PrepTest 141, Section 2, 20. The advent of chemical fertilizers…

How will the right answer fit in terms of support and conclusion?

Only the right answer will be support for the conclusion that doesn’t bring in anything new. That’s a simpler but still totally effective way of saying only the right answer must be true if the conclusion is true.

Highlight the main conclusion in the passage, if there is one:

to significantly improve the soil structure, farmers will need to abandon the use of chemical fertilizers.

[BACKGROUND]. As a result, [SUPPORT]. So [CONCLUSION].

This is pretty tricky. First you gotta key in on “As a result” and recognize the author is claiming cause-and-effect. What is the poor soil a result of? The conclusion makes it sound like “chemical fertilizers” are the cause, but the first sentence makes it sound like the fertilizer caused farmers to “abandon…growing a ‘green-manure’ crop”, and that’s what caused the soil problem.

So maybe the farmers could start doing the green-manure crops again and improve the soil, even though they’d still also be using the chemical fertilizer. See what I’m saying? If that works, it blows up the conclusion.

Map the wording of the answers to the wording of the passage:

(A) …will periodically grow alfalfa.

Ooh careful. Alfalfa was just an example of a group of crops in the passage, so the argument couldn’t rely on that. The farmers could just as easily grow some other “‘green-manure’ crop”.

(B) applying chemical fertilizers to green-manure crops…

This answer is getting itself mixed up. There’s nothing in the passage about using chemicals on the green-manure crops. This definitely doesn’t support the conclusion anyway, since it doesn’t connect at all to improving the soil.

(C) the most important factor…

There’s absolutely no comparison of factors in soil quality in the passage. Only soil structure even gets mentioned. So no way the author is assuming which factor is “most important”.

(D) chemical fertilizers themselves have a destructive effect…

I get why this would look good, but if you picked it you’re making the same assumption the author is. The fertilizers don’t have to have a “destructive effect”, as long as farmers will only grow the beneficial green-manure crops when they’re not using chemical fertilizers. Something tells me that’s what (E) is gonna say.

(E) …farmers in the region will not grow green-manure crops unless…

Boom! Now we’re seeing the whole cause-and-effect chain. The passage said the chemical fertilizers caused them to ditch the green-manure crops. But it didn’t say they couldn’t have kept doing both. This answer is explaining that “many, if not all” wouldn’t do both. And that definitely needs to be true to make the conclusion work. And of course, it sticks to the subject and only talks about stuff that’s in the passage.

(E) is the correct answer.

Common pattern/s in this question: This one’s a good example of how the LSAT can make a cause-and-effect argument a bit harder. But it also shows that no matter how confusing the passage gets, the right answer maps to the same cause-and-effect relationship.