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7.1 Discuss salinization, nutrient depletion and soil pollution as cause of soil degradation. E7: Soil. Where does it come from?. Physical means Weathering of rocks CaCO 3 + H 2 O + CO 2 -> Ca 2+ + 2HCO 3 - Chemical means - PowerPoint PPT Presentation
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E7: SOIL
7.1 Discuss salinization, nutrient depletion and soil pollution as cause
of soil degradation
Where does it come from? Physical means
Weathering of rocks○ CaCO3 + H2O + CO2 -> Ca2+ + 2HCO3
-
Chemical meansBacteria and fungi in the soil breakdown
organic matter which then makes more soil
Components of soil Inorganic matter
Largest component From weathering of rocks Contains
○ Silica○ Silicates○ aluminosilicates
Water/ Air The amount affects how life forms survive and then decay
Organic matter Bacteria and fungi convert organic matter into humus
○ A water insoluble mixture○ Half it’s mass is carbon and approx. 5% nitrogen
Inorganic Matter
SilicatesSilicon is covalently bonded to four oxygens
Aluminosilicates Al3+ has a similar size to siliconCan replace the silicon to form
aluminosilicates
Inorganic (cont’d) If Al3+ replaces a Si4+ then in every four tetrahedrons
there is 1 electron deficient These ions + electronegative oxygen = ability to hold
onto plant nutrients Plant nutrients
K+
○ Controls the amount of water that enters via osmosis NH4
+
○ Synthesis of amino acids and proteins Ca2+
○ plant cell wall synthesis Mg2+
○ Synthesis of chlorophyll
7.1 Salinization
Accumulations of water soluble ions or salts in the soil due to continual irrigation to crops
How?Small amounts of salts ( CaCl2, MgSO4,
NaCl) are in waterWhen irrigation doesn’t wash them away
they build up in the soil
salinity
Salinity is the total amount of dissolved salts in water; grams of salts per kilogram of water (g/kg) or as parts per thousand (ppt).
Seawater has 11 major constituents that make up more than 99.99% of all dissolved materials.
Although salinity may vary, the major constituents are well mixed and present in the same relative proportions.
Salts
Chloride (Cl-) 55.07% Sodium (Na+) 30.62% Sulfate (SO4
2-) 7.72% Magnesium (Mg 2+) 3.68% Calcium (Ca 2+) 1.17% Potassium (K+) 1.10% Bicarbonate (HCO3
-) 0.40% Bromide (Br -) 0.19% Strontium (Sr 2+) 0.02% Boron (B 3+) 0.01% Fluoride (F-) 0.01%
Salinity
Affects other properties of seawater, such as its density and the amount of dissolved oxygen.
Salinity Significant Values
The average salinity of the world’s oceans is 35 ppt.
Freshwater has a salinity of <1 ppt.
Inshore waters with salinity values between 1 - 25 ppt are called brackish.
Waters with salinity greater than 40 ppt are called hypersaline.
Salinity
Addition of salts to pure water causes an increase in density. Salinity can be calculated by measuring the specific gravity of a water sample using a hydrometer, correcting for the effect of temperature and converting the readings to salinity by using conversion tables.
Specific Gravity = density of sample Density of pure water
Salinity
Be sure hydrometer is clean Fill 500 mL graduated cylinder with sample water Determine the temperature of your sample Place the hydrometer in cylinder and let settle. It
should not touch the cylinder walls, and should be read from the bottom of the meniscus.
Read the specific gravity from the hydrometer scale
Using the specific gravity and temperature values, determine salinity from salinity table in Teacher’s Guide
Read three times. The values should be within 2 ppt of the average. Discard outliers.
Calibration35 ppt standard:
○ Measure out 17.5 g NaCl (table salt) and pour into a 500-mL graduated cylinder.
○ Fill the cylinder to the line with distilled water and carefully swirl the solution to mix the standard, until all salt crystals have dissolved.
○ Pour the solution into a 1-quart plastic bottle and label.
Prepare a blank using 500 ml of distilled water.Follow the directions for a water sample.Check technique every six months
.
Salinization
How?
Bad irrigationSmall amounts of salts ( CaCl2, MgSO4,
NaCl) are in waterWhen irrigation doesn’t wash them away
they build up in the soil Rise of the water table
Removal of native plants which leaves to reduction in evapo-transpiration○ Soil water gets close to the surface and
evaporates leaving behind the salts
Salinization Effects
Reduces plant growthIncrease in ions means a decrease in plants
ability to take up waterOsmosis is affected ---Suggested experiment: effect of time, temp., size of seed, type of soil, water
Nutrient Depletion
Decreases soil quality = decline in crop yield
How?crops that take nutrients and minerals from
the soil and are continually harvested reduce soil quality
Countering Nutrient Depletion
Replenishing minerals and nutrients Crop rotation Nitrate/ Phosphate fertilizers
Chemicals end up in water supply○ Leads to eutrophication (excess growth of
aquatic life)
Soil Pollution or Contamination
Due to pesticides, herbicides, fungicides Pesticides = kill insect pests
○ Lower crop yields – destroy flora/ fauna○ Pollute ground water
Herbicides = kill unwanted plants or weedsFungicides = controls fungi
Soil Contamination
Nitrogen/ Phosphate fertilizers Domestic/ industrial waste
Contain heavy metals (chromium, copper, mercury, lead, zinc)
Organic contaminants (PCBs, PAHs)
PAH
7.2 SOM
Soil organic matterThe mixture of non-living
organic components present in the soil in various stages of decomposition
arising from the chemical and biological action on plant
matter and organisms
SOM
Amount of carbon in the soil is a measure of the organic matter presentCan be tested through titration
using a dichromate(VI) solution
SOM (cont’d) Contains
Humic substances ○ Contain phenolic acid (ArOH) and carboxylic
acid (RCOOH) functional groups; weak acids RCOOH RCOO- + H+
The anion RCOO- binds to plant nutrients
Sugars Amino acidsHigh molecular mass polysaccharides and
proteins
Carboxylic acid Anion: Chelate to plant nutrients
Ca 2+ Fe 2+ Mg 2+ Ca 2+
Zn 2+ Mn 2+ Co 2+
Al 3+ > Mg 2+ > K
Higher the charge density, stronger the binding
Chelate
Chelate
Polysaccharides
polysaccharides
Commercial astragalus extracts have been standardized to 40-50% polysaccharides;
some sources claim ability to provide 70-90% polysaccharides.
Phenolic acid
Carboxylic acid
Carboxylic acid
Nylon
Relevance of SOM in Preventing Soil Degredation Plays important role in soil quality Deserts (SOM= Sweet soil)
Organic matter + sand = improved plant growth
Holds onto water Improves soil structure Reduces soil erosion E12.4 chemical function
SOM: Biological
Binds to nutrients – used by microbes and for plant growth
Bacteria and fungi decompose SOM SOM Has large amounts of
Nitrogen 5%○ Synthesis of proteins and chlorophyll
Phosphorus○ Synthesis of enzymes and storage of energy
Sulfur ○ Synthesis of amino acids
SOM: Mineralization /ongoing process Organic matter that contains nitrogen
and phosphorus is broken down or mineralized to release nitrogen and phosphorus to the root
N, P, K, S
SOM: Physical
Allows stable forms of soil clusters Reduces soil erosionIncrease water retention propertiesIncreases ability of air/ water to move
through soil More water affects thermal properties
Moist soil has a higher heat capacity than dry soil
Aka more water = smaller temperature change