CFA Soil Science and Testing 2 — Questions and Answers
Question 1: A soil test reports a cation exchange capacity (CEC) of 25 meq/100g. What does this indicate about the soil's nutrient-holding ability?
- Very low nutrient-holding capacity
- Moderate nutrient-holding capacity
- High nutrient-holding capacity (Correct answer)
- CEC does not relate to nutrient holding
Correct answer: High nutrient-holding capacity
A CEC of 25 meq/100g is considered high, meaning the soil can hold large amounts of positively charged nutrients like calcium, magnesium, and potassium.
Question 2: Which soil texture class typically has the highest water-holding capacity?
- Sand
- Loamy sand
- Clay loam (Correct answer)
- Gravel
Correct answer: Clay loam
Clay loam soils have a high proportion of fine particles with large surface area, allowing them to retain significantly more water than coarser-textured soils.
Question 3: When a soil test shows high phosphorus levels, a fertilizer applicator should:
- Double the phosphorus application to maximize crop uptake
- Reduce or eliminate phosphorus fertilizer applications (Correct answer)
- Switch to a high-nitrogen phosphorus blend
- Apply lime to reduce phosphorus availability
Correct answer: Reduce or eliminate phosphorus fertilizer applications
High soil phosphorus levels indicate no additional phosphorus is needed; over-application leads to runoff pollution and wasted resources.
Question 4: What is the primary purpose of measuring soil electrical conductivity (EC)?
- To determine soil pH
- To estimate soil salinity and ion concentration (Correct answer)
- To measure organic matter content
- To assess soil compaction
Correct answer: To estimate soil salinity and ion concentration
Soil EC measures the ability of soil to conduct electrical current, which directly correlates with dissolved salt concentration and overall ion content.
Question 5: A soil with a high silt content is most prone to which problem?
- Rapid drainage and drought stress
- Surface crusting and reduced water infiltration (Correct answer)
- Excessive potassium fixation
- Very high CEC
Correct answer: Surface crusting and reduced water infiltration
Silt particles are small but lack the cohesion of clay, making silt-dominated soils prone to surface crusting when wetted and dried repeatedly.
Question 6: Which nutrient becomes less available to plants as soil pH rises above 7.5?
- Molybdenum
- Iron (Correct answer)
- Calcium
- Magnesium
Correct answer: Iron
Iron solubility decreases sharply at high pH, often causing iron chlorosis (yellowing) in plants grown in alkaline soils.
Question 7: Soil organic matter content is best improved over the long term by:
- Frequent deep tillage
- Adding cover crops and crop residue (Correct answer)
- Applying anhydrous ammonia
- Increasing irrigation frequency
Correct answer: Adding cover crops and crop residue
Cover crops and returning crop residue to the soil consistently add carbon and support microbial activity, building organic matter over time.
CFA Soil Science and Testing 2
A soil test reports a cation exchange capacity (CEC) of 25 meq/100g.
What does this indicate about the soil's nutrient-holding ability?