Seasonal Grazing Does Not Significantly Alter the Particle Structure and Pore Characteristics of Grassland Soil

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall, very well written manuscript. Only minor changes and additions are suggested. More detail could be added on soil types of the study area and soil processing and handling after collecting. 

Discussion section could be improve. Instead of just summarizing prior work's findings, try to highlight the paper's significant findings and support them with literature.

Author Response

Reviewer #1:

• Overall, very well written manuscript. Only minor changes and additions are suggested. More detail could be added on soil types of the study area and soil processing and handling after collecting.

We appreciate the reviewer’s suggestion, and now add soil type and soil texture in study area in 2.1. Study Area:

“The soil type in the study area was classified as calcicorthic aridisol, characterized by a calcic horizon and nutrient-poor sandy loam. The soil texture was predominantly sandy loam, exhibiting high aeration and drainage but poor water retention capacity[1].”

 

• Discussion section could be improve. Instead of just summarizing prior work's findings, try to highlight the paper's significant findings and support them with literature.

We appreciate the reviewer’s suggestion, and we have revised the discussion section as per your suggestions. The updated section now highlights our results more prominently and integrates relevant literature for a thorough explanation and discussion. Additionally, we have included new references to support our arguments:

“4. Discussion

4.1. Changes in Soil Physics Caused by Livestock Trampling

Previous studies have shown that livestock trampling negatively affects soil, leading to soil compaction in the surface layer. This compaction restricted water infiltration and root growth and extends to deeper soil layers, resulting in a denser soil structure and increased bulk density, which further inhibits root growth[22]. Brito et al. (2018) characterized soil compaction using soil resistivity (RP) and found a significant increase in RP values due to grazing, leading to reduced soil aeration and permeability[23]. Frozzi et al. (2020) observed that livestock trampling rearranges soil particles, altering soil structure and potentially disrupting soil aggregation, which made the soil more vulnerable to erosion and water runoff [24].

Brito et al. (2018) also used the mean weight diameter (MWD) of soil aggregates to examine the impact of grazing on soil structure. They found that grazed soils had a higher MWD compared to soils from cultivated grasslands, although higher MWD values do not necessarily indicate an ideal soil structure[23]. The increased MWD in grazed soils could be due to soil compaction and greater resistance to fracturing. Conte et al. (2011) suggested that larger aggregates in grassland areas might result from animal trampling, which brings mineral particles closer together. MWD values are influenced by clay and total organic carbon (TOC) content, both of which play significant roles in the formation and stability of soil aggregates[25].

The structure of grazed soils was influenced by grazing management and climatic conditions[26]. High grazing intensity, especially during periods of elevated soil moisture like the rainy season from October to June, can cause increased structural damage to the soil. Concentrated animal weight in small areas, particularly hooves, exerts high pressure on the soil. Animal trampling could impose contact pressures of 350 to 400 kPa on the soil, and these pressures can increase when animals were in motion, as the entire weight was concentrated on a single claw, distributing the force over a smaller surface area[27].

4.2. The Impact of Seasonal Grazing on Soil Structure

Our findings confirmed previous reports that there were no significant differences in soil particle composition and pore characteristics between different grazing methods and non-grazed grassland soils under moderate grazing conditions[25]. This aligned with studies using GPS data to analyze livestock movement trajectories under continuous and seasonal grazing[26]. These studies established connections between grazing patterns and soil structure, indicating that grazing cattle's movement patterns were dependent on pasture area rather than shape, orientation, topography, or selective attention. Both continuous and seasonal grazing systems exhibited similar soil compaction, evidenced by higher bulk density and soil penetration resistance induced by grazing. Soares et al. (2021) demonstrated that soil cone penetration resistance (RP) in grazed areas ranged from 1.40 to 1.49 MPa, higher than in non-grazed areas, but not leading to soil compaction[22].

The impact of grazing on soil structure was influenced by factors including grazing intensity, animal movement patterns, and soil clay content, and others[27]. Seasonal grazing tended to exert lighter grazing pressure compared to year-round continuous grazing. Recent research suggested that shorter grazing periods followed by longer recovery periods can reduce soil compaction, allowing more time for natural soil recovery. Seasonal grazing might also positively impact vegetation growth and distribution, contributing to soil structure maintenance. Moderate seasonal grazing could promote the expansion of vegetation roots, improving soil stability and reducing erosion rates[28-29]. Additionally, seasonal grazing affected soil microbial communities, creating a more intricate soil microenvironment that supports greater microbial diversity and contributes to soil ecological balance.

4.3. Relationships Between Soil Structure and Soil Ecological Functions

Our findings demonstrated a significant correlation between soil carbon-nitrogen content and soil particle composition. Soares et al. (2021) observed a decrease in soil cone penetration resistance (RP) in grazed areas, attributed to higher levels of organic matter[22]. This increase in organic matter led to a decrease in soil bulk density and an increase in macroporosity. Some studies found a strong association between total organic carbon (TOC) and mean weighted diameter (MWD) of aggregates. Higher levels of TOC, microorganisms, and robust biological activity, including root systems, can lead to the formation of channels and biopores, consequently altering soil structure[30-31]. Abundant organic matter promoted soil structure development, facilitating a balanced distribution of particles (sand, silt, clay) and creating pores for water and air storage, providing favorable conditions for plant root growth. Organic matter also retained moisture, preventing it from acting as a lubricant between mineral particles, and enhances the cohesion between soil particles, establishing connections among them[32-33].

Soil permeability and compaction status were influenced by organic matter content, microbial activity, roots, exchangeable cations, and soil texture[35]. Recent studies suggested that soils with higher sand content are more prone to compaction, whereas soils with higher clay content tend to resist compaction due to clay's ability to adsorb organic anions, increasing colloid surface charge and enhancing the diffusion layer of associated with the surface[35-37].”

 

1. Brito, W.B.M., Campos, M.C.C., Mantovanelli, B.C., da Cunha, J.M., Franciscon, U., Soares, M.D.R. Spatial variability of soil physical properties in Archeological Dark Earths under different uses in southern Amazon. Soil Tillage Res 2018, 182, 103–111.
2. Frozzi, J.C., da Cunha, J.M., Campos, M.C.C., Bergamin, A.C., Brito, W.B.M., Fraciscon, U., da Silva, D.M.P., de Lima, A.F.L., de Brito Filho, E.G. Physical attributes and organic carbon in soils under natural and anthropogenic environments in the South Amazon region. Earth Sci. 2020, 79, 251.
3. Conte, O., Flores, J.P.C., Cassol, L.C., Anghinoni, I., Carvalho, P.C. de F., Levien, R., Wesp, C. de L. Evoluç˜ao de atributos físicos de solo em sistema de integraç˜ao lavoura-pecu´aria. Pesqui. Bras 2011, 46, 1301–1309.
4. Drewry, J.J., Cameron, K.C., Buchan, G.D. Pasture yield and soil physical propertyresponses to soil compaction from treading and grazing - a review. Austr. Soil Res. 2008, 46, 237–256.
5. Nie, Z.N., Ward, G.N., Michael, A.T., 2001. Impact of pugging by dairy cows on pastures and indicators of pugging damage to pasture soil in south-western Victoria. Aust. Agric. Res. 2001, 52, 37–43.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The name of the plants species must be written by italics letters.

Author Response

Reviewer #2:

• The name of the plants species must be written by italics letters.

We appreciate the reviewer’s suggestion, and now write the name of the plants species by italics letters:

“The vegetation in the study area predominantly comprised perennial plants, including Stipa krylovii Roshev, Leymus chinensis (Trin.) Tzvel., Cleistogenes squarrosa (Trin.) Keng, and others. These plants are characteristic of the typical grassland type[16].”

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

This is a useful paper, particularly with the International Year of Pastoral area coming up. The English in the paper is very good and I can find no concerns in that regard. Thank you for the opportunity to be exposed to your work. Comments are below.

Introduction

Line 61:  It appears that you intended to insert citations here but forgot.

Line 70: same as above

Methods

Line 98: please check the verb tense. It should be past not present.

Please give more information on the study design. Were the 3 replicates of each treatment randomly assigned and not from a single area of that treatment. This is important because you do not have the initial value for the physiochemical values such as particle size distribution. If treatment replicates were randomly assigned when being established in 2011, then one can assume that variability is accounted for. If not, then the question is whether the particle differences existed at the initiation of the study and not a result of treatments. More detail would be useful.

Each treatment had 9 soil samples to 20 cm. I assume these were sacrificed for the physiochemical analysis. So, the question remains as to what samples was the SEM used on, how many and at what depth? More methods here would be useful.

Table 1: It appears that the %moisture was a one time measurement when the samples were taken. One-time measurements like this do not have much meaning. Questions arise such as uneven rainfall as the cause. Please make it clear that lines 133 to 138 are a footnote to Table 1. Same comment for other tables.

Discussion

Section 4.1: This section appears to be more of a literature review and could go in the introduction as background for your study.

Line 252: “This aligns with the findings of ???,”  It seems like something is missing here.

I am not seeing any discussion of your data up to line 277, just more literature review.

 Conclusion:

It would be helpful in the conclusion to provide the reader with a specific recommendation for grazing based on results and the implications to the land manager for that recommendation.

General: It will be useful to provide a better description of the study plan and the physical layout in the field. It is not possible to evaluate the randomness of the layout with the current level of information. If the treatments were not established in a completely random, randomized block, etc. design, then one needs to be concerned about the validity of the statistics used. Some discussion around that would them be useful; particularly when it comes to particle size analysis. One does not expect to see any change in particle size unless there is movement of clay particles out of the soil zone due to treatment. Meaning that any differences may reflect pre-treatment differences already in place. Some discussion to discount this possibility may be useful.

In methods in general could be more detailed as mentioned in the comments.

Author Response

Reviewer 3：

This is a useful paper, particularly with the International Year of Pastoral area coming up. The English in the paper is very good and I can find no concerns in that regard. Thank you for the opportunity to be exposed to your work. Comments are below.

• Introduction Line 61:  It appears that you intended to insert citations here but forgot. Line 70: same as above

We appreciate the reviewer’s suggestion. To clarify our points and highlight the contributions of the previously cited literature, we deleted a sentence, and rewrote a sentence:

“These meticulous observation offers a comprehensive understanding of how soil structure evolves under different grazing management conditions, which is valuable for sustainable grassland management.”

 

• Methods

Line 98: please check the verb tense. It should be past not present.

We appreciate the reviewer’s suggestion. We have revised the methods section to ensure it is consistently written in the past tense.

 

• Please give more information on the study design. Were the 3 replicates of each treatment randomly assigned and not from a single area of that treatment. This is important because you do not have the initial value for the physiochemical values such as particle size distribution. If treatment replicates were randomly assigned when being established in 2011, then one can assume that variability is accounted for. If not, then the question is whether the particle differences existed at the initiation of the study and not a result of treatments. More detail would be useful.

We appreciate the reviewer’s suggestion. We have revised the methods section to include more detailed information about the study sites, including soil types and soil textures. Additionally, we have specified that each grazing management type was replicated with three plots. The grazing plots were set up randomly, and for each plot, three soil samples were randomly collected and then mixed for the determination of soil physical and chemical properties:

“The soil type in the study area was classified as calcicorthic aridisol, characterized by a calcic horizon and nutrient-poor sandy loam. The soil texture was predominantly sandy loam, exhibiting high aeration and drainage but poor water retention capacity[1].”

 

“The experiment consisted of five grazing treatments, and each grazing treatment was replicated with three plots: no grazing (NG), continuous grazing from May to September (CG), grazing in May and July (G57), grazing in June and August (G68), and grazing in July and September (G79).”

 

“Three soil samples were collected from each plot, specifically from the 0-20 cm surface layer, and then mixed for physicochemical analysis.”

 

• Each treatment had 9 soil samples to 20 cm. I assume these were sacrificed for the physiochemical analysis. So, the question remains as to what samples was the SEM used on, how many and at what depth? More methods here would be useful.

We appreciate the reviewer’s suggestion. We have revised the methods section to include the following details: Each treatment was subjected to three replicate SEM analyses. We conducted pore structure analysis as part of these SEM tests. Figure 1 was created by randomly selecting one of the images to form a composite image:

“Each treatment underwent triplicate Scanning Electron Microscopy (SEM) analyses. Pore structure analysis was performed as an integral part of these SEM examinations. Figure 1 was generated by randomly selecting one representative image to construct a composite figure.”

 

• Table 1: It appears that the %moisture was a one time measurement when the samples were taken. One-time measurements like this do not have much meaning. Questions arise such as uneven rainfall as the cause. Please make it clear that lines 133 to 138 are a footnote to Table 1. Same comment for other tables.

We appreciate the reviewer’s suggestion. We have supplemented the data analysis and results for bulk density (BD) in Table 1 and section 3.1 "Soil Properties", and we made it clear a footnote to Tables:

“The soil properties measured across different treatments showed ranges of 15.57 to 18.55 g kg-1 for total carbon (TC), 1.19 to 1.39 g kg-1 for total nitrogen (TN), and 0.30 to 0.39 g kg-1 for total phosphorus (TP). Bulk density (BD) values ranged from 0.89 to 0.94 g cm-3, indicating slight variations among the treatments. There were no significant differences in soil TC, TN, TP, and EC and BD values among the five treatments, which included no grazing, continuous grazing, and different seasonal grazing.”

Table 1 Presents the characteristics of soil physicochemical properties among the different grazing management practices

Soil properties	NG	CG	G57	G68	G79
TC (g kg-1)	16.03 ± 2.21a	17.23 ± 3.12 a	17.15 ± 3.07 a	15.57 ± 2.79 a	18.55 ±1.81 a
TN (g kg-1)	1.25 ± 0.19 a	1.19 ± 0.14 a	1.22 ± 0.22 a	1.30 ± 0.21 a	1.39 ± 0.11 a
TP (g kg-1)	0.34 ± 0.05 a	0.31 ± 0.03 a	0.39 ± 0.13 a	0.30 ± 0.03 a	0.33 ± 0.03 a
Water (%)	10.85 ± 1.15 a	10.78 ± 1.19 a	11.77 ± 2.25 ab	10.72 ± 1.30 a	14.03 ± 3.15b
EC (mS m-1)	12.32 ±0.53 a	12.87 ±1.07 a	13.18 ±0.68 a	13.30 ±1.71 a	13.18 ±0.68 a
pH BD (g cm-3)	8.70 ± 0.08 a 0.89 ± 0.003 a	8.67 ± 0.14 ab 0.92 ± 0.001 a	8.61 ± 0.14 abc 0.94 ± 0.001 a	8.57 ± 0.04bc 0.92 ± 0.001 a	8.53 ± 0.07c 0.91± 0.001 a

Note: The differences among different grazing management practices were analyzed by one-way analysis of variance, and the lowercase letters represent the significant differences (P<0.05). Ab-breviation: total soil carbon (TC), total soil nitrogen (TN), total phosphorus (TP), soil moisture content (Water), soil electrical conductivity (EC), bulk density (BD), no grazing (NG), continuous grazing from May to September (CG), grazing in May and July (G57), grazing in June and August (G68), and grazing in July and September (G79).

 

• Discussion Section 4.1: This section appears to be more of a literature review and could go in the introduction as background for your study.

Line 252: “This aligns with the findings of ???,”  It seems like something is missing here. I am not seeing any discussion of your data up to line 277, just more literature review.

We appreciate the reviewer’s suggestion, and we have revised the discussion section as per your suggestions. Additionally, we have included new references to support our arguments:

“4. Discussion

4.1. Changes in Soil Physics Caused by Livestock Trampling

Previous studies have shown that livestock trampling negatively affects soil, leading to soil compaction in the surface layer. This compaction restricted water infiltration and root growth and extends to deeper soil layers, resulting in a denser soil structure and increased bulk density, which further inhibits root growth[22]. Brito et al. (2018) characterized soil compaction using soil resistivity (RP) and found a significant increase in RP values due to grazing, leading to reduced soil aeration and permeability[23]. Frozzi et al. (2020) observed that livestock trampling rearranges soil particles, altering soil structure and potentially disrupting soil aggregation, which made the soil more vulnerable to erosion and water runoff [24].

Brito et al. (2018) also used the mean weight diameter (MWD) of soil aggregates to examine the impact of grazing on soil structure. They found that grazed soils had a higher MWD compared to soils from cultivated grasslands, although higher MWD values do not necessarily indicate an ideal soil structure[23]. The increased MWD in grazed soils could be due to soil compaction and greater resistance to fracturing. Conte et al. (2011) suggested that larger aggregates in grassland areas might result from animal trampling, which brings mineral particles closer together. MWD values are influenced by clay and total organic carbon (TOC) content, both of which play significant roles in the formation and stability of soil aggregates[25].

The structure of grazed soils was influenced by grazing management and climatic conditions[26]. High grazing intensity, especially during periods of elevated soil moisture like the rainy season from October to June, can cause increased structural damage to the soil. Concentrated animal weight in small areas, particularly hooves, exerts high pressure on the soil. Animal trampling could impose contact pressures of 350 to 400 kPa on the soil, and these pressures can increase when animals were in motion, as the entire weight was concentrated on a single claw, distributing the force over a smaller surface area[27].

4.2. The Impact of Seasonal Grazing on Soil Structure

Our findings confirmed previous reports that there were no significant differences in soil particle composition and pore characteristics between different grazing methods and non-grazed grassland soils under moderate grazing conditions[25]. This aligned with studies using GPS data to analyze livestock movement trajectories under continuous and seasonal grazing[26]. These studies established connections between grazing patterns and soil structure, indicating that grazing cattle's movement patterns were dependent on pasture area rather than shape, orientation, topography, or selective attention. Both continuous and seasonal grazing systems exhibited similar soil compaction, evidenced by higher bulk density and soil penetration resistance induced by grazing. Soares et al. (2021) demonstrated that soil cone penetration resistance (RP) in grazed areas ranged from 1.40 to 1.49 MPa, higher than in non-grazed areas, but not leading to soil compaction[22].

The impact of grazing on soil structure was influenced by factors including grazing intensity, animal movement patterns, and soil clay content, and others[27]. Seasonal grazing tended to exert lighter grazing pressure compared to year-round continuous grazing. Recent research suggested that shorter grazing periods followed by longer recovery periods can reduce soil compaction, allowing more time for natural soil recovery. Seasonal grazing might also positively impact vegetation growth and distribution, contributing to soil structure maintenance. Moderate seasonal grazing could promote the expansion of vegetation roots, improving soil stability and reducing erosion rates[28-29]. Additionally, seasonal grazing affected soil microbial communities, creating a more intricate soil microenvironment that supports greater microbial diversity and contributes to soil ecological balance.

4.3. Relationships Between Soil Structure and Soil Ecological Functions

Our findings demonstrated a significant correlation between soil carbon-nitrogen content and soil particle composition. Soares et al. (2021) observed a decrease in soil cone penetration resistance (RP) in grazed areas, attributed to higher levels of organic matter[22]. This increase in organic matter led to a decrease in soil bulk density and an increase in macroporosity. Some studies found a strong association between total organic carbon (TOC) and mean weighted diameter (MWD) of aggregates. Higher levels of TOC, microorganisms, and robust biological activity, including root systems, can lead to the formation of channels and biopores, consequently altering soil structure[30-31]. Abundant organic matter promoted soil structure development, facilitating a balanced distribution of particles (sand, silt, clay) and creating pores for water and air storage, providing favorable conditions for plant root growth. Organic matter also retained moisture, preventing it from acting as a lubricant between mineral particles, and enhances the cohesion between soil particles, establishing connections among them[32-33].

Soil permeability and compaction status were influenced by organic matter content, microbial activity, roots, exchangeable cations, and soil texture[35]. Recent studies suggested that soils with higher sand content are more prone to compaction, whereas soils with higher clay content tend to resist compaction due to clay's ability to adsorb organic anions, increasing colloid surface charge and enhancing the diffusion layer of associated with the surface[35-37].”

 

1. Brito, W.B.M., Campos, M.C.C., Mantovanelli, B.C., da Cunha, J.M., Franciscon, U., Soares, M.D.R. Spatial variability of soil physical properties in Archeological Dark Earths under different uses in southern Amazon. Soil Tillage Res 2018, 182, 103–111.
2. Frozzi, J.C., da Cunha, J.M., Campos, M.C.C., Bergamin, A.C., Brito, W.B.M., Fraciscon, U., da Silva, D.M.P., de Lima, A.F.L., de Brito Filho, E.G. Physical attributes and organic carbon in soils under natural and anthropogenic environments in the South Amazon region. Earth Sci. 2020, 79, 251.
3. Conte, O., Flores, J.P.C., Cassol, L.C., Anghinoni, I., Carvalho, P.C. de F., Levien, R., Wesp, C. de L. Evoluç˜ao de atributos físicos de solo em sistema de integraç˜ao lavoura-pecu´aria. Pesqui. Bras 2011, 46, 1301–1309.
4. Drewry, J.J., Cameron, K.C., Buchan, G.D. Pasture yield and soil physical propertyresponses to soil compaction from treading and grazing - a review. Austr. Soil Res. 2008, 46, 237–256.
5. Nie, Z.N., Ward, G.N., Michael, A.T., 2001. Impact of pugging by dairy cows on pastures and indicators of pugging damage to pasture soil in south-western Victoria. Aust. Agric. Res. 2001, 52, 37–43.

 

 

• Conclusion: It would be helpful in the conclusion to provide the reader with a specific recommendation for grazing based on results and the implications to the land manager for that recommendation.

We appreciate the reviewer’s suggestion. We have revised the conclusion to include specific recommendations for grazing management based on our results and the implications for land managers. The updated conclusion now emphasizes the benefits of seasonal grazing practices over continuous grazing, highlighting how seasonal grazing helps maintain soil structure and minimizes adverse changes in pore characteristics, thereby preserving soil health and function. These insights are aimed at supporting sustainable land management practices that balance agricultural productivity with environmental conservation:

“5. Conclusions

The investigation into soil characteristics under different grazing management showed no significant differences in particle distribution and pore structure. The prevalence of specific particle sizes and pore characteristics in both grazed and ungrazed plots indicates the complex relationship between grazing practices and soil composition. Continuous grazing appears to have a more noticeable impact on soil structure compared to seasonal grazing, as it significantly increases the pore area ratio and maximum pore diameter in the soil. In the case of seasonal grazing plots, particularly G57 and G79, there are no significant differences in soil particle structure or soil pore structure compared to ungrazed soil. Correlation analyses between soil physicochemical properties and particle size, as well as pore structure, reveal interesting connections that emphasize the influence of grazing on soil dynamics. These findings provide valuable insights for sustainable land management practices, highlighting the intricate interactions between grazing, soil properties, and ecological resilience. Specifically, our results suggest implementing seasonal grazing practices over continuous grazing, as seasonal grazing maintains soil structure and minimizes adverse changes in pore characteristics, thereby preserving soil health and function. Land managers should consider these practices to promote sustainable grazing that supports both agricultural productivity and environmental conservation.”

 

• General: It will be useful to provide a better description of the study plan and the physical layout in the field. It is not possible to evaluate the randomness of the layout with the current level of information. If the treatments were not established in a completely random, randomized block, etc. design, then one needs to be concerned about the validity of the statistics used. Some discussion around that would them be useful; particularly when it comes to particle size analysis. One does not expect to see any change in particle size unless there is movement of clay particles out of the soil zone due to treatment. Meaning that any differences may reflect pre-treatment differences already in place. Some discussion to discount this possibility may be useful.

In methods in general could be more detailed as mentioned in the comments.

We appreciate the reviewer’s suggestion. We have revised the methods section to provide more detailed information about the study sites and sampling scheme. Additionally, we expanded the discussion section to include a more thorough analysis of our results, integrating relevant literature and adding new references. Lastly, we updated the conclusion to include specific recommendations for grazing management based on our results and their implications for land managers. Please refer to our previous modifications and responses for detailed changes.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I appreciate the extensive revision by the authors. They met all of my concerns.