Cattle-Urine-Enriched Biochar Enhances Soil Fertility, Nutrient Uptake, and Yield of Maize in a Low-Productive Soil

Round 1

Reviewer 1 Report

The article submitted for review presents very important issues for agricultural practice. The obtained results of increasing corn yield are impressive and should be disseminated not only in the country of research, but also in other regions where this species is grown. I have no objections to the planned study, both the research methodology and statistical analyses, description of results and discussion are well conducted. Some of the results are missing parameters defining the quality of the corn cobs themselves, i.e. the average number of grains per cob, the weight of one corn grain. For an agrotechnician, such parameters are very important because they could indicate which crop quality parameters are influenced by the applied fertilization technologies. The presented results could be transferred to the cultivation of table corn, where grain size is crucial. If the authors of the work have measurements regarding the quality of the crop, please include them in the work, it would certainly increase the value of the article below.

Author Response

We thank the reviewers for their valuable appreciation and remarkable suggestions. During harvest, we measured the yield of the maize grain and biomass. We acknowledge the suggestions provided by the reviewer regarding the inclusion of additional yield parameters that would add value to the current study. We would consider these valuable suggestions in future studies.

Reviewer 2 Report

The manuscript entitled “Cattle urine enriched biochar enhances soil fertility, nutrient uptake, and yield of maize in a low productive soil presents the results of a field trial conducted in Nepal. This study compares the effects of various treatments, including biochar, biochar combined with manure, urine-enriched biochar combined with manure, and a control group, on soil properties and maize yield. The manuscript's overall structure and layout are appropriate, and the results are indeed interesting, with a suitable discussion. However, there are several points that require attention before acceptance for publication.

1. It would be valuable to include a treatment with manure alone to provide a more comprehensive comparison.
2. The manuscript should explain how the doses of amendments were determined.
3. Please provide information on the production capacity of the Kon-Tiki system, including the number of hours and tons of biomass required per hectare.
4. Detailed information about the soil type, including classification and texture, should be included.
5. The organic amendments used in the study should be fully characterized.
6. The economic assessment is incomplete, and certain assumptions are inaccurate. It's essential to consider the cost of human resources, including those related to the production and application of amendments and the transport of feedstock.
7. Given the low production rate of the Kon-Tiki system, it's crucial to account for the working hours and the volume of feedstock needed per hectare. These factors cannot be overlooked.
8. A more comprehensive discussion on excessive nitrogen fertilization and its potential hazard effects is required.

Please review the use of excessively long sentences.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Review: Cattle urine enriched biochar enhances soil fertility, nutrient uptake, and yield of maize in a low productive soil

The main objective of the submitted manuscript was to analyze the hypothesis that the urine-enriched biochar with its high fertilizing efficiency improves soil chemical properties (pH, OC), nutrient availability (N, P, and K), plant nutrient uptake, and increases maize productivity compared with non-biochar fertilized plot and non-enriched biochar (biochar added separately with organic and inorganic fertilizers) receiving the same amount of nutrient supplements.

The authors briefly and convincingly presented experimental studies using biochar enriched with manure and urine confirming the research thesis expressed in the purpose of the paper. The study is even the more valuable sincethe authors' attention focused on both the analyzing chanes on soil properties and the effect on maize yields.Currently, biochar is promising means to improve soil quality and increase soil fertility, as the authors of the manuscript proved by presenting their research study and quoting numerous publications. Conducted experimental studies have confirmed that biochar is an effective medium for nutrients. Thanks to its porous structure, it has the ability to retain and store nutrients such as nitrogen, phosphorus and potassium, helping to deliver them to plants in line with their needs. This means that biochar can help maintain the biological balance in the soil, which is crucial for soil fertilization. The added value of the submitted paper is the method of sourcing the material for biochar production and the simple way of its preparation. Considering the gained experience, I would recommend the authors of this paper to broaden the spectrum of research on the application of biochar in the future. Special attention should be paid to improve the structure of sandy soils in Nepal. Previous studies have shown that biochar, due to its porous structure, increases the conductivity of the soil, enabling better water and air flow. This favors plant roots, allowing them easier access to nutrients and providing better growing conditions. Improving soil structure is a key factor in the soil's ability to retain moisture and avoid erosion.

I consider the submitted manuscript is of great importance to both the environment and human well-being, so I accept it in its present form, but I recommend adding information on the definition of soil in the study area according to FAO-WRB, 2022 or Soil Taxonomy, 2022.

Author Response

We express our gratitude to the reviewers for their valuable appreciation and remarkable suggestions. We would consider these valuable suggestions in future studies. As suggested, we have added the information on soil “ “The soil was characterized as a moderately acidic silty loam, Dystrochrepts, Inceptisol”

Reviewer 4 Report

General comments:

 - The results should be considered preliminary, since the use of organic amendments implies that nutrients provided in organic forms may be available in successive years. Therefore, experiments with two or three crop cycles could show more robust results and, therefore, make more precise recommendations to farmers regarding the use of this type of amendments.

- If all treatments have an N-P-K fertilization that already covers the needs of the crop, the effects of organic amendments may not be noticeable in some cases. Wouldn't it be convenient to make the treatments based on the fertilizer units provided by each treatment?

 Specific remarks:

 - Line 33: Zea mays L. and Oryza sativa L. (L. non italic)

- Line 99: Ageratina adenophora (Spreng.) R. M. King & H. Rob.

- Line 105: m² g^-1

- Line 117: muriate of potash (MOP, KCl), respectively)

- Lines 121 – 122: It would be convenient to provide the reader with the composition of manure and urine in order to know the N supply to the crop in each treatment.

- Lines 122 – 124: The total contribution of each material in the treatments is not clear. The authors could provide a table with the contributions of C, N (organic and mineral), P and K in each treatment, accounting for organic amendments and mineral fertilizers.

- Lines 138 -139: It is not known when or how the soil sampling was done.

- Line 170 – 171: Shouldn't the denominator of the PFP index take into account all the nutrients that were contributed in each treatment? Here it seems that only the fertilizer input is considered.

- Line 197: 120 mg kg^-1 (BC+M)

- Table 1: Is there any explanation for the (non-significant) variation in sand, silt and clay content, is it due to the treatments, or is it just soil variability?

- Figures 3 and 4: They should be included and commented on in the results section, regardless of whether they are mentioned later in the discussion section.

- Section 6: It would be advisable to recommend new experiments, since a single crop cycle is scarce, as organic amendment inputs can have effects in successive years after their application.

Author Response

Please see the attachment 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The article is of interest and has been improved from the previous version. It is missing to support with references the estimated calculations on cost and benefit of biochar production and application, but apart from this and minor editing errors it can be sent to the preparation of proofs and final revision before publication.

No comments

Author Response

We appreciate the reviewer's insightful comments and remarks on the revised version of the manuscript.  We acknowledge the absence of a comprehensive cost-benefit analysis regarding biochar production and its soil application. We intended to provide an overview of the economic feasibility when farmers independently engage with minimal labor support in the preparation and application of biochar on their farms. The main objective of our present study is to assess the effect of urine-enriched biochar on yields and nutrient use efficiency. Thus, we have omitted the economic feasibility section and its connected part from the abstract and conclusion section. However, we would consider incorporating a thorough economic analysis with detailed data in future research endeavors. 

Reviewer 4 Report

I thank the authors for their response to my comments and suggestions made in the manuscript.
Here are some minor typos:

- Lines 33, 34 and 108: botanical name should be in italics

- Line 127: KCl

- Line 148: Ramírez-Sandoval et al

- Table 1: Available P (mg kg^-1) and Available K (mg kg^-1)

- Line 465: Biochar for improving crop production in Nepal

Author Response

We want to thank the reviewer for his valuable remarks.  We have corrected all the typos as suggested by the reviewer in the revised manuscript. 

Lines 33, 34 and 108: botanical name should be in italics

Corrected. 

- Line 127: KCl

Corrected. 

- Line 148: Ramírez-Sandoval et al

Added. 

- Table 1: Available P (mg kg^-1) and Available K (mg kg^-1)

Corrected. 

- Line 465: Biochar for improving crop production in Nepal

Corrected.