PSTR-D-21-00048

Farmers’ willingness to adopt sustainable agricultural practices: a meta-analysis

PLOS Sustainability and Transformation

Dear Dr. Boufous,

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Comments to the Author

1. Does this manuscript meet PLOS Sustainability and Transformation’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #1: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: An interesting study with policy relevant findings.

What would be interesting is in the discussion section to compare the findings of the meta analysis (wta approaches) with values defined by consumers for such an agriculture, even in an indicative level using findings in recent literature. For example, I found interesting results in Sustainable production and consumption 2021

Reviewer #2: This paper deals with an important topic in the technology adoption literature using standard meta-regression methods and novel meta-data from 59 (or 62?) studies. Unfortunately the analysis has been implemented with questionable categorisation, implementation and interpretation and seems to miss main points that concern non-US farmer’s adoption behaviours (as well as options). Given the wide readership of the journal PLOS Sustainability and Transformation with broad implications for policy, which has strict quality requirements, I do not think it is a good fit for publication in this journal.

Detailed comments:

1. In paragraph 47 in introduction hen the concept of technology adoption is discussed, an important element is missing that is essential for the assumption in the first sentence: perfectly functioning markets for credit, insurance, labor, inputs and information. When these markets are imperfect (as they are in most of Africa and Asia especially for small scale producers) the conceptual model presented falls apart and the analysis results cannot be trusted to use to guide any policy to increase the adoption of SAPs. Minor point: In general the introduction should present information on where the farmers, whose WTA will be discussed are, what type of producers, and what type of production environments.

2. Line 129 – and in general currency conversion issues: this line mentions that WTA have been converted into USD without any information on how. Given that data include continents with very different purchasing power parities (that also differ significantly within countries between rural and urban areas) some more detail on this step is crucial for the utility of findings. Has PPP been used? How?

3. The independent variables section continues into the sub-sample section without any clear indication and the reader ets lost. It may be best to combine these discussions and bring in sub-sample definitions when independent vars are discussed given that they are defined based on these variables.

4. Pollution category is very poorly thought out: it includes reduction of chemical use, climate smart agriculture (CSA) and biodiversity conservation (BDC). The first of these is the only one that could be considered a SAP, but ONLY in places where chemicals are overused. Fertilizer & input use remains well below recommended levels in most of Africa and parts of Asia, so even if the “pollution category” only included chemical use reduction it would not be valid for all countries in the data as a SAP. The latter two practices (CSA and BD) have nothing to do with pollution. First of all most of the practices captured in the other categories are actually part of CSA, so it is not clear at all what CSA is if not some of the BMP in soil and water conservation techniques, or energy categories. What relationship does biodiversity conservation have with pollution reduction?

5. Line 295-298: It is not clear why 2 dummy variables are created that are opposites of each other? How can they both be used in the regression? Please revise/clarify if misunderstood.

6. It would be useful to add a table with the number of studies and observations per continent before results section.

7. Table 4 – Africa row: How come the overall average of Africa dummy is 23% of overall data but it makes up more than 43% (up to 77%) of each category?

8. The Average WTA differences across continents should to be presented to put all findings in perspective.

9. If the funnel plot results are subjective and we do not even trust in them given FAT results, why is the funnel plot presented at all? Recommend dropping.

10. Table 6 & line 407: There are many more than 4 significant covariates that are significant at least at 10%. One is significant only at 10%, 5 at 5% and the rest at 1% - why does this sentence not match any of these findings?

11. Line 430: p=0.116 means that the coefficient is not significantly different from zero, better not to interpret any non-significant result. Otherwise why are we even using statistical significance to guide interpretation & findings?

12. Water conservation sub-set (starting in line 436): we are told first that at least 10 studies should be available for a meta-regression to be reliable and useful, then we are presented with results using only 8 studies. Any reason for this?

13. Line 467: The negative sign on the constant in this subsample is very curious, why is it very significant? The explanation in this sentence does not clearly explain the logic. Also I would think the interpretation would set all other values at their mean values rather than zero, and seems like they are willing to PAT rather than willing to accept payment to adopt these? But then again it is only based on 8 studies – so probably should not even interpret in any case.

14. Line 451: ths statement that farmers in Africa require lower incentives is a tautology ( especially it is nto clear whether these values are in PP or not). African farmers earn probably thousands of times less than those in the US or Denmark/Germany…etc. without clarifying this issue it is very unclear & questionable what these findings are telling us.

15. Table 11: The magnitudes of coefficients are never commented on except for the constant. We see that the WTA on average for this category is 2305, and then see that Grass dummy has a very significant coefficient that is greater than 2305. Does that mean that the WTA for Grass category is actually WTP equal to the difference (3452-2305 USD)??

16. Conclusions: A proxy for mean WTA is presented in conclusions as well although the subgroup analysis seems to negate these values for all but two sub-categories analysed later. These findings need to be put in context together. Also the currency conversion point in conclusions negate the findings of the study. If we cannot trust in the USD values in which WTA are expressed what is left? We were told that conjoint valuation is better for the case at hand, but the conclusions still discuss contingent valuation findings (para starting in line 569).

17. Line 692: WTA indicates that they are willing to accept that dollar value not that they are foregoing it. This is the whole point of this paper.

Reviewer #3: Review of “Farmers’ willingness to adopt sustainable agricultural practices: a meta-analysis.”

1. Summary of the research

A meta-analysis of farmers willingness to adopt sustainable agricultural practices is an important topic. The authors used a set of meta-regressions and statistical tests to analyze 59 studies providing 286 willingness to accept (WTA) estimates. The authors claimed to have found evidence for significant methodological factors affecting WTA values. In general, the findings narrated in this meta-analysis paper sound interesting. The paper is also well written, easy to read. However, I have some observations that I would like to share with the authors with the aim to improve the paper.

(i) Introduction

The strength of the introduction section is that the authors clearly stated that the study will elicit gaps in literature and highlight major findings of peer reviewed works to estimate the mean value to be used for how much farmers require incentives to adopt sustainable farming practices. No major weaknesses were observed in this section of the paper.

(ii) Materials and Methods

The strength of this section is the two phases of conducting the meta-analysis: literature search and the estimation of meta-regression. The meta regression formulas and explanations are detailed but a bit cumbersome.

(iii) Results

The summary statistics of the overall data and four subsets (soil, water, energy, and pollution) data is impressive. The meta regression analysis results also show some reasonable level of significance based on the F-test. It would have been useful to include some qualitative studies to better explain and triangulate the results.

(iv) Conclusions and Discussion

The discussion section is also impressive, but the authors should further explain what policy makers, program designers and implementers of sustainable agriculture should do with these results. It is ok to say they can make better decisions but how should they use it?

2. Minor issues

The paper has a useful list of literature, but some are quite old. I would recommend including more recent peer reviewed papers.

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Reviewer #1: Yes: Kostas Bithas

Reviewer #2: No

Reviewer #3: Yes: Dr. Hope Webber

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Comments to the Author

1. Does this manuscript meet PLOS Sustainability and Transformation’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #2: Partly

Reviewer #3: Yes

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Submitted filename: Review of Farmers Willingness to adopt_HW.docx

Farmers’ willingness to adopt sustainable agricultural practices: a meta-analysis

PSTR-D-21-00048R1

Dear Dr. Boufous,

We are pleased to inform you that your manuscript 'Farmers’ willingness to adopt sustainable agricultural practices: a meta-analysis' has been provisionally accepted for publication in PLOS Sustainability and Transformation.

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Best regards,

Isabel Marques

Section Editor

PLOS Sustainability and Transformation

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Reviewer Comments (if any, and for reference):