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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.

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  1. Potassium fixation in soils is most common in soils with high levels of:

    Answer: Illite and vermiculite clay minerals

    Illite and vermiculite clay minerals have interlayer spaces that trap potassium ions, making them unavailable for plant uptake — a process called potassium fixation.

  2. A field exhibits a soil pH of 6.8, which is considered ideal for most agronomic crops because:

    Answer: Most macro and micronutrients are at peak availability

    At pH 6.0–7.0, the availability of most essential plant nutrients — including nitrogen, phosphorus, and micronutrients — is maximized.

  3. Soil organic matter contributes to soil fertility primarily by:

    Answer: Releasing nutrients through mineralization and improving CEC

    As organic matter decomposes (mineralizes), it releases plant-available nitrogen, phosphorus, and sulfur, while also increasing cation exchange capacity.

  4. The Mehlich-3 soil test extraction method is widely used in the US because:

    Answer: It extracts multiple nutrients simultaneously with one solution

    Mehlich-3 is a universal extractant that removes phosphorus, potassium, calcium, magnesium, and several micronutrients in a single extraction, improving lab efficiency.

  5. Soil respiration measurements are useful for assessing:

    Answer: Microbial activity and biological soil health

    Soil respiration — the release of CO₂ by microorganisms — is a direct indicator of microbial activity and overall biological health of the soil.

  6. When a soil test report lists 'buffer pH' in addition to 'field pH,' the buffer pH is used to:

    Answer: Determine the lime requirement needed to raise field pH

    Buffer pH measures the soil's reserve acidity and is used in lime requirement calculations to determine how much lime is needed to reach the target pH.

  7. Zinc deficiency in crops is most likely to occur under which soil conditions?

    Answer: High pH soils with low organic matter and sandy texture

    Zinc availability decreases at high soil pH, and sandy soils low in organic matter have fewer sites to retain zinc, making deficiency most likely in alkaline, sandy conditions.