Chemical and Biological Properties of the Soil

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Chemical and Biological Properties of the Soil
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Lesson Objectives

• 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.

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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.

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What is the pH scale?

• The pH scale measures how acidic or basic a
  solution is.

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The pH scale

• The pH scale is the concentration of hydrogen
  ions in a given substance.

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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.

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Definitions of Acids and Bases

• An acid is a substance that breaks into
  ions in an aqueous solution.
• A Base (alkaline) is a substance that breaks into
  ions in an aqueous solution.
• Note aqueous solution is any solution where
  is the solvent.

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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!

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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

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Characteristics Of Acids

• Acids can be characterized by
• A sour taste.
• It turns blue litmus paper red
• It tastes sour. Try drinking lemon juice (citric
  acid)

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Characteristics of Bases

• A Base is characterized by
• A bitter taste. (Milk of Magnesia)
• It feels slippery. (Soapy Water)
• It turns Red Litmus Blue.

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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.

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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?

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How to calculate concentration of OH-?

• OH- 14 - pH

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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
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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

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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

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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

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Primary nutrient deficiency symptoms

• Potassium (K)
• Shorter plants
• Bronzing or browning of leaf color
• Lodging (bending of stem) occurs

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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

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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

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Macronutrients

• Nitrogen
• Phosphorus
• Potassium
• Calcium
• Magnesium
• Sulfur

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Micronutrients

• Boron
• Copper
• Iron
• Chloride
• Manganese
• Molybdenum
• Zinc

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pH

• Determines the solubility and availability of
  nutrients
• General range for most cases 6.5 to 7

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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

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Effect of pHon nutrient availability
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Cation Exchange Capacity

• soils 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

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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.

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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.

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Steps for Soil Sampling
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Steps for Soil Sampling
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Steps for Soil Sampling
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Steps for Soil Sampling
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Steps for Soil Sampling
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Steps for Soil Sampling