Climate Assessment of Vegetable Oil and Biodiesel from Camelina Grown as an Intermediate Crop in Cereal-Based Crop Rotations in Cold Climate Regions

Round 1

Reviewer 1 Report

The manuscript is written well however I have few suggestions to improve the quality of article.

The comments are below:

 Yield Trade-off: The study revealed that while the dry matter yield increased in the camelina crop rotation, there was a decrease in pea yields due to relay cropping with camelina. This trade-off raises concerns about the overall productivity and efficiency of the system. Farmers and biofuel producers may find it challenging to optimize both crop yields and biofuel production simultaneously.

 

Nutrient Intensive: The higher climate impacts observed in the camelina crop rotation were attributed to field operations and fertilizer use, resulting in increased nitrous oxide (N2O) emissions. This highlights the nutrient-intensive nature of camelina cultivation, which can contribute to eutrophication and environmental pollution if not managed properly. Strategies for reducing fertilizer use and optimizing nutrient management practices should be explored to mitigate these negative impacts.

Limited Biodiversity Assessment: While the study mentioned the assessment of biodiversity impacts in relation to crop rotation effects, the report lacks detailed findings or specific measures employed to evaluate biodiversity. A more comprehensive analysis of biodiversity impacts, including potential effects on flora and fauna, would provide a more holistic understanding of the ecological implications of camelina cultivation.

Reduction in Carbohydrate Production: The study found that the production of carbohydrates decreased in the camelina crop rotation. This reduction may have implications for food production and feedstock availability for other industries. Considering the growing demand for food and agricultural commodities, any decrease in carbohydrate production raises concerns about potential conflicts between biofuel production and food security.

Uncertainties in Soil Organic Carbon Effects: The estimation of global warming potential varied depending on whether soil organic carbon effects were included or not. The uncertainties surrounding these effects highlight the complexity of assessing the full climate impacts of camelina cultivation. More research is needed to accurately quantify the carbon sequestration potential and long-term sustainability of the soil under camelina crop rotations.

Limited Comparison to Alternative Biofuel Crops: The study mainly focused on the climate impacts of camelina as an oilseed crop for biofuel production. However, a broader comparison with other biofuel crops commonly grown in the region, such as rapeseed or soybeans, would have provided valuable insights into the relative sustainability and efficiency of different biofuel feedstocks.

Overall, while winter camelina shows potential as a biofuel crop in terms of reduced greenhouse gas emissions, there are challenges and trade-offs that need to be addressed. Further research, innovation, and sustainable practices are crucial for optimizing camelina cultivation, minimizing negative impacts, and ensuring its viability as a sustainable source of biofuel.

Comments for author File: Comments.pdf

Author Response

Thank you for your valuable comments. We have made changes to the manuscript accordingly, see comment below.

1. Yield Trade-off: The study revealed that while the dry matter yield increased in the camelina crop rotation, there was a decrease in pea yields due to relay cropping with camelina. This trade-off raises concerns about the overall productivity and efficiency of the system. Farmers and biofuel producers may find it challenging to optimize both crop yields and biofuel production simultaneously.

Reply: Yes, clearly, the introduction of an intermediate crop can change the production of the agricultural system, but the effects at this point are uncertain, as we know little about how the crop will perform in Swedish agroecosystems. We have added a sentence about this on page 8 (section 3.1.1).

2. Nutrient Intensive: The higher climate impacts observed in the camelina crop rotation were attributed to field operations and fertilizer use, resulting in increased nitrous oxide (N2O) emissions. This highlights the nutrient-intensive nature of camelina cultivation, which can contribute to eutrophication and environmental pollution if not managed properly. Strategies for reducing fertilizer use and optimizing nutrient management practices should be explored to mitigate these negative impacts.

Reply: as there is no data and experience of camelina grown as a relay crop in Swedish crop rotations there is no reliable data on fertilizer use. This was estimated from earlier studies that are to a great extent field trials (i.e. not real practice). We do not believe that there are reasons to believe that camelina is more nitrogen demanding than say rapeseed. The fertilization in real practice will depend on expected yield but also on the proceeding crops and available nitrogen in the soil. Under section 3.2. we have now included a short discussion around this.

 

3. Limited Biodiversity Assessment: While the study mentioned the assessment of biodiversity impacts in relation to crop rotation effects, the report lacks detailed findings or specific measures employed to evaluate biodiversity. A more comprehensive analysis of biodiversity impacts, including potential effects on flora and fauna, would provide a more holistic understanding of the ecological implications of camelina cultivation.

Thank you for pointing this out. We agree that the formulations in the abstract calls for a more thorough biodiversity assessment. However, due to lack of data and available methods to quantify the impact ion biodiversity we discuss these effects quantitatively. This is now changed in the abstract.

 

4. Reduction in Carbohydrate Production: The study found that the production of carbohydrates decreased in the camelina crop rotation. This reduction may have implications for food production and feedstock availability for other industries. Considering the growing demand for food and agricultural commodities, any decrease in carbohydrate production raises concerns about potential conflicts between biofuel production and food security. Reply: Thank you for this comment, we agree. The comment is related to the one on yield trade-offs therefore see that reply.

 

5. Uncertainties in Soil Organic Carbon Effects: The estimation of global warming potential varied depending on whether soil organic carbon effects were included or not. The uncertainties surrounding these effects highlight the complexity of assessing the full climate impacts of camelina cultivation. More research is needed to accurately quantify the carbon sequestration potential and long-term sustainability of the soil under camelina crop rotations. Reply: Yes, we fully agree. Uncertainty of SOC assessments are highlighted in the manuscript under 3.3.

 

 

6. Limited Comparison to Alternative Biofuel Crops: The study mainly focused on the climate impacts of camelina as an oilseed crop for biofuel production. However, a broader comparison with other biofuel crops commonly grown in the region, such as rapeseed or soybeans, would have provided valuable insights into the relative sustainability and efficiency of different biofuel feedstocks. Reply: thank you for commenting on this. We have now added two sentences about this on Rows: 364-366.

 

7. Overall, while winter camelina shows potential as a biofuel crop in terms of reduced greenhouse gas emissions, there are challenges and trade-offs that need to be addressed. Further research, innovation, and sustainable practices are crucial for optimizing camelina cultivation, minimizing negative impacts, and ensuring its viability as a sustainable source of biofuel. Reply: Yes we agree and the need for future studies have been highlighted in some places in the manuscript. We added some comments on this also in sections 3.2 and 2.3.1.

Reviewer 2 Report

Review of sustainability-2490649 Climate assessment of biodiesel produced from camelina grown as an intermediate crop in cereal-based crop rotations in cold climate regions

The topic of increasing/maintaining agricultural productivity while simultaneously decreasing the greenhouse gas emissions, fertilizer utilization and soil degradation is an interesting and important topic. This manuscript is well written such that this reviewer found no major issues. Suggestions for improving the manuscript relate to better educating readers who may be unfamiliar with agricultural practices, and to expand the discussion of possible future improvements using different crop rotation strategies. The explanation of what is meant by a “six-year crop rotation yielding camelina as an intermediate crop” is explained in Lines 199-200 and Figure 2, but the manuscript will be improved by including this information, at least partially, in the introduction section. Also an expanded discussion of the 6 year crop rotation depicted in Figure 2 would be helpful. Many readers may wonder if it would be possible to improve on the results reported here by increasing the use of camelina and/or other crops in the rotation cycle. Is the six-year crop rotation described optimized for decreasing the greenhouse gas emissions, fertilizer utilization and soil degradation? Can relay cropping of camelina be used with spring barley-winter wheat main crops? What other scenarios could/should be considered in life cycle assessment analyses and/or field tests?

Author Response

Thank you for the nice feedback and for all you valuable comments! We have made changes in the manuscript accordingly, please see our reply below.

Comments relate mostly around the selection of the crop rotation and if it could be done differently. These are very good questions, that we would need field trials to study, which is not the aim of the paper. Why we selected a six- year crop rotation and reasoning behind crop selection is now presented on page 5. Also we highlight that more research is needed to identify crop rotations where camelina could be cultivated. Regarding the comment on including description the crop rotation aspects in the introduction we have now highlighted that crop rotation effects are included in the assessments in the aim of the paper. Regarding the first question on educating readers on agricultural practices, we are not sure what is meant. We are happy to do this if it can be specified what practices that need better explanations.

Reviewer 3 Report

In general, although this paper discussing on the LCA or the climate impacts of growing winter camelina as an intermediate crop for production HVO. The authors just surfacely discussed the trend generated from their LCA study. A solid reason on the reason of contributing to the trend was not provided.

 

My comments are as below:

1. What is the reason for resource competition with camelina in early spring that caused the yield lower? Please explain further.

2. "..., production of fat more than doubled and production of protein and fiber increased marginally when camelina was included." Why?

3. "...Bajželj et al. [3]) showed that the introduction of camelina increased the production of valuable micronutrients." Why?

4. Section 3.2: What happened if we are considering SOC effects?

5. The cropping system had the highest impact in the different allocations, which indicates the importance of proper crop management and optimization of cropping systems to achieve sustainable crop production in practice. Please explain further what did the authors mean by proper crop management, give details examples to support their claim as well what is the optimization of cropping systems should be implemented.

 

As per my selection above

Author Response

Thank you for your valuable comments. We have made changes to the manuscript accordingly, see comment below.

1. What is the reason for resource competition with camelina in early spring that caused the yield lower? Please explain further. Reply: this is because in relay cropping the crop following camelina is planted in the growing crop, and therefor grow in the same field as camelina for some time, before the camelina crop is harvested. We have changed the formulations in the manuscript. In section 3.1.1.
2. Production of fat more than doubled and production of protein and fiber increased marginally when camelina was included." Why? Reply: This is because camelina is grown together with the following crop in the early spring, when the following crop is planted in the growing camelina. We have changed the text in section 3.1.1.
3. "...Bajželj et al. [3]) showed that the introduction of camelina increased the production of valuable micronutrients." Why? Reply: This is because in the crop rotation with camelina we have a higher production of fat and protein than if not camelina is grown. We have made changes in section 3.1.1 to clarify this point.
4. Section 3.2: What happened if we are considering SOC effects? Reply: Here we describe the results with and without including SOC effects. This is because these effects are uncertain and further, SOC effects may not be included in several standards for biofuels or carbon foot printing. However, we agree that this was a bit unclear in the text and clarifications have been made in section 3.2.
5. The cropping system had the highest impact in the different allocations, which indicates the importance of proper crop management and optimization of cropping systems to achieve sustainable crop production in practice. Please explain further what did the authors mean by proper crop management, give details examples to support their claim as well what is the optimization of cropping systems should be implemented. Reply: Thank you, we agree that this part of the text is not so specified. We have tried to specify it in section 3.2.

Round 2

Reviewer 3 Report

The submitted work can be accepted as it is.

Minor correction needed.