The Impact of Scoria-Filled Aeration Trenches on the N-cycle and Greenhouse Gases Emissions from a Clayey Soil

Baram, Shahar; Bar-Tal, Asher; Beriozkin, Anna; Katzir, Roee; Gal, Alon; Russo, David

doi:https://doi.org/10.5194/egusphere-2024-2140

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https://doi.org/10.5194/egusphere-2024-2140

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19 Aug 2024

| 19 Aug 2024

The Impact of Scoria-Filled Aeration Trenches on the N-cycle and Greenhouse Gases Emissions from a Clayey Soil

Shahar Baram, Asher Bar-Tal, Anna Beriozkin, Roee Katzir, Alon Gal, and David Russo

Abstract. Treated wastewater (TWW, i.e., treated effluents) is a growing water source. However, irrigation with TWW irrigation exacerbates oxygen deficiencies in the root zone, particularly in clayey soils. Coarse-textured filled trenches are used to ameliorate soil oxygen deficiencies in agriculture. This study aimed to investigate the impact of scoria-filled soil aeration trenches on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from clayey soil irrigated with TWW. N₂O and CO₂ fluxes were measured in the field for three years, along with soil water content monitoring (10 and 35 cm depth) and porewater (30 cm depth) sampling. Irrigation and intense rain events led to transient (hours-long) near-saturation conditions in the clay soil. Concomitantly, the soil at the bottom of the trench remained saturated for prolonged periods, extending to days and even weeks. Nitrate was the dominant N-form and showed a seasonal trend with high concentrations (>50 mgL^-1) between June and October. N₂O fluxes were positively correlated with fertilizer applications, and fluxes from the trenches were higher throughout the year, with maximal differences during the winter. CO₂ fluxes were higher from the trenches during the fertigation seasons yet lower during the winter. Simulation results of N₂O fluxes showed higher fluctuation in the scoria-filled trenches following fertigation events. Further, it showed that filling the trench with finer medium, aimed to maximize the rate of water uptake by the trees' roots, increased the emissions maxima, dampening its minima. Overall, our study shows that aeration trenches may serve as N₂O hotspots and that, during winter, they might be counterproductive. Further study is needed to find the optimal filling material that would maximize aeration yet minimize water build-up at the trench bottom.

Received: 10 Jul 2024 – Discussion started: 19 Aug 2024

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Shahar Baram, Asher Bar-Tal, Anna Beriozkin, Roee Katzir, Alon Gal, and David Russo

Status: final response (author comments only)

RC1:
'Comment on egusphere-2024-2140', Anonymous Referee #1, 15 Sep 2024

General comments:
This work examines the influence of aeration trenches in planted orchards, on the trends of N2O and CO2 emissions. I find the manuscript interesting, and the team has performed an extensive long year study to capture dynamics at various timescales. My main concern is whether the conclusions drawn are supported by the data. It seems that the authors are over-interpreting some of the results, or drawing conclusions that are not entirely supported by their experimental data, or there are analyses missing that would have been beneficial for their explanations.
Another issue that harms the reader’s flow and understanding, is the choice of symbols and colors in the figures, also, there are multiple grammar and formatting errors.
Below are some specific comments that I hope will help refine the manuscript.

Specific comments:
Line 43 – Why do N2O levels peak at 60-80% water capacity? It would be helpful to add an explanation.
Line 51 – Why has this been done specifically for planted orchards?
It would also be helpful to add a sentence on the knowledge gaps and what this study is contributing to previous knowledge.
Line 66 – please make sure there is a space between number and unit. 6m should be 6 m.
Line 237 – I am not sure there is any trend in the N2O values, especially when considering the error bars.
Fig 3 – Perhaps consider using different symbols or colors so the differences between treatments are easier to follow. This is particularly important in panel 3D – the black circles and squares look identical.
Fig 4 – The symbols are confusing. It seems like the exact same symbol is given for Ctrl and Irrigation.
Line 239 – The period in 2018 is not identical with that of 2019-2020. Fig. 4 shows the data starting from July 2018. How was the statistical analysis done for this comparison?
Fig. 5 – What are the A, B and C referring to? The figure caption does not seem to correlate with the data presented. Please correct this.
Line 278 – the differences in N2O emissions between 2018 and subsequent years is intriguing. I think the authors should provide a more thorough discussion on potential reasons for this difference. Insights into the pathways of N2O formation would be helpful to explain this difference in more detail.
Line 315 – it would have been interesting to monitor dissolved oxygen levels in this experiment, or other redox indicators, as this would give vital information on the presence and extent of anaerobic conditions.
Line 322 – Please use correct formatting of numbers and units.
Line 325 – I am not sure the results are indicative of nitrite buildup. Are the authors referring to the five points where NO2 levels were higher? (Also, this sentence should be rephrased as it does not read well)
Line 353 – Where is the weekly scale data shown? Also, there are multiple factors that will influence CO2 emissions, and I am not sure one can simply attribute CO2 trends to nitrate concentrations. Having data at least of DOC and DIC would have been vital to better understand C dynamics.
Line 356 – “aeration teaches”?

Citation: https://doi.org/10.5194/egusphere-2024-2140-RC1
- AC1:
  'Reply on RC1', Shahar Baram, 22 Sep 2024
  Reply to general comments made by an anonymous reviewer (RC1):
  General: This work examines the influence of aeration trenches in planted orchards, on the trends of N₂O and CO₂ emissions. I find the manuscript interesting, and the team has performed an extensive long-year study to capture dynamics at various timescales.
  Comment 1: My main concern is whether the conclusions drawn are supported by the data. It seems that the authors are over-interpreting some of the results, drawing conclusions that are not entirely supported by their experimental data, or missing analyses that would have been beneficial for their explanations.
  Reply – We thank the reviewer for his effort in reviewing the manuscript. The text was modified to highlight the soundness of the conclusions drawn from the presented data. We report data from 2.5 years of field measurements and use a 3D numerical model to link water flow, nutrient fate, and N₂O emissions. Like with any research, we were limited by the analytical instrument and funds at our disposal. We decided to focus on continuous in-situ monitoring of the main drivers of soil emissions (N-forms concentrations, temp, water content). Hence we present that data and use it in our discussion to explain our observations. We think that the presented data and conclusions are accurate and novel. The research could have benefited from the use of ¹⁵N, though its application and interpretation in field studies are not always simple. Similarly, DOC analysis would have contributed. In any case, we don’t think that the use of such techniques would have changed the conclusions.
  Comment 2: Another issue that harms the reader’s flow and understanding is the choice of symbols and colors in the figures. Also, there are multiple grammar and formatting errors.
  Reply – Following the comment, all the grammar formatting errors were corrected, and the symbols and color schemes in the figures were changed to enhance clarity. (See Figs 2, 3, and 4 in the revised manuscript)
  Specific comments:
  Comment 3: Line 43 – Why do N₂O levels peak at 60-80% water capacity? It would be helpful to add an explanation.
  Reply – Based on the comment the text was modified to highlight the relation between WFPS denitrification and nitrification
  Peak N₂O emissions typically occur when denitrification dominates at water-filled pore space (WFPS) values of 60-80% (Davidson et al., 2000), although varying soil types may exhibit significant emissions under different moisture conditions (Butterbach-Bahl et al., 2013; Zechmeister-Boltenstern et al., 2007). (line 43-44 in the revised manuscript)
  
  In clayey soils, good soil aeration status (WFPS < 0.6, was found to restrict denitrification and lower N₂O emissions (Rochette et al., 2008). (line 45-46 in the revised manuscript)
  
  Comment 4: Line 51 – Why has this been done specifically for planted orchards?
  Reply – The word "mainly" was added to the soil to highlight the discussed practices are not specific to orchards (Line 53 in the revised manuscript). Since the soil in the tree line of orchards cannot be tilled, unlike in field crops, other aeration methods must be used in them such as aeration trenches and profile mixing.
  Comment 5: It would also be helpful to add a sentence on the knowledge gaps and what this study is contributing to previous knowledge.
  Reply – Thank you for the comment. A sentence was added to explain the knowledge gaps (Lines 54-55, in the revised manuscript), and this study's contribution (Line 60 in the revised manuscript)
  Comment 6: Line 66 – please make sure there is a space between the number and the unit. 6m should be 6 m.
  Reply – Thank you for noticing the typo. A space was added between the number and the abbreviated units of measurement, in all of the manuscript (Line 68 in the revised manuscript).
  Comment 7: Line 237 – I am not sure there is any trend in the N₂O values, especially when considering the error bars.
  Reply – Based on the comment, a clarification was added to the text to indicate that the daily trend was not statistically significant. In any case, the fluxes were measured between 10 am and 2 pm and were thought to be representative of the daily flux (Lines 238-239 in the revised manuscript).
  Comment 8: Fig 3 – Perhaps consider using different symbols or colors so the differences between treatments are easier to follow. This is particularly important in panel 3D – the black circles and squares look identical.
  Reply – Following the comment the colors in Fig. 3D were changed (Tuff NO3-N), and the symbols enlarged.
  Comment 9: Fig 4 – The symbols are confusing. It seems like the exact same symbol is given for Ctrl and Irrigation.
  Reply – The legend was corrected. It is now easy to distinguish between the rain, irrigation, Ctrl, and Tuff.
  Comment 10: Line 239 – The period in 2018 is not identical with that of 2019-2020. Fig. 4 shows the data starting from July 2018. How was the statistical analysis done for this comparison?
  Reply – A t-test was used to compare all the emissions measured in a given month in every year. At each iteration, we only analyzed the differences between two similar months (e.g., July 2018 vs. July 2019, etc.). We also compared the cumulative emission for the same period between the two years (e.g., July-November 2018 vs. July-November 2019).
  Comment 11: Fig. 5 – What are the A, B and C referring to? The figure caption does not seem to correlate with the data presented. Please correct this.
  Reply – Thank you for noticing the mistake. Section (C) was deleted.
  Comment 12: Line 278 – the differences in N₂O emissions between 2018 and subsequent years are intriguing. I think the authors should provide a more thorough discussion of potential reasons for this difference. Insights into the pathways of N₂O formation would be helpful to explain this difference in more detail.
  Reply – As suggested, a possible explanation for the differences in N₂O emissions between 2018 and subsequent years, was added (Lines 287-295 in the revised text).
  Comment 13: Line 315 – it would have been interesting to monitor dissolved oxygen levels in this experiment, or other redox indicators, as this would give vital information on the presence and extent of anaerobic conditions.
  Reply – We agree; it would have been great if we had data on the redox and/or oxygen availability in the topsoil at the site during N₂O measurements. Based on the comment we cited the work done by a different group at the same site (Yalin et al., where both these parameters were measured (only in the control treatment) and indicated the formation of hypoxic conditions following TWW irrigation and rain events. (Lines 316 and 321-322 in the revised manuscript.
  Comment 14: Line 322 – Please use the correct formatting of numbers and units.
  Reply – All the numbers and units were corrected.
  Comment 15: Line 325 – I am not sure the results are indicative of nitrite buildup. Are the authors referring to the five points where NO₂ levels were higher? (Also, this sentence should be rephrased as it does not read well)
  Reply – The sentence was modified to increase clarity and to indicate that nitrite buildup was only seen on some occasions in this study.
  Comment 16: Line 353 – Where is the weekly scale data shown?
  Reply – The data is shown in Fig. SI3B. A reference to that figure was added to the text (Line 356 in the revised manuscript).
  Also, there are multiple factors that will influence CO₂ emissions, and I am not sure one can simply attribute CO₂ trends to nitrate concentrations. Having data at least of DOC and DIC would have been vital to better understand C dynamics.
  Reply – We wish to highlight that N is just one factor that is being discussed. Please refer to the text (lines 349-363) where we suggest that the aeasonal CO₂ emission was driven by:
  Soil temperature, (high emission during the summer (soil temp 27°C), and low emissions during the winter (soil temp 12°C) (Fig. SI4).
  
  Increased root activity (as suggested by plant physiology and CO₂ assimilation values at the site; Nemera et al., 2020).
  
  Diurnal CO₂ assimilation, and assimilates transport to the root system.
  
  N addition (Lu et al., 2011; Zhou et al., 2014).
  
  Soil moisture was probably not the main driver as the soil remained moist year-round (WFPS >40%) and did not show a clear impact on soil respiration (Fig. 2).
  We agree that DOC and/or DIC data would have contributed to our understanding of the C dynamics, yet like any research, we had limited funds and could not check these parameters.
  Comment 17: Line 356 – “aeration teaches”?
  Reply – Thank you for noticing the typo. It was corrected to "trenches" (Line 365 in the revised manuscript).
  
  Citation: https://doi.org/10.5194/egusphere-2024-2140-AC1
RC2: 'Comment on egusphere-2024-2140', Anonymous Referee #2, 09 Oct 2024

Review for Baram et al.
The manuscript is interesting and performed work fits well into the scope of the journal. I think that the manuscript requires editing (clarity, language, and presentation) and clarification before it can be published.
Specific comments:
Abstract:
The abstract does not convey the work and results well. Use of adjectives is not advised in technical writing (e.g. “even weeks”). “Fertigation” term is not defined. Simulation results are hinting on use of numerical (or other) model but are pretty surprising since modeling is not mentioned in the “methods” of the abstract.
Introduction:
The writing is too ambiguous and vague and needs to be focused. LL25-30: “regions facing a scarcity…” authors mean “drylands”? LL 30-35: “These irrigation practices” Which? LL35-40: “such conditions” Which? N2O significant degrader - ?? N2O is causing O3 destruction not degradation. LL40: “These emissions” – again Which? L44: “varying soil types may exhibit….” – why not to be specific? Tell us what soil types and how soil types will affect emissions.
Between the second and the third paragraph the flow is broken – I think it needs attention; from what I understand authors mean: problem is luck of aeration => solution are trenches with coarse textured materials = these need better connection.
Methods:
Cumulative fluxes have to be interpolated across all measurement time for average fluxes calculation – when authors use averages, they discard a lot of information (Hoben, J.P., Gehl, R.J., Millar, N., Grace, P.R., Robertson, G.P., 2011. Nonlinear nitrous oxide (N2O) response to nitrogen fertilizer in on-farm corn crops of the US Midwest. Global Change Biology 17, 1140–1152.)
Results:
Figure 3 is difficult to assess – maybe to remove NO2? Do you really need it? It’s now well established that NO2 can accumulate in soils. LL 240-245 maybe your “not significant” results stemmed from way of calculation and analysis? Figure 4: beside typos in the axis’s titles “N2O-N” is correct N-N2O is not. In CO2 panel you report µgCO2 or C? Fig 5: how your simulation results of cumulative fluxes are correlated with cumulative fluxes calculated by linear interpolation?
LL270-285 – all this “hand waving” and speculations regarding microbial community structure and use of heterogeneity and temporal variability – maybe all this is due to not correct calculation of average N2O flux? And sampling scarcity?
LL287 – 10 ppb is standard sensitivity of well-maintained GC.
LL 292 – chamber dimensions are important – if you think that 40 cm diameter needed to be used – why haven’t you used it? I think that this point of discussion is quite weak.
In general, the discussion between lines 274 and 315 needs to be rewritten and restructured after corrected fluxes calculation.
LL 316 – sudden and undescribed in the methods (and elsewhere) introduction of the emission factors… and if already introduced make sense to calculate the EF for all orchard, why to speculate if you have numbers?
CO2 fluxes – CO2 fluxes difficult to partition and authors use too much assumptions to include the CO2 into overall scope of the manuscript.
LL 370-373: Too speculative even for the discussion.
Conclusion – will be changed once the rest will be reorganized and edited.

Citation: https://doi.org/10.5194/egusphere-2024-2140-RC2
RC3: 'Comment on egusphere-2024-2140', Anonymous Referee #3, 09 Oct 2024

The authors present a study with filled trenches in an irrigated orchard made to improve soil aeration and therefore to reduce soil GHG emissions.
This study could have been of great significance even if the obtained results did not validate initial hypotheses. But, in its present form, the manuscript suffers of too many basic errors and it can not be accepted for publication.
When starting the review, I have tried to get informations on the level of the measured GHG fluxes. In the main text, N2O fluxes are presented in ng N-N2O cm-2 min-1. I’ve tried to convert them in g N ha-1 d-1 and in g ha-1, as the authors in supplementary informations. The values I obtained are very higher than those proposed by the authors. I also observed that the equation presented line 93 seems not homogeneous, …
Similarly, I was also surprised by the unit used for presenting the simulation results (figure 5) . Results suggest very very low fluxes. In the MM section, I did not find neither the soil bulk density values nor the Dp ones.
I also observed problems with the presentation of WC (line 204, line 209), ….
At this stage, a more rigorous presentation of the data is clearly required before continuing the review process.

Citation: https://doi.org/10.5194/egusphere-2024-2140-RC3

Shahar Baram, Asher Bar-Tal, Anna Beriozkin, Roee Katzir, Alon Gal, and David Russo

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Shahar Baram, Asher Bar-Tal, Anna Beriozkin, Roee Katzir, Alon Gal, and David Russo

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Short summary

We evaluate the impact of scoria-filled aeration trenches on N₂O and CO₂ emissions from a treated wastewater (TWW) irrigated orchard, using three years of field monitoring and 3-D numerical simulations. We show that trenches may increase the N₂O fluxes year-round, and that filling them with hydraulically optimal soil may increase water uptake but concomitantly increase the N₂O fluxes. Improved growth by the trees may balance the increased N₂O emissions from the trenches.


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