The Effect of Different Fertilization Treatments on Wheat Root Depth and Length Density Distribution in a Long-Term Experiment
Round 1
Reviewer 1 Report
The study takes advantage of long-term field experiments and analyses root system traits of winter wheat under different fertilization. Root system traits are relatively neglected in these experiments in comparison with crop yield and other shoot traits, which makes this study valuable.
Results section is relatively brief, but on point, and it presents the data accurately.
Discussion on the other hand is comprehensive and tries to put data into perspective of environmental data from the sites and previous literature in the field. Although in my opinion, the discussion fails to synthesize properly provided data with the literature and it fails to draw conclusions from the synthesis. On multiple occasions “data not shown” are referred, but there is no reason to exclude them from results, in my opinion. Also several times, claims, which are not comprehensively supported by the literature, are used.
In my opinion, addition of missing results and major changes to discussion would largely benefit the paper and would make it better.
Here I add specific comments to parts that should be improved throughout the paper.
- In table 1 and 3, the labels of columns should be edited. Enlarged spaces and different arrangement makes them harder to read.
- Throughout the discussion authors use terms like: “topsoil, deep subsoil” instead of the zones defined in cm in the tables in results. This usage makes links between discussion and results unclear.
- Lines 180 – 185: Authors claim, that MIN treatment enhanced root growth in deep subsoil but do not reduce depth of roots. They do not clarify whether it is common phenomena in other conditions. Also in reality both parameters were significantly enhanced in MIN treatment compared to NO, while “not reduced” implies they were the same.
- In the next paragraph (lines 186 – 193) authors discuss data that are not shown in this paper. It is rather pity in my opinion, as data on yield and N content might be used to better characterise the treatments and their impact on plants/plant roots.
- On lines 194 – 206 possibility, that root system density is affected by N supply in various studies, is discussed. Although authors do not address amount of N used in their study in context to other papers and whether same trend was observed.
- Line 216: “Results agree” should be replaced with “Results show” or similar.
- Line 224 mentions “other sites” without mentioning the prime site.
- On lines 230 – 238 potential stimulating effect of low nutrient supply is discussed. Firstly, it does not really belong to part “effect of site and year”. Secondly: only one study on root tuber crops is cited. I am convinced that literature on single elements (N, P, K, Ca) is available. For example, shortage of K reduces root growth in most treatments.
- Part “Root distribution” introduces results that are not in the “Results” part. Which is rather strange.
- Apendix A: Is poorly formatted and hard to read. It explains “topsoil” and other terms, but it is too late at the end of the paper. It probably contains some of the environmental data discussed as “not shown” but it is never mentioned in the text.
Author Response
Thanks for valuable comments.
We went through the manuscript carefully and tried to make adjustments as recommended.
1. Labels at Tab.1 and 3 were re-arranged to improve readibility
2. Terms topsoil, deep subsoil have been supplemented or replaced by an indication of depth
3. Lines 180 – 185: Authors claim, that MIN treatment enhanced root growth in deep subsoil but do not reduce depth of roots. They do not clarify whether it is common phenomena in other conditions. Also in reality both parameters were significantly enhanced in MIN treatment compared to NO, while “not reduced” implies they were the same.
3. We observed the impact of treatments on root maximum depth (RMD) was significant but weaker (p = 0.033) than that of site. The expression "not reduced" was used as reaction to some concerns about possible reduction of root depth under (high) mineral N ferilization as duscussed latter. We agree with the reviewer and modified the sentence.
4. The yields of wheat and correlations with root traits were added
5. On lines 194 – 206 possibility, that root system density is affected by N supply in various studies, is discussed. Although authors do not address amount of N used in their study in context to other papers and whether same trend was observed.
5. We agree, however the interpretation of N fertilization effects should demand also data on available soil mineral N supply (will be presented in another contribution) and rather complex problems of N demand (probably using N dilution curves etc.). We tried, in the manuscript, to remind about the possible impact of N fertilization on roots. In the VOP the fertilization level usually produced yields slightly under or near maximum ones. We added the information and the corresponding comment.
6. line 216 Corrected
7. Line 224 mentions “other sites” without mentioning the prime site.
7. Sites were added
8. On lines 230 – 238 potential stimulating effect of low nutrient supply is discussed. Firstly, it does not really belong to part “effect of site and year”. Secondly: only one study on root tuber crops is cited. I am convinced that literature on single elements (N, P, K, Ca) is available. For example, shortage of K reduces root growth in most treatments.
8. Thank your for the comment, we agree, but we tried to keep the number of citations at a reasonable level. Several citations were added
9. Part “Root distribution” introduces results that are not in the “Results” part. Which is rather strange.
9. Thank your for reminding, we agree. The text was corrected.
10. Apendix A: Is poorly formatted and hard to read. It explains “topsoil” and other terms, but it is too late at the end of the paper. It probably contains some of the environmental data discussed as “not shown” but it is never mentioned in the text.
10. The aim of the Appendix was to supply more data characterizing in more detail the conditions of the experimental sites. We agree and modified the table, however it is difficult to put all data in one table.
Reviewer 2 Report
General comments:
Svoboda et al. present a study on wheat root growth in three Czech long-term field experiments with different fertilization treatments. The study is novel as root growth has rarely been analysed in the context of long-term management effects. However, the present manuscript suffers from the fact that a large part of the discussion is based on data that appear to be available but were not included in this study. Further, the sampling design and the statistical analyses are not well explained and the denomination of parameters (root distribution, root length, root density) changes throughout the manuscript. I therefore, recommend a major revision of this manuscript.
Specific comments
L59-68: This paragraph creates an expectation that you will present analyses of nutrient balances and leaching – which you do not – but it does not give a clear justification for the parameters you chose to present (root length and rooting depth).
L87: which protocol was used for texture analysis? The given size classes correspond neither to USDA nor to WRB classifications
L93: what is the design of the field experiment, which randomisation?
L100: how was root sampling done? Soil pits, auger, …?
L105: were all plots sampled to 120 cm depth or just those that reached 110 cm (compare L 97/98)? In Fig. 3 it appears that all plots were sampled to 150 cm?
L108: inconsistent units, compare root density in km m-2 in L102
L114: which factorial design? The design of the field experiment (full or partial randomisation) should be considered and years should be analysed as repeated measurements, if samples were always taken from the same plots.
L121 “large” instead of “great”
L131ff: It appears that root length distribution (in introduction) = root density (in methods) = root length (in results and discussion). I would recommend to consistently use one term for the same parameter
L173: Which correlation analysis? Not mentioned in methods.
L175: is this annual precipitation? What about precipitation distribution, precipitation in specific growth phases? Similarly for temperature
Table 2 and 3: it is not really clear from the methods, which years were analysed
L177: should be Table 2
L183-185: This conclusion seems not to be justified by the results in the sentences before.
L187: what is “r”?
L179-211: if Nmin, water and biomass/yield data are so important for the interpretation of the results, they should be included in the paper
L221: give references for those studies
L224: which other sites
L230-238: this is not an effect of the year, should be moved to a different section
L280: less volume weight of the soil?
L304-305: is this the difference in effective root depth among treatments or among sites, and if the latter, which ones?
Author Response
Thank you for your helpful comments. We went through the manuscript carefully and tried to make adjustments as recommended. 1. L59-68: This paragraph creates an expectation that you will present analyses of nutrient balances and leaching – which you do not – but it does not give a clear justification for the parameters you chose to present (root length and rooting depth).
1. We tried, perhaps clumsily, to place root study in the broader context of determining nutrient balance and changes in nutrient content only in topsoil. Determining the depth of the roots indicates (as discussed below) the risk of loss of N (and other nutrients) by leaching out of reach of the roots.
We have modified the paragraph to more accurately reflect our intent.
2. L87: which protocol was used for texture analysis? The given size classes correspond neither to USDA nor to WRB classifications
2. The soil texture was determined according to the categories used in the Czech Republic. Because the article does not focus directly on soil water, we did not explain the details (conversion to category <0.002 mm). The description was slightly modified.
3. L93: what is the design of the field experiment, which randomisation?
3. The design was added
4. L100: how was root sampling done? Soil pits, auger, …?
4. Soil samples were taken with a hand-held corer of 5.6 cm diameter (Eiejkelkamp, NL) in 10 cm segments, (line 99-100) - added
5. L105: were all plots sampled to 120 cm depth or just those that reached 110 cm (compare L 97/98)? In Fig. 3 it appears that all plots were sampled to 150 cm?
6. The roots were sampled to at least 120 cm; the wording was modified
7. L108: inconsistent units, compare root density in km m-2 in L102
7. Thank you for reminder; corrected
8. nL114: which factorial design? The design of the field experiment (full or partial randomisation) should be considered and years should be analysed as repeated measurements, if samples were always taken from the same plots.
8. The design of the exeriment was described in Methods. Samples were taken from the same plots-treatments but the different part of the experimental due to crop rotation.
9. L121 “large” instead of “great”
9. Thank you, corrected
10. L131ff: It appears that root length distribution (in introduction) = root density (in methods) = root length (in results and discussion). I would recommend to consistently use one term for the same parameter
10. We agree and used the terms more consistently. In our view, the root length distribution corresponds to the root density distribution but might be confusing.
11. L173: Which correlation analysis? Not mentioned in methods.
11. Added
12. l. L175: is this annual precipitation? What about precipitation distribution, precipitation in specific growth phases? Similarly for temperature
13 We show monthly average temperature and sum of precipitation however we did not present correlation analysis of TRL in table form, only within text.
l.13 Table 2 and 3: it is not really clear from the methods, which years were analysed
14. Thank you for reminder, it true that the experimental years in Experimental Design and Details are a bit hidden. We corrected and added the experimentals years.
15. L177: should be Table 2
15. Thank you for your great care and detection of the error; corrected
16. L183-185: This conclusion seems not to be justified by the results in the sentences before.
16. We agree, the sentence is confusing, unclear. It was modfied, hopefully, it is now more clear for readers
17. L187: what is “r”?
17. Thank you for reminder, added corr. coeficient
18. L179-211: if Nmin, water and biomass/yield data are so important for the interpretation of the results, they should be included in the paper
l.18 Yields and correlations with average root data were added to the manuscript. The presentation and the use of data on Nmin and soil moisture would demand further analysis and interpretation and were hence only mentioned within discussion of results.
19. L221: give references for those studies
19. The references are given in following lines, however we added two more references on the effect of deficiency of nutrients on root growth or depth
20. L224: which other sites
20. Text modified
21. L230-238: this is not an effect of the year, should be moved to a different section
21. We agree and moved the paragraph to previous section
22. L280: less volume weight of the soil?
22. Thanks for reminder, soil was added
23. L304-305: is this the difference in effective root depth among treatments or among sites, and if the latter, which ones?
23. Thank you, the sentence was modified
Round 2
Reviewer 1 Report
The paper was largely improved according to suggestions of both reviewers. Added data made it more self explanatory. Authors improved the discussion which now shows the data in deeper context and supports the conclusions. Considering above mentioned improvements.
Author Response
The reviewer states the paper was improved according to suggestions.
The original manuscript was corrected for English by dr. Peter Lemkin, an experienced American teacher living in Prague (Peter [email protected]). Dr. Lemkin has been performing correction of scientific English texts for years. However, as modifications and corrections have been performed during reviewing process the manuscript was sent again to him for corrections. The corrected manuscript was uploaded (the correction of common errors as definite and indefinite articles, prepositions have not been performed within revisions tomaintain the clarity of the text mopdifications)
Reviewer 2 Report
The authors have generally responded adequately to the previous comments. However, I am not convinced by answer no. 18 that "The presentation and the use of data on Nmin and soil moisture would demand further analysis and interpretation and were hence only mentioned within discussion of results". Either the Nmin and moisture data are available and were thouroughly tested to support the statements given in the text (l 234-236; l 269-271, l 290-29) - and in that case you may as well include the data in the text - or they were not analysed and tested - in that case all statements based on them should be removed.
Also I would strongly recommend language editing, the errors are mostly minor but there are a number of them.
Author Response
The reviewer states the authors adequately responded to the previous comments, however he proposes to include also data on soil mineral N and water content. The data represent a large amount of data (three sites x three years x two terms of sampling x seven soil layers) and their analysis was not the aim of this study. However, to satisfy the opponent, we present data on Nmin relevant to discussion as demanded, in the form of Appendix B. I agree there are many important and interesting interactions among roots and other factors and it seems pity not point to some of them even without presenting and analysing other experimental yet unpublished data.
The original manuscript was corrected for English by dr. Peter Lemkin, an experienced American teacher living in Prague (Peter [email protected]). Dr. Lemkin has been performing correction of scientific English texts for years. However, as modifications and corrections have been performed during reviewing process the manuscript was sent again to him for corrections. The corrected manuscript was uploaded (the correction of common errors as definite and indefinite articles, prepositions have not been performed within revisions tomaintain the clarity of the text mopdifications).
