Status: this preprint is open for discussion and under review for SOIL (SOIL).
Crop fertilization as a key determinant of croplands’ soil carbon stocks
Vincent Chaplotand Pardon Muchaonyerwa
Abstract. Soil organic matter (SOM), which associates organic carbon to key plant nutrients, is a corner stone of soil health, agricultural productivity and ecosystem functioning. While virgin lands (forest or grassland) exhibit the highest SOM stocks, their cultivation leads to their sharp decrease and that of crop yields in the first decade(s), even when zero tillage and cover crops are promoted. The decline in SOM is less acute when crops are fertilized with N, P, K at rates recommended to meet crop needs than when not fertilized, and is often reversed when nutrients are applied above recommendations. This points to the key role of fertilization to manage croplands’ soil carbon that needs to be better understood to mitigate against soil degradation for promoting sustainable agriculture, while minimizing environmental hazards such as water pollution.
Received: 18 Aug 2025 – Discussion started: 17 Sep 2025
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This paper is a very brief overview of soil organic carbon stock changes under land use change and the impacts of fertilization on either attenuating those losses or helping to increase soil organic carbon stock accrual. The paper is not a comprehensive literature review or meta-analysis and because of that, it is somewhat underdeveloped in terms of its contributions to help advance our understanding or synthesize available evidence. Reporting substantial losses of SOC stocks after land use change does not provide any new information that is not already adopted into our understand of how cultivation impacts SOC loss and the role of stochiometric constraints in trying to build SOM.
Specific comments:
Line 16: I am a bit confused - is this saying that cultivation of virgin lands leads to a decrease in SOM and crop yields? The way this sentence is structured makes that somewhat unclear.
Lines 26-29: This short abstract is very redundant. Is there a more effective way to use these few sentences to communicate other ideas/contributions in this piece?
Line 55-56: Are the data from Finland that show SOM declines from cropland? Or from monitoring sites across different land uses? From the sentence prior, there seems to be an emphasis on cropped soils, but the mention of these losses from Finland refer to the whole country, so this is unclear.
Line 68: I think 0.33% yr-1 should be 0.033% yr-1
Line 74: 2.0% yr-1 seems high has does the 7% yr-1 reported in line 76 – are these values correct? This paragraph reads a bit like a laundry list of results with some numbers that I think need some double checking. Further, loss of SOM upon cultivation is not necessarily new, so I am left wondering how this is contributing to advancing our understanding (e.g., McLauchlan, 2006; Sanderman et al., 2017).
Line 82: What is meant by agricultural exports? This is unclear.
Line 83: “rate of SOM decrease consecutive to cropping” – I am not sure what is meant by this?
Lines 88-91: For the German study, was SOM loss fully halted as shown in areas that were fertilized and compared to non fertilized areas that did not receive fertilization? Or did the declines in SOM stop once the area was fertilized? The description of this study is quite coarse and so difficult to interpret here.
Lines 97-98: If we're doubling the rates of fertilization, we may be helping to build SOC stocks but this could also be associated with big trade offs in terms of N losses! This is a critical point that underpins a key message of this paper and has been highlighted before in the context of 4 per mille (van Groenigen et al., 2017). This comes up again in line 108 in reference to enhancing organic carbon stocks: if the goal is only to increase carbon stocks, then that might be accomplished -- but doubling rates to this extent should not be viewed as a positive given all the environmental and climate concerns associated with over fertilization. Accounting for the net GHG impacts of such practices is essential.
Line 112-113: The decline in SOM in response to over fertilization with pig slurry is an interesting result to introduce here, but the authors don’t provide any follow up as to why this might be the case?
Line 130-132: This is a pretty coarse back of the envelope calculation based on one study that doesn’t account for differences in soil type, climate, or other management factors, therefore, I find it somewhat of a leap to say that applying nutrients in this way will avoid priming.
Line 138: This paper reviews some evidence, but it is not systematic and cites only a handful of studies that show crop fertilization impacts on SOM levels. I also feel like it presents a dangerous and ill advised recommendation of fertilization above recommended levels – this could have overwhelmingly negative impacts on N losses that could lead to increased N2O emissions and increased losses of nitrate.
References
McLauchlan, K. (2006). The Nature and Longevity of Agricultural Impacts on Soil Carbon and Nutrients: A Review. Ecosystems, 9(8), 1364–1382. https://doi.org/10.1007/s10021-005-0135-1
Sanderman, J., Hengl, T., & Fiske, G. J. (2017). Soil carbon debt of 12,000 years of human land use. Proceedings of the National Academy of Sciences, 114(36), 9575–9580. https://doi.org/10.1073/pnas.1706103114
van Groenigen, J. W., van Kessel, C., Hungate, B. A., Oenema, O., Powlson, D. S., & van Groenigen, K. J. (2017). Sequestering Soil Organic Carbon: A Nitrogen Dilemma. Environmental Science & Technology, 51(9), 4738–4739. https://doi.org/10.1021/acs.est.7b01427
University of KwaZulu-Natal, School of Agricultural, Earth & Environmental Sciences, Scottsville, 3209 Pietermaritzburg, South Africa
Laboratoire d’Océanographie et du Climat: Expérimentations et approches numériques (LOCEAN), UMR 7159, IRD/CNRS/UPMC/MNHN, IPSL, 4, Place Jussieu, 75252 Paris, France
Virgin lands converted to croplands loose staggering amounts of soil organic carbon. The available litterature shows that proper soil fertiliation may allow to revert the decline in SOM which is less acute when crops are fertilized with N, P, K at rates recommended to meet crop needs than when not fertilized. The SOM decline is often reversed when nutrients are applied above recommendations thus pointing to necessary reconsideration of actual soils policies.
Virgin lands converted to croplands loose staggering amounts of soil organic carbon. The...
This paper is a very brief overview of soil organic carbon stock changes under land use change and the impacts of fertilization on either attenuating those losses or helping to increase soil organic carbon stock accrual. The paper is not a comprehensive literature review or meta-analysis and because of that, it is somewhat underdeveloped in terms of its contributions to help advance our understanding or synthesize available evidence. Reporting substantial losses of SOC stocks after land use change does not provide any new information that is not already adopted into our understand of how cultivation impacts SOC loss and the role of stochiometric constraints in trying to build SOM.
Specific comments:
Line 16: I am a bit confused - is this saying that cultivation of virgin lands leads to a decrease in SOM and crop yields? The way this sentence is structured makes that somewhat unclear.
Lines 26-29: This short abstract is very redundant. Is there a more effective way to use these few sentences to communicate other ideas/contributions in this piece?
Line 55-56: Are the data from Finland that show SOM declines from cropland? Or from monitoring sites across different land uses? From the sentence prior, there seems to be an emphasis on cropped soils, but the mention of these losses from Finland refer to the whole country, so this is unclear.
Line 68: I think 0.33% yr-1 should be 0.033% yr-1
Line 74: 2.0% yr-1 seems high has does the 7% yr-1 reported in line 76 – are these values correct? This paragraph reads a bit like a laundry list of results with some numbers that I think need some double checking. Further, loss of SOM upon cultivation is not necessarily new, so I am left wondering how this is contributing to advancing our understanding (e.g., McLauchlan, 2006; Sanderman et al., 2017).
Line 82: What is meant by agricultural exports? This is unclear.
Line 83: “rate of SOM decrease consecutive to cropping” – I am not sure what is meant by this?
Lines 88-91: For the German study, was SOM loss fully halted as shown in areas that were fertilized and compared to non fertilized areas that did not receive fertilization? Or did the declines in SOM stop once the area was fertilized? The description of this study is quite coarse and so difficult to interpret here.
Lines 97-98: If we're doubling the rates of fertilization, we may be helping to build SOC stocks but this could also be associated with big trade offs in terms of N losses! This is a critical point that underpins a key message of this paper and has been highlighted before in the context of 4 per mille (van Groenigen et al., 2017). This comes up again in line 108 in reference to enhancing organic carbon stocks: if the goal is only to increase carbon stocks, then that might be accomplished -- but doubling rates to this extent should not be viewed as a positive given all the environmental and climate concerns associated with over fertilization. Accounting for the net GHG impacts of such practices is essential.
Line 112-113: The decline in SOM in response to over fertilization with pig slurry is an interesting result to introduce here, but the authors don’t provide any follow up as to why this might be the case?
Line 130-132: This is a pretty coarse back of the envelope calculation based on one study that doesn’t account for differences in soil type, climate, or other management factors, therefore, I find it somewhat of a leap to say that applying nutrients in this way will avoid priming.
Line 138: This paper reviews some evidence, but it is not systematic and cites only a handful of studies that show crop fertilization impacts on SOM levels. I also feel like it presents a dangerous and ill advised recommendation of fertilization above recommended levels – this could have overwhelmingly negative impacts on N losses that could lead to increased N2O emissions and increased losses of nitrate.
References
McLauchlan, K. (2006). The Nature and Longevity of Agricultural Impacts on Soil Carbon and Nutrients: A Review. Ecosystems, 9(8), 1364–1382. https://doi.org/10.1007/s10021-005-0135-1
Sanderman, J., Hengl, T., & Fiske, G. J. (2017). Soil carbon debt of 12,000 years of human land use. Proceedings of the National Academy of Sciences, 114(36), 9575–9580. https://doi.org/10.1073/pnas.1706103114
van Groenigen, J. W., van Kessel, C., Hungate, B. A., Oenema, O., Powlson, D. S., & van Groenigen, K. J. (2017). Sequestering Soil Organic Carbon: A Nitrogen Dilemma. Environmental Science & Technology, 51(9), 4738–4739. https://doi.org/10.1021/acs.est.7b01427