Soil Moisture Outweighs Climatic Factors in Critical Periods for Rainfed Cereal Yields: An Analysis in Spain

Round 1

Reviewer 1 Report

Manuscript ID: agriculture-1654960

Title: Soil moisture outweighs climatic factors in critical periods for rainfed cereal yields: An analysis in Spain

Gaona et al. studied the effects of soil moisture and climatic factors on rainfed cereal yields, and found soil moisture outweighs climatic factors in critical periods. This study falls within the scope of Agriculture journal. Generally speaking, this study work is well-done, and I can capture some interesting findings that appeal to me. However, there could be found questionable contents, that is, the graphic format is not uniform, and some figures are unclear.

Some detailed comments are in below.

Line 137, please indicate the parameter meaning of equation 1, such as T_base, and t.

Lines 141-145, please indicate the reference to equation 2.

Line 158, change 0.1×0.1^o into 0.1^o×0.1^o.

Line 164, “LISFLOOD model” instead of “LISFLOOD”.

Line 168, change “5 km×5 km” into “5×5 km”.

Lines 203, 208, and 218, the abbreviation (S and H) of “sowing and harvesting” is unnecessary.

Line 226, please give the full name of “Z7” at the first mention.

Figures 4-6, it's hard to distinguish nine black/ gray lines.

Figure 7, use “Months” as the title in horizontal axis.

Conclusion is too much and needs to be simplified.

Line 654, change “Figure 1” into “Figure A1”.

Author Response

Reviewer 1

General comments

“This study falls within the scope of Agriculture journal. Generally speaking, this study work is well-done, and I can capture some interesting findings that appeal to me….There could be found questionable contents, that is, the graphic format is not uniform, and some figures are unclear”

We thank the reviewer for appreciating that the scope and general impression of the content and results are positive. We understand the difficulties interpreting some of the plots included in the results, which have been carefully revised following his/her constructive and detailed comments.

Specific comments

"Line 137, please indicate the parameter meaning of equation 1, such as T_base, and t."

• The meaning of the parameters in Eq. 1 has been further explained including that t refers to the point of time at which the GDD is accumulated. T_base definition and reference are also clarified. Lines 140-144

"Lines 141-145, please indicate the reference to equation 2."

• It was already included [38, Ortiz-Monasterio et al., 1994] next to the (Eq. 2). Nonetheless, the reference has been clarified. Lines 145-147

"Line 158, change 0.1×0.1^o into 0.1^o×0.1^o."

• Line 165

"Line 164, “LISFLOOD model” instead of “LISFLOOD”."

• Line 171

"Line 168, change “5 km×5 km” into “5×5 km”."

• Line 175

"In lines 203, 208, and 218, the abbreviation (S and H) of “sowing and harvesting” is unnecessary."

• The abbreviations have been removed in the text. We further indicate that the use of abbreviations is limited to figures, as introduced in lines 240-244.

"Line 226, please give the full name of “Z7” at the first mention."

• Lines 229-234

"In figures 4-6, it's hard to distinguish nine black/grey lines."

• The purpose of the style is to primarily portray the period of statistical significance (colored) or non-significance (grey) of correlations between climate variables/soil moisture and yield and secondarily to illustrate the spread of such correlations among provinces of the same region (using an individual line for each province). Symbol sequences are shown over the lines at monthly scale from top to bottom aim to facilitate the identification of the provinces from most to least affected on each month for the readers who are interested in differentiating the nine/five lines of the provinces of each region. To explicitly describe this aid to identify lines we mention it in the caption of the first figure of the type (Lines 285-287).

"Figure 7, uses “Months” as the title on the horizontal axis."

• Either in figure 7 or in the rest of figs. 4-A2, months are shown in abbreviations but a mention in the captions has been included clarifying that x-axis labels refer to months. Lines 291, 359, 431, 545

"The conclusion is too much and needs to be simplified."

• Conclusions are now written in a clearer and more concise manner. Lines 596-631

"Line 654, change “Figure 1” into “Figure A1”."

• Line 652

Author Response File: Author Response.docx

Reviewer 2 Report

The work " Soil moisture outweighs climatic factors in critical periods for rainfed cereal yields: An analysis in Spain" concerns the analysis of soil moisture and climatic indicators to determine the critical periods in wheat and barley yielding.

A valuable aspect of the work is the methodological study of the "course of research", which synthetically presents the sequence of the analyses performed. An innovative approach is to use the information set on the soil moisture databases ERA5-Land and LISFLOOD and climate data obtained from ECMWF resources. The presented research is an important stage for further analyses, which may allow to monitor plant growth and forecast the yield in the future. However, the results presented in the paper do not contribute much to the current state of knowledge.

The soil moisture indicator correlates very well with the yield, which is obvious. In the critical period, the dependence of the yield on the availability of water in the soil is linear. It is worth mentioning that the availability of water in soil for plants may vary due to the different ability of the soil to retain water. Soil quality in the analysed regions should be discussed.

 The fact is that the yield of crops is largely influenced by weather conditions. However, the relationship between meteorological elements and the yield is difficult to describe and formalize due to their non-linearity.

 It seems that adopting a linear relationship for all analysed indicators is a great simplification, therefore it requires particular caution when forming conclusions and interpreting the results.

The value of the work would be greater if the authors performed an analysis verifying the possibility of using the analysed indicators, in particular soil moisture, to forecast the yield of cereals.

Specific Comments:

Introduction

The work requires supplementing information on the analysed climatic indicators, which influence the yield of cereals: maximum temperature (Tmax), minimum temperature (Tmin), accumulated precipitation (RR), relative humidity (RH), and global radiation (RAD) and: growing degree days (GDD), diurnal temperature range (DTR), photo thermal quotient (PTQ), and vapor pressure deficit (VPD).

 From line 75-96. The description applies to information that should be included in the methodology other than the Introduction

Methods

This section is well written.

But the use of one filter of a 30-day moving average proved for all analysed parameters seems unjustified. For example, the use of such a filter for Tmax causes a flattening of the stress effect due to high temperatures on plants.

Results

The description of the development phases needs to be supplemented. Have the dates of the development phase in the examined period (1981-2018) not changed.

It is necessary to explain why there is a difference in the timing of occurrence of the maximum R values ​​for soil moisture in Figures 4, 5 and 6. In Figure 4 they are earlier (Z3-Z7) than in Figures 5 and 6 (Z7-H).

Author Response

Reviewer 2

General comments

“…However, the results presented in the paper do not contribute much to the current state of knowledge. The soil moisture indicator correlates very well with the yield, which is obvious.

It is worth mentioning that the availability of water in the soil for plants may vary due to the different ability of the soil to retain water. Soil quality in the analyzed regions should be discussed.

However, the relationship between meteorological elements and the yield is difficult to describe and formalize due to their non-linearity. It seems that adopting a linear relationship for all analyzed indicators is a great simplification.

The value of the work would be greater if the authors performed an analysis verifying the possibility of using the analyzed indicators, in particular soil moisture, to forecast the yield of cereals…”

• We sincerely appreciate the valuable comments from the reviewer on multiple complex aspects of the analysis of climate and soil moisture on cereal yield. Nonetheless, we consider our current focus on evaluating the role of soil moisture on crops yield compared to climatic variables is worthwhile in itself, given the lack of studies including soil moisture to assess yield variability at a regional scale. We are aware of the complex role of climatic indicators and especially soil moisture may have to evaluate crops yield. For this reason, we propose this study as the cornerstone, once the determining role of soil moisture has been identified, to support the forthcoming studies addressing issues suggested by the reviewer as the non-linearity of the processes, the influence of soil properties, and in the long run, the development of a reliable forecasting tool for cereal yields at regional or national scale implementing soil moisture as a critical variable. This is feasible now since the scientific community has reliable soil moisture databases at the most appropriate temporal and spatial scales, generated by modelling or remote sensing.

Specific comments

"The work requires supplementing information on the analysed climatic indicators in the introduction, which influence the yield of cereals: maximum temperature (Tmax), minimum temperature (Tmin), accumulated precipitation (RR), relative humidity (RH), and global radiation (RAD) and growing degree days (GDD), diurnal temperature range (DTR), photothermal quotient (PTQ), and vapor pressure deficit (VPD)."

• Since it is demanded to include supplementary information about the selected variables in the introduction, we have compiled in between Lines 39 and 47 a short description of the relevance and convenience of incorporating these variables according to the experience of previous research works.

"From line 75-96. The description applies to information that should be included in the methodology other than the Introduction"

• Some of the specifications given in Lines 75-96 have been moved to other sections to make this paragraph more concise. However, we find it relevant to keep some essential descriptions of the aim, scale, methodology, data, results, and scope of the study in this last paragraph of the introduction to give an accurate idea of the study as a whole.

"In the methodology section, the use of one filter of a 30-day moving average proved for all analysed parameters seems unjustified. For example, the use of such a filter for Tmax causes a flattening of the stress effect due to high temperatures on plants."

• Even though the influence of temperatures and other quickly evolving variables might be of impact at shorter temporal scales, we adopt the 30-day moving average filter as a middle ground in between the variables changing at short time scales and the one evolving dampened and lagged. In previous works, we have found that this approach is able to reduce noise and gives good results in this type of analysis.

"In the description of the development phases the dates of the development phase in the examined period (1981-2018) have not changed."

• While we really appreciate the indication that development phases may actually vary with time and agree with the reviewer, the scope of the study is to determine an average framework of correspondence of the climate and soil moisture interactions with yields for a sufficiently long time series After a detailed analysis for elaborating section 2.4.2., we concluded that this phenological framework was sufficiently representative.
• Moreover, this is the common approach when meteorological data is used which provides a basis to further analysis regarding crop’s dependencies, and their trends with time. We hope to further elaborate on the temporal evolution of both the dependencies and the development phases of the crops in future studies.

"It is necessary to explain why there is a difference in the timing of occurrence of the maximum R values ​​for soil moisture in Figures 4, 5 and 6. In Figure 4 they are earlier (Z3-Z7) than in Figures 5 and 6 (Z7-H)."

• We thank the reviewer for pointing out this aspect on the interpretation of Figures that may be confusing.

Plots in Figure 4 display the soil moisture-yield correlations for each ERA5-Land and LISFLOOD databases which indeed differ between barley and wheat at the time of the peak of correlation.

However, the difference indicated by the reviewer refers to the confusion with the reference soil moisture correlations of the specific region and crop in Figures 5 and 6. The plots of soil moisture correlations with barley yields in CYL shown in Figure 5 correspond to subplot a1 of Figure 4, while those of CLM shown in Figure 6 correspond to the subplot a3 of Figure 4.

To clarify the interpretation of the Figures and facilitate proper guidance to readers and reviewers, we include a reference to Figure 4 in the captions of Figures 5 and 6 and A1 and A2 when soil moisture is described: “… .Periods of significant correlation of ERA5-Land soil moisture with annual barley yields (Figure 4 a1) are shown in green…

Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors, the manuscript you have prepared is especially meaningful for rainfed agriculture regions. Please review the manuscript, paying attention to the minor revision explanations I have added to the text.

Comments for author File: Comments.pdf

Author Response

Reviewer 3

General comments:

“Dear authors, the manuscript you have prepared is especially meaningful for rainfed agriculture regions. Please review the manuscript, paying attention to the minor revision explanations I have added to the text”.

• We thank the reviewer for understanding the relevance of the study for rainfed crops. We paid careful attention to the specific comments and checked accordingly to include some clarifications or further explanations.

Specific comments:

“Line 76, include facts about production of the two regions of study”.

• The average regional statistics of production of CYL and CLM regions or winter wheat and barley from the Eurostat regional database (citation [29]) have been cited in the text in that final paragraph of the introduction and expanded in the last sentences of the description of the study area (Lines 111-114”): “In spite of these natural constraints, CYL and CLM represent the breadbaskets of Spain and important contributors to the European cereal production, averaging 2.6 and 0.6 Mt of winter wheat and 2.85 and 2.39 Mt of barley production, respectively, in the period 2013-2021”.

“Line 113, specify which soil characteristic limit crop production”

• The text now further mentions the soil characteristics such as shallowness, texture and organic properties that could unfavorably affect crop production. Lines 112-114

“Line 343, specify the varieties most grown in the two regions of study”

• Unfortunately, there are no official statistics of the most grown varieties of wheat and barley in CYL and CLM.

“Extensive editing of English language and style required”

• The whole text has been carefully revised for the correctness and clarity of the description. We hope the current changes have significantly increased the ease of reading. The text has been extensively revised by the editing company American Journal Experts, you can get their provided certificate in the following link: https://secure.aje.com/api/certificate/D7E8-F737-A415-A306-EE1C/pdf

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thank you for the replies and corrections made in the article.