Does Drone Data Allow the Assessment of Phosphorus and Potassium in Soil Based on Field Experiments with Winter Rye?

Round 1

Reviewer 1 Report

 

Manuscript, entitled (Relationships Between UAV Remote Sensing Multispectral
Data and Soil Available Phosphorus and Potassium in Long Term Field Experiments with Winter Rye) reported that The effect of phosphorus and potassium fertilization on the UAV-derived spectral reflectance of winter rye was weak, weaker in comparison to effect of nitrogen fertilization. The effect of phosphorus and potassium fertilization on spectral reflectance was stronger in the experiment with monoculture than in the experiment with crop rotation. Negative relationships were proved between available soil potassium with spectral reflectance in range of blue, green and red bands and positive with red edge and near infra-red bands. There are several shortcomings that should be included in order to enhance the final manuscript for the readers.

Title

·         The title is traditional. It should be modified to be attractive for the reader.

Abstract

·         The abstract is needed to support by introduction to present the important of this work and also the conclusion of this work at end of the abstract.

·          The abstract is more description the important results of Correlation coefficients of bands as well as for PCA should be presented.

Introduction

·         Line 30 to 32. What about the short near infrared from 1500 to 2500 nm for assess the plant stress.

·         Line 34 -35. More details about this sentence should be added (Spectral reflectance can only be useful in detecting nutrient deficiency if one
factor is involved). It is not clear for the reader.

• Line 46 to 49. There were several spectral indices to assess the nitrogen in plant better than NDVI. NDVI has saturation affected by high nitrogen and biomass levels. Please support this area of study by other references DOI: 10.1016/j.eja.2021.126286.
• Please give the full definition for spectral indices in introduction such as RVI, GRVI,… and else which were presented at the first time.

·         The authors presented several studies which related to potassium or Phosphorus  for that what is the novelty (originality) of the work? And what is new in your work that makes a difference in the body of knowledge? What has been done that goes beyond the existing research?

 

 

Materials and methods ·          In figure 1.The design of long-term field experiments covered by the study together with the map of NDVI but the NDVI is not the optimized spectral index. Please try to solve this issue. ·         Location map of this area should be added. ·         There was no data bout the physical, and mechanical of the soil. Please present this data in table.     Results ·         The biggest issue here in this study, why the authors did not measure the potassium, phosphorus and nitrogen in the leaves of the crop to see the range of them. May be the change in spectra reflectance is affected by internal and external factors. How to solve this issue? ·         The authors should add the correlation matrix between pH      ,P, K, Mg , Grain yield to know if there was the interrelationships or no. As we see, the grain yield presented good relation with the most different bands. ·         Why the authors did not present the data of the relationships between the spectral indices with these measured parameters and presented only with the wavelength in different dates. Since the spectral indices included two or several bands. Please present this data to see what is best? ·         Please added the significant levels in table 3 and 4? Discussions  

·         The discussion is well written.  But is still need to discuss PCA.

·         Please, write the practical applications of your work in a separate section, before the conclusions and provide your good perspectives?

Conclusions ·         Conclusions totally should be written again is similar to abstract.

·         Please write about the limitations of this work in details in conclusion section?

Manuscript, entitled (Relationships Between UAV Remote Sensing Multispectral
Data and Soil Available Phosphorus and Potassium in Long Term Field Experiments with Winter Rye) reported that The effect of phosphorus and potassium fertilization on the UAV-derived spectral reflectance of winter rye was weak, weaker in comparison to effect of nitrogen fertilization. The effect of phosphorus and potassium fertilization on spectral reflectance was stronger in the experiment with monoculture than in the experiment with crop rotation. Negative relationships were proved between available soil potassium with spectral reflectance in range of blue, green and red bands and positive with red edge and near infra-red bands. There are several shortcomings that should be included in order to enhance the final manuscript for the readers.

Title

·         The title is traditional. It should be modified to be attractive for the reader.

Abstract

·         The abstract is needed to support by introduction to present the important of this work and also the conclusion of this work at end of the abstract.

·          The abstract is more description the important results of Correlation coefficients of bands as well as for PCA should be presented.

Introduction

·         Line 30 to 32. What about the short near infrared from 1500 to 2500 nm for assess the plant stress.

·         Line 34 -35. More details about this sentence should be added (Spectral reflectance can only be useful in detecting nutrient deficiency if one
factor is involved). It is not clear for the reader.

• Line 46 to 49. There were several spectral indices to assess the nitrogen in plant better than NDVI. NDVI has saturation affected by high nitrogen and biomass levels. Please support this area of study by other references DOI: 10.1016/j.eja.2021.126286.
• Please give the full definition for spectral indices in introduction such as RVI, GRVI,… and else which were presented at the first time.

·         The authors presented several studies which related to potassium or Phosphorus  for that what is the novelty (originality) of the work? And what is new in your work that makes a difference in the body of knowledge? What has been done that goes beyond the existing research?

 

 

Materials and methods ·          In figure 1.The design of long-term field experiments covered by the study together with the map of NDVI but the NDVI is not the optimized spectral index. Please try to solve this issue. ·         Location map of this area should be added. ·         There was no data bout the physical, and mechanical of the soil. Please present this data in table.     Results ·         The biggest issue here in this study, why the authors did not measure the potassium, phosphorus and nitrogen in the leaves of the crop to see the range of them. May be the change in spectra reflectance is affected by internal and external factors. How to solve this issue? ·         The authors should add the correlation matrix between pH      ,P, K, Mg , Grain yield to know if there was the interrelationships or no. As we see, the grain yield presented good relation with the most different bands. ·         Why the authors did not present the data of the relationships between the spectral indices with these measured parameters and presented only with the wavelength in different dates. Since the spectral indices included two or several bands. Please present this data to see what is best? ·         Please added the significant levels in table 3 and 4? Discussions  

·         The discussion is well written.  But is still need to discuss PCA.

·         Please, write the practical applications of your work in a separate section, before the conclusions and provide your good perspectives?

Conclusions ·         Conclusions totally should be written again is similar to abstract.

·         Please write about the limitations of this work in details in conclusion section?

Author Response

Authors: Thank you very much for all the comments

Manuscript, entitled (Relationships Between UAV Remote Sensing Multispectral 
Data and Soil Available Phosphorus and Potassium in Long Term Field Experiments with Winter Rye) reported that The effect of phosphorus and potassium fertilization on the UAV-derived spectral reflectance of winter rye was weak, weaker in comparison to effect of nitrogen fertilization. The effect of phosphorus and potassium fertilization on spectral reflectance was stronger in the experiment with monoculture than in the experiment with crop rotation. Negative relationships were proved between available soil potassium with spectral reflectance in range of blue, green and red bands and positive with red edge and near infra-red bands. There are several shortcomings that should be included in order to enhance the final manuscript for the readers.
Title
·         The title is traditional. It should be modified to be attractive for the reader.
 Authors: The title of the manuscript was changed to following: “Does Drone Data Allow the Assessment of Phosphorus and Potassium in Soil Based on Field Experiments with Winter Rye?”. We hope that such title is more attractive for the readers.

Abstract
·         The abstract is needed to support by introduction to present the important of this work and also the conclusion of this work at end of the abstract.
·          The abstract is more description the important results of Correlation coefficients of bands as well as for PCA should be presented.
Authors: The abstract was extended, i.e. in the beginning introduction which present importance of the study was added and in the end more results of PCA were described.
Introduction 
·         Line 30 to 32. What about the short near infrared from 1500 to 2500 nm for assess the plant stress.
Authors: In the Introduction possibilities of usage of SWIR range (1500 - 2500 nm) was described and three new references on this topic were added.

·         Line 34 -35. More details about this sentence should be added (Spectral reflectance can only be useful in detecting nutrient deficiency if one 
factor is involved). It is not clear for the reader.
Authors: In the sentence a phrase was added on deficiency caused by two or more nutrients is very difficult to diagnose. Moreover, new reference which supports the statement was added.

•    Line 46 to 49. There were several spectral indices to assess the nitrogen in plant better than NDVI. NDVI has saturation affected by high nitrogen and biomass levels. Please support this area of study by other references DOI: 10.1016/j.eja.2021.126286.
Authors: Information about three band vegetation indices (e.g. NPDI) was added together with. new reference.
•    Please give the full definition for spectral indices in introduction such as RVI, GRVI,… and else which were presented at the first time.
Authors: Full definition of the spectral indices were added in Introduction.
•    
·         The authors presented several studies which related to potassium or Phosphorus  for that what is the novelty (originality) of the work? And what is new in your work that makes a difference in the body of knowledge? What has been done that goes beyond the existing research?

Authors: There are not many publications on the possibility of detecting phosphorus and potassium deficiency in crops using spectral data. This is due to the fact that obtaining a severe deficiency of these nutrients requires long-term experiments, where phosphate and potassium fertilizers were not applied for many years. There have not been many such studies on cereals and the studies on rye are the only ones, so it can be considered that we are expanding knowledge in this area. Such information was added in the end of introduction.

 
Materials and methods ·          In figure 1.The design of long-term field experiments covered by the study together with the map of NDVI but the NDVI is not the optimized spectral index. Please try to solve this issue. ·         Location map of this area should be added. ·

Authors: The maps in Figure 1 were changed to RGB map instead of NDVI. Moreover, location of the study area on the map of Europe was added.

         There was no data bout the physical, and mechanical of the soil. Please present this data in table.    

Authors: The table which presents percentage of soil fractions (according particle diameter) for each soil horizon for both experiments was added as Table 1 to the manuscript together with the description.

 Results ·         The biggest issue here in this study, why the authors did not measure the potassium, phosphorus and nitrogen in the leaves of the crop to see the range of them. May be the change in spectra reflectance is affected by internal and external factors. How to solve this issue? ·         

Authors: Unfortunately, we do not have plant chemical composition for the year of the study. However, the experiment is long-term, in the same design from 1974 and we have archival results of chemical composition (grain and straw during harvest). We have added these results to the manuscript to the Material and methods.

The authors should add the correlation matrix between pH    ,P, K, Mg , Grain yield to know if there was the interrelationships or no. As we see, the grain yield presented good relation with the most different bands. ·         
Authors: Correlation matrix between pH, P, K, Mg, grain yield was added to the results for both experiments (in current Tables 6 and 7).

 

Why the authors did not present the data of the relationships between the spectral indices with these measured parameters and presented only with the wavelength in different dates. Since the spectral indices included two or several bands. Please present this data to see what is best?

Authors: The aim of the study is evaluation of the relationships between individual bands of reflectance as well spectral profiles with reflectance of rye during vegetation with different nutrient availability. Similar study in which we studied relationships between various spectral indices was already published (https://doi.org/10.3390/agriculture12101671) and is cited in Discussion. We have added evaluation of both approaches in Discussion.  

 ·         Please added the significant levels in table 3 and 4? Discussions   
Authors: P-values for correlation coefficients were added to the Tables (in current Tables 6 and 7).

·         The discussion is well written.  But is still need to discuss PCA.
Authors: The discussion was extended and contains more information about the PCA results.

·         Please, write the practical applications of your work in a separate section, before the conclusions and provide your good perspectives?
Authors: In the discussion we have added possible future applications of the results of our study.

Conclusions ·         Conclusions totally should be written again is similar to abstract. 
Authors: Conclusions was rewritten and improved. .

·         Please write about the limitations of this work in details in conclusion section?
Authors: In the Conclusions limitation of the work was added.

 

Reviewer 2 Report

This MS focus on the relationships Between UAV  Data and Soil Phosphorus and Potassium in Long-Term Field Experiments. The analysis should improve the understanding of this relationship. But some issues should be considered in the revised version.

 

Major comments:

1.      The soil samples were collected from each plot from the arable layer (0-20cm of depth). However, the penetration for UAVs is limited to the surface. How to solve this problem is important. Although you analyze the relationship between the reflectance and P K content, the depth is mismatched. This point should be further discussed.

2.      multivariate statistical analyses are mentioned but missed in the result.

3.      Due to the relationship between the reflectance and P, K content is very weak, what is the meaning of PCA analysis? please further explain.

 

Specific comments:

1.      Introduction is too long. You may split it into several paragraphs with one central sentence.

2.      Lines 115-135 can be included in a table.

3.      The location of the study area is missing. A figure should make it clearer.

4.      Could you convert table 1 into figures? Because the figures could easily be understood. I know the relationship is not that strong, but you could choose the significant one for display.

 

5.      Low quality for Figure 2. Please make it beautiful and compact

Author Response

This MS focus on the relationships Between UAV  Data and Soil Phosphorus and Potassium in Long-Term Field Experiments. The analysis should improve the understanding of this relationship. But some issues should be considered in the revised version. 
  Authors: Thank you very much for all the comments
Major comments: 
1.    The soil samples were collected from each plot from the arable layer (0-20cm of depth). However, the penetration for UAVs is limited to the surface. How to solve this problem is important. Although you analyze the relationship between the reflectance and P K content, the depth is mismatched. This point should be further discussed. 
Authors: The study is focused on spectral reflectance of the crop surface not bare soil. All images were taken in growth stages during where plant cover most of the soil. Further research is necessary for evaluation of the spectral reflectance of bare soil which we plan in the future. 
2.    multivariate statistical analyses are mentioned but missed in the result.
Authors: The multivariate results are presented in subchapter 3.3. We have changed the title of this subchapter to be more specific. Moreover, we have added discussion of the PCA results in the Discussion. 

3.    Due to the relationship between the reflectance and P, K content is very weak, what is the meaning of PCA analysis? please further explain. 
Authors: We have added more information about the PCA results to the Discussion. We agree that effect of P and K is not very strong. 

 
Specific comments:
1.    Introduction is too long. You may split it into several paragraphs with one central sentence. 
Authors: We split Introduction into several paragraphs to be more clear. Moreover, some changes in the Introduction was introduced. 

2.    Lines 115-135 can be included in a table. 
Authors: We have converted the text in lines 115-135 to the new table. 

3.    The location of the study area is missing. A figure should make it clearer. 
Authors: We have added map of the Europe which presents location of the study in Figure 1. 

4.      Could you convert table 1 into figures? Because the figures could easily be understood. I know the relationship is not that strong, but you could choose the significant one for display. 
 Authors: Unfortunately the Table 1 (current number is Table 5) cannot be converted to one figure because contain too much of data. 

5.      Low quality for Figure 2. Please make it beautiful and compact
Authors: Formatting of the Figures 2 and 3 were changed to be more clear.

Round 2

Reviewer 1 Report

The authors did significant improvment acording to my comments. It can be accepted for publication.