Drainage N Loads Under Climate Change with Winter Rye Cover Crop in a Northern Mississippi River Basin Corn-Soybean Rotation
, Jerry Hatfield 1, Dennis Todey 1, Jade Gerlitz 3, Quanxiao Fang 4, Matthew Sima 5, Anna Radke 1, Liwang Ma 6, Zhiming Qi 7, Huaiqing Wu 8, Dan Jaynes 1 and Thomas Kaspar 1Round 1
Reviewer 1 Report
In this study the authors investigated the effects of implementing winter rye cover crop in a corn-soybean rotation on reducing drainage N load in the Mississippi River Basin. The field-tested RZWQM model was used for the estimation. The well-written article’s topic is in line with the aims and scope of the journal. There is no obvious logic flaw in this article; all the conclusions drawn from the study are strongly supported by the results and discussion. In my opinion, this paper can be published as is.
Please delete Lines 745-771 (guideline text from the journal).
Author Response
We thank the reviewers and editors for comments and suggestions that were helpful to improve the paper. We responded to comments with hyphens “- “following the comments. Just let us know if more changes will be helpful. Thanks again.
Reviewer 1
In this study the authors investigated the effects of implementing winter rye cover crop in a corn-soybean rotation on reducing drainage N load in the Mississippi River Basin. The field-tested RZWQM model was used for the estimation. The well-written article’s topic is in line with the aims and scope of the journal. There is no obvious logic flaw in this article; all the conclusions drawn from the study are strongly supported by the results and discussion. In my opinion, this paper can be published as is.
- We thank the reviewer for the encouraging remarks.
Please delete Lines 745-771 (guideline text from the journal).
- we removed the journal guidelines.
Reviewer 2 Report
Authors studied field-tested Root Zone Water Quality Model (RZWQM) to estimate drainage N loads, crop yield, and rye growth in central Iowa corn-soybean rotations. RZWQM scenarios included baseline (BL) observed weather0 (1991-2011) and ambient CO2 with cover crop and no cover crop treatments (BL_CC and BL_NCC). Scenarios also included projected future temperature and precipitation change (2065-2085) from six Global Circulation Models (GCMs) and elevated CO2 with cover crop and no cover crop treatments (CC and NCC). Average annual drainage N loads under NCC, BL_NCC, CC and BL_CC were 63.6, 47.5, 17.0, and 18.9 kg N ha-1. Annual CC drainage N loads were reduced compared with BL_NCC more than the targeted 41% for 18 to 20 years of the 21-year simulation depending on the GCM. Authors suggested implementing winter rye cover crop in a corn-soybean rotation effectively addresses the goal of drainage N load reduction under climate change in a northern Mississippi River Basin agricultural system without affecting cash crop production. The topic is within the scope of this journal. However, the manuscript preparation does not reach to the standards of scientific publication.
- Abstract: Abstract is not clear. Please improve the abstract section.
- Introduction: Background of the study should be made to very clear. Provide more details of introduction and review of the work.
- Please speculate about the reasons for the obtained results.
- Conclusion: the authors should add the significance of this research to potential practical application.
Author Response
We thank the reviewers and editors for comments and suggestions that were helpful to improve the paper. We responded to comments with hyphens “- “following the comments. Just let us know if more changes will be helpful. Thanks again.
Reviewer 2
Authors studied field-tested Root Zone Water Quality Model (RZWQM) to estimate drainage N loads, crop yield, and rye growth in central Iowa corn-soybean rotations. RZWQM scenarios included baseline (BL) observed weather0 (1991-2011) and ambient CO2 with cover crop and no cover crop treatments (BL_CC and BL_NCC). Scenarios also included projected future temperature and precipitation change (2065-2085) from six Global Circulation Models (GCMs) and elevated CO2 with cover crop and no cover crop treatments (CC and NCC). Average annual drainage N loads under NCC, BL_NCC, CC and BL_CC were 63.6, 47.5, 17.0, and 18.9 kg N ha-1. Annual CC drainage N loads were reduced compared with BL_NCC more than the targeted 41% for 18 to 20 years of the 21-year simulation depending on the GCM. Authors suggested implementing winter rye cover crop in a corn-soybean rotation effectively addresses the goal of drainage N load reduction under climate change in a northern Mississippi River Basin agricultural system without affecting cash crop production. The topic is within the scope of this journal. However, the manuscript preparation does not reach to the standards of scientific publication.
Abstract: Abstract is not clear. Please improve the abstract section.
- We added the following sentence to the abstract: “Winter rye cover crop was more effective at reducing drainage N losses under climate change than under baseline conditions (73 and 60% for future and baseline climate), mostly because the increased projected temperatures and atmospheric CO2 resulted in greater rye growth and crop N uptake.”
Introduction: Background of the study should be made to very clear. Provide more details of introduction and review of the work.
- One of the reasons more background was not provided is that we’re not aware of another study that investigated subsurface drainage N loss in corn-soybean rotations with winter rye cover crops in the Mississippi River Basin under future climate change. We clarify this in the revised Introduction with the sentence: “While few if any studies have investigated both corn-soybean production and N loss to subsurface drainage with winter rye cover crops under climate change in the Mississippi River Basin, the SWAT model has been used to investigate winter rye cover crop effectiveness on reducing N loads to streams within the Chesapeake Bay Watershed under climate change (Lee et al., 2017).” A few additional revisions were made to the Introduction for clarity that included adding a few citations supporting that temperature, CO2, and precipitation patterns are expected to change in the future that will affect future drainage N loss in ag systems with winter rye cover crop.
Please speculate about the reasons for the obtained results.
- We added a sentence to results section: “These results are consistent with Malone et al. (2014) that discussed the effectiveness of winter rye cover crop to reduce drainage N loss improved with higher spring and fall temperatures (Figure 1) and increased cover crop growth (Table 1) and N uptake (Figure 3)”. Malone et al. (2014) discussed in some detail the reasons for the effectiveness of winter rye cover crop to reduce N loss to drainage.
Conclusion: the authors should add the significance of this research to potential practical application.
- We added a few sentences to the Conclusion section clarifying the significance of the research, along with a few additional citations.
Round 2
Reviewer 2 Report
Requested corrections were completed.
