Using the Haney Soil Test to Predict Nitrogen Requirements in Winter Wheat (Triticum aestivum L.)
Round 1
Reviewer 1 Report
The use of mineral nitrogen doses adequate to the nutritional needs of plants and soil properties is important in environmental and economic terms. The dynamics of nitrogen transformations in different soils and climate condition makes it a great challenge for science to improve the efficiency of nitrogen fertilization. Therefore, studies undertaken by the authors of this paper on the possibility of using the Haney Soil Test to predict nitrogen requirement in winter wheat are an important issue.
The manuscript is a well-written and structured and minor comments are only on the technical side of the manuscript:
Table 1: there is a C:N ratio in the title, but no such data in the table?
Table 2: abbreviations for model fitting parameters: RMSE, R2, AIC should be explained
Author Response
The use of mineral nitrogen doses adequate to the nutritional needs of plants and soil properties is important in environmental and economic terms. The dynamics of nitrogen transformations in different soils and climate condition makes it a great challenge for science to improve the efficiency of nitrogen fertilization. Therefore, studies undertaken by the authors of this paper on the possibility of using the Haney Soil Test to predict nitrogen requirement in winter wheat are an important issue.
The manuscript is a well-written and structured and minor comments are only on the technical side of the manuscript:
Table 1: there is a C:N ratio in the title, but no such data in the table?
Response: Thanks for denoting that, we have removed C:N ratio from the title.
Table 2: abbreviations for model fitting parameters: RMSE, R2, AIC should be explained
Response: Thanks for the suggestion. We have added the abbreviations in the table title.
Reviewer 2 Report
The paper seems written primarily for those who already work with the specified soil testing methodology in the area of the USA in which the trials were carried out. The results are of potentially wider relevance to methodologies for estimating N requirements of a crop, but these more general aspects of the paper need to be drawn out and made accessible to an international readership. Some sort of explanatory diagram (e.g. based on yield-N response curve) is needed to explain and consolidate what all the different terms mean which at present would be highly confusing (e.g. Tables 3, 4) for a non-specialist.
Introduction
It would help focus the intention if it was clearly stated that the aim of the study is to compare two approaches to defining N–requirement of crops - an economics-based approach that ignores soil N with the Haney test that specifically measures soil N.
Methods
Line 63: what was unresponsive to N and flooding – need to fully justify why these site years were omitted.
For the international reader please clarify Feekes 4.
Table 1 is incomplete: needs units throughout and does not include C:N ratio as the legend says it does. Also, there is a very large difference in SOM between the three years at the Wall location. Surely it is not possible unless the trials were in very different soils. Can this be explained?
The equation on line 98: difficult to see how it works. If YG is dry matter, it will be several thousand kg per hectare, whereas HSTN will be several hundred. So several thousand minus several hundred is still several thousand which can’t be a fertiliser recommendation. And the ‘2.5’ needs explanation for the international reader not familiar with the approach used in South Dakota.
Line 103; Maximum Return to N approach needs explaining for the general reader.
Table 2. Description of all abbreviations (acronyms) needed.
Linear and quadratic plateau estimates – and joint point - need to be defined. A N-yield diagram using original trial data is needed to explain the analyses. Similarly an example is require to show returns from an economic analysis for each N-application rate. Otherwise it is unclear what the curve fitting might obscure. It is essential that the reader can work out how the data in Tables 3 and 4 are derived.
Results
Uncertainty in the original data and fitting procedure makes it very difficult for Tables 3 and 4 to be understood (see above)
The only site reported for the three years is Wall and then only for the 0-15 cm soil layer. Can the authors justify more strongly their assertion that rainfall has a decisive influence. While Fig. 2 looks conclusive – and yes the point about limited data is acknowledged in the Conclusions lines 228-29 - the authors should consider how much of the variation is due to site factors generally and how much to rainfall.
Line 132: the relevance of the Pearson correlation and P values needs to be stated explicitly.
Conclusions
Line 207: does that mean N mineralisation during crop growth? (also line 222)
Can the authors explain clearly for the generalist reader why the HST underestimates N mineralisation in dry conditions – i.e. what soil processes or test procedure are responsible?
Author Response
The paper seems written primarily for those who already work with the specified soil testing methodology in the area of the USA in which the trials were carried out. The results are of potentially wider relevance to methodologies for estimating N requirements of a crop, but these more general aspects of the paper need to be drawn out and made accessible to an international readership. Some sort of explanatory diagram (e.g., based on yield-N response curve) is needed to explain and consolidate what all the different terms mean which at present would be highly confusing (e.g. Tables 3, 4) for a non-specialist.
Response: Thank you so much for your suggestions. We have revised the manuscript according to your suggestions to reach the most audiences.
Introduction
It would help focus the intention if it was clearly stated that the aim of the study is to compare two approaches to defining N–requirement of crops - an economics-based approach that ignores soil N with the Haney test that specifically measures soil N.
Response: Thanks for the suggestion. We have added an explanation accordingly. Please see lines: 55-58.
Methods
Line 63: what was unresponsive to N and flooding – need to fully justify why these site years were omitted.
Response: Thanks for the suggestion. We have added an explanation accordingly, please see lines: 68-70.
For the international reader please clarify Feekes 4.
Response: Thanks, we have added an explanation of the growth stage. Please see lines: 74-75.
Table 1 is incomplete: needs units throughout and does not include C:N ratio as the legend says it does. Also, there is a very large difference in SOM between the three years at the Wall location. Surely it is not possible unless the trials were in very different soils. Can this be explained?
Response: Thanks for pointing this out. We have removed C:N from the title and included measuring units in the table. About SOM% at Wall, it’s just field variability, we could not find any reason to attest the high range. We added an explanation, see lines: 64-66.
The equation on line 98: difficult to see how it works. If YG is dry matter, it will be several thousand kg per hectare, whereas HSTN will be several hundred. So several thousand minus several hundred is still several thousand which can’t be a fertiliser recommendation. And the ‘2.5’ needs explanation for the international reader not familiar with the approach used in South Dakota.
Response: Thanks for the suggestion. We have added an explanation for the units and conversion factors. The ‘2.5’ is a numeric factor, derived from N rate studies in South Dakota. Please see the explanation in lines: 109-112.
Line 103; Maximum Return to N approach needs explaining for the general reader.
Response: Thanks for the suggestion. We have added a brief explanation alongside a reference. Please see lines 115-120.
Table 2. Description of all abbreviations (acronyms) needed.
Response: Thanks for the suggestion, we have included the acronyms.
Linear and quadratic plateau estimates – and joint point - need to be defined. A N-yield diagram using original trial data is needed to explain the analyses. Similarly an example is require to show returns from an economic analysis for each N-application rate. Otherwise it is unclear what the curve fitting might obscure. It is essential that the reader can work out how the data in Tables 3 and 4 are derived.
Response: Thanks for the comment. We have added an explanation and two new figures, Figure 2 and 3 to show how data on table 3 and 4 are derived. Please see lines 120-146.
Results
Uncertainty in the original data and fitting procedure makes it very difficult for Tables 3 and 4 to be understood (see above)
The only site reported for the three years is Wall and then only for the 0-15 cm soil layer. Can the authors justify more strongly their assertion that rainfall has a decisive influence. While Fig. 2 looks conclusive – and yes the point about limited data is acknowledged in the Conclusions lines 228-29 - the authors should consider how much of the variation is due to site factors generally and how much to rainfall.
Response: Thanks for the comment. Our study did not specifically design to address the influence of climatic phenomena like rainfall. Therefore, we are mostly speculating based on the range and trend of the data. We added an additional statement acknowledging that site-specific attributes may also affect this conclusion and that this phenomenon deserves further attention.
Line 132: the relevance of the Pearson correlation and P values needs to be stated explicitly.
Response: Thanks for the suggestion. We have added an explanation, please see lines: 165-173.
Conclusions
Line 207: does that mean N mineralisation during crop growth? (also line 222)
Can the authors explain clearly for the generalist reader why the HST underestimates N mineralisation in dry conditions – i.e. what soil processes or test procedure are responsible?
Response: yes, that is correct. For clarification, we have changed the sentence accordingly. Also added an explanation, please see lines 263-267.
*** Please note that line number corresponds to the revised version of the manuscript when 'track changes' are hidden.
Round 2
Reviewer 2 Report
This reviewer appreciates the efforts by the authors to respond to comments and suggestions. The paper has been greatly improved but the following points still need to be attended to.
Fig. 2 certainly brings an improvement to the understanding of the approach, but on this reviewer’s copy the details are indistinct; the lines, symbols and text need to be clearer and the symbols need to be defined in the legend. Also, need to define c in equ 3.
Fig 3 – needs to be understood without reference to the text – the legend needs to describe in full what is going on, eg what are the two horizontal dashed lines.
Text at lines 189-196 and Table 4. Referring to the dry 2017 and the difference between HST and MRTN in Table 4, the values cited (for example, 361 kg/ha lower when a linear plateau curve was used) seem to be averages of the three sites, which differed considerable, for example, Vivian 2017 being the same for LP. Can the authors explain why sites differed. Also comparing data columns 3 and 6 in Table 4, why are most values identical?
Lines 174-178: please state explicitly why the 0-60 cm sample decrease the HSTNR.
Line 63- about SOM at Wall. The variation is still very surprising if the plots in different years had similar soil types and management!
Lines 68-70 - So how often does flooding occur – does its frequency limit the wide applicability of the test.
Author Response
Author responses are in red font:
Fig. 2 certainly brings an improvement to the understanding of the approach, but on this reviewer’s copy the details are indistinct; the lines, symbols and text need to be clearer and the symbols need to be defined in the legend. Also, need to define c in equ 3.
Further explanation was added to the figure caption, which hopefully add clarifty. Further, we added letters to each graph to help delineate between figures
Fig 3 – needs to be understood without reference to the text – the legend needs to describe in full what is going on, eg what are the two horizontal dashed lines.
We apologize for the omission. Further clarification was added to the figure caption
Text at lines 189-196 and Table 4. Referring to the dry 2017 and the difference between HST and MRTN in Table 4, the values cited (for example, 361 kg/ha lower when a linear plateau curve was used) seem to be averages of the three sites, which differed considerable, for example, Vivian 2017 being the same for LP. Can the authors explain why sites differed. Also comparing data columns 3 and 6 in Table 4, why are most values identical?
Thanks for bringing this up. The identical numbers are a result of over prediction in the N rate, which means that the estimated yield is beyond the linear portion and out on the plateau (generally a sign decreasing economic efficiency). By definition all yield beyond that point will be equal. The values noted are averages. We did add a bit more discussion on that part, which hopefully adds a bit of clarity. While not noted explicitly, I think this actually helps bolster our point about dry weather conditions and low mineralization as expressed in the added language.
Lines 174-178: please state explicitly why the 0-60 cm sample decrease the HSTNR.
This language was added.
Line 63- about SOM at Wall. The variation is still very surprising if the plots in different years had similar soil types and management!
We agree, we checked the values and this is what it came back as. These are farmer-cooperator fields and we do not have an accounting of long-term cropping history (>5years). It is conceivable that at some point in the past this part of the farm was operated differently or perhaps had livestock integrated. For what it is worth, the yield trends and fit statistics are not dramatically different from the other years. In fact, this site had the best statistical fit of all sites. In theory, this should not matter as the Haney Test is supposed to account for these differences and indeed it is reflected in a higher SHC in Table 1.
Lines 68-70 - So how often does flooding occur – does its frequency limit the wide applicability of the test.
This is not a common occurrence for our region. It would limit applicability but only to the extent that there was no plant growth at the site (completely washed out). So no test would be effective under these conditions.
