Chemical and Biological Properties of the Soil

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.

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. Lesson Objectives continued

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.

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.

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.

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 Broccoli Cabbage Cantaloupe Cauliflower Cucumber Eggplant Garlic Okra Peanuts

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

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

Potassium (K) -Shorter plants -Bronzing or browning of leaf color -Lodging (bending of stem) occurs Primary 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 Secondary nutrient deficiency symptoms

Macronutrients Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur

Micronutrients 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