Sward Diversity Modulates Soil Carbon Dynamics After Ploughing Temporary Grassland

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript reported the changes in soil respiration and related soil properties as well as plant biomass following different management manners in a grassland. The results would provide a basis for reasonably enhancing soil carbon content and decreasing C loss in grasslands. Some special comments are shown at the bottom for the authors' revisions。

1） Title: soil respiration and carbon emission, would have a same meaning. The authors should make a revision for this title.

2) In abstract: line 24-26, the content is not clear. line 27, a higher priming effect was observed. The authors should give an explanation about the calculation of this priming effect, which should be nicely mentioned in the M&M section.

3) In the introduction section, the authors mentioned a priming effect on soil organic carbon decomposition. However, there was no message about this priming effect in the M&M section and the following sections of the text.

4) Lines 124-131, the contents are not clear. Afterwards, the authors mentioned the addition of straw. At present experimental treatments are not clear. The authors would give a table for nicely explaining experimental treatments in the M&M section.

5) For CO2 measurement, soil PVC was installed in the soil at 10 cm depth. However, soil samples were collected at 0-30, 30-60, and 60-90 cm, respectively. Soil bulk density and roots samples were collected at depths of 5cm and 15cm as well as 0-15 and 15-30 cm, respectively. The disagreement of these sampling depths would affect the analysis of the relationships between soil respiration and related variables. In fact, the authors did not give any analysis for nicely documenting the dynamics of soil CO2 flux across all treatments. This would be a great surprising for a scientific report.

6) line 171: what is the meaning of 17.03.2000?

7) line 188-189, the incorporated C and N content is not clear.

8) Figures 1 and 2, standard errors at each sampling should be added.

9)  In Figure 3, added straw was mentioned. However, the authors did not mention this straw addition in the M&M section.

10) Section 4.4 limitations: the authors mentioned soil properties. However, there are not any results about the relationships between soil respiration and other variables in the text, except additional descriptions of measurement in the M&M section. 

      

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors,

This manuscript is titled “Impact of Sward Mixture on Soil Respiration and Carbon Emissions Following Ploughing of Temporary Grassland.

Some comments for your manuscript

-27% plagiarism is not acceptable

-What is your novelty?

-Explain temporary and permanent grassland in the Introduction and Methodology section and how your study is important in this stance.

-Most of the references are old, better to update them.

-Add recent references in each section.

Title

-Can improve with attractive findings.

Abstract

-“agricultural grasslands” Means?

-“The ploughing effect on CO₂ emissions was evident for bare soils.” How?

- Main results but significant and with novel findings, not all (for abstract)?

- Better to present significant results in the abstract and then details in the results section of the manuscript.

-“higher priming effect was observed in the BM treatment” Values? Comparison?

-recommendation?

Materials and methods

-No references for using methods? Please provide references as well.

-What is the frequency of gas sampling?  Provide details.

Results and discussion

-In fig1, how about statistical analysis to differentiate within treatments? How is it different from Fig 3? Can combine as a, b, c….about emissions and cumulative fluxes.

-Improve Fig 2 with better resolution and using coloration will be more effective.

-“After day one, straw was added to the various treatments and included in the total 280 mean accumulated CO₂ emissions over the rest of the experimental period (24/03/2020 to 281 11/08/2020).” Why?

Details provided in the methodology section about the addition of straw with references?

-From line 3101 to 304, Why underline?

-“Some species mixtures are known to have deeper and denser rooting systems,” Which specie mention their names with references.

References

-Should be consistent. Check again and revise carefully.

-Add recent references.

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

ID: agriculture-3542430

Title: Impact of Sward Mixture on Soil Respiration and Carbon Emissions Following Ploughing of Temporary Grassland

Authors: Hendrik P.J. Smit, Hanna Anders, Christof Kluß, Friedhelm Taube, Ralf Loges and Arne Poyda

General comment

Effects of ploughing different grassland cultures on CO2 emissions from soils are not often studied. Grassland can usually serve as a type of conservation agriculture practice with a scope to reduce GHG and sequestrate soil carbon. Ploughing naturally cause higher CO2 emissions. Here, I miss better explanation of the scope for a similar research. The aim to study only the priming effects of sward diversity on CO2 emissions after ploughing without other explanation seems me to be too little. Was one of aims to study CO2 emissions after ploughing different kinds of swards for instance counting with an eventual restoration of pastures or new more nutritionally richer grasslands in future? I can also imagine that one of scopes could be to find a grassland mixture with good nutritional properties, which in the future after repeated ploughing could produce less CO2 emissions than others. In this context, the incorporation of straw (which type?) bringing other easily decomposable organic matter increasing CO2 emissions seems me counterproductive. In addition, there exist also no-tillage practices which possibly could be used to enrich grasslands with direct seeding of new species without disturbing soils so much as ploughing. In addition, ploughing enhances not only CO2 emissions, but due to higher soil mineralization (mainly in presence of clovers) could also cause higher risk of nitrate leaching in deeper soil horizons and ground waters. It is a pity that effects of only one year 2020 after so long preparation of different types of swards was studied. I hope that it was only the first part of the research and authors continued in their studies for instance by seeding innovated grassland mixtures on plots or at least studied CO2 emissions in following year 2021 and later.

Specific comments

Materials and Methods

Line 129 – which type of straw was added and in which quantity?

Indicate the depth of ploughing and also the depth of straw incorporation and which type of incorporation – chiselling and ploughing, only ploughing? Was part of plots in the experiment ploughed twice to incorporate a straw?  It is important for understanding CO2 emissions from soils.

Line 130 – It is a pity that there was not also a treatment of bare plots not ploughed with a straw. The mulch cover with straw could give an answer how much more CO2 was emitted from ploughed soils and how much carbon was lost by ploughing. 

Line 138 – Please, indicate better the chambers used in the equipment with LI 820 used for rings with diameter 60 cm. On difference from type of CO2 analyser LI 820, the type of chambers is not clear. Newer types of chambers for LI-8100 or LI- 7810 have standard diameter 20 cm of rings. Did authors modify their chambers to the diameter 60 cm, eventually how?  Sincerely, greater diameter for CO2 measurements is much better as there can be a notable hetereogeneity which could be alleviated by a greater area of rings.

Starting CO2 measurements few minutes after ploughing is sincerely technically very difficult. It is necessary to count whole time of ploughing, after that incorporation of rings on the whole experimental area and laying the measuring chambers. Eventually, how many analysers LI 820 had authors for disposition to measure CO2 emissions in the whole experimental area and each plot to be able to state that all measurements started only minutes after ploughing?

Results

Lines 207-210 - bellowground biomass in BNP  and B treatments  - How the bare soils were maintained before starting the experiment. The belowground biomass indicate that possibly weeds or some other plants were sometimes on bare plots. How was the bare plots cleaned from plants? Were the bare plots well separated from plots with different grass-clover mixtures? Some roots could reach the bare plots.

Line 236  - Measuring only few minutes after ploughing – as comment  to Materials and Methods.

Figure 2 – Only a part of the figure 2 is possible to see in the PDF file. It is necessary to enlarge it on the full page – to its left side. 

Line 255, 268 – What was the WC treatment? I did not found it in Materials and Methods.

Line 280 – Were the soils ploughed two times to incorporate straw? It is not clear from Materials and Methods where only ploughing is mentioned. Which quantity of straw was added?

Discussion

Lines 301-308 – The aboveground biomass was sampled on March 23 2020. This is quite early after the winter. Did authors took in consideration that different plant species could have also different times of starting growth and growth rate at a start of vegetation season? Some species can start their growth earlier than others. Here possibly could be one of advantages of more complex plant mixtures to grow more than only simple combination of grass and clover.  Did authors study separately the growth of single species in the experiment? Did they maintain in time the same composition as when they were sieved?

Line 324 – higher N content – there can be also effect of N concentration in lower amount of biomass and contrary dilution effect in case of greater amount of biomass. Simply, similar N source lead to greater N uptake when lower amount of biomass was produced and vice versa.

References 34, 35 – it is true, but in the presented research three types of mixtures of grasses and clovers with ability of symbiotic fixation were used. So, here probably the roots of grasses and clovers were not separated to understand better the N uptake by roots.

As it is possible to understand from the manuscript, soils were the first ploughed and a day after the straw was incorporated. It means twice soil disturbation which also lead to higher CO2 emissions.

Line 395 - narrow ratio C:N.  - Without the knowledge of the type of incorporated straw, it is difficult to understand why was it so narrow. Naturally, grass mixtures with clovers incorporated by ploughing had lower C:N. On the other hand, for instance the wheat straw has C:N very high close to 100:1.

Line 405 - increase of soil moisture after straw addition – here is should be distinguished. Shortly after straw incorporation, no increase of soil moisture can be expected as a straw (which is typically dry) could take a water from soils. Later after precipitation, it can really hold more water than soils without straw.

Lines 425 – 435 – I agree with this part, but it is a pity that so much questions remained unclarified. More research could certainly have been done from 2020 to 2025 to understand better the CO2 emissions in the next period under grassland cover or bare soils. I understand that there was not possible to plough other part of grasslands in next years, but some continuation, possibly, seeding of new grass and clover mixtures or measuring the bare soils in the next year was possible. However, I hope that such research was done since 2020.

Conclusions

Some expectations about future research or what to manage the soils and grasslands in future souls be added in conclusions

References
According to Instructions to Authors, no spaces between single references should be given. Please, check it.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors improved their manuscript and followed all comments.

Figures 1 and 2, check again and make them better before final publication.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Reviewer 3

ID:Agronomy-3542430

Title_ Sward Diversity Modulates Soil Carbon Dynamics After Ploughing Temporary Grassland

Reviewers comment:

The authors improved substantially the manuscript and answered precisely my questions, but some new appeared. The amount 5 g of straw added in a bag to the ring of a diameter 60 cm means that about 177 kg of wheat straw was added per hectare. Even, if I consider that the main biomass was from different clover-grass mixtures, this amount is quite low. The crop residue in the normal wheat field will reach tons of straw per ha. The amount less 200 kg straw per hectare seems me practically invisible and difficult to reach about twice CO2 emissions compared with treatments without a straw. However, if there will be considered the bellow ground and above ground biomass from sward mixtures and a possible priming effect on CO2 losses caused by even a little straw addition, there can be a significant effect on CO2 emissions. How authors can explain so high CO2 emissions reaching in case BM+s almost 20 t CO2 ha-1 (twice than BM) and CM+s reaching twice CO2 losses (about 10 t CO2 ha-1) in comparison with CM (see Figure 4). Possibly, some short explanation regarding also the BM and CM mixtures compared to TM added in a discussion could help the manuscript and answer last doubts.

For the next time, some calculation of carbon balance could help as for instance 10 t of CO2: 3,667 = 2,73 t carbon (considering atomic weights of CO2 and carbon).  So, considering BM+s (losses of about 5.4 t C ha-1), added carbon in the bellowground biomasss (Table 3) in this mixture was practically lost during the experiment without sufficient carbon addition in a straw.

Author Response

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Author Response File: Author Response.pdf