Dual-Purpose Rye, Wheat, and Triticale Cover Crops Offer Increased Forage Production and Nutrient Management but Demonstrate Nitrogen Immobilization Dynamics
Round 1
Reviewer 1 Report
Review comments:
In this MS, the authors investigated evaluated rye, wheat, and triticale as DPCC in a manured field and their potential impact on subsequent corn silage production. It contributes to gaining a comprehensive understanding of the potential to affect fertility needs of corn in a multi-year rotation. However, your article needs some revisions before publication. My suggestions and questions regarding this article are listed below.
1. There are too many preface paragraphs, it is recommended to merge them into 4-5 paragraphs
2. Please provide additional explanations on your main scientific issues
3. L89-91. What is the basis of your research hypothesis? Please provide a detailed description.
4. L103-105. Where is the data for 2018? Please provide additional analysis.
5.L112-120. Please add the mean and SD of the pH and other value (like Ca and Mg) used for your experiments.
6.References: The format of the references does not strictly follow requirements.
7.Fig. 1b. The legend should be moved up a bit
Author Response
Reviewer 1:
In this study, the author hypothesized that the high C:N residue left after removing dual-purpose cover crops (DPCC) biomass above 7.6 cm would encourage a community of decomposers, which compete for N and cause N-immobilization in corn systems. The results of this experiment suggested that in addition to capturing nutrients from the fall manure application, DPCC captured nutrients already present in the soil. While these findings did not impede corn yields in this study, they demonstrate the potential to affect the fertility needs of corn in a multi-year rotation. This study evaluated rye, wheat, and triticale as DPCC in a manured field and their potential impact on subsequent corn silage production. The results are important references for agronomists to understand the DPCC. Overall, the experiment is well-designed, and the manuscript is composed correctly. I can't provide suggestions about the writing details of the manuscript due to my non-native English speaking. I have several opinions as follows.
(1) Please list p-value for statistical significance (Line 210, 225, 273, 344, 352).
Response:
P-values were added throughout the manuscript.
(2) Please list the mean value and standard deviation or standard error in Table 1 and Table 2.
Response:
Having SD in tables is not a required format. While some manuscripts may present SD some don't. Additionally, in order to have the SD values, as one reviewer suggested, we have to re-run a huge set of three years of data which cannot be done in a short time.
(3) Separate descriptions of conclusions and discussions are encouraged in academic writing unless this undermines the paper's structural integrity.
Response:
Thanks for the valuable comment. A separate conclusion section was added to the manuscript.
Reviewer 2 Report
This manuscript used a three years field experiments to explore the yield and decomposition of dual-purpose cover crops and the effect of cover crops on corn silage yield and quality . I could suggest this paper for publication in Agronomy after modifying with the following suggestions:
(1) the title is too long, it could be shorter.
(2) The experiments design should be more detail and it should add a short conclusion at the last sentence in the abstract.
(3) Please delete some keywords, the present keywords are too many, no more than 5.
(4) Why did you choose the rye (Secale cereale L.), wheat (Triticum aestivum), and triticale (xTriticosecale) as DPCC? It should add in the Introduction.
(5) Line 122,"Lime was applied as recommended." should add the amount of lime.
(6) It is recommended to add graphics of experiment so the readers could understand better experiment.
(7) Line155-166 "Synthetic N in the form of calcium ammonium nitrate (27%)", the amount should be added.
(8) Why did the experiment only study the decomposition of DPCC, but didn't test the soil nurients.
(9) The data in the table 1 and table 2 should add the data in each year (2016,2017 and 2018)
(10) Only 50% of DPCC (Fresh tissue) was decomposed after 11 weeks? It should carefully check.
(11) The manuscript should add a conclusion.
Author Response
Reviewer 2:
This is a well written article, describing an apparently well-run trial yielding useful results. My main criticisms relate to the order in which information is introduced.For example, the discussion of N immobilisation toward the end of the introduction is a little disjointed. I suggest the explanation given in L 91-94 should be brought forward to the first introduction of the concept, followed by the C:N ratio information, then your hypothesis that the DPCC residue will promote N immobilisation.
Response:
Thanks for the comment. We rearranged the introduction to address the reviewer’s comment.
Subsequently, in the Methods section, it would be helpful to have an overview of the annual cycle of management before getting to the specifics of plot sizes and planting dates. For example, at L 130-132: “In each replication, a block was planted with a DPCC, and served as the “no dual-purpose cover crop” treatment.” The distinction between this treatment and the DPCC blocks should be explained before this point – i.e. that (in “normal” cover crop management) the biomass is not harvested, but left in place until killed by herbicide before the planting of the maize silage crop.
Response:
Thanks again, we have revised the Material and Methods section.
Similarly, at L 145: “Samples were removed during sidedress N application.” The planting of the subsequent maize crop has not yet been mentioned. Presumably it is in before the side-dressing.
Response:
Revised.
L 59: Removal of P – that removed by the cover crop is not removed from the landscape, if it is then eaten and urinated by the cows. It seems to me that, if there is a benefit resulting from less P run-off, it is derived from not buying in as much feed. However, if it instead allows the farm to carry more cattle, then the environmental benefit is lost.
Response
The authors addressed the comment with additional text in the introduction to clarify nutrient cycling pathways.
L 118: Remove the superscript after Mg. Maybe some global replace function put -1 after Mg meaning “per megagram” but accidentally caught this use of Mg meaning magnesium.
Response:
Good catch. Done.
L 114: There is no mention of when the liquid manure is applied. I am only guessing that it is before planting the cover crop, since somewhere it is mentioned that there is no base fertilisation of the maize crop. What is the rationale for such heavy fertilisation of a cover crop, if the main problem this study is addressing is nutrient loss to the environment? The study begs the question, why is the land being overfertilized with manure? If this is to simulate farmers’ practice, why are dairy farmers not exporting this valuable commodity to non-dairy crop land nearby?
Response:
Manure application dates added. This volume is not atypical for farmers in the Northeast U.S.A. Farmers are limited by manure storage and manure application is often based on logistics, not nutrient programs. Most farmers in the Northeast US produce animals and forage on the same farm so there is no other cropland to export to. Vegetable farms rarely use uncomposted manure due to potential health liability. Manure could be better used by applying to hay land and silage fields further from the barn, but the cost of transport (fuel and time) often results in manure being applied to fields of relatively close proximity to the barn. This is a central motif of manure management in the region.
L 139-147: I’m familiar with the use of decomposition bags, but I wonder, in this environment, how much of the stubble would normally be processed by worms, which presumably are excluded from the bags.
Response:
Additional detail is provided in the text.
L 154: Was there no corn crop planted in 2016? It is later explained that it was planted, but the data from that crop was discarded. The planting date should still be included at L 154, (and just the year, rather than the date, stated at L 158) because it relates to the soil management.
Response:
The date of planting of corn in first year was added to the Materials and Methods.
L 162: The corn harvesting date for 2017 (2 Sept) is after the stated planting date for the DPCC (1 Sept).
Response:
Detailed dates adjusted/provided for key time points.
L 214: Remove line break.
Response:
The authors agree post review formatting is needed. However, we are not able to easily format for appearance in this format. We believe this should occur by formatting the editor prior to publication.
Table 1: At this point, I am wondering why rye had the same crude protein level as wheat but a lower relative feed value. This is explained at L 279-282, but it should be explained at L 212. What is never mentioned is that the farmer can maximise relative feed value by cutting the cover crop before stem elongation. The research trial cut all three species on the same date, rather than timing their harvest to their own stage of growth, and this disadvantaged the early-maturing rye. Since rye apparently yielded the most biomass and protein, it seems odd that the main conclusion of the paper is that rye underperformed against the other two, based on the relative feed value being the only parameter that gave you statistical significance at the 5% level. This conclusion appears to be more about variability management (failure to have enough reps to demonstrate a statistical difference in biomass and Milk ha-1) than best advice to farmers.
Response:
The interpretation of the data is discussed in the discussion section, not in the results. This handling of RFV and CP follows this format.
Rye, although early maturing, was not at an advanced state of maturation that would cause quality declines. Rye was in fact at an optimum stage of harvest. If anything, wheat and triticale could be left to grow longer (and mature more), which would result in a yield and quality trade-off. However, to facilitate timely corn planting, the DPCC must be harvested regardless of their potential to grow more.
The main conclusion is not that rye underperformed. A major conclusion is that there is a classic yield and quality trade-off. There is a statistically significant reduction in milk production on a per Mg basis for rye due to the developmental stages of harvest necessitated by the DPCC and corn crop rotation. However, this point is rendered somewhat moot as there is no difference on a per-hectare basis.
The presented data represents a collective of 12 reps over three years and reveals the substantial variability of these systems. It is relevant for farmers to anticipate this variability, which may be alleviated in the future with DPCC-specific breeding, but is relevant in the interim.
L 231-236: The first statement that decomposition was linear is contradicted by the remaining description. I would assume that the irregularity of the relationship in Figure 3a is due to variability, which your single sample at each sampling time did not capture. There might also have been an effect of removing the bags during the top-dressing, disturbing fungal hyphae, but it is not stated when that was. There is no discussion of the replacement of crop residue biomass with fungal biomass within the bags, which might explain the rise in N concentration.
Response:
There is not a single sample at each time point. There are 4 samples at each time point, conducted across three years, for a total of 12 samples at each time point.
The experimental design was clarified to state the side dress occurred six weeks following decomp bag placement.
The fungal biomass hypothesis proposed is interesting and could be explored in a separate study. Given the range in C:N of fungal species, this analysis would require both identification and quantification. It would also require a strong knowledge of the C:N of the component fungi, which may be difficult given that many fungi are not easily cultured. Such an analysis is outside the scope of the study.
L 270: “the Northeast” – change to “Northeast USA” for the sake of international readers.
Response:
Changed.
L 316: I have been wondering why you did not report soil carbon levels, rather than just speculating about them.
Response:
We would expect it to take 5 years to detect changes to soil carbon (or soil organic matter). This is beyond the duration of the study. We agree that there is a need for long-term studies that measure changes to soil C/ SOM under DPCC management. Such work is in progress.
L 387: “The soils at the research site had 1.8 – 2.1% soil organic matter in each year 387 of this study.” (Do you mean soil carbon?) So, soil C was measured, and presumably no trend was observed over the three years? Again, this information could be introduced earlier when talking about the potential to boost soil carbon.
Response:
No, soil organic matter was measured using loss on combustion. Soil C would be measured with an elemental analyzer. The Bemmelen factor can be used to convert between the two but relies on the assumption that all SOM is 58%. For the purpose of this study, such an assumption is not needed. The SOM information is relevant to understand the potential for mineralizable nitrogen in the system in addition to the supplement inputs and also provides insight into soil quality.
L 391-398: There seems to be some tension between the objective of removing excess N that is at risk of contributing to eutrophication, and wanting to avoid even the briefest possibility of the crop experiencing sub-optimal N access. This latter concern seems over-stressed, given you didn’t detect any yield penalty in the trial.
Response:
The latter concern is very commonly expressed by farmers and researchers. Research is ongoing to optimize balancing high C inputs with N fertilizer regimes. As noted in the introduction, there are many explanations for the variable response of corn to prior CC, and a commonly proposed hypothesis is nitrogen immobilization. This is why it is key that we found evidence that such a situation can occur, but we also found this was offset by proper management (such as the use of the PSNT test) to supply the appropriate amount of in-season N.
L 420: The paper would be improved by a conclusion that brought back the two hypotheses on which the study was based. Currently, it ends with observations on the yield of corn silage, without mentioning that the total yield of fodder per hectare can be substantially increased using DPCCs (your first hypothesis). Also, state something about P removal (the second hypothesis).
Response:
Thanks for the comment. A separate conclusion section was added to the manuscript.
Reviewer 3 Report
In this study, the author hypothesized that the high C:N residue left after removing dual-purpose cover crops (DPCC) biomass above 7.6 cm would encourage a community of decomposers, which compete for N and cause N-immobilization in corn systems. The results of this experiment suggested that in addition to capturing nutrients from the fall manure application, DPCC captured nutrients already present in the soil. While these findings did not impede corn yields in this study, they demonstrate the potential to affect the fertility needs of corn in a multi-year rotation. This study evaluated rye, wheat, and triticale as DPCC in a manured field and their potential impact on subsequent corn silage production. The results are important references for agronomists to understand the DPCC. Overall, the experiment is well-designed, and the manuscript is composed correctly. I can't provide suggestions about the writing details of the manuscript due to my non-native English speaking. I have several opinions as follows.
(1) Please list p-value for statistical significance (Line 210, 225, 273, 344, 352).
(2) Please list the mean value and standard deviation or standard error in Table 1 and Table 2.
(3) Separate descriptions of conclusions and discussions are encouraged in academic writing unless this undermines the paper's structural integrity.
I can't provide suggestions about the writing details of the manuscript due to my non-native English speaking.
Author Response
(1) Please list p-value for statistical significance (Line 210, 225, 273, 344, 352).
Response:
Done.
(2) Please list the mean value and standard deviation or standard error in Table 1 and Table 2.
Response:
Having SD in tables is not a required format. While some manuscripts may present SD some don't. Additionally, in order to have the SD values, as one reviewer suggested, we have to re-run a huge set of three years of data which cannot be done in a short time.
(3) Separate descriptions of conclusions and discussions are encouraged in academic writing unless this undermines the paper's structural integrity.
Response:
A separate conclusion section was added to the manuscript.
Reviewer 4 Report
The manuscript deals with the role of dual purpose cover crops in nutrient management in the Northeast United States. The significance of the work lies in the fact that the method presented it has the potential to reduce environmental impacts compared to the traditional cover crop best management practices.
Minor comments:
1. Does the water use by the cover crops (Rye-Wheat-Triticale) affect the water availability for the corn crop?If so, how does it affect nutrient leaching and Nitrogen immobilization?
2. Line 314-315: "The high C input associated with the DPCC residue (1.6 Mg ha-1, on average) indicates that DPCC residue alone has the potential to build soil carbon". Is it dependent on the soil type?
3. Is it possible that a shift in the planting dates of cover crops change the Nitrogen accumulation ?
Author Response
Minor comments:
- Does the water use by the cover crops (Rye-Wheat-Triticale) affect the water availability for the corn crop? If so, how does it affect nutrient leaching and Nitrogen immobilization?
Response:
This has been shown to be relevant in areas prone to drought in so far as water availability for corn. The impact in the Northeast USA on CC water impact on nitrogen dynamics in subsequent corn production has not been a significant area of interest.
- Line 314-315: "The high C input associated with the DPCC residue (1.6 Mg ha-1, on average) indicates that DPCC residue alone has the potential to build soil carbon". Is it dependent on the soil type?
Response:
Of course. The results must be considered in the context of each system, but we see that a significant amount of carbon is associated with the residues.
- Is it possible that a shift in the planting dates of cover crops change the Nitrogen accumulation
Response:
Yes. This has been well studied by the authors in other publications. The DPCC planting date was chosen because it is known to be an optimum planting date.
Reviewer 5 Report
This is a well written article, describing an apparently well-run trial yielding useful results. My main criticisms relate to the order in which information is introduced.
For example, the discussion of N immobilisation toward the end of the introduction is a little disjointed. I suggest the explanation given in L 91-94 should be brought forward to the first introduction of the concept, followed by the C:N ratio information, then your hypothesis that the DPCC residue will promote N immobilisation.
Subsequently, in the Methods section, it would be helpful to have an overview of the annual cycle of management before getting to the specifics of plot sizes and planting dates. For example, at L 130-132: “In each replication, a block was planted with a DPCC, and served as the “no dual-purpose cover crop” treatment.” The distinction between this treatment and the DPCC blocks should be explained before this point – i.e. that (in “normal” cover crop management) the biomass is not harvested, but left in place until killed by herbicide before the planting of the maize silage crop.
Similarly, at L 145: “Samples were removed during sidedress N application.” The planting of the subsequent maize crop has not yet been mentioned. Presumably it is in before the side-dressing.
L 59: Removal of P – that removed by the cover crop is not removed from the landscape, if it is then eaten and urinated by the cows. It seems to me that, if there is a benefit resulting from less P run-off, it is derived from not buying in as much feed. However, if it instead allows the farm to carry more cattle, then the environmental benefit is lost.
L 118: Remove the superscript after Mg. Maybe some global replace function put -1 after Mg meaning “per megagram” but accidentally caught this use of Mg meaning magnesium.
L 114: There is no mention of when the liquid manure is applied. I am only guessing that it is before planting the cover crop, since somewhere it is mentioned that there is no base fertilisation of the maize crop. What is the rationale for such heavy fertilisation of a cover crop, if the main problem this study is addressing is nutrient loss to the environment? The study begs the question, why is the land being overfertilized with manure? If this is to simulate farmers’ practice, why are dairy farmers not exporting this valuable commodity to non-dairy crop land nearby?
L 139-147: I’m familiar with the use of decomposition bags, but I wonder, in this environment, how much of the stubble would normally be processed by worms, which presumably are excluded from the bags.
L 154: Was there no corn crop planted in 2016? It is later explained that it was planted, but the data from that crop was discarded. The planting date should still be included at L 154, (and just the year, rather than the date, stated at L 158) because it relates to the soil management.
L 162: The corn harvesting date for 2017 (2 Sept) is after the stated planting date for the DPCC (1 Sept).
L 214: Remove line break.
Table 1: At this point, I am wondering why rye had the same crude protein level as wheat but a lower relative feed value. This is explained at L 279-282, but it should be explained at L 212. What is never mentioned is that the farmer can maximise relative feed value by cutting the cover crop before stem elongation. The research trial cut all three species on the same date, rather than timing their harvest to their own stage of growth, and this disadvantaged the early-maturing rye. Since rye apparently yielded the most biomass and protein, it seems odd that the main conclusion of the paper is that rye underperformed against the other two, based on the relative feed value being the only parameter that gave you statistical significance at the 5% level. This conclusion appears to be more about variability management (failure to have enough reps to demonstrate a statistical difference in biomass and Milk ha-1) than best advice to farmers.
L 231-236: The first statement that decomposition was linear is contradicted by the remaining description. I would assume that the irregularity of the relationship in Figure 3a is due to variability, which your single sample at each sampling time did not capture. There might also have been an effect of removing the bags during the top-dressing, disturbing fungal hyphae, but it is not stated when that was. There is no discussion of the replacement of crop residue biomass with fungal biomass within the bags, which might explain the rise in N concentration.
L 270: “the Northeast” – change to “Northeast USA” for the sake of international readers.
L 316: I have been wondering why you did not report soil carbon levels, rather than just speculating about them.
L 387: “The soils at the research site had 1.8 – 2.1% soil organic matter in each year 387 of this study.” (Do you mean soil carbon?) So, soil C was measured, and presumably no trend was observed over the three years? Again, this information could be introduced earlier when talking about the potential to boost soil carbon.
L 391-398: There seems to be some tension between the objective of removing excess N that is at risk of contributing to eutrophication, and wanting to avoid even the briefest possibility of the crop experiencing sub-optimal N access. This latter concern seems over-stressed, given you didn’t detect any yield penalty in the trial.
L 420: The paper would be improved by a conclusion that brought back the two hypotheses on which the study was based. Currently, it ends with observations on the yield of corn silage, without mentioning that the total yield of fodder per hectare can be substantially increased using DPCCs (your first hypothesis). Also state something about P removal (the second hypothesis).
Author Response
This is a well-written article, describing an apparently well-run trial yielding useful results. My main criticisms relate to the order in which information is introduced.For example, the discussion of N immobilisation toward the end of the introduction is a little disjointed. I suggest the explanation given in L 91-94 should be brought forward to the first introduction of the concept, followed by the C:N ratio information, then your hypothesis that the DPCC residue will promote N immobilisation.
Response:
Thanks for the comment. We rearranged the introduction to address the reviewer’s comment.
Subsequently, in the Methods section, it would be helpful to have an overview of the annual cycle of management before getting to the specifics of plot sizes and planting dates. For example, at L 130-132: “In each replication, a block was planted with a DPCC, and served as the “no dual-purpose cover crop” treatment.” The distinction between this treatment and the DPCC blocks should be explained before this point – i.e. that (in “normal” cover crop management) the biomass is not harvested, but left in place until killed by herbicide before the planting of the maize silage crop.
Response:
Thanks again, we have revised the Material and Methods section.
Similarly, at L 145: “Samples were removed during sidedress N application.” The planting of the subsequent maize crop has not yet been mentioned. Presumably it is in before the side-dressing.
Response:
Revised.
L 59: Removal of P – that removed by the cover crop is not removed from the landscape, if it is then eaten and urinated by the cows. It seems to me that, if there is a benefit resulting from less P run-off, it is derived from not buying in as much feed. However, if it instead allows the farm to carry more cattle, then the environmental benefit is lost.
Response
The authors addressed the comment with additional text in the introduction to clarify nutrient cycling pathways.
L 118: Remove the superscript after Mg. Maybe some global replace function put -1 after Mg meaning “per megagram” but accidentally caught this use of Mg meaning magnesium.
Response:
Good catch. Done.
L 114: There is no mention of when the liquid manure is applied. I am only guessing that it is before planting the cover crop, since somewhere it is mentioned that there is no base fertilisation of the maize crop. What is the rationale for such heavy fertilisation of a cover crop, if the main problem this study is addressing is nutrient loss to the environment? The study begs the question, why is the land being overfertilized with manure? If this is to simulate farmers’ practice, why are dairy farmers not exporting this valuable commodity to non-dairy crop land nearby?
Response:
Manure application dates added. This volume is not atypical for farmers in the Northeast U.S.A. Farmers are limited by manure storage and manure application is often based on logistics, not nutrient programs. Most farmers in the Northeast US produce animals and forage on the same farm so there is no other cropland to export to. Vegetable farms rarely use uncomposted manure due to potential health liability. Manure could be better used by applying to hay land and silage fields further from the barn, but the cost of transport (fuel and time) often results in manure being applied to fields of relatively close proximity to the barn. This is a central motif of manure management in the region.
L 139-147: I’m familiar with the use of decomposition bags, but I wonder, in this environment, how much of the stubble would normally be processed by worms, which presumably are excluded from the bags.
Response:
Additional detail is provided in the text.
L 154: Was there no corn crop planted in 2016? It is later explained that it was planted, but the data from that crop was discarded. The planting date should still be included at L 154, (and just the year, rather than the date, stated at L 158) because it relates to the soil management.
Response:
The date of planting of corn in first year was added to the Materials and Methods.
L 162: The corn harvesting date for 2017 (2 Sept) is after the stated planting date for the DPCC (1 Sept).
Response:
Detailed dates adjusted/provided for key time points.
L 214: Remove line break.
Response:
The authors agree post review formatting is needed. However, we are not able to easily format for appearance in this format. We believe this should occur by formatting the editor prior to publication.
Table 1: At this point, I am wondering why rye had the same crude protein level as wheat but a lower relative feed value. This is explained at L 279-282, but it should be explained at L 212. What is never mentioned is that the farmer can maximise relative feed value by cutting the cover crop before stem elongation. The research trial cut all three species on the same date, rather than timing their harvest to their own stage of growth, and this disadvantaged the early-maturing rye. Since rye apparently yielded the most biomass and protein, it seems odd that the main conclusion of the paper is that rye underperformed against the other two, based on the relative feed value being the only parameter that gave you statistical significance at the 5% level. This conclusion appears to be more about variability management (failure to have enough reps to demonstrate a statistical difference in biomass and Milk ha-1) than best advice to farmers.
Response:
The interpretation of the data is discussed in the discussion section, not in the results. This handling of RFV and CP follows this format.
Rye, although early maturing, was not at an advanced state of maturation that would cause quality declines. Rye was in fact at an optimum stage of harvest. If anything, wheat and triticale could be left to grow longer (and mature more), which would result in a yield and quality trade-off. However, to facilitate timely corn planting, the DPCC must be harvested regardless of their potential to grow more.
The main conclusion is not that rye underperformed. A major conclusion is that there is a classic yield and quality trade-off. There is a statistically significant reduction in milk production on a per Mg basis for rye due to the developmental stages of harvest necessitated by the DPCC and corn crop rotation. However, this point is rendered somewhat moot as there is no difference on a per-hectare basis.
The presented data represents a collective of 12 reps over three years and reveals the substantial variability of these systems. It is relevant for farmers to anticipate this variability, which may be alleviated in the future with DPCC-specific breeding, but is relevant in the interim.
L 231-236: The first statement that decomposition was linear is contradicted by the remaining description. I would assume that the irregularity of the relationship in Figure 3a is due to variability, which your single sample at each sampling time did not capture. There might also have been an effect of removing the bags during the top-dressing, disturbing fungal hyphae, but it is not stated when that was. There is no discussion of the replacement of crop residue biomass with fungal biomass within the bags, which might explain the rise in N concentration.
Response:
There is not a single sample at each time point. There are 4 samples at each time point, conducted across three years, for a total of 12 samples at each time point.
The experimental design was clarified to state the side dress occurred six weeks following decomp bag placement.
The fungal biomass hypothesis proposed is interesting and could be explored in a separate study. Given the range in C:N of fungal species, this analysis would require both identification and quantification. It would also require a strong knowledge of the C:N of the component fungi, which may be difficult given that many fungi are not easily cultured. Such an analysis is outside the scope of the study.
L 270: “the Northeast” – change to “Northeast USA” for the sake of international readers.
Response:
Changed.
L 316: I have been wondering why you did not report soil carbon levels, rather than just speculating about them.
Response:
We would expect it to take 5 years to detect changes to soil carbon (or soil organic matter). This is beyond the duration of the study. We agree that there is a need for long-term studies that measure changes to soil C/ SOM under DPCC management. Such work is in progress.
L 387: “The soils at the research site had 1.8 – 2.1% soil organic matter in each year 387 of this study.” (Do you mean soil carbon?) So, soil C was measured, and presumably no trend was observed over the three years? Again, this information could be introduced earlier when talking about the potential to boost soil carbon.
Response:
No, soil organic matter was measured using loss on combustion. Soil C would be measured with an elemental analyzer. The Bemmelen factor can be used to convert between the two but relies on the assumption that all SOM is 58%. For the purpose of this study, such an assumption is not needed. The SOM information is relevant to understand the potential for mineralizable nitrogen in the system in addition to the supplement inputs and also provides insight into soil quality.
L 391-398: There seems to be some tension between the objective of removing excess N that is at risk of contributing to eutrophication, and wanting to avoid even the briefest possibility of the crop experiencing sub-optimal N access. This latter concern seems over-stressed, given you didn’t detect any yield penalty in the trial.
Response:
The latter concern is very commonly expressed by farmers and researchers. Research is ongoing to optimize balancing high C inputs with N fertilizer regimes. As noted in the introduction, there are many explanations for the variable response of corn to prior CC, and a commonly proposed hypothesis is nitrogen immobilization. This is why it is key that we found evidence that such a situation can occur, but we also found this was offset by proper management (such as the use of the PSNT test) to supply the appropriate amount of in-season N.
L 420: The paper would be improved by a conclusion that brought back the two hypotheses on which the study was based. Currently, it ends with observations on the yield of corn silage, without mentioning that the total yield of fodder per hectare can be substantially increased using DPCCs (your first hypothesis). Also, state something about P removal (the second hypothesis).
Response:
Thanks for the comment. A separate conclusion section was added to the manuscript.
Round 2
Reviewer 1 Report
In this MS, the author studied the evaluation of rye, wheat and triticale as DPCC in fertilized fields and their potential impact on the subsequent production of corn silage. It helps to comprehensively understand the potential of affecting the growth and development demand of corn in multi-year rotation. However, there are too many preambular paragraphs and it is recommended to merge them into 4-5 paragraphs. I hope you can make some modifications.
Author Response
We have edited the introduction section to remove ~100 words so that the length is more consistent with other Agronomy papers. We have also rearranged and merged some paragraphs so there are fewer separate and very short paragraphs. Some of the length is due to comments from other reviewers that requested additional information be added to the introduction.
Reviewer 2 Report
There are many modifications in this manuscript. But i have not seen the Response for my suggestions. Such as:
(1) the title is too long, it could be shorter.
(3) Please delete some keywords, the present keywords are too many, no more than 5.
(4) Why did you choose the rye (Secale cereale L.), wheat (Triticum aestivum), and triticale (xTriticosecale) as DPCC? It should add in the Introduction.
(5) Line 122,"Lime was applied as recommended." should add the amount of lime.
(6) It is recommended to add graphics of experiment so the readers could understand better experiment.
(7) Line155-166 "Synthetic N in the form of calcium ammonium nitrate (27%)", the amount should be added.
(8) Why did the experiment only study the decomposition of DPCC, but didn't test the soil nurients.
(9) The data in the table 1 and table 2 should add the data in each year (2016,2017 and 2018)
(10) Only 50% of DPCC (Fresh tissue) was decomposed after 11 weeks? It should carefully check.
Author Response
The reviewer notes: “There are many modifications in this manuscript. But i have not seen the Response for my suggestions. Such as…” The authors note that we received and replied to responses from two reviewers in the first round of revisions. This reviewer’s responses were not included at that time. We received the revisions from this additional reviewer in the second round and address the comments in this most recent version of the manuscript.
1) the title is too long, it could be shorter.
We respectfully disagree with this suggestion.
Note, there is no “item (2)” in this list.
(3) Please delete some keywords, the present keywords are too many, no more than 5.
We will make this amendment.
(4) Why did you choose the rye (Secale cereale L.), wheat (Triticum aestivum), and triticale (xTriticosecale) as DPCC? It should add in the Introduction.
This information was included in the original version of the manuscript and remains unchanged. It can be found in the second to last paragraph of the introduction.
(5) Line 122,"Lime was applied as recommended." should add the amount of lime.
We have added this detail in text.
(6) It is recommended to add graphics of experiment so the readers could understand better experiment.
We respectfully disagree with this suggestion. This is not common for field research with a standard experimental design.
(7) Line155-166 "Synthetic N in the form of calcium ammonium nitrate (27%)", the amount should be added.
We have added this detail in text.
(8) Why did the experiment only study the decomposition of DPCC, but didn't test the soil nurients.
This is outside of the scope of this experiment. The authors have separately published about the effects on soil P in an on-farm research trial.
(9) The data in the table 1 and table 2 should add the data in each year (2016,2017 and 2018)
This would be appropriate only if year was a fixed variable, but it is not.
(10) Only 50% of DPCC (Fresh tissue) was decomposed after 11 weeks? It should carefully check.
The authors did carefully check as the experiment was conducted for three years with four replications each year. This is an important result of the study, and is not unexpected given high C content of the residue. Corn in the Northeast USA is also rainfed, so moisture for decomposition can be limiting throughout the season. Also, while fresh tissue was added, the % lost is based on dry weight lost, not based on fresh weight lost.
