CFA Soil Properties and Testing 2 — Questions and Answers
Question 1: A soil sample has a bulk density of 1.6 g/cm³. Which condition does this most likely indicate?
- Highly compacted soil with restricted root growth (Correct answer)
- Loose, well-aerated sandy loam
- Organic-rich topsoil with good structure
- Freshly tilled soil with high porosity
Correct answer: Highly compacted soil with restricted root growth
Bulk densities above 1.4–1.6 g/cm³ typically indicate compaction that restricts root penetration and water infiltration.
Question 2: Which soil textural class holds the most plant-available water while still draining adequately?
- Sand
- Clay
- Loam (Correct answer)
- Silt
Correct answer: Loam
Loam soils balance macropores for drainage and micropores for water retention, making them ideal for plant-available water.
Question 3: When interpreting a soil test report, a base saturation of potassium (K) at 5% is considered:
- Deficient for most crops
- Adequate for most crops (Correct answer)
- Excessive and potentially toxic
- Irrelevant without knowing CEC
Correct answer: Adequate for most crops
A K base saturation of 3–5% of CEC is generally considered adequate for most crops.
Question 4: Which extraction method is most commonly used to assess plant-available phosphorus in neutral to alkaline soils in the western US?
- Mehlich-3
- Bray P-1
- Olsen (sodium bicarbonate) (Correct answer)
- Morgan
Correct answer: Olsen (sodium bicarbonate)
The Olsen method using sodium bicarbonate is preferred for calcareous (alkaline) soils because it doesn't dissolve calcium phosphates.
Question 5: Soil organic matter is most accurately measured in a laboratory by:
- Munsell color chart comparison
- Loss-on-ignition (LOI) or Walkley-Black wet oxidation (Correct answer)
- Electrical conductivity meter
- Penetrometer resistance readings
Correct answer: Loss-on-ignition (LOI) or Walkley-Black wet oxidation
Loss-on-ignition and Walkley-Black wet oxidation are standard laboratory methods to quantify soil organic matter content.
Question 6: A soil pH of 5.2 would most likely cause deficiency of which nutrient in corn production?
- Iron (Fe)
- Molybdenum (Mo)
- Phosphorus (P) (Correct answer)
- Manganese (Mn)
Correct answer: Phosphorus (P)
Phosphorus availability sharply declines below pH 6.0 as it becomes fixed with aluminum and iron compounds.
Question 7: What does a low soil electrical conductivity (EC) reading indicate in a field used for vegetable production?
- High salinity stress risk
- Adequate nutrient levels for crop growth
- Low soluble salt concentration, possible nutrient deficiency risk (Correct answer)
- Excessive organic matter decomposition
Correct answer: Low soluble salt concentration, possible nutrient deficiency risk
Very low EC suggests few dissolved salts, which may indicate nutrient-poor soils requiring fertilizer inputs.
CFA Soil Properties and Testing 2
A soil sample has a bulk density of 1.6 g/cm³.
Which condition does this most likely indicate?