Agronomy Agronomy MCQ 4 — Questions and Answers
Question 1: Which tillage practice leaves at least 30% crop residue on the soil surface?
- Conventional tillage
- Conservation tillage (Correct answer)
- Deep tillage
- Clean tillage
Correct answer: Conservation tillage
Conservation tillage is defined by the USDA as any system leaving at least 30% residue cover, reducing erosion and improving soil health.
Question 2: The law of the minimum, attributed to Justus von Liebig, states that:
- Crop yield increases proportionally with each added nutrient
- Growth is limited by the nutrient present in the least relative amount (Correct answer)
- Excessive nutrients are as harmful as deficiencies
- Nutrients interact synergistically to maximize yield
Correct answer: Growth is limited by the nutrient present in the least relative amount
Liebig's Law of the Minimum states that plant growth is constrained by the single most limiting nutrient, regardless of other nutrient levels.
Question 3: Which soil pH range is generally considered optimal for most agronomic crops?
- 4.5–5.5
- 6.0–7.0 (Correct answer)
- 7.5–8.5
- 3.5–4.5
Correct answer: 6.0–7.0
Most agronomic crops grow best between pH 6.0 and 7.0, where nutrient availability is maximized and toxic elements are minimized.
Question 4: What is the primary function of phosphorus in plant metabolism?
- Chlorophyll synthesis
- Energy transfer via ATP (Correct answer)
- Protein structure
- Cell wall rigidity
Correct answer: Energy transfer via ATP
Phosphorus is a key component of ATP (adenosine triphosphate), which drives energy transfer in virtually all metabolic processes.
Question 5: A field with a soil compaction layer (hardpan) would most likely benefit from which practice?
- Surface liming
- Subsoil tillage (deep ripping) (Correct answer)
- Increased irrigation frequency
- Broadcasting nitrogen fertilizer
Correct answer: Subsoil tillage (deep ripping)
Subsoil tillage or deep ripping mechanically breaks up compaction layers, improving root penetration, drainage, and aeration.
Question 6: Which physiological process in plants is most directly affected by nitrogen deficiency?
- Root hair formation
- Protein synthesis and chlorophyll production (Correct answer)
- Seed coat hardening
- Epicuticular wax deposition
Correct answer: Protein synthesis and chlorophyll production
Nitrogen is a building block of amino acids, proteins, and chlorophyll, so its deficiency causes stunted growth and characteristic yellowing (chlorosis).
Question 7: Which crop is classified as a C3 plant?
- Corn (Zea mays)
- Sugarcane
- Wheat (Triticum aestivum) (Correct answer)
- Sorghum
Correct answer: Wheat (Triticum aestivum)
Wheat uses the C3 photosynthetic pathway, fixing CO₂ directly via RuBisCO without a prior carbon-concentration step.
Agronomy Agronomy MCQ 4
Which tillage practice leaves at least 30% crop residue on the soil surface?