Transcript Chemical and Biological Properties of the Soil

Chemical and
Biological
Properties of the
Soil
Lesson Objectives
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Describe the properties of acids and
bases.
Differentiate between strong and weak
acids, strong bases and weak bases.
Use the pH scale to calculate and
measure the concentration of oH.
Relate soil pH to nutrient availability.
Lesson Objectives
continued
• Investigate the effect of soil pH on
plant growth.
• Develop a plan for changing soil
pH to meet crop needs.
• Determine how to take a soil
sample for testing.
What is the pH scale?
• The pH
scale
measures
how acidic
or basic a
solution is.
The pH scale
• The pH scale is the concentration
of hydrogen ions in a given
substance.
 
pH   log H

Identifying Acids and Bases
• Acids have a ph from 0-7
• Lower pH value indicates a
stronger acid.
• Bases have a pH from 7-14
• Higher pH value indicates a
stronger base.
OH 

Definitions of Acids and Bases
• An acid is a substance that breaks
into H   ions in an aqueous
solution.
• A Base (alkaline) is a substance
that breaks into OH   ions in an
aqueous solution.
• Note: aqueous solution is any
solution where H 2 O is the
solvent.
Did we Miss something??
• What happens when the pH of a
substance is 7?
• Ans: A pH level of 7 indicates a
Neutral Substance i.e: Water!
Test Your Knowledge
• What is the range of an ACID on
the pH scale?
Ans: 0-7
• What is the range of a BASE and
what is another name for a BASE?
Ans: 7-14, Alkaline
Characteristics Of Acids
Acids can be characterized by:
1. A sour taste.
2. It turns blue litmus paper red
3. It tastes sour. Try drinking lemon
juice (citric acid)
Characteristics of Bases
A Base is characterized by:
1. A bitter taste. (Milk of Magnesia)
2. It feels slippery. (Soapy Water)
3. It turns Red Litmus Blue.
pH Scale
• Each pH point multiplies acidity by
a factor of 10.
• A pH of 5.0 is 10 times more acid
than pH 6.0 and 100 times more
acid than pH 7.0.
Why Learn about Acids & Bases?
• What do you think is the pH level
of (Your Town) tap water?
• The pH of a swimming pool must
be checked periodically. Why?
• Is it important for Lakes & Rivers
to maintain a certain pH?
How to calculate
concentration of OH-?
OH-= 14 - pH
Soil pH requirements
Beans
6.0-7.0
Broccoli
6.0-7.0
Cabbage
5.6-6.6
Cantaloupe
6.0-7.0
Cauliflower
6.0-7.0
Cucumber
5.0-6.0
Eggplant
5.0-6.0
Garlic
5.0-6.0
Okra
6.0-8.0
Peanuts
5.0-6.0
Symptoms of nutrient
deficiencies
• Deficiency- plant
condition where
an essential
nutrient is not
sufficiently
available.
• Symptom- a
visual sign or
condition that
results from a
deficiency
Primary nutrient deficiency symptoms
• Nitrogen (N)
- Stunted and spindly
- yellow, yellowish green or light
green in leaf color (chlorosis)
- Older leaves affected first, starting
at the tip and moves along the
middle of the leaf
Primary nutrient deficiency symptoms
• Phosphorus (P)
- stunted growth
- Very dark green color
- Purple leaves or portions of leaves
in advanced stages
- Older leaves affected first
Primary nutrient deficiency symptoms
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Potassium (K)
Shorter plants
Bronzing or browning of leaf color
Lodging (bending of stem) occurs
Secondary nutrient deficiency
symptoms
• Sulfur (S)
- Young plants have stunted
appearance
- Leaves have light-green to yellow
coloring
- Stems are thin and spindly
- Sulfur deficiency symptoms are
similar in appearance to Nitrogen
deficiency symptoms
Secondary nutrient deficiency
symptoms
• Magnesium (Mg)
- Leaf parts between veins show a
whitish color
- Leaf tissue becomes yellow, veins
remain green
- Leaves curl upward along the
margins
Macronutrients
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Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Sulfur
Micronutrients
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Boron
Copper
Iron
Chloride
Manganese
Molybdenum
Zinc
pH
• Determines the solubility and
availability of nutrients
• General range for most cases: 6.5
to 7
Biological Effects on pH
• More organic matter (decaying
plant matter and animal debris)
lowers soil pH
• More organic matter can support
larger number of microorganisms
• Microorganisms release Nitrogen
into the soil and make N more
available
Effect of
pH
on nutrient
availability
Cation Exchange
Capacity
• soil’s ability to exchange and retain
cations
• cation- positively charged ion
• anion- negatively charged ion
• A high CEC soil will be able to resist
changes in pH
Macronutrients
• Most macronutrients are more available
within a pH range of 6.5 to 8.
• the exception to this is P, which likes
the pH to be from 6 to 7.
• Ca, K, and Mg are prone to leaching at
a low pH.
• Plant uptake of N and P is restricted at
pH below 6.
Micronutrients
• Most micronutrients (B, Cu, Fe, Mn, Ni,
and Zn) are more available within a pH
range of 5 to 7
• Metals (Cu, Fe, Mn, Ni, and Zn) and
bound tighter to the soil at high pH.
Low pHs can cause toxicities.
• Micronutrients decrease in availability
as pH approaches 8.
• Chlorine is rarely deficient at high pH
levels, but can become toxic as pH
increases.
Steps for Soil Sampling
Steps for Soil Sampling
Steps for Soil Sampling
Steps for Soil Sampling
Steps for Soil Sampling
Steps for Soil Sampling