Drought treatments in field experiment include 1/12P, /1/4P, 1/2P, 3/4P , P. P represents the plot receiving natural precipitaion. I do a linear regression between drought treatments and response variables. The reviewer think that this analysis was inappropirate. Can you help me? explain why
You need to justify why you chose the treatments. This can be supported by doing frequency analysis of drought in your area. Also, drought affects different crops differently so you need to specify the crop.
It makes sense to determine the trend over those treatments.
My opinion is that it would be fine to treat those treatments as quantitative treatments. Having five levels isn't ideal for this application, but I think it makes sense.
Another approach, though, is to conduct the analysis with those treatments treated as categorical treatments (e.g. as in anova). You can then apply polynomial contrasts to determine if there is a linear or quadratic trend over those treatments. This is a traditional technique in agronomic studies. The problem with this in this application is that the treatments are decidedly and intentionally not equally spaced.
This might be helpful with polynomial contrasts: https://www.ndsu.edu/faculty/horsley/Polycnst.pdf
Another idea: You might take a look at my paper at the following link. Here, we treated the treatments as categorical treatments throughout the paper, but then used them as the independent variable in a linear regression (Fig. 6). This approach might be okay with your reviewers.
Article Fall Fertilization Timing Effects on Nitrate Leaching and Tu...
You have to consider that the response to the amount of water available cannot be linear over the whole range of possible situations. There is an optimum beyond which production no longer increases, but decreases (e.g. due to root asphyxiation)
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