PT07.S3.Q18 - crop rotation increase yields

Sarah889

Hey All,

You can never have too much practice with RC, right? Which is why you should definitely go check out this passage and then help a girl out with a question that is causing her to pull her hair out

E is saying that phytopathogens typically attack some plant species but find other species to be unsuitable hosts. I eliminated this answer choice because the passage never says that it is the species that causes them to be unsuitable hosts. Rather, it is the fact that the crops are rotated, not giving the soil a chance to become suppressive.

Plant A is sowed in a field, lets say. But the crops aren't rotated so the phytopathogens do their thing and the yields decrease. But then, the farmer notices this decrease in yield, so Plant B is sowed in Plant A's place. But after a while, the soil become suppressive again and the phytopathogens come back into the picture. Then Plant C replaces Plant B, etc.

Furthermore, the passage says: "The problem can be cured by crop rotation, denying the pathogens a suitable host for a period of time." (emphasis added)

The species of plant is irrelevant. The phytopathogens are "triggered" by lack of crop rotation and they can only be stalled for a period of time. I mean, I know we can't infer that every single plant species is in danger of phytophathogen wrath, but I definitely don't see how we can infer that there are some species that are not.

I chose D, which I realized was wrong because of "majority," but E just seems completely unsupported.

potatocowpower

I am trying to follow your logic but couldn't this follow still even if you have to perpetually crop rotate it is still an increase from the otherwise decreased yields from not rotating crops?

Also maybe your emphasis on for a period of time might be unwarranted? The period of time its referring to is denial of a suitable host. In addition, even if you choose to interpret it as stalling for a period of time does sentence does say that crop rotations can cure the problem and explains how it does so. And I don't believe stalling can be inferred. I understood it as after denying suitable hosts for a period of time, the problem is cured.

Here's how I understand it through an analogous sentence. Animals can be killed by neglect, denying them food for a period of time. Neglect can kill animals in part by denying them food for a period of time.

Also isn't suppressive soil a good thing in this case? It is suppressive to those diseases. Also I don't quite understand your interpretation of E. The species don't cause them to be unsuitable hosts, they just are unsuitable hosts. I'm understanding it like this: I eat certain species of animals but find other species to be unsuitable for consumption

Sami

@bswise2 said:
The problem can be cured by crop rotation, denying the pathogens a suitable host for a period of time."

Hey,

So the reason answer choice "E" works is because if you are rotating crops and by doing so you are denying these pathogens a suitable host, then that means that plant is an unsuitable host to these pathogens.

@bswise2 said:
I eliminated this answer choice because the passage never says that it is the species that causes them to be unsuitable hosts.

You are right when you say that the passage never says that it is the species that causes them to be unsuitable hosts. They don't share a cause and effect relationship. But they do share a relationship like the one you quoted above that these pathogens cannot find these plants suitable and therefore cannot increase in population like they do when they do find suitable host (line 4-5). That's why crop rotation works. Because these plants that are rotated are not suitable hosts for the pathogens. Which means some plants are unsuitable hosts for these pathogen, which is what answer choice "E" is saying.

@bswise2 said:
. But then, the farmer notices this decrease in yield, so Plant B is sowed in Plant A's place. But after a while, the soil become suppressive again and the phytopathogens come back into the picture.

I do find you are making an assumption about the part where you are mentioning that after a period of time after plant B is sowed the soil become supressive again and pathogens come back into the picture. That's not the reasoning given by that passage. The passage is saying it works because "we are denying these pathogens a suitable host" (line 6-8) not another host like you are thinking plant B is actually doing. Plant B according to the passage would work in crop rotation because it is not a suitable host to these pathogens.

I hope this helped. Let me know what you think : )

Sarah889

First off, thank you both for responding. I wasn't sure if anyone would because RC passages could be tedious, so I appreciate it.

@potatocowpower said:
Also isn't suppressive soil a good thing in this case? It is suppressive to those diseases. Also I don't quite understand your interpretation of E. The species don't cause them to be unsuitable hosts, they just are unsuitable hosts. I'm understanding it like this: I eat certain species of animals but find other species to be unsuitable for consumption

I do realize now that I was reading the consequence of "suppressive soil" incorrectly, which may have played a part in my misunderstanding of this question. However, just to clarify my issue with E-- E is seemingly specifying species as being the reason why these plants are unsuitable hosts. The passage does not say that. My issue was that the passage says that the solution to the problem is crop rotation. (The solution is not replacing one species with another). Therefore, if the solution is crop rotation, then the problem isn't the type of species, it's how long the plant goes without crop rotation. In your example, eating certain species of animals and not eating others because they are unsuitable for consumption doesn't parallel what the passage is talking about. For example, I eat chicken, but not walruses. That is 100% not going to change (voluntarily at least). That element of determinism does not exist in our example. Phytopathogens are the "walrus" at first, but then, if the crops are not rotated, they become the "chicken." There seems to be an adaptation that occurs (more specifically, they are able to increase in the soil surrounding the roots. See lines 4 and 5). This increase in phytopathogens around the roots could or could not be the case for every species...the point is, we don't know. It doesn't tell us. It could be that this is an issue for all plants, or that this is only an issue for a few plants. That is information the passage doesn't talk about. E seems to make the assumption that we can know. And please, let me know if I'm missing something. I clearly am because I'm still struggling with this question.

(I wrote the above before my revelation below...haha. I decided to keep the above so you guys could see where my error occurred and why I was struggling with E.)

@Sami said:
I do find you are making an assumption about the part where you are mentioning that after a period of time after plant B is sowed the soil become supressive again and pathogens come back into the picture. That's not the reasoning given by that passage. The passage is saying it works because "we are denying these pathogens a suitable host" (line 6-8) not another host like you are thinking plant B is actually doing. Plant B according to the passage would work in crop rotation because it is not a suitable host to these pathogens.

So, I started writing out a response to this and then I had a revelation after reading your response a few times. I am completely misunderstanding the definition of crop rotation...

What I thought when reading this passage/writing this question: Crop rotation meant that you have to continuously change the crops planted in a given field because if not, over time, the phytopathogens increase in number surrounding plant roots. I did not interpret this to be plant specific, but more just an inevitable consequence. For example, if you don't shower, you're going to be dirty. That is true for just about anyone. In this case, the shower is the crop rotation and the dirtiness correlates with the yield decrease. In context of my analogy, I was reading E as: some people get dirty from not showing and some don't.

Now I see that the author intended to write that crop rotation is because phytopathogens are somewhat plant specific. In my above analogy, Plant A is the species susceptible to phytopathogen issues, but Plant B is not. So Plant B is sowed and the phytopathens decrease, thus allowing Plant A to be sowed again. In this scenario, answer E becomes very clear.

I see now I clearly read the passage incorrectly...I guess I'm now more concerned with my misreading to begin with. The crux of my issue is that I didn't understand the definition of crop rotation and as I am rereading the passage again, I don't really see any clues that I overlooked that would have led me to the correct definition. In other words, I don't see my initial understanding of crop rotation as erroneous given what the passage says about it. Let me know if either of you disagree with this.

Sami

@bswise2 said:
The crux of my issue is that I didn't understand the definition of crop rotation and as I am rereading the passage again, I don't really see any clues that I overlooked that would have led me to the correct definition.

I think what you are doing is bringing in outside knowledge about crop rotation is and making it fit with what the passage says about crop rotation.

In Reading Comprehension that's the last thing you want to do. Especially if like question 18 of this passage its asking for an inference. Treat this question like a MBT LR question.

The only thing the passage says about crop rotation is that the problem of increasing pathogens can be solved by crop rotation because it denies these pathogens a suitable host (meaning it cannot be parasitic on this plant).

That's it. So because its a MBT question, we want to look for this inference (denies a suitable host) in answer choices. If you take a look at the answer choices, the only answer choice that talks about why crop rotation works because the pathogens cannot use them as host is answer choice "E".

A) talks about the cause being hardier and more resistant to disease.
this is talking about Psudeomenos Fluorescens bacteria, these are the antagonistic bacteria to pathogens. (not the "host" answer we are looking for).
C) this is talking about roots of plants producing a compound.
D) this is talking about what causes most of the plant diseases (this one does not even talk crop rotation).
E) is the only one that directly even talks about how crop rotation might deny these pathogens host. None of the answers even come close to talking about the only thing the passage talks about why crop rotation works except answer choice "E".

And if we take a direct look at answer choice "E", it is totally supported by lines (4-8). We already know that pathogens use plants as host to increase in soil (line 4-5). So this means that pathogens attack some plant species.
But the next lines, 6-8 say that crop rotation denies them a suitable host, so they can't attack these plants. In other words now these plants are not suitable hosts.

I think the takeaway that I would take from this question is to not make assumptions on RC questions that ask you for an inference based on statements from the passage. Treat them like a MBT or most likely to be true and see what information the passage gives about the subject of that question. Then I would use that and only that to go through the answer choices.

potatocowpower

I think a couple of clues that phytopathogens are plant specific are the fact that the paragraph opens by discussing "cultivation of a single crop" and explains how crop rotation works: by denying the phytopathogens of a "suitable host". If they weren't plant specific I'm understanding that rotating crops just provide them with a new host that, while less infested, would still be suitable (maybe the phytopathogens might even be happier with newer plants). If they weren't plant specific as well I think crop rotation would not be as effective as something like crop removal, that just lets all the phytopathogens die out.

brennan

The idea is that different species of phytopathogen prefer hosts that are different species of crop.

Let's say phytopathogens x and y inhabit the soil; x kills plant A and y kills plant B.

Initially the levels of both phytopathogens are low (or zero). You plant A. After a while, x colonizes the plants. Over time, due to their having a nice host (the plant A) they are able to multiply in number. Now the levels of x are high and y is still low. Because x is high, yields of A decrease.

Now one season you plant B instead of A. Levels of y are low (or zero), so B thrives. Since x can't colonize B (it only colonizes A), its levels decrease and are eventually low again. By the time there are a lot of y (hurting the yields of , hopefully x will be low and it's safe to plant A again.

brennan

You also say:

> My issue was that the passage says that the solution to the problem is crop rotation. (The solution is not replacing one species with another).

Replacing one species of plant with another is exactly what crop rotation means, though.

Sarah889

@Sami and @potatocowpower I definitely see what you both are saying and you're totally right. I'm bringing my own idea of crop rotation into my interpretation of the passage. Thank you both so much.

@brennan When I said "My issue was that the passage says the solution to the problem is crop rotation (The solution to the problem isn't replacing one species with another)" I meant permanently. Clearly one species is being replaced with another, but I meant, instead of rotating them after a certain amount of time (making the temporal element the main trigger), why not just replace one species with another species which doesn't have the same weakness to phytopathogens permanently (making the species element the main trigger).

In real life, there are many legitimate answers to this question (because this specific crop is in high demand, etc). But for an inference question, my contention was that their identifying a solution and a problem that don't seem to match.

I understand the issue now. If you read my last response, it explains how I realize my main issue with this passage was that I misinterpreted what crop rotation meant. Understanding this now, it is clear to me why E is the answer. Thanks!