GAP Soil Science & Analysis 2 — Questions and Answers
Question 1: A soil test reports a cation exchange capacity (CEC) of 5 meq/100g. This soil is best described as:
- High fertility with excellent nutrient retention
- Sandy with low nutrient-holding capacity (Correct answer)
- Clay-rich with high buffering ability
- Ideal loam requiring no amendments
Correct answer: Sandy with low nutrient-holding capacity
A CEC of 5 meq/100g indicates a coarse, sandy soil with limited ability to retain cations like calcium, magnesium, and potassium.
Question 2: Which nutrient is most commonly tied up and unavailable to plants when soil pH drops below 5.5?
- Phosphorus (Correct answer)
- Nitrogen
- Potassium
- Sulfur
Correct answer: Phosphorus
Phosphorus becomes fixed by iron and aluminum compounds in acidic soils below pH 5.5, making it largely unavailable to plants.
Question 3: What does a high electrical conductivity (EC) reading in a soil test indicate?
- Low organic matter content
- Excessive soluble salts that may harm crops (Correct answer)
- Ideal moisture retention
- Healthy microbial activity
Correct answer: Excessive soluble salts that may harm crops
High EC indicates excessive soluble salts in the soil, which can cause osmotic stress, reducing water uptake and crop yields.
Question 4: In the context of GAP, why is it important to test soil for heavy metals before growing fresh produce?
- Heavy metals improve crop flavor profiles
- Contaminated soil can transfer heavy metals to edible crops, posing food safety risks (Correct answer)
- Heavy metals are required micronutrients at all concentrations
- Testing is only needed for organic certification
Correct answer: Contaminated soil can transfer heavy metals to edible crops, posing food safety risks
Heavy metals like lead, cadmium, and arsenic can accumulate in produce grown in contaminated soil and pose serious health risks to consumers.
Question 5: Which soil texture has the best balance of drainage and water-holding capacity for most vegetable crops?
- Sand
- Clay
- Silt loam (Correct answer)
- Gravel
Correct answer: Silt loam
Silt loam provides a good balance of pore sizes, allowing adequate drainage while retaining sufficient moisture and nutrients for vegetable production.
Question 6: A farmer notices soil crusting after rain events, making seedling emergence difficult. The most likely soil problem is:
- Excess organic matter
- Low clay content
- Low aggregate stability and compaction-prone surface (Correct answer)
- Overly alkaline pH
Correct answer: Low aggregate stability and compaction-prone surface
Soil crusting is caused by poor aggregate stability — raindrops break apart surface aggregates, and they seal when dry, creating a hard crust that impedes emergence.
Question 7: Which of the following best describes the role of mycorrhizal fungi in soil science relevant to GAP?
- They fix atmospheric nitrogen directly
- They extend plant root systems to improve nutrient and water uptake (Correct answer)
- They decompose pesticide residues in soil
- They increase soil pH in acidic fields
Correct answer: They extend plant root systems to improve nutrient and water uptake
Mycorrhizal fungi form symbiotic associations with plant roots, extending effective root surface area to enhance uptake of phosphorus, water, and other nutrients.
GAP Soil Science & Analysis 2
A soil test reports a cation exchange capacity (CEC) of 5 meq/100g.
This soil is best described as: