the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Mar 2026
Fresh and degraded maize shoot and root residues temporarily change soil hydraulic properties
Abstract. Mulching and incorporation of crop residues (CR) into soils are common strategies to sustain soil carbon stocks, return nutrients, and regulate water losses through bare soil evaporation. To date, implementing the effect of mulching strategies into soil-plant-atmosphere models remains challenging due to limited information on their influence on soil hydraulic properties (SHP) as well as on the persistence of these effects over time. We hypothesized that increasing amounts of incorporated maize CR benefits water retention and reduces unsaturated hydraulic conductivity, and that the quality of the CR would determine the persistence of the effects, i.e., that mulching with relatively fast decaying shoot residues would be less persistent than incorporating root residues.
In a laboratory study, we quantified the effect of maize CR in various concentrations (0, 2, and 5 wt.%) on the SHP of a loam soil and additionally measured the SHP of a mulch layer (100 wt.% CR) from saturation to oven dryness. We differentiated between shoot and root CR to quantify the effect of biomass quality and adapted the simplified evaporation method to measure the hydraulic properties of 100 % CR layer. The experiments were run in triplicate and repeated after three weeks of incubation under optimal conditions for biological activity (30 °C, 90 % RH) to simulate organic matter degradation after harvest. Comparing the SHP before and after incubation provided information about the temporal dynamics of CR effects on SHP.
Compared to the control, water retention increased systematically by 2 to 5 vol.-% across the CR-soil mixtures from saturation to field capacity while the unsaturated hydraulic conductivity was slightly reduced. Incubation reduced carbon mass about 46–50 % in 100 % CR layers, 7–15 % in root-soil mixtures and 21–27 % in shoot–soil mixtures, simultaneously altering residue carbon and nitrogen concentrations. Despite this degradation, a positive effect on the soil water retention curve persisted, with water content increasing on average by 1.45 vol.% per gram of carbon per kilogram of soil. However, soil hydraulic properties measured after three weeks showed that much of the beneficial effect had diminished, most notably for shoot residues, which decomposed most rapidly.
Overall, the study demonstrates that the beneficial effects of CR incorporation on the SHP of a loam soil increase with CR amount and persist for at least one month after harvest. In agroecosystems, this post‑harvest period and the mulching process are crucial for defining the initial soil conditions for the subsequent crop. Furthermore, the reduced unsaturated hydraulic conductivity of the 100 % CR layer confirms field observations that mulch layers can effectively reduce water losses through bare soil evaporation.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2026-1063', Anonymous Referee #1, 22 Apr 2026
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AC1: 'Reply on RC1', Frederic Leuther, 29 Jul 2026
We would like to thank the reviewer for the positive feedback and valuable suggestions. We fully agree that measurements of saturated and near-saturated hydraulic conductivity could have provided additional information on the hydraulic conductivity curve. However, there are several reasons why we did not include these measurements in the present study:
First, the study design: We wanted to keep the time after harvest, as well as the time during which the sample was in a state of complete saturation (anaerobic conditions), as short as possible. On the one hand, to perform the first measurement (pre-incubation) with crop residues that were as fresh as possible (to reflect post-harvest conditions); on the other hand, to avoid biological feedback effects caused by significant changes in the micro-environmental conditions within the sample.
Second, the technical aspects: The method mentioned by the reviewer (Multi-Step Flux) was not fully established in our laboratory until after this study had been completed and, in addition, not yet been adapted for the small sample volumes used in the 100% crop residue treatments. In our view, the adaptation of the HYPROP method for small sample volumes already represents a significant methodological advancement for determining the hydraulic properties of crop residues.
Third, the relevance: Fully saturated conditions are unlikely to occur in topsoil immediately after harvest or within a mulch layer under field conditions. For this reason, and considering the constraints outlined above, we chose to focus on how the incorporation and degradation of maize shoot and root residues affect soil water retention and unsaturated hydraulic conductivity.
In the revised manuscript, we will address these aspects in greater detail and explicitly discuss the limitations of the current study, as well as opportunities for future research, including the potential integration of direct measurements of saturated and near-saturated hydraulic conductivity.
Citation: https://doi.org/10.5194/egusphere-2026-1063-AC1
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AC1: 'Reply on RC1', Frederic Leuther, 29 Jul 2026
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RC2: 'Comment on egusphere-2026-1063', Anonymous Referee #2, 08 Jun 2026
This manuscript investigates the effects of fresh and degraded maize shoot and root residues on soil hydraulic properties (soil water retention and hydraulic conductivity) using controlled laboratory experiments. The topic is relevant to soil physics, residue management, and agroecosystem water dynamics. The study provides valuable experimental data on the temporal evolution of hydraulic properties following crop residue incorporation and decomposition. The manuscript presents valuable and potentially publishable findings. However, several methodological limitations, particularly regarding statistical robustness, interpretation of hydraulic conductivity results, decomposition during measurements, and extrapolation to field conditions, require further clarification and discussion.
- The study relies on a relatively small number of replicates (mostly n = 3), and in several cases the number of replicates decreases after incubation due to biomass loss. The authors acknowledge this limitation, yet strong conclusions are drawn regarding differences between treatments and decomposition effects. Confidence intervals are reported for fitted parameters, but no statistical comparison is provided for the hydraulic curves themselves. A more rigorous uncertainty analysis and statistical evaluation of treatment effects on hydraulic parameters is needed.
- One important methodological concern is that residue decomposition already occurred during the first HYPROP measurements, as acknowledged by the authors. Consequently, the "fresh residue" treatment was not truly fresh throughout the measurement period. This complicates the interpretation of treatment effects and weakens the distinction between pre-incubation and post-incubation conditions. The implications of this limitation should be discussed more explicitly, preferably in a dedicated subsection of the Discussion.
- The study was conducted using a single loam soil under controlled laboratory conditions. Since soil texture strongly influences residue-soil interactions and hydraulic behavior, the conclusions should be restricted to the investigated soil type. The manuscript occasionally presents findings in a generalized manner that may not be applicable to sandy or clayey soils.
- The discussion concerning unsaturated hydraulic conductivity remains somewhat speculative. The authors themselves note that conductivity measurements were limited to specific pF ranges and that fitting parameters showed substantial uncertainty. Given these limitations, conclusions regarding conductivity changes should be presented more cautiously. Additional discussion of the reliability of the conductivity estimates is required.
- The manuscript attributes many observed changes to modifications in pore architecture, residue morphology, and soil-residue interfaces. However, no direct measurements of soil structure (e.g., X-ray CT imaging, pore-size distribution analysis, microscopy) were conducted. As a result, several mechanistic explanations remain hypothetical. This limitation should be emphasized more clearly.
- The experiments were conducted under constant temperature and humidity conditions that do not represent field environments where wetting-drying cycles, rainfall, biological activity, and root growth occur simultaneously. A dedicated discussion is needed regarding how these laboratory findings can be extrapolated to field conditions and what limitations exist for practical agricultural applications.
Citation: https://doi.org/10.5194/egusphere-2026-1063-RC2 -
AC2: 'Reply on RC2', Frederic Leuther, 29 Jul 2026
We would like to thank the reviewer for the positive feedback and valuable suggestions. The answers to the individual comments are given below each indivudal comment.
1.The study relies on a relatively small number of replicates (mostly n = 3), and in several cases the number of replicates decreases after incubation due to biomass loss. The authors acknowledge this limitation, yet strong conclusions are drawn regarding differences between treatments and decomposition effects. Confidence intervals are reported for fitted parameters, but no statistical comparison is provided for the hydraulic curves themselves. A more rigorous uncertainty analysis and statistical evaluation of treatment effects on hydraulic parameters is needed.Answer: Preliminary experiments demonstrated a high reproducibility of hydraulic measurements on repacked samples when a strictly standardized packing protocol was followed, as described in the manuscript. Based on these findings, we considered three replicates per treatment sufficient for the objectives of this study.The selected experimental design allowed us to investigate a wide range of shoot and root residue concentrations simultaneously while ensuring identical plant material quality and environmental conditions across treatments. This required a substantial number of HYPROP devices, climate-controlled laboratory space, incubation capacity, and additional samples for carbon and nitrogen analyses.Nevertheless, we agree that the limited number of replicates contributes to uncertainty in the estimation of soil hydraulic parameters, particularly for treatments where the number of valid replicates decreased after incubation. We therefore acknowledge that the statistical power for detecting treatment effects is limited.In response to this comment, we will revise the manuscript to provide a more comprehensive assessment of uncertainty associated with the fitted soil hydraulic functions. Rather than focusing solely on confidence intervals of individual model parameters, we will explore the uncertainty of the predicted water retention and hydraulic conductivity functions themselves. This will allow readers to directly assess the reliability of the predicted hydraulic functions over the investigated pressure head range. In addition, we will further emphasize the uncertainty associated with the hydraulic conductivity estimates, particularly for treatments with limited data support, and revise the discussion and conclusions accordingly to avoid overinterpretation of treatment effects.
2. One important methodological concern is that residue decomposition already occurred during the first HYPROP measurements, as acknowledged by the authors. Consequently, the "fresh residue" treatment was not truly fresh throughout the measurement period. This complicates the interpretation of treatment effects and weakens the distinction between pre-incubation and post-incubation conditions. The implications of this limitation should be discussed more explicitly, preferably in a dedicated subsection of the Discussion.
Answer: We agree, measured and acknowledge that some decomposition occurred during the HYPROP measurements of the pre-incubation treatments. Consequently, the term "fresh residue" should not be interpreted as completely undecomposed residue throughout the measurement period. Rather, it refers to residue that was analysed immediately after sample preparation and prior to the dedicated incubation treatment.The intended contrast of our experimental design was therefore between pre-incubation and post-incubation conditions, rather than between completely undecomposed and strongly decomposed residues. While biological decomposition likely commenced during the hydraulic measurements, this period was short compared to the incubation and thus still represents the earliest stage of decomposition investigated in this study.We acknowledge that decomposition is a continuous process and that the distinction between treatments should therefore be interpreted as differences in the degree of decomposition rather than as discrete states.Since we distinguished between fresh, pre-incubation, and post-incubation treatments in the carbon and nitrogen analyses, we will revisit the terminology used throughout the manuscript to ensure consistency and clarity. For the soil hydraulic measurements, however, only pre-incubation and post-incubation conditions were investigated, and this distinction is already consistently reflected in the figures and tables. We will further clarify this point in the revised manuscript and expand the discussion of the implications of decomposition during the hydraulic measurements as a study limitation.
The study was conducted using a single loam soil under controlled laboratory conditions. Since soil texture strongly influences residue-soil interactions and hydraulic behavior, the conclusions should be restricted to the investigated soil type. The manuscript occasionally presents findings in a generalized manner that may not be applicable to sandy or clayey soils.
Answer: The study focuses on the influence of crop residues on soil hydraulic properties and on the properties of the crop residues themselves. Since the effects examined occurred primarily in the range of low pF values and corresponded to mesopores and macropores, this suggests that the effect of crop residues on the hydraulic properties of the soil is largely independent of soil texture. Nevertheless, we can only discuss this in relation to our soil texture and based on existing literature. We will therefore take great care to present our results with a focus on loamy soils.
3. The discussion concerning unsaturated hydraulic conductivity remains somewhat speculative. The authors themselves note that conductivity measurements were limited to specific pF ranges and that fitting parameters showed substantial uncertainty. Given these limitations, conclusions regarding conductivity changes should be presented more cautiously. Additional discussion of the reliability of the conductivity estimates is required.
Answer: We thank the reviewer for this important comment and agree that the interpretation of the unsaturated hydraulic conductivity results should be made with appropriate caution.In particular, the estimates for the 100% crop residue treatments are associated with considerable uncertainty because hydraulic conductivity measurements were available only over a limited matric potential range, resulting in greater uncertainty in the fitted hydraulic conductivity functions and parameters. We discussed internally whether these results should be included at all. However, given the lack of comparable data on the hydraulic properties of pure crop residue materials in the literature, we considered it valuable to present these results while clearly highlighting their limitations and uncertainty.In the revised manuscript, we will revise the discussion accordingly, place greater emphasis on the uncertainty associated with the conductivity estimates, and avoid overinterpreting observed differences among treatments. We will also expand the discussion of the methodological limitations and the reliability of the fitted hydraulic conductivity functions, particularly for treatments where the available measurement range was restricted.
4. The manuscript attributes many observed changes to modifications in pore architecture, residue morphology, and soil-residue interfaces. However, no direct measurements of soil structure (e.g., X-ray CT imaging, pore-size distribution analysis, microscopy) were conducted. As a result, several mechanistic explanations remain hypothetical. This limitation should be emphasized more clearly.
Answer: We thank the reviewer for this comment. Yes, unfortunately, we did not have access to X-ray CT at the time, which would have allowed us to conduct explicit analyses of the effect of crop residues on soil structure. However, in the new version, we will address the effect of crop residues on pore size distribution derived by the water retention curve. This is an excellent idea.5. The experiments were conducted under constant temperature and humidity conditions that do not represent field environments where wetting-drying cycles, rainfall, biological activity, and root growth occur simultaneously. A dedicated discussion is needed regarding how these laboratory findings can be extrapolated to field conditions and what limitations exist for practical agricultural applications.
Answer: As mentioned in a previous response to Reviewer I, we will explicitly address the study’s limitations in the new version of the manuscript. The conditions of the experiment are significantly less dynamic than in field trials; nevertheless, we also included a wetting/drying cycle as a result of the experimental setup (pre-incubation/incubation/post-incubation), two climatic conditions (HYPROP/incubation), and rooting should also not play a role in the post-harvest phase in the field. But of course, this laboratory experiment primarily focused on investigating the mechanism.
Citation: https://doi.org/10.5194/egusphere-2026-1063-AC2
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RC3: 'Comment on egusphere-2026-1063', Anonymous Referee #3, 08 Jul 2026
Leuther et al. present the results of a controlled incubation experiment investigating how the incorporation and degradation of maize shoot and root residues affect soil water retention and unsaturated hydraulic conductivity. The study addresses a relevant question and provides potentially valuable experimental data on the temporal dynamics of soil hydraulic properties following crop residue addition. The manuscript is generally clearly written and structured, and I agree that the work could be of interest to readers of SOIL.
Generally, I agree with the comments of Reviewer 2, particularly regarding the need to address the major limitations of the study more thoroughly in the Discussion. These include the lack of truly “fresh” measurements because decomposition already occurred during the initial HYPROP measurements, the inclusion of only one soil type, the absence of direct measurements supporting several of the proposed mechanistic interpretations, and the limitations involved in extrapolating results obtained under controlled laboratory conditions to field applications.
However, I have a couple additional concerns:
1. I do not understand the basis for the repeated-measures ANOVA used to compare fresh, pre-incubation, and post-incubation C and N concentrations. A repeated-measures analysis requires observations from the same independent experimental units across time. However, the Methods appear to indicate that the C and N analyses involved initial subsamples of fresh material, separate dummy samples at the pre-incubation stage, and final experimental samples at the post-incubation stage. Please clarify which experimental units were repeatedly measured or paired across the three time points. If the observations at the different time points came from different samples, a repeated-measures ANOVA would not seem appropriate.
The statement that normality and homogeneity of variance were assumed “due to the low number of technical replicates” should also be reconsidered. Low replication makes these assumptions difficult to evaluate, but it does not provide a statistical basis for assuming that they are met. Please also clarify what constitutes a “technical replicate” and whether technical replicates were treated as independent observations in the statistical analyses.
2. The basis and interpretation of the value of 1.45 vol.% per g C kg⁻¹ reported in the Abstract require clarification. As I understand it, this value appears to be the arithmetic mean of four separate regression slopes from Figure 6 (1.5 and 1.5 at pF 0 and 1.8 pre-incubation, and 1.5 and 1.3 post-incubation). If so, this averaged value is not itself a directly estimated relationship and combines regressions from different matric potentials and experimental stages. Please explain how this value was derived and clarify the rationale for presenting itas a single quantitative effect of C concentration on water retention.
Minor comments:
1. The reported soil texture fractions sum to 90% (33% sand + 48% silt + 9% clay), rather than 100%. Please check these values.
2. The caption of Table 2 states that 95% confidence intervals are shown in parentheses, but these do not appear to be presented in the table. Please check the table or caption.
3. The fresh root N concentration is reported in the Results as 0.7 g kg⁻¹, whereas Table 4 reports 7.1 g kg⁻¹.
Citation: https://doi.org/10.5194/egusphere-2026-1063-RC3 -
AC3: 'Reply on RC3', Frederic Leuther, 29 Jul 2026
We would like to thank the reviewer for the overall positive feedback, valuable suggestions and for highlighting some concerns already mentioned by Reviewer II. We evaluated the individual suggestions and especialy the applied statistical tools. Answers to the individual comments are given below.
I do not understand the basis for the repeated-measures ANOVA used to compare fresh, pre-incubation, and post-incubation C and N concentrations. A repeated-measures analysis requires observations from the same independent experimental units across time. However, the Methods appear to indicate that the C and N analyses involved initial subsamples of fresh material, separate dummy samples at the pre-incubation stage, and final experimental samples at the post-incubation stage. Please clarify which experimental units were repeatedly measured or paired across the three time points. If the observations at the different time points came from different samples, a repeated-measures ANOVA would not seem appropriate. The statement that normality and homogeneity of variance were assumed “due to the low number of technical replicates” should also be reconsidered. Low replication makes these assumptions difficult to evaluate, but it does not provide a statistical basis for assuming that they are met. Please also clarify what constitutes a “technical replicate” and whether technical replicates were treated as independent observations in the statistical analyses.
Answer: We can see the concerns of the reviewer about the statistical evaluation and we appreciate this important observation. The observations at the three sampling stages did originate from the same pool (fresh), but the experimental units for pre-incubation and post-incubation were different and therefore do not satisfy the assumptions of a repeated-measures ANOVA. In addition, we acknowledge the concerns about the statement regarding the assumptions of normality and homogeneity of variance. The low number of technical replicates does not justify assuming that these assumptions are met. The reported replicates were technical replicates derived from pooled samples and therefore do not represent independent biological observations. Consequently, formal statistical comparisons of C and N concentrations will not be performed in the revised manuscript. We will remove the repeated-measures ANOVA from the revised manuscript and focus on the descriptive presentation of the results. In order to discuss and illustrate carbon turnover dynamics, we will use exponential decay models assuming a stable background soil carbon pool corresponding to the carbon concentration measured in the control treatment. These models will provide temporal trends of the C and an estimate of the turnover of plant-derived residues in our experimental setup. The derived carbon turnover time (t 95 %) is similar to a previous study by “Elias et al 2024: Microbial and mineral interactions decouplelitter quality from soil organic matter. Nature Communications” where the authors investigated respiration of fresh litter and the interactions between litter quality and soil mineralogy.
The basis and interpretation of the value of 1.45 vol.% per g C kg⁻¹ reported in the Abstract require clarification. As I understand it, this value appears to be the arithmetic mean of four separate regression slopes from Figure 6 (1.5 and 1.5 at pF 0 and 1.8 pre-incubation, and 1.5 and 1.3 post-incubation). If so, this averaged value is not itself a directly estimated relationship and combines regressions from different matric potentials and experimental stages. Please explain how this value was derived and clarify the rationale for presenting itas a single quantitative effect of C concentration on water retention.
Answer: The 1.45 vol.% per g C kg⁻¹ referred to the previous sentences, which discussed water content at saturation and field capacity. The value was presented here as the mean slope of both regressions for the experiments conducted after incubation. You are correct that this was not entirely clear and we will rephrase the section. In the new version of the manuscript, we will specify the slope for both saturation and field capacity and clearly state that it applies to the measurements taken after incubation.
Minor comments
Minor comments:
The reported soil texture fractions sum to 90% (33% sand + 48% silt + 9% clay), rather than 100%. Please check these values.
Answer: Correct. The soil texture consists of 33% sand + 48% silt + 19% clay as reported by Vetterlein et al. 2021: Experimental platforms for the investigation of spatiotemporal patterns in the rhizosphere—Laboratory and field scale, J. Plant. Nutr. Soil Sci., 184, 35–50, doi:10.1002/jpln.202000079
The caption of Table 2 states that 95% confidence intervals are shown in parentheses, but these do not appear to be presented in the table. Please check the table or caption.
Answer: Thank you very much for your thoughtful reading of the manuscript. We will revise the section on assessing the quality of the fitting parameters again, incorporating the ideas suggested by Reviewer II.
The fresh root N concentration is reported in the Results as 0.7 g kg⁻¹, whereas Table 4 reports 7.1 g kg⁻¹.
Answer: Correct. As reported in Table 4 and Figure 5 the initial N concentration was 7.1 g kg-1 . We will correct the value in the new version of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2026-1063-AC3
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AC3: 'Reply on RC3', Frederic Leuther, 29 Jul 2026
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This laboratory study evaluates the effect on soil hydraulic parameters (SHP) after mulching and incorporation of maize crop residues in a loam soil.
The authors presented a robust protocol for determining soil hydraulic characteristic curves of packed soil–residue samples with different concentrations and pre- and post-incubation treatments, using a combination of HYPROP and WCR4 devices.
As noted by the authors, the effects are mainly observed at low matric suction. I would therefore question why unsaturated flow was not measured directly using tension devices in the near-saturation range (e.g., using a KSAT device), instead of relying on an indirect method based on fitting procedures, which reduces K_s to merely a fitting parameter.
I understand that this is a posteriori analysis, although it is not far from the authors’ initial hypothesis and is not entirely unexpected, given that the same authors adopted this approach in a parallel manuscript currently under review for this same journal, “Integrating the Multi-Step Flux Method for full-range soil hydraulic characterization: from saturation to oven dryness.”
I therefore suggest that the authors consider discussing the potential integration of such direct measurements within their protocol, as well as clarifying the differences between the two manuscripts, with particular reference to the potential advantages for future research of integrating the present protocol with a Multi-Step approach.
A further consideration for the authors: although I have not reviewed the other paper in detail, the authors might wish to consider positioning the two manuscripts as companion papers, one being more methodological and the present one an application. I leave this suggestion for their consideration.
Overall, I appreciated the authors’ clarity and the linearity of their presentation of the results, and I believe the manuscript could be of interest to SOIL’s readers.