E7 and E12: Soil (UNMODIFIED)

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 soilCauses: 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 DepletionWhat'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 compoundsOrganic:based on carbon-containing compounds

Pesticide Use:Pros:Improve Crop YieldsCons: 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 depletionPros:Improve crop yieldsCons:Leaching of NO3- and POV 3- into bodies of water causes eutrophication

Domestic and Industrial WasteTypes: 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 + SourceAgrochemicalInsecticides, herbicides and fungicides (NOT artificial fertilizers which are inorganic)PCBsLeakage from electrical transformers or hydraulic fluidsVOCs Leaks from oil fields, pipelines, gasoline, some household cleaning products, industrial solvents, chemicals from glues; markers; and paintsOrganotin CompoundsFungicides, bactericides (used to treat wood and paper), anti-fouling paint on ship hullsPAHTar, 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 SOMCation 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 systemBuffers 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