The Analysis of Wheat Yield Variability Based on Experimental Data from 2008–2018 to Understand the Yield Gap
Round 1
Reviewer 1 Report
The study may be useful, but the presentation and evaluation of the results as well as their discussion is rather primitive. The yield variability is not clear, also, the yield gap what concerned and wanted to close is not clear. Since you have collected the data covering 11 years and many fields in 16 regions of Poland. I want to know the dynamic changes of the yields within the 11 years and , the differences across the fields in the same year. General, the M & M is not very clear, the analysis of results is not very deep.
Figure 2 and figure 3 actually represent the same thing, but they have not exactly consistent indicating. The most important factor in Figure 2 is soil quality, but the most one is nitrogen in figure 3. why?
The evidence of the most important result "the winter wheat yield variability was mostly dependent on the amount of nitrogen" is insufficient. It is better to do correlation analysis between the yield and nitrogen dosage at both temporal and spatial scale.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper reports results from a study that aimed to understand the possible causes of gaps between the grain yield in farmers paddocks and experimental farms throughout Poland between 2008 and 2018 compared to those predicted by biophysical simulation modelling using DSSAT. The authors have assembled a large data set and use a relatively new form of regression analysis (CART) to identify the main factors influencing yield. The overall approach (Methodology) appears generally sound (but does lack detail – see comment below). The authors present a sound case why such a study is required. This paper is not novel in that a similar methodological approach has been used in several studies in recent years to better understand the nature of yield gaps in farmers paddocks (as indicated by the comprehensive list of recent literature cited by the authors), it none the less is a potentially interesting paper (and of particular importance to Poland). The authors need however to address several general issues.
I recommend ‘Reconsider after major revision’
General issues:
There is considerable scope to improve the overall quality of English used (see some examples listed below).
The Methods need to provide sufficient detail to allow the study to be repeatable by another party. At present this is not possible. In particular I am concerned by the very sparse detail about the DSSAT modelling undertaken (in contrast there is a relatively good description of the CART procedure used). What parameters were used to determine ‘non limiting yield’ – the Methods say that yield was only limited by ‘genetic potential’ – but factors such as sowing time (in relation to phenology of the culture used) can have a very large influence on yield potential and initial soil starting conditions e.g. plant available water and background nutrients would strongly influence the relative response to management factors such as rate of N fertiliser.
The authors appear to have used a very comprehensive list of recent (and relevant) literature. However I felt that the current version of the Discussion really failed to fully interpret the Results. For example, what new insights or unexpected results were found? Can you better explain the results? What are the implications of this study (for further research or extension to farmers)?
Specific issues:
L27: In ‘the’ case ….
L38: … winter wheat ‘In Poland’ has improved
L55: nutrient supply ‘from’
L59: ….. throughout Poland between 2008-2018.
L60: No clear hypothesis presented.
L103: what no continuous data?
L112: Was sowing date recorded?
L132-133: Much greater detail than ‘In order to determine the potential yield of winter wheat we used the DSSAT program’. What version? How accurate were the modelling simulations (RMSE?) and what form of validation used?
L160: reword this sentence
L173: This information (r2) should be added to Figure 3 so that the figure can be interpreted without referring to the text.
L174-177: I’m at a loss to understand what is meant by ‘This section may be divided by subheadings?
L179: insert ‘a’ between covering and long
L182-183: reword sentence
L184-189: In most dryland cropping systems, ‘weather’ (rainfall amount and distribution, frost and heat shock) is the primary determinant of grain yield. The use of ‘grain yield’ (t/ha) rather than water use efficiency (kg yield/mm water/ha) helps to account for the influence of weather and provides a much better understanding of the relative importance of management factors (fertilisers etc).
L190-200: making generalisation such as x kg of N/ha is next to meaningless as the amount applied should reflect the target yield (and quality). Why not use a simple indication of N use efficiency e.g. kg yield/kg N fertiliser applied? Grain protein (critical concentration ca. 11.0 - 11.5%) has been used successfully to (retrospectively) indicate the adequacy of N supplied.
L201: delete ‘most’ – two variables cannot both be the most important.
L212-213: unsure what it meant by ‘balanced yield?
L214: reword . ‘When there is sufficient N to meet plant demand, other factors become limiting ….
L217-218: Using the correct chemical and applying it in the recommended manner (timing and conditions) is often more important in determining agrochemical efficiency than ‘amount’ applied.
L223: ‘study’, not ‘studies’
L225-226: why? Due to the influence of more pests and cereal diseases and poorer N nutrition compared to use of diverse rotations.
L231: … in this study ranged from 6.5 …
L232: .. values ‘are’ in agreement … ; delete ‘indeed’
L238: the yield gap may increase with ‘climate change but they do not necessarily explain your current results … please minimise speculation in the Discussion, especially given you have a lot of scope to better discuss your immediate results. There are some circumstances (admittedly rare) where grain yields may increase in future climates.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have tried to address the main concerns raised in my previous review. I feel however that the standard of English could still be improved so as to enhance the overall readibility of the paper.
Author Response
Thank you for your comment.
We tried to improve the readability of the article in the shortest possible time. We hope that we have achieved this to a great extent.
