Deep tillage is even more deleterious to the world's topsoil

Question

Deep tillage is even more deleterious to the world's topsoil supply than previously believed. For example, farmers who till deeply are ten times more likely to lose topsoil to erosion than are farmers who use no-till methods. Results like these make it clear that farmers who now till deeply should strive, by using other topsoil aeration techniques, to incorporate no-till methods instead.

The argument depends on assuming which one of the following?

A. Topsoil erosion does not make farmers want to till more deeply.
B. In deep-tillage farming, the deeper one tills, the greater the susceptibility to topsoil erosion.
C. Tilling by any method other than deep tillage is not a viable option.
D. The most expensive farming methods employ topsoil aeration techniques other than deep tillage.
E. On average, topsoil that is no-tilled is more aerated than topsoil that is tilled deeply.

 please explain your answer.

hilairity · Answer

Not an obvious one. Let's try it. 

 The argument depends on assuming which one of the following?  
 A. Topsoil erosion does not make farmers want to till more deeply.  
Whether or not farmers want to till more deeply is not relevant to the conclusion that deep tilling is bad. Farmers could just be misinformed, or have poor instincts.

 B. In deep-tillage farming, the deeper one tills, the greater the susceptibility to topsoil erosion.  
Deep-till is deep-till, it's all bad. Degree of susceptibility to soil erosion is outside the scope of the question.

 C. Tilling by any method other than deep tillage is not a viable option.  
This isn't a great answer, but it's the best one. The argument basically says "deep till bad, therefore don't till at all". If you reverse this answer choice to read "tilling by another method IS a viable option", that weakens the conclusion, so you know you have an assumption upon which the argument is based. This is the correct answer, I believe. 

 D. The most expensive farming methods employ topsoil aeration techniques other than deep tillage.  
The argument doesn't care how much any aeration technique costs, it's outside scope.

 E. On average, topsoil that is no-tilled is more aerated than topsoil that is tilled deeply. 
Not necessary for no-tilled topsoil to be MORE aerated than deeply tilled topsoil. Incorrect. 

 My choice: C

kdhong · Answer

So if you negate an answer choice such as C, the objective is to weaken the conclusion right? And if you want to weaken an answer, after you negate the answer choice, you want the answer choice to strengthen the conclusion?

hilairity · Answer

The technique, which is taught by Powerscore for the LSAT, says that if you have an Assumption question (the question asks you to identify an assumption upon which the argument is based), if you negate all answer choices, ONE of them will attack the argument. That is your answer. Makes sense if you think about it. If you assume something, and the opposite is true, whatever you concluded on the basis of that assumption is going to have to be defended some other way, or won't be true at all.

Deep tillage is even more deleterious to the world's topsoil

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