CFA Nutrient Sources and Management 3 — Questions and Answers
Question 1: Denitrification in waterlogged soils converts nitrate primarily into:
- Ammonium (NH₄⁺)
- Nitrogen gases (N₂ and N₂O) (Correct answer)
- Urea
- Nitrite that accumulates in the soil
Correct answer: Nitrogen gases (N₂ and N₂O)
Under anaerobic conditions, bacteria convert nitrate through denitrification to nitrogen gases (N₂ and N₂O) that escape into the atmosphere.
Question 2: Which micronutrient is most commonly deficient in high-pH, calcareous soils because it precipitates as insoluble compounds?
- Boron
- Molybdenum
- Iron (Correct answer)
- Chlorine
Correct answer: Iron
Iron availability drops sharply in high-pH soils because iron forms insoluble hydroxide and carbonate compounds, causing iron chlorosis.
Question 3: The nutrient management concept of the '4Rs' refers to right:
- Rate, Ratio, Row spacing, Record-keeping
- Source, Rate, Time, Place (Correct answer)
- Nitrogen, Phosphorus, Potassium, Sulfur
- Soil test, Application, Crop response, Return on investment
Correct answer: Source, Rate, Time, Place
The 4R Nutrient Stewardship framework stands for the right Source, right Rate, right Time, and right Place of fertilizer application.
Question 4: Which nitrogen source has the highest potential for ammonia volatilization when surface-applied to high-pH soils without incorporation?
- Ammonium nitrate
- Urea (Correct answer)
- Ammonium sulfate
- Calcium nitrate
Correct answer: Urea
Urea hydrolyzes rapidly to ammonium carbonate, which readily releases ammonia gas—especially problematic on high-pH soils.
Question 5: Luxury consumption of potassium occurs when:
- Plants absorb K beyond their growth needs when soil K is high (Correct answer)
- Excess K triggers magnesium deficiency in crops
- K leaches below the root zone during heavy rainfall
- Plants compete with weeds for limited soil K
Correct answer: Plants absorb K beyond their growth needs when soil K is high
Luxury consumption means plants absorb more potassium than required for maximum yield when soil potassium levels are high.
Question 6: Foliar fertilizer applications are most beneficial for correcting:
- Severe macronutrient deficiencies affecting entire fields
- Acute micronutrient deficiencies detected mid-season (Correct answer)
- Soil pH imbalances limiting nutrient uptake
- Nitrogen needs during vegetative growth stages
Correct answer: Acute micronutrient deficiencies detected mid-season
Foliar applications are best suited for correcting mid-season micronutrient deficiencies quickly because nutrients are absorbed directly through leaf tissue.
Question 7: Which soil property most strongly governs cation exchange capacity (CEC) and thus the ability to hold calcium, magnesium, and potassium?
- Soil color and parent material
- Soil texture and organic matter content (Correct answer)
- Soil drainage class and slope
- Bulk density and compaction level
Correct answer: Soil texture and organic matter content
CEC is primarily determined by clay content (texture) and organic matter, both of which carry negative charges that retain cations.
CFA Nutrient Sources and Management 3
Denitrification in waterlogged soils converts nitrate primarily into: