

Remove links in the food chain

Reduce soil biodiversity

Leaching into water supply

Artificial Fertilizers Use:

What is it?

A source of plant nutrients such as NO3- and POV 3- for soil with nutrient depletion

Pros:

Improve crop yields

Cons:

Leaching of NO3- and POV 3- into bodies of water causes eutrophication

Domestic and Industrial Waste

Types:

Landfill Sites (leaching of variety of pollutants into the soil)

Industries (leaching from containment ponds or direct dumping onto the soil or into bodies of water)

General Effects:

Disruption of soil food chain with a resultant decrease in soil quality

Runoff (or leaching) of hazardous chemicals into ground waters and waterways

Organic Soil Pollutants + Source

Agrochemical

Insecticides, herbicides and fungicides (NOT artificial fertilizers which are inorganic)

PCBs

Leakage from electrical transformers or hydraulic fluids

VOCs

Leaks from oil fields, pipelines, gasoline, some household cleaning products, industrial solvents, chemicals from glues; markers; and paints

Organotin Compounds

Fungicides, bactericides (used to treat wood and paper), anti-fouling paint on ship hulls

PAH

Tar, crude oil spills, incomplete combustion of wood or vegetation

SOM:|| The organic component of soil.||

Plant + Animal Tissues

Soil Biomass (worms, bacteria, insects, roots, etc)

Partial decomposition products of plant+ animals (humus (polysaccharides and proteins; simple sugars and amino acids)

Benefits:

Prevents soil degration

Improve crop yields

Reservoir of nutrients

Holds on to water

Improves soil texture

Prevents soil erosion

Biological Effects of SOM:

Source of energy

Source of N/ P/ S containing nutrients which are needed to make proteins and DNA in plant cells

Phys

Physical Effects of SOM

Loosens soil (therefore allows room for root growth and improves air retention)

Absorbs heat energy (the very dark color of humus absorbs and retains heat)

Increases ability to retain moisture (SOM particles have many carboxyl groups that can form hydrogen bonds with water)

Chemical Effects of SOM

Cation Exchange Capacity

Definition: The amount of exchangeable cations in the soil; The number of moles of singly-charged cations that may be held by 1kg of clay/soil

The higher the CEC, the higher the quality of the soil

Since clay and humus particle have many negative charge (due to the presence of ions such as COO- and SiO4- (clay))

Various cations can be held by the clap and soil particles

Other cations dissolved in the soil can be bounded/ exchanged for other ions [H+ (clay) + K+ (aq) --> K+ (clay)+ H+(aq))

Improved Retention of Soil Nutrients

CEC of humus allows soil particle to bind and hold on to nutrients

These nutrients will be less likely to be washed away via rain

Reduced Leaching of Metal Ions into Bodies of Water

CEC of humus also allow soil particles to bind and hold onto potentially toxic metal ions

Prevents leaching of the metal ions into bodies of water

HOWEVER: may decrease soil quality

SOM particles act as an acid-base buffer system

Buffers keep the pH of solutions at a fairly constant level when small amounts of acid or base are added

SEE EQUILIBRIUM AND ACIDS/ BASES TO FINISH THIS CHAPTER!!

Background

Soil Degration

Soil Pollution

Soil Pollutants

Soil Organic Matter