Presentation on theme: "Soils An essential natural resource for the way that we live."— Presentation transcript:
Soils An essential natural resource for the way that we live.
Next class we will begin evaluating our soil samples. The end product of this soil testing will be a soil quality report. You will be expected to follow this format.this format For Homework tonight, you should begin to write up the “explanation of significance” section of the report based upon your research plus what we review in class today.
Before we begin reviewing content today… You need to prepare your soil sample for chemical testing (which will happen in the next class). FIRST Combine 50 ml of your soil with 250 ml of water in a 400ml beaker. Stir for 1 minute and let it settle until the next class. (label your beaker and put it on the window sill) During the next class you will be able to use the water to test for nutrients.
Why are we so dependent upon soils as a resource? Plants that we eat use soil to: –Anchor themselves into the ground –Gather water & nutrients for growth Plants are essential since they transform energy from the sun into complex molecules that we (and other animals) eat in order to get energy to survive. If soil did not exist, life would probably never evolve out of the oceans.
Where does soil come from? Weathering of rock + Organic matter
How does rock weather in nature? Acid Weathering Oxidation (rusting) Thermal expansion/contraction Frost wedging Abrasion
There are 4 components in the ideal soil mixture Rock fragments (inorganic matter) Humus (organic matter) Water Air What percentage is ideal for each?
Why is it bad if your soil is too dense? It won’t have enough pore spaces for water and air (essential for most plants to grow) It will make it too difficult for roots to grow into This is why gardeners often ‘turn over’ the soil and aerate it. The texture of a soil can affect the density too
What are the 3 particle sizes that contribute to a soil’s texture? Sand—largest Silt—medium Clay--smallest
How will we test for soil texture? Follow the flow chart given on the lab table. It will have you doing things to the soil— like making a ball and rubbing it between your fingers.
Why does soil texture matter? Sandy soils tend to allow water to pass right through them—thus plants not adapted to low water conditions will die from lack of water. Clay soils soak water in slowly and once they soak it in, it tends to stay there and fills all pore spaces—thus drowning a plant that is not adapted to that condition. Note that a “loam” soil is considered an ideal texture for growing many plants. Loam is generally considered to be 40% Sand, 40% Silt, and 20% Clay.
How can you fix a sandy or clay soil? Add Humus Organic matter both… --provides air/water spaces in clay soils & --soaks up/retains moisture in sandy soils However, too much organic matter can cause the soil to be too loose and unstable.
How can you test a soil sample for organic content? Living things have an enzyme that breaks down Hydrogen Peroxide into water and Oxygen gas. When organic matter partially decays, the enzyme is still present. You can tell how much organic matter is present by testing how quickly the soil breaks down Hydrogen Peroxide in one minute.
Our Testing Technique Use 5ml of Hydrogen Peroxide and 30 ml of soil. How to interpret your results… 0 to 10 ml collected = extremely low 10 to 20 ml collected = low 20 to 30 ml collected = adequate more than 30 ml collected = surplus
Have you ever heard that a soil on a farm can get less and less fertile over time? How does that happen? When crops are grown they remove nutrients from the soil. Then the crops are harvested & shipped elsewhere—thus the overall amount of nutrients in the soil decreases. Another factor affecting nutrients is pH
How does pH affect soil fertility? Acids in the soil can cause the nutrients in the soil to become unusable b/c they recombine with them to form different compounds. This makes them get ‘leeched’ away by rainwater For most plants, a neutral pH is best If soil is acidic you can add limestone to neutralize it.
How do we test pH? Add your soil into the green test chamber up to the ‘fill with soil’ line. Then add the green chemical ‘pill’. Finally use a dropper to add water to the ‘fill with water’ line. Cap it and shake. Let it sit one minute. Compare the color to determine the pH.
The 3 Major Soil Nutrients are… Nitrogen (N) Phosphorus (P) Potassium (K) These are mostly what makes up fertilizer. Fertilizers are labeled with three numbers: EX. 30 – 3 – 10 This corresponds to the relative amount of N – P - K
Nitrogen (N) Important for green color of leaves & general growth Plants deficient in nitrogen tend to have yellowish color of leaves
Phosphorus (P) Important for growth of flowers and fruits. DNA needs lots of Phosphorus to replicate itself—thus when a plant is reproducing (which is what fruits and flowers are all about) it needs a significant amount of phosphorus.
Potassium (K) Important for building strong roots & shoots (stems). ‘Winterizer’ lawn fertilizers applied in the fall tend to have more potassium to help the grass survive the winter.
How will we test soil nutrients? Pour the ‘soil water’ from the prepared beaker into a test chamber (they are color coded). Add the same color ‘pill’ (separate the capsule and drop the chemical in) to the chamber & shake. Allow 10 minutes for the color to fully develop. Then hold it up to daylight (not direct sunlight) to determine the closest matching color.