Agronomy MCQ Flashcards

What is the cation exchange capacity (CEC) of soil a measure of?

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.

Which herbicide mode of action inhibits acetolactate synthase (ALS)?

Answer: Sulfonylureas

Sulfonylurea herbicides inhibit the ALS enzyme, which is critical for the biosynthesis of branched-chain amino acids in plants.

Soil organic matter contributes most directly to which soil property?

Answer: Improved soil structure and water retention

Soil organic matter improves aggregation, tilth, and water-holding capacity, making soils more productive and erosion-resistant.

The term 'harvest index' refers to:

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).

Which factor most limits soybean yield in humid temperate climates?

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.

What is the primary role of potassium (K) in plant physiology?

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.

In integrated pest management (IPM), the 'economic threshold' is defined as:

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.