Question 21·Easy·Inferences
On 60 commercial corn farms, researchers compared two groups of fields: in one group, corn seeds were coated with a strain of beneficial fungi before planting, and in the other, the same corn variety was planted without the coating. All other farming practices, including the amount of fertilizer applied, were identical. At harvest, the coated-seed fields produced, on average, 18 percent more corn per acre. Soil tests from these fields also showed higher levels of nitrogen remaining in the soil than tests from the uncoated-seed fields.
Taken together, these results most strongly suggest that
Which choice most logically completes the text?
For SAT inference questions like this, first identify what changed in the experiment and what was kept the same; then list the concrete results reported. Look for the answer that logically links the measured outcomes back to the one changed factor, without assuming any extra conditions or future scenarios. Eliminate any choices that introduce new variables (like different fertilizer amounts or irrigation) or that contradict the reported data.
Hints
Focus on the controlled variable
Notice that both groups received the same kind and amount of fertilizer. What, then, is the one major difference between the two groups that could explain the different results?
Use both pieces of evidence
The coated fields produced more corn and had more nitrogen left in the soil. How might those two facts be related to each other?
Watch out for new, unsupported ideas
Check each choice and ask: does the passage actually mention this factor (like changing fertilizer amounts or water use), or is the choice adding something new that was never tested or described?
Step-by-step Explanation
Identify what was changed in the experiment
The researchers compared two groups of corn fields:
- Group 1: seeds coated with beneficial fungi
- Group 2: the same seeds without the coating
All other farming practices, including the amount of fertilizer, were kept the same. So any consistent difference in results between the groups is most likely due to the fungal coating.
Understand the two key results
Two main outcomes are reported for the coated-seed fields:
- They produced, on average, 18% more corn per acre.
- Soil tests showed higher levels of nitrogen remaining in the soil than in fields with uncoated seeds.
So the coated fields both grew more corn and ended with more nitrogen left over in the soil.
Connect the nitrogen result to the growth result
Nitrogen is a key nutrient in fertilizer that plants need to grow. The coated-seed fields used the same amount of fertilizer but produced more corn and still had more nitrogen left in the soil than the uncoated fields.
This pattern suggests that the fungal coating affects how nitrogen is used or stays in the field–crop system, in a way that is linked to better growth.
Match this combined pattern to the best answer choice
Now compare the choices to the evidence:
- Any choice that talks about needing more or less fertilizer (changing fertilizer amounts) goes beyond the experiment, because fertilizer was kept constant.
- Any choice about irrigation or water use is unsupported, because water was never mentioned.
- The only answer that ties together better growth and a change in how nitrogen is handled in a way consistent with the data is:
A) the fungal coating likely enhances corn growth partly by improving the crop’s use or retention of nitrogen.