Soil Science and Testing Flashcards
7 cards from real CFA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Soil Science and Testing flashcards as text
A soil sample is taken from a field where crops have shown stunted growth and purple leaf coloration. Which deficiency does this most likely indicate?
Answer: Phosphorus
Purple or reddish leaf discoloration, especially in young plants, is a classic symptom of phosphorus deficiency because anthocyanin pigments accumulate.
Which soil horizon is most important for crop production and is the primary focus of agronomic soil testing?
Answer: A horizon
The A horizon (topsoil) is the primary rooting zone for most crops and contains the highest concentration of organic matter and biological activity.
What does a low soil pH reading of 4.5 indicate about aluminum availability?
Answer: Aluminum toxicity risk is high
At pH below 5.0, aluminum becomes soluble and reaches toxic levels for most crops, inhibiting root growth and phosphorus uptake.
Soil sampling recommendations generally require collecting cores from multiple locations in a field because:
Answer: Multiple samples account for natural soil variability across a field
Soil nutrients, pH, and organic matter vary spatially within a field, so composite samples from 15–20 cores provide a representative average.
The soil water characteristic curve (water retention curve) describes the relationship between:
Answer: Soil water content and matric potential
The water retention curve shows how tightly water is held in soil pores at different moisture contents, expressed as matric potential.
When interpreting a soil test for a new field, which factor most affects the critical nutrient threshold values used?
Answer: The crop to be grown and yield goal
Nutrient sufficiency ranges and critical thresholds are crop-specific and also depend on expected yield goals, which determine nutrient demand.
Which soil amendment is most appropriate to raise pH in a highly acidic sandy soil?
Answer: Agricultural lime (calcium carbonate)
Agricultural lime (CaCO₃) neutralizes soil acidity by reacting with hydrogen ions, raising pH — it is the standard and most cost-effective liming material.