Agronomy Agronomy MCQ 3 — Questions and Answers
Question 1: What is the cation exchange capacity (CEC) of soil a measure of?
- Soil's ability to retain anions
- Soil's ability to hold positively charged nutrient ions (Correct answer)
- Rate of water infiltration
- Soil organic matter percentage
Correct answer: Soil's ability to hold positively charged nutrient ions
CEC measures how many positively charged cations (like Ca²⁺, Mg²⁺, K⁺) a soil can hold and exchange with plant roots.
Question 2: Which herbicide mode of action inhibits acetolactate synthase (ALS)?
- Glyphosate
- Atrazine
- Sulfonylureas (Correct answer)
- Paraquat
Correct answer: Sulfonylureas
Sulfonylurea herbicides inhibit the ALS enzyme, which is critical for the biosynthesis of branched-chain amino acids in plants.
Question 3: Soil organic matter contributes most directly to which soil property?
- Increased soil pH
- Improved soil structure and water retention (Correct answer)
- Reduced microbial activity
- Decreased nutrient availability
Correct answer: Improved soil structure and water retention
Soil organic matter improves aggregation, tilth, and water-holding capacity, making soils more productive and erosion-resistant.
Question 4: The term 'harvest index' refers to:
- Days from planting to harvest
- Ratio of grain yield to total above-ground biomass (Correct answer)
- Number of harvests per season
- Percentage moisture at harvest
Correct answer: Ratio of grain yield to total above-ground biomass
Harvest index is the proportion of above-ground dry matter that is partitioned into the harvested product (e.g., grain).
Question 5: Which factor most limits soybean yield in humid temperate climates?
- Extreme heat during vegetative stages
- Drought stress during the reproductive period (Correct answer)
- Excess nitrogen fertilization
- Low atmospheric CO₂ concentration
Correct answer: Drought stress during the reproductive period
Soybean is most sensitive to water stress during flowering and pod fill, which directly reduces pod set and seed size.
Question 6: What is the primary role of potassium (K) in plant physiology?
- Structural component of proteins
- Enzyme activation and stomatal regulation (Correct answer)
- Component of chlorophyll molecule
- Nucleic acid synthesis
Correct answer: Enzyme activation and stomatal regulation
Potassium activates over 60 enzymes and is essential for guard cell function, which controls stomatal opening and water use efficiency.
Question 7: In integrated pest management (IPM), the 'economic threshold' is defined as:
- Maximum allowable pesticide cost per acre
- Pest density at which control action must be taken to prevent economic loss (Correct answer)
- Point at which all pests are eliminated
- Minimum yield loss acceptable to the grower
Correct answer: Pest density at which control action must be taken to prevent economic loss
The economic threshold is the pest population level at which the cost of management equals the economic damage caused, triggering a control decision.
Agronomy Agronomy MCQ 3
What is the cation exchange capacity (CEC) of soil a measure of?