Agronomy Soil Science and Fertility 1 — Questions and Answers
Question 1: What soil pH range is generally considered optimal for most agronomic crops in the US?
- 4.5–5.5
- 6.0–7.0 (Correct answer)
- 7.5–8.5
- 8.0–9.0
Correct answer: 6.0–7.0
A pH of 6.0–7.0 supports nutrient availability and beneficial microbial activity for most crops.
Question 2: Which macronutrient is primarily responsible for vegetative growth and green color in plants?
- Phosphorus
- Potassium
- Nitrogen (Correct answer)
- Calcium
Correct answer: Nitrogen
Nitrogen is a key component of chlorophyll and amino acids, driving vegetative growth and green coloration.
Question 3: The cation exchange capacity (CEC) of a soil indicates its ability to do what?
- Drain excess water
- Hold and supply nutrients (Correct answer)
- Fix atmospheric nitrogen
- Resist compaction
Correct answer: Hold and supply nutrients
CEC measures the soil's capacity to hold positively charged nutrient ions and supply them to plants.
Question 4: Which soil textural class has the highest water-holding capacity?
- Sand
- Loam
- Clay (Correct answer)
- Gravel
Correct answer: Clay
Clay soils have small particles with large surface areas, giving them the greatest water-holding capacity.
Question 5: What is the primary function of phosphorus in plant nutrition?
- Chlorophyll synthesis
- Energy transfer and root development (Correct answer)
- Disease resistance
- Water regulation
Correct answer: Energy transfer and root development
Phosphorus is critical for ATP synthesis, energy transfer, and promoting root and seed development.
Question 6: Which process converts ammonium (NH4+) to nitrate (NO3-) in the soil?
- Denitrification
- Mineralization
- Nitrification (Correct answer)
- Immobilization
Correct answer: Nitrification
Nitrification is a two-step microbial process that oxidizes ammonium to nitrite and then to nitrate.
Agronomy Soil Science and Fertility 1
What soil pH range is generally considered optimal for most agronomic crops in the US?