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Difficulty: MediumMust Be True / Most Strongly Supported

Agricultural scientists monitoring soil chemistry across regional test plots established the following conditions:

• Any soil amendment containing mycorrhizal inoculants enhances phosphorus uptake in legume crops only if the soil pH remains strictly below 7.0.
• Every experimental plot treated with calcified biochar maintains a soil pH of 7.4 or higher throughout the growing season.
• All experimental plots in the valley trial were treated with calcified biochar.
• During the previous season, several experimental plots in the valley trial produced legume crops that exhibited enhanced phosphorus uptake.

If the statements above are true, which one of the following must also be true on the basis of them?

  1. A
    Any experimental plot in which the soil pH remains below 7.0 will produce legume crops that exhibit enhanced phosphorus uptake.
  2. B
    Treating an experimental plot with mycorrhizal inoculants is sufficient to prevent the soil pH from reaching 7.4.
  3. In at least some experimental plots where legume crops exhibited enhanced phosphorus uptake, the applied soil amendment did not contain mycorrhizal inoculants.Answer
  4. D
    No experimental plot treated with calcified biochar can sustain any form of nutrient uptake in legume crops.
  5. E
    The experimental plots in the valley trial produced higher overall crop yields than plots treated with mycorrhizal inoculants.

Answer

In at least some experimental plots where legume crops exhibited enhanced phosphorus uptake, the applied soil amendment did not contain mycorrhizal inoculants.
The conclusion logically follows from the premises: every plot in the valley trial was treated with calcified biochar (yielding pH >= 7.4), which precludes mycorrhizal inoculants from enhancing phosphorus uptake (since mycorrhizal enhancement requires pH < 7.0). Because several valley trial plots nevertheless had legume crops with enhanced phosphorus uptake, those specific enhancements must have occurred without mycorrhizal inoculants.

Step-by-Step Solution

1
Analyze the conditional requirement for mycorrhizal effectiveness and determine its contrapositive.
Mycorrhizal inoculants enhance phosphorus uptake only if soil pH < 7.0. The contrapositive dictates that if soil pH is 7.0 or higher, any enhanced phosphorus uptake cannot be attributed to mycorrhizal inoculants.
Contrapositive deduction defines the boundary condition under which mycorrhizal enhancement is impossible.
2
Determine the soil pH condition across all plots in the valley trial.
Since every plot in the valley trial received calcified biochar, and biochar maintains a pH of 7.4 or higher, all valley trial plots had a soil pH of at least 7.4.
Combining universal categorical premises establishes a uniform factual baseline for the trial.
3
Synthesize the valley trial observations with the deduced contrapositive.
Several plots in the valley trial had enhanced phosphorus uptake while maintaining a pH of 7.4 or higher. Thus, in those plots, the enhancement occurred without mycorrhizal inoculants.
Applying the existential statement ('several plots') to the universal restriction guarantees the existence of non-mycorrhizal enhancements.

Key Concept

Combining universal conditional statements and existential premises via contrapositive deduction
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Topics

Must Be True / Most Strongly Supported

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