the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jun 2025
Circular economy approach in phosphorus fertilization based on vivianite must be tailored to soil properties
Abstract. Although there is relevant knowledge based on the effect of soil properties on the efficiency of common commercial fertilizers, this effect remains poorly understood for the use of vivianite from water purification as an innovative P fertilizer meeting a circular economy approach. This study aimed to evaluate the effect of soil properties on the efficiency of vivianite recovered from water purification as a P fertilizer and to provide practical recommendations for its effective use. Vivianite and a soluble mineral P fertilizer (superphosphate) were compared at two P application rates (50 and 100 mg P kg–1) in soils ranging widely in properties in a pot experiment using wheat. Soluble P fertilizer provided the best results in terms of dry matter (DM) yield, P uptake, and Olsen P in soils, while vivianite led to the best results of DTPA extractable Fe in soils after crop harvest. The application of vivianite as a P fertilizer was more efficient in acidic soils (pH < 6.6). The effect of vivianite on dry matter (DM) yield was equivalent on average to 26 or 40 %, depending on the rate, of the same amount of soluble fertilizer in these acidic soils (i.e., P fertilizer replacement value –PFRV– on DM basis), it being around 50 % in some cases. The effect on Olsen P in soil was equivalent, on average, to 49 or 61 %, depending on the rate, of the same amount applied as soluble mineral fertilizer in acidic soils. This can be explained by the increased solubility of this fertilizer product under acidic conditions, supported by the highest increase in DTPA extractable Fe in these soils. Acidic soils were those with initial Olsen P below the threshold value for fertilizer response (TV). However, PFRV on different approaches (DM, P uptake, and Olsen P) decreased more consistently with increased values of the difference between initial Olsen P and TV (46 to 87 % of the variance explained) than with increased pH. This reveals that besides soil pH, a low P availability to plants can trigger plant and microbial mobilization mechanisms, leading to increased efficiency of vivianite as a P fertilizer. Further studies are needed to assess the residual effect of vivianite and its effectiveness under field conditions, particularly in soils with low P availability status and an acidic pH.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-1460', Anonymous Referee #1, 01 Jul 2025
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AC1: 'Reply on RC1', Tolulope Ayeyemi, 12 Jul 2025
The authors are grateful for a comprehensive review of the manuscript. The comment has been well received and will be worked on.
Thank you.Citation: https://doi.org/10.5194/egusphere-2025-1460-AC1
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AC1: 'Reply on RC1', Tolulope Ayeyemi, 12 Jul 2025
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CC1: 'Comment on egusphere-2025-1460', Vito Armando Laudicina, 05 Aug 2025
This study evaluates whether vivianite recovered from wastewater can substitute mineral superphosphate across 12 soils with varying properties by measuring dry matter yield, phosphorus uptake and Olsen P; the topic aligns with journals focusing on nutrient cycling and circular economy. The use of vivianite as a phosphorus source has been reported, but previous studies rarely compared its performance across multiple soil types; the present investigation leverages 12 soils, two fertilizer rates and a replacement‑value approach. Comparative multi‑soil testing adds value. The authors used a randomized complete block design with 12 contrasting soils and three replicates per treatment. Each pot contained one wheat plant receiving one of two P rates (50 and 100 mg kg⁻¹) of either vivianite or superphosphate plus an unfertilized control. The experiment was carried out under controlled conditions. The Ms. is generally clear and well structured; sentences are coherent and vocabulary appropriate. Occasional minor grammatical slips and typographical errors could be corrected, but they do not impede comprehension.
My main concerns are as follows:
- Extrapolating short pot experiments to field recommendations seems premature; a fuller discussion of limitations and negative responses would strengthen the Ms.
- The authors should clarify how negative replacement values should be interpreted, and temper field recommendations. A deeper discussion of soil microbial factors and a clearer statement of what constitutes an agronomically acceptable replacement value would strengthen the Ms.
- The Results section begins with the sentence: 'There was wide variation in the properties of the set of soils used in this experiment (Table 1), especially clay content and calcium carbonate equivalent (CCE), which are relevant properties affecting P dynamics in soils.' In the Conclusions, the Authors refer to the acidic condition of the investigated soils (and thus mention calcium carbonate content), but make no reference to soil texture. If no relationship was found with texture, this should also be explicitly stated.
Citation: https://doi.org/10.5194/egusphere-2025-1460-CC1 -
RC2: 'Comment on egusphere-2025-1460', Anonymous Referee #2, 18 Aug 2025
This study evaluates whether vivianite recovered from wastewater can substitute mineral superphosphate across 12 soils with varying properties by measuring dry matter yield, phosphorus uptake and Olsen P; the topic aligns with journals focusing on nutrient cycling and circular economy. The use of vivianite as a phosphorus source has been reported, but previous studies rarely compared its performance across multiple soil types; the present investigation leverages 12 soils, two fertilizer rates and a replacement‑value approach. Comparative multi‑soil testing adds value. The authors used a randomized complete block design with 12 contrasting soils and three replicates per treatment. Each pot contained one wheat plant receiving one of two P rates (50 and 100 mg kg⁻¹) of either vivianite or superphosphate plus an unfertilized control. The experiment was carried out under controlled conditions. The Ms. is generally clear and well structured; sentences are coherent and vocabulary appropriate. Occasional minor grammatical slips and typographical errors could be corrected, but they do not impede comprehension.
My main concerns are as follows:
- Extrapolating short pot experiments to field recommendations seems premature; a fuller discussion of limitations and negative responses would strengthen the Ms.
- The authors should clarify how negative replacement values should be interpreted, and temper field recommendations. A deeper discussion of soil microbial factors and a clearer statement of what constitutes an agronomically acceptable replacement value would strengthen the Ms.
- The Results section begins with the sentence: 'There was wide variation in the properties of the set of soils used in this experiment (Table 1), especially clay content and calcium carbonate equivalent (CCE), which are relevant properties affecting P dynamics in soils.' In the Conclusions, the Authors refer to the acidic condition of the investigated soils (and thus mention calcium carbonate content), but make no reference to soil texture. If no relationship was found with texture, this should also be explicitly stated.
Citation: https://doi.org/10.5194/egusphere-2025-1460-RC2 -
AC2: 'Reply on RC2', Tolulope Ayeyemi, 25 Aug 2025
The authors are grateful for a comprehensive review of the manuscript. The comment has been well-received and will be worked on.
Thank you.Citation: https://doi.org/10.5194/egusphere-2025-1460-AC2
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EC1: 'Comment on egusphere-2025-1460', Ping He, 12 Sep 2025
This study evaluates whether vivianite recovered from wastewater can substitute mineral superphosphate across 12 soils with varying properties by measuring dry matter yield, phosphorus uptake and Olsen P. I have reviewed the comments from the two reviewers. They both agreed that the study is of significant to the P fertilization. However, many concerns from them are needed to be addressed by the authors. Therefore, I would like to invite the authors to reply to each of the comments and concerns.
Citation: https://doi.org/10.5194/egusphere-2025-1460-EC1
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The manuscript presents a pot experiment evaluating the efficacy of vivianite mostly obtained from wastewater treatment plants as a phosphorus (P) fertilizer. The study compares vivianite to a conventional soluble P fertilizer (superphosphate) at two application rates across twelve different soils with a wide range of properties. The authors use wheat as a test crop and measure dry matter (DM) yield, P uptake, and post-harvest soil P (Olsen P) and Fe (DTPA Fe) levels. The central finding is that vivianite's effectiveness is highly dependent on soil properties, performing best in acidic soils that are also deficient in plant-available P. The study introduces and uses the P fertilizer replacement value (PFRV) to quantify vivianite's equivalence to superphosphate. A key conclusion is that vivianite is more effective in acidic soils having P below threshold value. Overall, manuscript is well structured and written. My biggest comments are for introduction and discussion sections.
The Introduction provides a thorough explanation of soil properties relevant to phosphorus dynamics; however, it offers limited background on vivianite. It would strengthen the manuscript to include more context on the origins of vivianite, specifically, whether wastewater treatment plants are the only viable source. Discussing the major sources of vivianite and highlighting the significance of wastewater streams as a sustainable and potentially abundant supply would provide valuable context. Furthermore, a brief discussion on the economic feasibility of recovering vivianite and its potential advantages over other recycled P sources would be useful. Including its chemical composition, especially the phosphorus content by percentage, would also help readers understand its agronomic value.
The Discussion section is comprehensive, and the authors provide a detailed interpretation of how soil properties, particularly pH and Olsen P status, influence the effectiveness of vivianite as a phosphorus fertilizer. However, the section at times reads like an extended summary of the Introduction and Results sections rather than a focused synthesis of key findings. Several parts reiterate previously stated information, which affects the clarity and conciseness of the discussion. Condensing the text to avoid repetition and emphasizing how the study’s findings advance current knowledge would significantly improve the section. Reorganizing the content into thematically coherent and concise paragraphs would enhance readability and help readers more easily grasp the significance of the findings.
Although the abstract states that the study aims to provide "practical recommendations for vivianite's effective use," these recommendations are not clearly presented in the manuscript. The insights about soil pH, Olsen P status, and P fertilizer replacement value are valuable, but they are scattered throughout the results and discussion. To better fulfill the stated objective, the authors should consider summarizing these findings into a concise, standalone section—either as a paragraph in the discussion or a separate recommendations section—outlining when, where, and how vivianite should be applied, possibly with threshold guidelines or a decision matrix. This would greatly enhance the practical relevance and clarity of the manuscript.