Agronomy Agronomy MCQ 3

Question 1

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

Accepted Answer

Soil's ability to hold positively charged nutrient ions

Answer

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)?

Accepted Answer

Sulfonylureas

Answer

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?

Accepted Answer

Improved soil structure and water retention

Answer

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:

Accepted Answer

Ratio of grain yield to total above-ground biomass

Answer

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?

Accepted Answer

Drought stress during the reproductive period

Answer

Soybean is most sensitive to water stress during flowering and pod fill, which directly reduces pod set and seed size.

Agronomy Practice Test