Variability of Soil Water Heat and Energy Transfer Under Different Cover Conditions in a Seasonally Frozen Soil Area
Round 1
Reviewer 1 Report
This is an interesting and very well written manuscript. The science and methodology is well presented and referenced.
I have a few minor observations, as follows:
- Line 100 - 'soil hydrothermal environmental monitoring system' - more details required, sensor types and manufacturer details,
- Line 102 - 'neutron meter' - as above,
- Line 106 - 'frozen soil apparatus' - as above,
- Line 109 - should this list also include total and net radiation? These measurements are referenced in section 3.3
- Line 109 - should there be an equation for saturated vapour pressure?
- Line 134 - KJ - should this be kJ?
- Line 287 - '[28]' should this be '[28].' ?
One observation is that I found the graphs in Figure 1 & 2 a little too small to quickly see the depth effects.
This is probably beyond the defined scope of the paper (lines 32 & 33) but I kept wondering how these results might impact on larger issues of, for example: agricultural land use, soil erosion and water management etc. Perhaps some of the benefits are described in the references 1-20 and could be included in the Introduction?
Author Response
Point 1: This is an interesting and very well written manuscript. The science and methodology is well presented and referenced. I have a few minor observations, as follows:
Line 100 - 'soil hydrothermal environmental monitoring system' - more details required, sensor types and manufacturer details
Response 1: Thank you for putting forward very good advices about our manuscript. We have supplemented the basic information of soil hydrothermal environmental monitoring system, including sensor types and manufacturer, please see lines 102-104 in the revised manuscript and the specific modifications are as follows:
The test site was divided into 4 plots, and a soil hydrothermal environment monitoring system (ET100, Dongfangshengtai, China) was installed in each plot to monitor the soil temperature and liquid water content at soil depths of 10, 20, 30, ..., 100 cm at a recording interval of 1 d/time.
Point 2: Line 102 - 'neutron meter' - as above
Response 2: Thank you for putting forward very good advices about our manuscript. We have supplemented the basic information of neutron meter, including sensor types and manufacturer, please see lines 104-106 in the revised manuscript and the specific modifications are as follows:
A neutron meter (CNC503DR, CPN company, USA) was used to measure the total water content of the soil.
Point 3: Line 106 - 'frozen soil apparatus' - as above
Response 3: Thank you for putting forward very good advices about our manuscript. We have supplemented the basic information of frozen soil apparatus, including sensor types and manufacturer, please see lines 108-110 in the revised manuscript and the specific modifications are as follows:
a frozen soil apparatus (LQX-DT, Jinzhouyangguang, China) was buried in each plot to record the freezing depth of the soil
Point 4: Line 109 - should this list also include total and net radiation? These measurements are referenced in section 3.3
Response 4: Thank you for putting forward very good advices about our manuscript. Yes, we have listed the total and net radiation in section 2.2, please see lines 111-113 in the revised manuscript and the specific modifications are as follows:
such as the ambient temperature, ambient humidity, evaporation, total radiation, net radiation and saturated vapour pressure in the atmospheric environment.
Point 5: Line 109 - should there be an equation for saturated vapour pressure?
Response 5: Thank you for putting forward very good advices about our manuscript. We have supplemented the equation for saturated vapour pressure and relevant reference in section 2.2, please see lines 113-114 in the revised manuscript and the specific modifications are as follows:
and the equation for saturated vapor pressure is shown below [21]:
(1)
Where ew is saturated vapour pressure, hpa; t is the thermodynamic temperature of air, ℃.
[21] WMO. Guide to Meteorological Instruments and Methods of Observation, 7th ed.; WHO: Geneva, Switzerland, 2008; pp. 29-30.
Point 6: Line 134 - KJ - should this be kJ?
Response 6: Thank you for your good advices. We have examined the full text carefully and have replaced all the unit KJ with the unit kJ.
Point 7: Line 287 - '[28]' should this be '[28].' ?
Response 7: Thank you for your good advices. Because of adding references, the reference number [28] has been changed to the number [33], and '[33]' should be '[33].'. Please see lines 290 in the revised manuscript.
Point 8: One observation is that I found the graphs in Figure 1 & 2 a little too small to quickly see the depth effects.
Response 8: Thank you for your good advices. We have already redrawn the Figure 1 and Figure2. In order to make the figures clearer, we have also divided Figure 1 into three figures (Figure 1, Figure 2 and Figure 3) and adjusted the order of the figures correspondingly. Please see the revised manuscript.
Point 9: This is probably beyond the defined scope of the paper (lines 32 & 33) but I kept wondering how these results might impact on larger issues of, for example: agricultural land use, soil erosion and water management etc. Perhaps some of the benefits are described in the references 1-20 and could be included in the Introduction?
Response 9: Thank you for your good advices. We have analyzed the influence of water-heat variability and energy transfer on agricultural water resource management, moisture and so on and have revised the first paragraph in Section 1. Please see lines 41-53 in the revised manuscript and the specific modifications are as follows:
It is generally known that seasonally frozen soil, as part of the Soil-Plant-Atmosphere Continuum system, frequently alternates between freezing and thawing and is the main location of energy-water-gas exchange between the atmosphere and land surfaces in cold regions [1-3]. The freeze-thaw process of soil, changes the effects of sensible heat and latent heat between the soil and the atmosphere and affects the hydraulic properties of the soil itself, which directly affects the process of soil water migration [4, 5]. As a result of thawing-freezing, water in the soil undergoes a phase change and redistribution; under the influence of the water potential gradient, water migrates to the frozen front, leading to an increase in the total water content in the frozen zone [6-8]. Moreover, in the period of soil melting, the thawed water infiltration increases the amount of water in shallow soil layers and reduces the transfer and dissipation of heat in the soil, which has a significant effect on mitigating water resources shortages and spring drought and correspondingly benefiting for crop growth at seedling stage [9, 10]. Therefore, the energy transfer between soil and environment affects the interaction effect of water and heat in soil [11-13].
Author Response File: 
Author Response.docx
Reviewer 2 Report
General Comments
This paper is written well and adds good information to existing literature.
The title sounds a little off. What do you mean by variation characteristics? May be “Variability of soil water …………….” might be better
All figure captions and table titles need to be more informative. A table or figure needs to stand by itself.
Abstract
Line 15: Include a broad opening sentence/or two before jumping to the methodology.
Line 27: Add the value for BL, so that the comparison with other treatment makes sense.
Introduction
Line 74-80: The objective paragraph is too vague. Develop specific objectives to get more focus.
Materials and Methods
Line 111: What is this unit? Not clear.
I like how you presented the Theory clearly. Nice job.
Line 161: Need references to software and tests.
Results and Discussion
Line 270: Table 4 caption doesn’t stand by itself. Make the title more informative.
Conclusion
The conclusion contains redundant information from Discussion. Your Discussion is short so you might want to consider merging these two sections.
Also, provide broad applicability this research and future research recommendations.
Follow your specific objectives to create a clear conclusion.
Author Response
Point 1: This paper is written well and adds good information to existing literature.
The title sounds a little off. What do you mean by variation characteristics? May be “Variability of soil water …………….” might be better
Response 1: Thank you for your good advices. We have changed the title of our manuscript as " Variability of soil water heat and energy transfer under different cover conditions in a seasonally frozen soil area". Please see our revised manuscript.
Point 2: All figure captions and table titles need to be more informative. A table or figure needs to stand by itself.
Response 2: Thank you for your good advices. We have revised all figure captions and table titles, please see lines 99-100, 199-201, 202-204, 205-207, 238-240, 241-242, 257-258, 268-269 in the revised manuscript and the specific modifications are as follows:
Table 1. Soil physical characteristic parameters of different soil depths under four treatment conditions
Figure 1. Variability of soil temperature of different soil depths under four treatment conditions. (a) represents the BL treatment; (b) represents the CS treatment; (c) represents the JS treatment; (d) represents the CJS treatment.
Figure 2. Variability of soil liquid water content of different soil depths under four treatment conditions. (a) represents the BL treatment; (b) represents the CS treatment; (c) represents the JS treatment; (d) represents the CJS treatment.
Figure 3. Variability of soil total water content of different soil depths under four treatment conditions. (a) represents the BL treatment; (b) represents the CS treatment; (c) represents the JS treatment; (d) represents the CJS treatment.
Figure 4. Effects of the soil energy budget under four treatment conditions during the freezing-thawing period. (a) represents the BL treatment; (b) represents the CS treatment; (c) represents the JS treatment; (d) represents the CJS treatment.
Table 2. Spectral entropy (SE) of the soil energy budget of different soil depths under four treatment conditions during the freezing-thawing period.
Table 3. Response function of soil energy transfer and meteorological factors in 10 cm soil layer under four treatment conditions during the freezing-thawing period.
Table 4. Test result of response function of soil energy transfer and meteorological factors of different soil depths under four treatment conditions during the freezing-thawing period.
Point 3: Line 15: Include a broad opening sentence/or two before jumping to the methodology.
Response 3: Thank you for your good advices. We have revised the abstract and added a broad opening sentence at the beginning of abstract, please see lines 17-19 in the revised manuscript and the specific modifications are as follows:
In seasonally frozen soil area, there is frequent energy exchange between soil and environment, which changes the hydrological cycle process, and then has a certain impact on the prediction and management of agricultural soil moisture.
Point 4: Line 27: Add the value for BL, so that the comparison with other treatment makes sense.
Response 4: Thank you for your good advices. We have added the value for BL in the abstract. please see lines 29-32 in the revised manuscript and the specific modifications are as follows:
At a soil depth of 10 cm, the spectral entropy of a time series of the soil net energy was 0.837 under BL treatment, and the CS, JS, and CJS treatments decreased by 0.015, 0.059, and 0.045, respectively, compared to the BL treatment.
Point 5: Line 74-80: The objective paragraph is too vague. Develop specific objectives to get more focus.
Response 5: Thank you for your good advices. We have revised the study objectives in Section 1. Please see lines 76-81 in the revised manuscript and the specific modifications are as follows:
In this study, biochar and straw as soil conditioner, based on the analysis of soil water and heat status, the budget of soil energy in different regulation modes was analyzed. Furthermore, the soil energy transfer function was constructed by combining sensitive meteorological factors, and the mechanism of soil energy transfer and conversion was elucidated under freezing and thawing conditions. This study aims to provide theoretical and technical support for the efficient use of hydrothermal resources in frozen-thawed soils.
Point 6: What is this unit? Not clear.
Response 6: Thank you for your good advices. We have revised and perfected the unit. Please see lines 116-118 in the revised manuscript and the specific modifications are as follows:
Plant straw and biochar were chosen as regulation materials. In each plot, treatments, which included biochar cover (CS, the amount of addition was 20 t/hm2), straw cover (JS, the amount of addition was 12 t/hm2), a combined biochar and straw cover (CJS, the amount of biochar and straw addition was 10 t/hm2 and 6 t/hm2, respectively), and bare land (BL) as a natural control, were established.
Point 7: I like how you presented the Theory clearly. Nice job.
Response 7: Thank you very much for your recognition and high praise for our work.
Point 8: Need references to software and tests.
Response 8: Thank you for your good advices. We have added the references to software and tests. Please see lines 170 and line 417-422 in the revised manuscript and the specific modifications are as follows:
26.Miescke K. J.; Liese M. Statistical decision theory-estimation, testing, and selection; Springer-Verlag: New York, USA, 2008; pp.198-232.
27.Kiusalaas J. Numerical Methods in Engineering With MATLAB; Cambridge University Press: New York, USA, 2005; pp.26-27
28.Systat Software, Inc. Using SigmaStat Statistics in SigmaPlot; Systat Software, Inc.: Chicago, USA, 2012; 416-430.
Point 9: Thank you for your good advices. We have revised the Table 4 caption. Please see lines 268-269 in the revised manuscript and the specific modifications are as follows:
Table 4. Test result of response function of soil energy transfer and meteorological factors of different soil depths under four treatment conditions during the freezing-thawing period.
Response 9: Thank you for your good advices. We have analyzed the influence of water-heat variability and energy transfer on agricultural water resource management, moisture and so on and have revised the first paragraph in Section 1. Please see lines 41-53 in the revised manuscript and the specific modifications are as follows:
It is generally known that seasonally frozen soil, as part of the Soil-Plant-Atmosphere Continuum system, frequently alternates between freezing and thawing and is the main location of energy-water-gas exchange between the atmosphere and land surfaces in cold regions [1-3]. The freeze-thaw process of soil, changes the effects of sensible heat and latent heat between the soil and the atmosphere and affects the hydraulic properties of the soil itself, which directly affects the process of soil water migration [4, 5]. As a result of thawing-freezing, water in the soil undergoes a phase change and redistribution; under the influence of the water potential gradient, water migrates to the frozen front, leading to an increase in the total water content in the frozen zone [6-8]. Moreover, in the period of soil melting, the thawed water infiltration increases the amount of water in shallow soil layers and reduces the transfer and dissipation of heat in the soil, which has a significant effect on mitigating water resources shortages and spring drought and correspondingly benefiting for crop growth at seedling stage [9, 10]. Therefore, the energy transfer between soil and environment affects the interaction effect of water and heat in soil [11-13].
Point 10: The conclusion contains redundant information from Discussion. Your Discussion is short so you might want to consider merging these two sections. Also, provide broad applicability this research and future research recommendations. Follow your specific objectives to create a clear conclusion.
Response 10: Thank you for your professional comments. We have revised the discussion and conclusion. Meanwhile, we have divided the discussion into two parts and provided broad applicability this research and future research recommendations in the conclusion. Please see lines 275-345 in the revised manuscript and the specific modifications are as follows:
- Discussion
4.1. Effect of biochar and straw on soil water and heat variation
During the soil freezing process, energy in the soil is gradually transferred to the atmospheric environment, and the soil temperature is lowered accordingly; as a result, the liquid water in the soil is transformed into solid ice, and a frozen front is formed at the ground surface. Driven by the temperature gradient, the unfrozen water gradually migrates to the frozen front and accumulates at the ground surface [31]. Therefore, during the freezing period, the liquid water content in the frozen soil layer decreased significantly, while the total water content showed an upward trend, and the hydrological environment in the frozen soil region fluctuated to a certain extent. Due to the insulation and low thermal conductivity of plant straw, straw inhibits the decrease in soil temperature and reduces the freezing rate of the soil to a certain extent [32]. Therefore, with the JS treatment, the liquid water content of the soil and the total water content at the soil surface are high. In this study, the comparative analysis showed that during the freezing period, the average total water content at a depth of 20 cm under the JS treatment was increased by 2.31%, 1.85%, and 0.56% compared to that under the BL, CS, and CJS treatments, respectively, which is consistent with the research conclusions of San et al. [33]. Simultaneously, the application of biochar reduces the thermal conductivity and thermal diffusivity of the soil, hinders the heat loss of the soil, weakens the phase transformation ability of the liquid water in the soil, and most of the liquid water continuously accumulates to the surface layer [34]. Under the CS treatment, the total water content of soil at 20cm soil layer was also increased compared with BL treatment, and the water storage capacity of surface soil was increased. During the thawing period, as the ambient temperature and atmospheric radiation increase, the soil draws a large quantity of energy from the environment and begins to melt, and the solid ice is converted into liquid water. Meanwhile, the infiltration of snowmelt water can also replenish the water content in the soil. When biochar, which has a strong water-holding capacity, is coupled with straw, which increases the temperature and preserves the soil moisture, the synergistic effect of this combination can effectively increase the soil water content [35]. As Wu et al. [36] found, biochar can effectively improve soil and water loss on sloping farmland in black soil areas, and the soil saturated water content, field capacity and soil water storage capacity were enhanced with the increase in biochar application.
4.2. Effects of biochar and straw on soil energy budget
During the freezing period, as the ambient temperature decreases, the soil heat flux increases, and energy is gradually dissipated. At the same time, with the increase of ambient temperature, the radiation effect of the atmosphere effectively replenishes the energy in the soil, which effectively stimulates the soil energy budget cycle. In the process of energy transfer in the soil, there is a lot of loss phenomena, which leads to the weakening of energy budget effect in deep soil. During the freezing period, with the decrease of ambient temperature, soil and atmosphere exchange energy frequently, however, biochar has low thermal conductivity and low specific heat capacity, which leads to a decrease in the fluctuation of the soil energy budget, and weakens the response relationship between soil energy and environmental factors. As an inadequate conductor of heat, straw hinders the energy exchange between the soil and the external environment and thus minimizes the fluctuation of the net soil energy time series [37]. As Zhao et al. [38] found, in the northern cold region, the application of biochar reduces the soil bulk density, and the thermal conductivity of the soil is weakened, resulting in the reduction of the response relationship between the soil and the environment. Singh et al. [39] Also confirmed through field experiments that straw mulched farmland weakened the driving effect of environmental factors on soil water and heat, reduced the evaporation rate of soil water, and weakened the energy transfer effect. During the thawing period, as the ambient temperature increases, atmospheric radiation replenishes the energy in the soil, accelerating the cycling process of the soil energy budget [40]. A large quantity of energy is lost during the soil transfer process, resulting in a weakened energy budget in deep soils [1]. Biochar promotes the accumulation of soil energy, and its heat absorption is far greater than its heat release. Therefore, in this study, under the conditions of the CS and CJS treatments, the frequency of energy exchange between the soil and the environment was increased, leading to an increased fluctuation. In contrast, the straw covering hindered energy transfer, and the fluctuation of the soil energy decreased.
- Conclusion
Biochar and straw effectively regulate soil hydrothermal conditions. During the freezing period, straw mulching effectively promoted the accumulation of water content in the frozen area, and the decrease in soil temperature weakened. During the thawing period, the combined regulation of biochar and straw most effectively inhibited the migration and diffusion of soil moisture and improved the water-holding capacity of topsoil.
During the freezing period, the soil energy showed a deficit state, and the straw most effectively suppressed the energy loss and reduced the soil net energy fluctuation. During the thawing period, the endothermic property of biochar promoted the absorption of soil energy to atmosphere, enhanced the energy exchange effect between soil and environment, and increased the spectral entropy of soil net energy time series. However, straw hinders the absorption of environmental energy by soil, and then reduces the variation of soil energy budget.
This study revealed the effect of biochar and straw mulch on soil energy conversion, and provided technical support for soil water and heat regulation in seasonal frozen soil area. At present, this study only calculates the energy change process from the perspective of soil water phase change, while the quantitative description of energy transfer effect from the perspective of energy conservation needs further exploration.
Author Response File: Author Response.docx
