Question

There is an increase in soil ____and \rule{1.5cm}{0.15mm} following forest fire.

• A. pH and EC
• B. EC and CEC
• C. OC and CEC
• D. EC and OC

Hint:

Ash is a fertilizer in the short term. It raises the pH (makes it less acidic) and floods the soil with salts (raising EC). However, the loss of organic matter and microbial life are negative long-term impacts.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks which chemical properties of soil generally show a temporary increase immediately after a forest fire.
Detailed Explanation:

• Increase in pH: Forest fires burn organic matter (biomass and litter), converting it into ash. Wood ash is rich in basic cations (Calcium, Magnesium, Potassium, Sodium) and carbonates. When this ash mixes with the soil, it acts like lime, neutralizing acidity and causing an increase in soil pH.

• Increase in EC (Electrical Conductivity): The combustion process mineralizes organic-bound nutrients into soluble salts. The sudden release of these concentrated salts into the soil solution increases the soil's EC, which is a measure of total dissolved salts.

• Decrease/Change in other factors: - OC (Organic Carbon): This typically decreases in the surface layer because it is consumed by the fire. - CEC (Cation Exchange Capacity): This often decreases because the organic matter, which provides many exchange sites, is lost.

Step 2: Final Answer:
Post-fire soils typically show an increase in pH (due to ash) and EC (due to released salts).