A Comparative Study of Rotation Patterns on Soil Organic Carbon in China’s Arid and Semi-Arid Regions

Round 1

Reviewer 1 Report

Very weak hypothesis. Instead of stating the obvious differences in SOC between crop rotation types, the authors should speculate the mechanistic reasons why or why not crop rotations would result in differences in SOC.

The Abstract only summarized the data of SOC differences between cropping systems in the 0-10 cm soil depths, what about the other layers or the total profile?

The methodology is inadequate and unclear: 1) how many years did the site of the study perform the 4 rotation patterns? 2) was the experiment planned as a phase crop rotation, i.e. the 3 phases in each rotation occurred in each year? The picture does not show anything about the experimental setup. 3) how the field cultivation was performed?, e.g. tillage, planting, fertilization, weeding, cultivation, dates of planting and harvest, etc. 4) soil properties, e.g. soil texture, particle size analysis, SOM, etc. 5) soil sampler ring. No need to include the ring volume as different increments were used. Instead the ring diameter should be given. 6) How many replications of the experiment? Did the investigation repeat over time?

Results

3.1 To which depth and at what growth stage, the SWC (e.g. 8.43%) and SBD (1.19 Mg m^-3) are reported?

3.2 similarly, to which depth the SOC and pH are reported?

3.3. These are not unexpected results.

Discussion

Several statements had no solid data to support.

Table 3 with such small R² values, was any of the regressions statistically significant and scientifically sound?

Have you collected any yield results to support the price estimates in Table 4?

Author Response

Dear Editors and Reviewers:

Thank you for your valuable comments on our manuscript titled ‘A comparative study of rotation patterns on soil organic carbon in China's arid and semi-arid regions’ (agronomy-646148). We have addressed all the comments that were proposed by the two reviewers. In addition, other edits were also made in order to be more clear, and more accurate.

In this letter, we provide a point-by-point explanation of all revisions. These are noted in red.

Give the extensive revisions that we have performed to satisfy the two reviewers, the authors now believe the paper has improved quite a lot in its quality and hope it can be accepted in this journal.

Thank you for your continued support in the review process.

Sincerely,

Wei and co-authors

Response to Reviewer 1

Comment

Very weak hypothesis. Instead of stating the obvious differences in SOC between crop rotation types, the authors should speculate the mechanistic reasons why or why not crop rotations would result in differences in SOC.

Response

Thanks for your suggestion. In order to speculate the mechanistic reasons why crop rotations may result in differences in SOC, we added this sentence (including the necessary references): The researchers hypothesize that different crop rotation patterns may have different effects on SOC sequestration, as previous studies found that SWC, SBD, and soil pH are often influenced by the crop rotation patterns, and variation in these soil properties can result in difference in SOC [26-29] (P2, L68-71)

Zhou, G., Liu, S., Li, Z., Zhang, D., Tang, X., Zhou, C. Old-growth forests can accumulate carbon in soils. Science 2006, 314, 1417-1417. Wang W.J., Qiu, L., Zu Y.G., Su, D.X., An, J., Wang, H.Y., Zheng, G.Y., Sun, W., Chen, X.Q. Changes in soil organic carbon, nitrogen, ph and bulk density with the development of larch (larix gmelinii) plantations in China. global change boil. 2011, 17, 2657-2676. Haden, V., Adam C., Dornbush, Mathew E. Patterns of root decomposition in response to soil moisture best explain high soil organic carbon heterogeneity within a mesic, restored prairie. Ecosyst. Environ. 2014, 185, 188-196. Tavakkoli, E., Rengasamy, P., Smith, E., Mcdonald, G. K. The effect of cation-anion interactions on soil ph and solubility of organic carbon. J. soil sci. 2015, 66, 1054-1062.

Comment

The Abstract only summarized the data of SOC differences between cropping systems in the 0-10 cm soil depths, what about the other layers or the total profile?

Response

Thanks for your suggestion. In fact, we summarized the data of SOC differences between cropping systems in the 0-100 cm instead of 0-10 cm soil depth. In addition, in order to avoid the length of Abstract is too long, we did not list the data of SOC differences between cropping systems at other soil layers, including 0-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, and 80-100 cm.

Comment

The methodology is inadequate and unclear: 1) how many years did the site of the study perform the 4 rotation patterns? 2) was the experiment planned as a phase crop rotation, i.e. the 3 phases in each rotation occurred in each year? The picture does not show anything about the experimental setup. 3) how the field cultivation was performed?, e.g. tillage, planting, fertilization, weeding, cultivation, dates of planting and harvest, etc. 4) soil properties, e.g. soil texture, particle size analysis, SOM, etc. 5) soil sampler ring. No need to include the ring volume as different increments were used. Instead the ring diameter should be given. 6) How many replications of the experiment?

Response

Thanks for your these constructive suggestions. As question 1, we added the following information: About 20 years ago, the mulching technique was used in dry farming industry, and maize (Zea mays L.) was introduced in this area. After that, four primary inter-annually crop rotations patterns co-occurred, including the two types of Lentil-Wheat -Maize and Wheat-Maize-Potato, and the two types of Wheat-Potato-Lentil and Wheat-Flax-Pea that have been existed since the rural lands were contracted to households in 1978 as each household can manage its lands. (P2,L85-90).

As question 2, we added the following information: For a long time, wheat (Triticum æstivum L.), Flax (Linum usitatissimum L.), Potato (Solanum tuberosum L.), Pea (Pisum sativum), and Lentil (Lens culinaris) are the major regional crops, and each crop is planted and harvested once a year due to its limited ecological amplitude and scare of water resources (P2, L82-85). In addition, as you suggested, we deleted this picture.

As question 3, we added the following information: The primary cultivation way for all crops in this area was similar. Animals were a key source of draft power 15 years ago, but later farm machineries were universally used in agriculture production. The wheat is planted in February and harvested in July, while maize and potato are planted in May, and harvested in October; flax and legumes such as peas and lentil, are often planted in March and harvested in August. In the study area, there are no irrigation in all growth stage of crops, and crop straw is fed to domestic livestock or used as fuel. The most of manure is returned to the field as primary fertilizer, and a small amount of chemical fertilizer is used for crops. Weeds in field are mainly removed by farms and herbicides are seldomly used (P2-3, L91-158).

As question 4, we added the following information: Soils in this area mainly are of a loessial type, field capacity between 13–25%, and permanent wilting point between 3-8%. Soils in this area mainly are of a loessial type, with field capacity being between 13–25%, and permanent wilting point being between 3-8%. In terms of soil composition, silt, clay and sand account for above 60%, 5% and 30% of the soil particles, respectively [31] (P2, L78-81). As regard to SOM, we can assess it based on SOC by × 1.7.

As question 5, we provided the diameter of the ring with its value being 5 cm (P3, L188).

As question 5, we added the following information: There were 12 plots for each crop rotation. In each plot, the soil profile was excavated to a depth of 1.0 m at three 1 m × 1 m quadrats, spaced along the diagonal (one at each end and one at the mid-point), and thus a total of 216 soil samples were collected for each crop rotation. (P3, L170-172).

Comment

3.1 To which depth and at what growth stage, the SWC (e.g. 8.43%) and SBD (1.19 Mg m^-3) are reported?

Response

Sorry for our previous carelessness. We added the depth of soil for reported SWC and SBD at the beginning of the first paragraph of section 3.1 as following: At the 1.0 m soil depth profile (P4,L322, 333, 341,356).

The growth stage was added in section 2.2 as following: Overall, three sites (Fig. 1) were selected to explore the effects of crop rotations on SOC, SWC, SBD and soil pH at the later growth or harvest state of crops, during the period of the late of July to September 2017 in Huining County. (P3, L162-164).

Comment

3.2 similarly, to which depth the SOC and pH are reported?

Response

Thanks again. We did the same as above-mentioned. the depth of soil for reported SWC and SBD was at the 1.0 m soil depth profile (P4,L341,356).

Comment

3.3. These are not unexpected results

Response

Surely, most of these results are expected, but for some they are unexpected. For example, Cao et al. (2018) and Qin et al. (2016) reported that the SOC has no correlation with soil pH, Gebrehiwot et al. (2018) reported that soil pH has no significant impact on SOC, and soil bulk density is positively correlated with SOC. In this case, we think that these results are necessary to present.

Cao, J.J., Wang, X.Y., Li, M.T., Yang, S.R., Xu, X.Y., Gong, Y.F. Effects of grassland management on soil nutrients and their spatial distribution on the Qinghai-Tibetan Plateau, China. Chinese Journal of Applied Ecology, 2018, 29 6. (in Chinese)

Qin, Y.Y., Feng, Q., Holden, N.M., Cao, JJ . Variation in soil organic carbon by slope aspect in the middle of the Qilian mountains in the upper Heihe river basin, china. Catena, 2016, 147, 308-314.

Gebrehiwot, K., Desalegn, T., Woldu, Z., Demissew, S., Teferi, E. Soil organic carbon stock in abune yosef afroalpine and sub-afroalpine vegetation, northern ethiopia. Ecological Processes, 2018, 7, 6.

Comment

Several statements had no solid data to support.

Response

Thanks for your comments. Surely, we have no data about some statements, such as legumes tending to increase SWC, inclusion of legumes into a crop rotation having positive effects on SOC, and root distribution influencing the variations of SOC, however, we provided these evidence from other literatures (Zhao et al., 2014; Hou, et al., 2011; De Deyn et al., 2011; Gan et al., 2009; An et al., 2018). As the references of the former two already existed in previous manuscript, we added the references of the latter one as following:

Also, Haden et al. (2014) has reported that roots are the main contributor to SOC formation. Based on Hou (2011) and Liu et al. (2009), the roots of wheat and maize are mainly concentrated in the 0-0.2 m, while for potato they are mainly located in 0-0.1 m (An et al., 2018).(P7, L479-482).

Zhao, J.; Wang, X.; Wang, X.; Fu, S. Legume-soil interactions: legume addition enhances the complexity of the soil food web. Plant Soil 2014, 385, 273-286.

De Deyn, G.B.; Shiel, R.S.; Ostle, N.J.; Mcnamara, N.P.; Oakley, S.; Young, I.; Freeman, C.; Fenner, N.; Quirk, H.; Bardgett, R.D. Additional carbon sequestration benefits of grassland diversity restoration. J. Appl. Ecol. 2011, 48, 600-608

Hou, H.T. Effects of fertilization application rate on crop cultivation and soil organic carbon. Nanjing Agriculture University, 2011. (in Chinese)

Gan, Y.T., Campbell, C.A., Janzen, H.H., Lemke, R., Liu, L.P., Basnyat, P. Root mass for oilseed and pulse crops: growth and distribution in the soil profile. Canadian Journal of Plant Science, 2009, 89(5), 883-893.

An, T.X., Yang, Y.M., Zhou, F., Fan, Z.W., Chen, M.L., Lu, J., Wu B.Z. Effect of Maize and Potato Intercropping on Their Root Growth and Distribution. Journal of Yunnan Agricultural University (Natural Science), 2018 151, 2, 195-202. (in Chinese)

Haden, V., Adam C., Dornbush, Mathew E. Patterns of root decomposition in response to soil moisture best explain high soil organic carbon heterogeneity within a mesic, restored prairie. Agr. Ecosyst. Environ. 2014, 185, 188-196.

Liu, J.M.,  An, S.Q., Liao, R.W., Ren S.X.,  Liang H. Temporal variation and spatial distribution of the root system of corn in a soil profile. Chinese Journal Of Eco-Agriculture. 2009, 3, 117-121.

Comment

Table 3 with such small R² values, was any of the regressions statistically significant and scientifically sound?

Response

Yes, any of the regressions statistically is significant and scientifically sound. This problem we also encountered before, and asked a statistician to do various analysis, but the results were the same (you can see Cao et al., 2018).

Cao, J. , Xu, X. , Deo, R. C. , Holden, N. M. , & Liu, M.  Multi-household grazing management pattern maintains better soil fertility. Agronomy for Sustainable Development, 2018,38, 6.

Comment

Have you collected any yield results to support the price estimates in Table 4?

Response

We confirmed that the yield may be variable but the price is relative stable because stabilize food price is one of the important polices of Chinese government.

Reviewer 2 Report

This article reports the soil organic carbon with respect to different crop rotations in China. The manuscript is well written but data collected is not sufficient enough to conclude the findings. Measurements of Soil organic carbon, soil water content, bulk density and pH are not enough to predict C sequestration potential of 4 crop rotation patterns. Baseline data and more timepoints are required. This minimum data set is inconclusive.

Figure 1 needs a better resolution.

Experimental design requires detailed information such as exact dates of soil sampling for every single crop rotation pattern and the total number of soil samples taken from each single rotation pattern. Were soil samples collected at one-time point or multiple times from each crop rotation pattern?

Data analysis section does not describe anything about regression analysis.

The discussion is very vague. For explanation, all the results were indirectly linked to rooting depth however rooting depth data was neither collected in this study nor provided from the literature review.

Author Response

Dear Editors and Reviewers:

Thank you for your valuable comments on our manuscript titled ‘A comparative study of rotation patterns on soil organic carbon in China's arid and semi-arid regions’ (agronomy-646148). We have addressed all the comments that were proposed by the two reviewers. In addition, other edits were also made in order to be more clear, and more accurate.

In this letter, we provide a point-by-point explanation of all revisions. These are noted in red.

Give the extensive revisions that we have performed to satisfy the two reviewers, the authors now believe the paper has improved quite a lot in its quality and hope it can be accepted in this journal.

Thank you for your continued support in the review process.

Sincerely,

Wei and co-authors

Response to Reviewer 2

Comment

This article reports the soil organic carbon with respect to different crop rotations in China. The manuscript is well written but data collected is not sufficient enough to conclude the findings. Measurements of soil organic carbon, soil water content, bulk density and pH are not enough to predict C sequestration potential of 4 crop rotation patterns. Baseline data and more time points are required. This minimum data set is inconclusive.

Response

Thanks for your comments. Surely there are few indicators to predict C sequestration in the present study, and we will strengthen this work in future However, in other studies, this minimum data were also used for predict C sequestration potential. For example, Zimmermann et al. (2012) has reported that soil properties (pH, soil bulk density) have an important effect on C sequestration, Qin et al. (2016) has reported soil bulk density could explain 69.0% of the variation in SOC, and Xie et al. (2007) has reported soil bulk density is strong correlated with C sequestration. In addition, we also discussed other parameters that may impact on C sequestration. For example, straw and roots were considered as following although some data comes from others; In the study area, there are no irrigation in all growth stage of crops, and crop straw is fed to domestic livestock or used as fuel (P3, L169-170); Also, Haden et al. (2014) has reported that roots are the main contributor to SOC formation. Based on Hou (2011) and Liu et al. (2009), the roots of wheat and maize are mainly concentrated in the 0-0.2 m, while for potato they are mainly located in 0-0.1 m (An et al., 2018). (P7, L 479-482).

Furthermore, we added this minimum data as our study weakness in the end of the conclusion section as following:

And other factors that influence SOC, such as roots, microbe, and crop water requirement, which we did not consider in the current study, also should be taken into consideration when do these research in future (P9, L 613-615).

Zimmermann, J., Dauber, J., Jones, M.B. Soil carbon sequestration during the establishment phase of miscanthus×giganteus: a regional-scale study on commercial farms using 13c natural abundance. Global Change Biology Bioenergy, 2012, 4(4), 453-461.

Qin, Y.Y., Feng, Q, Holden, N.M., Cao, JJ . Variation in soil organic carbon by slope aspect in the middle of the Qilian mountains in the upper Heihe river basin, China. Catena, 2016, 147, 308-314.

Franzluebbers, A. J., Hons, F.M. , Zuberer, D.A. Tillage and crop effects on seasonal dynamics of soil co₂ evolution, water content, temperature, and bulk density. Applied Soil Ecology, 1995, 2(2), 95-109.

Haden, V., Adam C., Dornbush, M.E. Patterns of root decomposition in response to soil moisture best explain high soil organic carbon heterogeneity within a mesic, restored prairie. Agriculture Ecosystems & Environment, 2014, 185, 188-196.

Olupot, G., Daniel, H., Lockwood, P., Mchenry, M., Mcleod, M. Root contributions to long-term storage of soil organic carbon: theories, mechanisms and gaps. Proceedings of the 19th World Congress of Soil Science: Soil solutions for a changing world, Brisbane, Australia, 2010, 1-6

Hou, H.T. Effects of fertilization application rate on crop cultivation and soil organic carbon. Nanjing Agriculture University, 2011. (in Chinese)

Liu, J.M.,  An, S.Q., Liao, R.W.,  Ren S.X.,  Liang H. Temporal variation and spatial distribution of the root system of corn in a soil profile. Chinese Journal Of Eco-Agriculture. 2009, 3, 117-121.

Gan, Y.T., Campbell, C.A., Janzen, H.H., Lemke, R., Liu, L.P., Basnyat, P. Root mass for oilseed and pulse crops: growth and distribution in the soil profile. Canadian Journal of Plant Science, 2009, 89(5), 883-893.

An, T.X., Yang, Y.M., Zhou, F., Fan, Z.W., Chen, M.L., Lu, J., Wu B.Z. Effect of Maize and Potato Intercropping on Their Root Growth and Distribution. Journal of Yunnan Agricultural University (Natural Science), 2018151, 2, 195-202. (in chinese)

Xie, Z.B., Zhu, J.G., Liu, G. Soil organic carbon stocks in China and changes from 1980s to 2000s. Global Change Biology, 2007, 13, 1989–2007.

Comment

Figure 1 needs a better resolution

Response

Thanks for your suggestion, we have improved the resolution of Figure 1

P3, L176

Comment

Experimental design requires detailed information such as exact dates of soil sampling for every single crop rotation pattern and the total number of soil samples taken from each single rotation pattern. Were soil samples collected at one-time point or multiple times from each crop rotation pattern?

Response

Thanks for your suggestion. This comment was also proposed as comment 3 by review1. We have addressed it in detailed as mentioned before. I hope you can see it (P2-3 in this response letter).

In addition, to clarity correction of one-time point of sampling, we added the following information:

In order to investigate the response of SOC to crop rotations over time, a space-for-time substitution approach was employed in the present study, as it has been adopted and successfully used in similarly targeted field studies [32-34].(P3, L160-162).

Mekuria, W., Veldkamp, E.,. Restoration of native vegetation following exclosure establishment on communal grazing lands in Tigray, Ethiopia. Veg. Sci. 2012, 15, 71–83. doi.org/10.1111/j.1654-109X.2011.01145.x Mekuria, W., Langan, S., Noble, A., Johnston, R. Soil restoration after seven years of exclosure management in northwestern Ethiopia. Land Degrad. Dev. 2016, 28, 1287–1297. doi.org/10.1002/ldr.2527 Cao, J.J., Li G.D., Adamowski, J.F., Holden N.M., Ravinesh C.D., Hu, Z.Y., Zhu, G.F., Xu, X.Y., Feng, Q. Suitable exclosure duration for the restoration of degraded alpine grasslands on the Qinghai-Tibetan Plateau. Land Use Policy 2019, 86, 261-267. doi.org/10.1016/j.landusepol.2019.05.008.

Comment

Data analysis section does not describe anything about regression analysis

Response

Thanks for your suggestion, we have added this part into 2.4 data analysis as following:

Linear regression was used to identify those soil factors that influence SOC sequestration of each crop rotation pattern.( P4, L 318-319)

Comment

The discussion is very vague. For explanation, all the results were indirectly linked to rooting depth however rooting depth data was neither collected in this study nor provided from the literature review.

Response

Thanks for your comments that can improve the quality of this paper, we have provided ther literatures as following:

Also, Haden et al. (2014) [28]has reported that roots are the main contributor to SOC formation. Based on Hou (2011) [59]and Liu et al. (2009) [60], the roots of wheat and maize are mainly concentrated in the 0-0.2 m, while for potato they are mainly located in 0-0.1 m [61]. (P7, L479-482).

28  Haden, V., Adam C., Dornbush, Mathew E. Patterns of root decomposition in response to soil moisture best explain high soil organic carbon heterogeneity within a mesic, restored prairie. Agr. Ecosyst. Environ. 2014, 185, 188-196. doi.org/10.1016/j.agee.2013.12.027

Hou, H.T. Effects of fertilization application rate on crop cultivation and soil organic carbon. Nanjing Agriculture University, Nanjing, 2011. (in chinese) Liu, J.M., An, S.Q., Liao, R.W.,  Ren S.X., Liang H. Temporal variation and spatial distribution of the root system of corn in a soil profile. Chinese Journal of Eco-Agriculture. 2009, 3, 117-121.(in chinese) An, T.X., Yang, Y.M., Zhou, F., Fan, Z.W., Chen, M.L., Lu, J., Wu B.Z. Effect of Maize and Potato Intercropping on Their Root Growth and Distribution. Journal of Yunnan Agricultural University (Natural Science), 2018, 151, 2, 195-202. (in chinese)

Round 2

Reviewer 1 Report

The authors have adequately addressed my previous comments.

Reviewer 2 Report

The authors have addressed some of the comments. Overall, I would encourage more data collection in terms of more parameters and timepoints so that it could warrant publication in the Agronomy Journal.