7.1 Discuss salinization, nutrient depletion and soil pollution as cause of soil degradation

Where does it come from?  Physical means Weathering of rocks ○ CaCO 3 + H 2 O + CO 2 -> Ca HCO 3 -  Chemical means Bacteria 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  Silicates Silicon is covalently bonded to four oxygens  Aluminosilicates Al 3+ has a similar size to silicon Can replace the silicon to form aluminosilicates

Inorganic (cont’d)  If Al3+ replaces a Si 4+ 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 NH 4 + ○ Synthesis of amino acids and proteins Ca 2+ ○ plant cell wall synthesis Mg 2+ ○ 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 ( CaCl 2, MgSO 4, NaCl) are in water When 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 (SO 4 2- )7.72%  Magnesium (Mg 2+ )3.68%  Calcium (Ca 2+ )1.17%  Potassium (K + )1.10%  Bicarbonate (HCO 3 - )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 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.

Calibration 35 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 irrigation Small amounts of salts ( CaCl 2, MgSO 4, NaCl) are in water When 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 growth Increase in ions means a decrease in plants ability to take up water Osmosis 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 weeds Fungicides = 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 matter The 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 present Can 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 acids High 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

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

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 erosion Increase water retention properties Increases 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