Extreme Weather and Grazing Management Influence Soil Carbon and Compaction

Round 1

Reviewer 1 Report

The manuscript "Extreme Weather and Grazing management Influence Soil Carbon and Compaction " is well written. The conclusion is supported by their previous studies. Before the publication of this paper, some minor issues should be solved/explained. 

Line 219: Why the LOI in the upper elevations showed an increase for both CHD and STR pastures?

Line 246: type error-Ttwo.

P-value in the Figures should have a consistent format. 

Author Response

Comments and Suggestions for Authors

We have made all suggested changes as requested by Reviewer 1.  Below please find Reviewers comments (bold) followed by our response.

The Manuscript "Extreme Weather and Grazing management Influence Soil Carbon and Compaction " is well written. The conclusion is supported by their previous studies. Before the publication of this paper, some minor issues should be solved/explained. 

Line 219: Why the LOI in the upper elevations showed an increase for both CHD and STR pastures?

Management did have influence on distribution of LOI carbon on the landscape or within a pasture. “In STR pastures, animals were lured uphill/upper elevations using shade, hay, and waterers thereby allowing greater deposition of manure. With laxed rotational grazing, animals spent more time in upper elevations on landscape than in low-lying exclusions and concentrated flow paths. In CHD pastures, hay was rolled out in the upper elevations to lure animals to those areas. We account this to both added hay and cattle distribution.  In the CHD system we have suggested that it is more likely due to hay input and hay placement. In the STR management system changed distribution is a response to exclusion and placement of water, hay, and shade.  While it is clear that hay was used in both grazing systems, there was three fold more hay bales needed in CHD (102 haybales) therefore more hay was rolled out in CHD than in STR (34 haybales) as described by Subedi et al. (2020).  In response to Reviewer 2 and as a response to this comment we have added  “However, for this to be the case in the CHD pastures, farm managers should not distribute hay within 20-meters of the CFPs so as to retain nutrients within the grazing system for forage production. In the STR pastures, managing cattle where they spend more time in areas less vulnerable to erosion (CFPs), helped dampen the loss of carbon to a greater extent and facilitated greater deposition of manure and associated nutrients in the upper landscape positions of each of the STR pastures. This paper showed that management practices such as excluding and over-seeding areas vulnerable to erosion can convert denuded areas to areas which can provide forage to cattle during drought while also reducing compaction. “ to the Conclusion section of this manuscript Thank you for this comment reminding us to further explain the grazing systems.

Line 246: type error-Ttwo

The typo has been corrected to “two” now on line 267.

P-value in the Figures should have a consistent format. 

Where p-values were mentioned, throughout the manuscript, actual p-values are now given to add consistency as suggested (we removed the ns).

Reviewer 2 Report

The article deals with a very topical and, against the background of climate change, also very relevant issue. The experimental approach would be suitable to answer the questions raised. Unfortunately, the paper has significant shortcomings, among which the most serious is the lack of a discussion chapter. But also the biometric approaches to data evaluation remain intransparent in crucial cases. I recommend the authors to revise the manuscript again carefully and intensively.

Comments for author File: Comments.pdf

Author Response

Below please find out response to Reviewer 2's requested amendments.  We have made most of the changes as requested.  We did keep Results and Discussion together as our coauthors felt this was necessary to help readers understand the complexity and inter relationship of carbon mineralization and Authors instructions indicate that in complex manuscripts this is appropriate.  We did increase discussion within the Conclusions as suggested.  We are grateful the Reviewer 2's comments as the greatly improved our manuscript.

Please note Reviewer's comments are in bold and our responses are in normal type.  We did use track changes as requested.

Reviewer 2

line 32 – Introduction: There are a lot of investigations addressing these issues, so that the limitation to one author (Teague) does not seem appropriate. Cattle production depends upon forage quality and productivity everywhere; it's not limited to the United States.

We have added two more references to support the background of our study. Scott et al. (2000) in a grazing experiment in Australia and Dahlin et al. (2005) which discusses several case studies on low-input grasslands in Europe.

Line 28-31 was “Managing beef grazing pastures to promote soil health and reduce losses of soil and nutrients is challenge that cattle farmer in the USA and around the world must address to be sustainable (Teague, 2018). Pastures can become source of deleterious nutrients to nearby streams if poorly managed or can capture and retain carbon and improve water infiltration into the soil if well managed (Teague et al., 2016).”

Line 28-35 is now “Managing beef grazing pastures to promote soil health and reduce soil and nutrient losses is a challenge that cattle farmers in the USA and around the world must address to be sustainable (Dahlin et al., 2005; Teague, 2018). Pastures can become source of deleterious nutrients to nearby streams if poorly managed, or if well managed they can capture and retain carbon and improve rainfall infiltration (capture) into the soil (Scott et al., 2000; Dahlin et al., 2005; Teague et al., 2016; Harmel et al., 2021). However additional research is needed to determine which grazing system is best for which ecosystem (Harmel et al., 2021).”

And

We updated the sentence ….. to, “Beef cattle production depends upon forage quality and productivity” on line 35.

line 36 – Introduction: “…such as N and P.”  When first mentioned, abbreviations should be written out, with the abbreviation in parentheses. The dot after P hast to be deleted.

“….such as N and P.” on line 36 has been changed to “…of nitrogen (N), and phosphorus (P)”. The dot after P has been removed. Now line 39.

Furthermore, a specification of the kind of external input (additional forage, manure, fertilizer ?) would provide more clarity.

The external inputs include external mineral or organic fertilizers, additional hay supplement, and all associated external inputs. We restructured the sentence on lines 33-36 which read “Managing soil fertility through regenerative grazing management actions may improve forage quality and productivity through internal inputs, which is important due to the rising cost of external inputs such as N and P”, which now reads (on lines 35-41) “Managing soil fertility through regenerative grazing management actions may help accomplish forage quality and productivity through internal inputs such as hay (grown on-farm) and capturing nutrients in manure and urine, which is important due to the rising cost of external inputs of nitrogen (N) and phosphorus (P) mineral fertilizers, organic fertilizers, and outsourced supplemental hay needed to feed grazing animals during drier periods (Silveira and Kohmann, 2020).”

line 44 – Introduction: “…that soil N is least …” – which kind of soil N is addressed: plant available, mineral, total? Please specify.

We have included the forms of nitrogen addressed in the referred article as NO₃-N, total inorganic nitrogen, and total nitrogen. We restructured the sentence (lines 44-46), “Sigua et al. (2010) indicated that soil N is least when cattle graze most frequently in the bottom foot slope landscape position, although it was unclear how grazing density differed between landscape positions.”, to (now lines 48-50)“Sigua et al. (2010) indicated that NO₃-N, total inorganic nitrogen, and total nitrogen is least at bottom foot slope landscape position where cattle graze most frequently, although it was unclear how grazing density differed between landscape positions.”

line 55 – Introduction: Here, for the first time, the target feature soil compaction is brought into the field, which is a bit out of the blue. It seems useful to briefly explain the contribution of soil compaction to both the processes of humus accumulation and decomposition.

We have added three more sentences with respective references on influence of soil compaction in pasture productivity, rainfall infiltration, and soil aeration. We have added “Grazing cattle can increase compaction and consequently reduce air-filled porosity and water infiltration rate of pasture soil (Martinez and Zinck, 2004). The same study reported up to 58% reduction in yield of forage from treaded pastures compared to pastures not treaded on by grazing animals. A study on New Zealand pastures reported 2.5% decline in production for each 0.01 cm³ cm^-3 decrease in microporosity along with 51-84% increased N₂O emissions (Hu et al., 2011).” Now sentence starting on line 57.

line 73-74 – Introduction: It is not the task of an introduction to give an outlook on the character of the study described in the following, but to define the knowledge gap and to show how one intends to close it with the investigation.

We have removed the description of the study from lines 73-74 and have added information about knowledge gaps on lines 33-34 and which are relevant to extreme weather events on lines 86-89.

line 77-85 – Introduction: The hypotheses are based on the experimental questions in the narrower sense, which in turn are not really a logical consequence of the preceding introduction section. What about weathering extremes, as suggested in the title? Why are the test characteristics of the soils in your investigations limited to LOI and compaction?

We updated lines 77-85 to, “In pastures experiencing an annual drought followed by two years of extreme rainfall we hypothesized that: 1) Both CHD and STR grazing systems would increase LOI and reduce BD compared to CG; 2) BD will be reduced and LOI carbon will be increased more in STR than in CHD; 3) changes in LOI and BD will be influenced by changes in cattle density (CD) in STR more than in CHD; 4) CD and BD will decrease in STR where during Baseline cattle tended to congregate.” The changes are now on lines 97-102.

Introduction, general: This part is not entirely convincing, as it is poorly structured, the justification for limiting it to the two test characteristics is missing, and the literature references are limited to a few examples, all from the U.S., which are then only outlined in broad strokes. If the paper were placed within the larger framework of climate change and carbon sequestration, which definitely makes sense, the relationships between the test characteristics and the causalities for the observed findings and processes would need to be better elaborated.

We have added a paragraph in the introduction starting at line 81 to highlight the literature on climate extremes along with its impacts on soil carbon. “Extreme weather events like drought and extreme precipitation events have been predicted to increase globally (Seneviratne et al., 2012). In addition, duration and severity of soil water stress are also projected to in-crease (Knapp et al., 2008). Extreme precipitation events (greater volume and rate) may result in greater soil erosion and losses of carbon (in both sediments and in dissolved forms) (Frank et al., 2015). Extreme drought events can have both direct and prolonged influence on soil moisture, microbial communities associated with nutrient cycling, biomass productivity and thus the soil carbon balance (Frank et al., 2015).  One of the key strategies for mitigating the impact of extreme weather events is soil carbon friendly management yet there is a paucity of information on effects of weather extremes on farm scale soil carbon and nutrient cycling for various soil types and ecosystems (Khan et al., 2021).”  In total we have added 10 more references and added more information on extreme events and soil carbon. The changes are on line 33-35, 57-62, 81-86, and in References section.

line 88 – 91 - Materials and Methods Please add not only the state but also the country (U.S.) to the location information.

We have added country information along with the existing location, county, and state of study pastures on lines 105-108.

line 91 – 97 - Materials and Methods The representation of the climate (Fig. 1) is not optimal, since the annual course and not the annual mean is relevant for the assessment of weather extremes. The connection of the annual means with a line is inappropriate, because it is not a verifiable trend. An example of an alternative plot can be found here: https://ropenspain.github.io/climaemet/reference/climatogram_normal.html line

We have remade Figure 1 (now line 115) to show mean monthly average precipitation and average monthly temperature of study locations for the 2015-2018 study period. Additionally, we added the 30-year normal (1991-2020) for both sites to make comparison of the extreme weather events during the study period climate. We have made subsequent changes in the figure caption and lines 109-113 in section 2.1.

112 – Materials and Methods Why are the words “Baseline” and “Continuously” written with capital initial letters?

We used capital letters for “Baseline” and “Continuously” because they are proper nouns identifying treatments and their treatment times.

line 118 - Materials and Methods Table 1: “Exclusion cattle density” should be specified and supplemented by the duration of flash grazing, as the table appears before the explanation of the treatments

We have added two sentences on lines 143-146 in methods to describe flash grazing. We added, “Flash-grazing of the exclusions was done based on forage availability in each of the exclusions approximately once a month during June, July, August, September and March. Each flash-grazing lasted approximately four to eight hours as exclusions were opened for grazing in the morning and closed in the afternoon prior to farm manager leaving for the evening.”

line 122 - Materials and Methods "Baseline" was written with a capital initial letter again.

We capitalized “Baseline” and “Continuously” because they are proper nouns identifying treatments and their treatment times.

line 122 - Materials and Methods "…using a Giddings probe (manufacturing company, city, country) please complete the information marked in red line

We have added the company information of the Gidding’s probe on line 152 as “(Giddings Machine Company Inc., Windsor, U.S.) and GPS collars on line 167-168 as (Lotek Engineering, Newmarket, Canada)”.

171 - Materials and Methods "…(ESRI, Redlands, California, U.S.) please complete the information marked in red

We have updated the company information of ESRI on line 192 as “(ESRI, Redlands, California, U.S.)”.

line 181 - Materials and Methods "…(model F6010, Thermo Fisher Scientific Inc., Asheville, North Carolina, U.S.). please complete the information marked in red line

We added the company information of Thermo Fisher company as “(Thermo Fisher Scientific Inc., Asheville, North Carolina, U.S.)” on line 202.

179-183 - Materials and Methods LOI results can be overestimated for two reasons: the release of CO2 from carbonates and the release of water bound in clay minerals. First threat can be eliminated by prior dissolution of carbonates by sample treatment with hydrochloric acid. Was it done by your laboratory? If not, please report the CaCO3-content of the study sites additionally.

The soils in our study locations are not calcareous and lime has not been added to the pastures. We corrected all soil samples for moisture as described in the methods. Soils were predominantly loamy sands, sandy loams, and sandy clay loams. Please note that these are surface soils (0-20 cm). On line 202-204 we had already noted the relationship of LOI in our soils with soil organic carbon in these soils.

line 187 - Materials and Methods Which ANOVA-model was used? This was not reported, but is crucial for the result output, especially in this case of nested-design experimental setup with only 2 true replicates. The factors were probably the grazing management and the year. What about using the distance to CFP as a co-variate in the model?

The comparison of LOI and BD between sampling dates were done using one-way ANOVA. We have better described the type of ANOVA used on lines 208 and 211. The pastures used in this study were on average 17 ha. Each of the pasture unit had multiple sub-watersheds with no influence between pastures. Although we had two locations, we had two reps at each location for a total of four reps of each treatment. Each pasture unit was composed of multiple soil types, and variable landscape properties such as slope, aspect, and concentrated flow paths.

line 200-208 – Results This is the Results-Chapter and not a combination of Results and Discussion. Here, the results should only be shown concisely, but not discussed. Therefore, this passage belongs in the discussion section.

According to the instruction to authors of the MDPI Agronomy journal, the Results and Discussion sections can be combined. The reason we combine the Results and Discussion is to explain multiple factors influencing carbon mineralization, movement across the landscape, and within the soil profile.

Apart from this gaffe: line 205 “Prolonged drought in 2016 (Figure 1)” This cannot be seen from the figure

While we agree it was an annual drought, it was severe enough to have impacts on grazing management and carbon sequestration. We have updated Figure 1 and believe it is now more apparent that there was little rain in most of 2016 and the temperatures were slightly higher than the 30-year average. The graph also illustrates more extreme rainfall in the year 2017.

Line 208 “…mineralization of LOI into more labile C, N, and P pools” is not correct, since LOI is a percentual weight loss and a gravimetric loss can hardly be mineralized. Obviously, the organic soil fraction is meant.

We have updated the sentence to (now on lines 228-230), “…..supporting mineralization of organic soil carbon fraction into more labile C, N, and P pools.”

line 246 - Results “Ttwo years of STR…” Misspelling, cross out a T

The typo has been corrected now on line 267.

line 244-254 - Results As already mentioned before, discussions are not appropriate in the result section.

Please note we were following instructions to authors. And we believe this format makes it easier for the reader.

line 254-260 - Results Fig. 3: This image is definitely too small and therefore illegible. The boxes of the boxplots contain two lines, one solid and one dashed. Which of these is the median and which is the mean? This should be clear from the figure caption, as well as what the significance differences refer to (probably the means).

We have increased the size of the figure and additionally we have added a sentence in figure caption denoting the meanings of the dashed and solid horizontal lines inside the boxplots on lines 279-280. We added, “The solid and dashed lines inside the box-plots represent median and mean respectively.”

line 267-268 - Results Fig. 4 caption: “…Comparison of slopes were done by checking significance of interaction between year and LOI at 5-10 cm in the model.” This methodological remark belongs in chapter 2.7. (Statistical Analysis) and requires there a specification of the model.

We have removed the specified sentence from figure caption as it has already been mentioned in section 2.7 on lines 214-215.

line 274 - Results “…for the 0- 5 cm” Delete blank space before the 5

The typo has been corrected and is now on line 294.

line 277-278 - Results belongs to the Discussion

Please see above comments.

line 297-299 - Results belongs to the Conclusions

We have moved them to Conclusions as suggested.

line 324-337 - Results belongs to the Discussion

We have moved them to Conclusions.

.

lines 350-425 - Conclusions The conclusions section is a combination of discussion and summary with few real conclusions. It needs a fundamental revision. Which conclusions are to be drawn for practical application, which for further investigations?

We have expanded the Conclusions to describe how application of CHD or STR could help improve grazing system sustainability.

line 387 – References Far too few scientific sources have been consulted, so there is still a lot of literature research to be done. In addition, the few sources are limited to the U.S., but the problematic addressed is not limited to these regions and the readership of "Agronomy" is international. Reference numbers 1, 3, 4, 5, 11, 12, and 14: The names of the corresponding journals are misspelled, the initial letters should be capitalized

As per the reviewer’s suggestion we have added 10 more references in the introduction section and the references include research and reviews from around the world including Australia, New-Zealand, England, Columbia, and Switzerland.

We have updated the references with correct names of journal and added references at their respective order of citation in the manuscript.