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.

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:

1. Extrapolating short pot experiments to field recommendations seems premature; a fuller discussion of limitations and negative responses would strengthen the Ms.
2. 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.
3. 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.