Question 51·Hard·Central Ideas and Details
Agronomist Elaine Kiefer analyzed ten years of crop‐rotation records from Midwestern farms to assess the consequences of planting cover crops such as rye and clover between cash‐crop seasons. Her data showed that incorporating cover crops left first-year corn or soybean yields statistically unchanged, contradicting farmers’ fears of short-term losses. Yet she also documented steadier yields during drought years, reduced fertilizer expenses after three seasons, and gradual increases in overall farm profit. Kiefer argues that these delayed benefits stem from improved soil structure and microbial activity fostered by cover cropping, benefits that conventional yield trials rarely capture.
Which choice best states the main idea of the text?
For main-idea questions, paraphrase the passage in one sentence that includes the key contrast (often signaled by words like “Yet”). Then choose the option that captures the full scope—both what does not happen immediately and what does happen over time—and eliminate options that are true but too narrow (single-detail summaries) or that shift the focus to a supporting point (like a comment about study methods).
Hints
Summarize in one sentence
In one sentence, describe what the research shows overall about cover crops (include both the early result and what happens later).
Spot the pivot word
The word “Yet” signals a shift. What does the passage say before “Yet,” and what does it say after it?
Avoid choices that mention only one effect
If an option focuses mainly on drought years, mainly on fertilizer costs, or mainly on yield trials, it’s probably too narrow for the main idea.
Step-by-step Explanation
Identify the topic and what the research evaluates
Kiefer studies ten years of records to assess the consequences of planting cover crops between cash-crop seasons, so the main idea must summarize what her research shows about using cover crops.
Track the key contrast in findings
The passage first notes no short-term yield change (first-year yields are “statistically unchanged”), then shifts with “Yet” to delayed benefits (steadier drought-year yields, reduced fertilizer expenses after three seasons, and increased profit).
Use the author’s explanation to confirm the takeaway
Kiefer attributes the delayed benefits to improved soil structure and microbial activity, and notes these benefits are often missed by conventional yield trials—reinforcing that the value of cover crops is not captured by short-term yield changes alone.
Choose the option that matches the whole paragraph (not a single detail)
The best main idea is the option that combines unchanged short-term yields with cumulative soil and economic benefits over time:
Cover crops may not boost first-year yields, but over time they improve soil and profits, making them worthwhile.