the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jan 2024
N dynamics during a 3-year crop rotation fertilized with digestates and cattle effluents
Abstract. On-farm anaerobic digestion is used as a means of producing biogas, with the resulting digestates serving as organic fertilizers. However, such digestates have different fertilizer properties than undigested animal effluents, and are associated with different degrees of N loss. We conducted a field experiment in which cattle slurry and farmyard manure were co-digested with urban and agro-industrial wastes, which represented slightly more than two-thirds of the total. We managed a three-year crop succession (wheat – rapeseed – wheat) with five fertilization systems: no fertilization, mineral fertilizers, cattle manure and slurry, raw digestate, or separated solid and liquid digestates. An exogenous organic matter (EOM) (cattle slurry, liquid or raw digestates) or mineral fertilizer was applied five times in winter and spring. A different type of EOM (cattle manure, solid or raw digestates) was applied twice in summer. After each fertilizer application, we measured ammonia volatilization and N2O emissions, along with crop N uptake and soil mineral N stocks. Across the three-year rotation, the NH3 volatilization rate was the lowest in the plot treated with mineral fertilizers (2 % of applied total N, TN), followed by cattle effluents (7 % TN), liquid and solid digestates (9 % TN), and raw digestate (18 % TN). Seasonal cumulative N2O emissions were similar between mineral fertilizers and digestates, and were lower with cattle effluent, mainly because of lower ammoniacal N inputs. Compared to unfertilized crops, the surplus crop N uptake strongly reflected the mineral N content of fertilizers, ammonia volatilization, and the decomposition of EOM in the soil. Liquid digestate and cattle slurry had similar N use efficiencies (37 % to 60 % depending on the cropping season), while values for raw digestate were lower (25 to 41 %), likely due to its larger NH3 volatilization. Overall, digestates served as an effective N fertilizer but require particular attention to NH3 volatilization.
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RC1: 'Comment on egusphere-2024-161', Anonymous Referee #1, 01 Mar 2024
The paper presents a well-designed experiment that compares digestates, their potential to replace mineral fertilisers and nutrient (nitrogen) efficiency. As such the paper has potential, however there are some issues that need to be addressed before publication. Thereby I am suggesting to revise the paper for potential reconsideration. The main issue with the paper is that as it is written it lacks originality and the novel contribution to science needs to be much clearer. Many other papers have described the potential of digestates to replace mineral fertiliser and have also compared different types of digestate. I think authors need to articulate the novel contribution to the field before it is published. Grammatically it is generally ok (although often excessively wordy in places which could be reduced easily), but there is a lot of ambiguity that needs to be cleared up. For example, it is not always clear where "effects" are statistically robust or not. In addition, terminology such as "treatments varied somewhat in their N inputs", "slightly lower", "similar or slightly higher" (there are many other examples) need to be tidied up as they don't mean anything. The last paragraph of the introduction identifying the objectives needs to be tidied up and made much sharper. Methods in is mostly ok with some corrections. The results section often seems to be mixed up with discussion comments, authors need to ensure that results sections are for results only and not discussion comments. There seems to be various "data not shown", my question is why it isn't shown. Also, some information/results seem to be in the supplementary information that could be better in the main manuscript. Are all the data manipulations described in the statistical analysis section? I think some aspects of the stats section are incomplete Statements such as "therefore no statistical tests were performed to compare treatments" and "could not be determined for replicates" in a statistics section represent a concern as if no statistical analysis was performed you cannot ascertain whether there were treatment effects. If statistical analysis could not be performed then the data cannot be presented as results in a scientific publication. Discussions (and conclusions) seems to back-up existing work but doesn't really being our originality (what is different to the other work, what is the new knowledge). So, in summary with a major revise and represent the work could be turned into a paper if these issues are addressed. Additional comments are added on the PDF.
- AC1: 'Reply on RC1', Florent Levavasseur, 02 Apr 2024
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RC2: 'Comment on egusphere-2024-161', Anonymous Referee #2, 03 Mar 2024
In this study, the authors investigated the dynamics of nitrogen (N) flow over a 3-year crop rotation cycle using digestates and cattle effluents as fertilizers. Given the significance of nitrogen loss through processes like ammonia volatilization and N2O emission, which contribute to nutrient depletion and climate change, the study's objective aligns well with the need to manage nitrogen sustainably in agricultural ecosystems. The experimental design, which includes a three-year crop rotation and compares various fertilization practices, offers a thorough assessment of how different approaches impact nitrogen dynamics, including emissions, crop N uptake, and soil mineral N stocks following each fertilizer application. Moreover, the obtained results were logically and systematically arranged and discussed. Therefore, this manuscript needs a minor revision and my concerns are given as follows. Data presentation in some figures lacks clarity, making it difficult to differentiate between control and treatment groups. For example, in Figure 1 and Figure 2, the authors need to include data from unfertilized plots and compare them with fertilized plots to provide a comprehensive understanding. Additionally, the legends of Figure 1 require improvement in clarity to enhance reader comprehension. It would also be beneficial for the authors to ensure that significant differences in data are clearly indicated in figures and tables, probably using different letters. Overall, addressing these issues will enhance the clarity and impact of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-161-RC2 - AC2: 'Reply on RC2', Florent Levavasseur, 02 Apr 2024
Data sets
Metametha dataset Catherine Pasquier et al. https://doi.org/10.15454/5MOZKJ
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