Experimental Evaluation of Conservation Agriculture with Drip Irrigation for Water Productivity in Sub-Saharan Africa

Round 1

Reviewer 1 Report

This manuscript describes a series of field experiments in Africa to determine the effects of drip irrigation on yield of vegetables under conventional and conservation agricultural management conditions.  The work was undertaken on farmer plots rather than in experimental fields; the goal was to optimally balance water usage with yields.  I believe that this participatory approach is very important, but I do have a number of comments and questions, especially about experimental design and the use of statistics.  There are quite a number of issues with English usage, some just typos and grammatical errors that a copy editor can resolve.  But in several places, I do not really understand what the authors intend to convey.  I have pointed out a number of important issues that relate to statistics, but I am not an expert, and so I do recommend that at least one other reviewer examine the paper in depth from this perspective.

 

Here are my comments, keyed to line number in the manuscript:

 

26     The abstract is quite lengthy, and I think that the sentences beginning on lines 29 and 33 could be deleted.  But the authors do need to provide a brief description here of CA (line 7), which can take various forms.  This will help readers to understand the remainder of the abstract.

42     Should be “depends.”  Line 43 should be “a majority.”  Line 48 should be “causes.”  There are many examples of minor grammatical errors like this throughout the manuscript that must be corrected.

52     Make it “…on the environment.  This process is called sustainable intensification.”

55     It is odd that you view home gardens as effective for sustainable agriculture yet earlier (lines 45/46) view small farm size as a challenge.  How can small be both beneficial and detrimental?   Please explain.

90     ….of mulch, not much.

126  This figure is not of much value.  The map is too big—the entire continent.  The satellite photos do not provide information, and they contain extraneous, drop-shaped markers.  I also note that the Robit and the Dangishita maps appear to be from a single satellite photo with a white horizontal line drawn across it.  Yet these two sites do not appear to be directly north and south of one another on the map.  I suggest that this figure be replaced with close up maps, one from Ghana and one from Ethiopia. These would show the location of the sites in more detail.   Satellite images could be included, but these should be free of the extraneous markers and should focus on actual plot areas at reasonable resolution.  It would be helpful if the geographical coordinates of the three sites could be included in the legend.

129  It is important that CA and CT be described in more detail.  Most readers will not know much about conventional tillage practices at the sites, so these must be described.  How do farmers normally grow these crops?  And then with respect to CA: Were these sites used conventionally the year before the CA experiments began?  What kind of mulch was used?  And what kinds of rotation?  Different farmers were participating, so it is important to understand if each one followed a standard rotation scheme, for example.  Or were they allowed to determine their own rotation schemes?  Line 136 indicates there may have been a great deal of variability in how farmers actually grew crops in the experimental fields. This means that the experiments were conducted under normal agricultural conditions, but it also has the potential to complicate the statistical analysis in ways that could confound data interpretation. 

156  More information would also be helpful here.  This sentence implies that the farmers may not have known how to grow the crops used in the experiments.  Please be explicit on this point—it is one thing for farmers to grow traditional crops in new ways and yet another for farmers to grow entirely new crops in new ways.    

173  I take this sentence to mean that farmers traditionally irrigate by other means and thus understand when water must be supplied.  You might want to make this point—that farmers are used to applying water, and so the difference in the experiments is the method by which water is supplied.

179  The presentation in Table 1 relates to my questions above at Line 129.  I read the table to indicate that everyone at Dangishita grew garlic from Nov-Feb and then some grew onion while others grew more garlic. Similarly, at Robit, everyone grew tomato from Nov-Mar, garlic from Apr-Jul, and then cabbage the next season. If this is correct, then the table is ok, but if this is not correct, then the table must be modified.  I do think the table would be clearer if the names of the crops were to be removed from within the bars (only some are labeled) and included in the legend, i.e. yellow = garlic, etc.

181  More details are needed here—timing of fertilizer and pesticide applications, for example.  Should be urea, not UREA.  Also, identify what DAP stands for.  Also, are these standard agricultural practices that farmers would be following even when they are not participating in experiments?  Or are these special conditions set up for the experiments? This is important.

188  The paragraph that begins on this line can be deleted.

195  Crop, not op yield.

197  Did farmers actually measure the amount of rainfall and then apply an equal amount of irrigation?  Is this typical?  And what about the other crops.  Was there any rain during the growing season? 

200  The table shows that irrigation water use was decreased under irrigation, but line 23 states that it was increased.

206  What is meant by dry season?  Is this a component of the annual rainfall cycle at the site?  Or does it refer to year-year variability?  Also, I could only find 3 seasons, not 4.

222  I do not understand the relationship between the number of replicates listed here and the number of farmer participants listed elsewhere (line 103).  Please clarify.

225  I suggest that you not include the sweet potato data in the figures or tables. These results, from just a single year, are really just preliminary.  You could provide information in the text, and use the figures to highlight the multi-year experiments in Ethiopia.

226  A 42-fold yield difference is immense.  Given that only a modest number of farmers participated in the experiments, I am concerned about how such differences influence the analysis and conclusions.

236  How do you know that it was a sufficient amount of fertilizer?  What are the criteria?  Similarly (line 244), how do you know that an insufficient amount was applied here?

280  This section should be more concise and focus sharply on conclusions.  Almost everything in the section as written is a repeat from elsewhere and not really a conclusion (but the sentence that begins on line 298 is an exception—this is a conclusion).  Also note the following:  At line 289, how do you know that the effect is due to improvement in soil quality? Where is the evidence?  At line 294, what is meant by competition for mulch (line 295—mulch was from forage?). 

Author Response

Thank you for your valuable comments.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper is a writeup of a three-year experiment to test the water productivity of conservation agriculture for home gardens. The researchers installed irrigation systems and trained farmers in conservation agriculture and measurement techniques, and supervised the farmers through the growing and harvesting seasons. It provides an important addition to the literature, namely the quantification of increased water productivity for smallholder agriculture through the use of specific conservation practices. 

This paper is a logical step forward in the conversation surrounding agriculture and nutritional needs. The literature review and methods are good, and I appreciated the bullet-point list of opportunities and challenges, although I was surprised that the cost of drip irrigation systems was not listed among the challenges. There were a few places that the paper could be improved. The only major error seemed to be the disagreement between the abstract and results regarding the water demand of crops under conservation agriculture vs. conventional tillage - the abstract states that the CA crops used more water, while the results state that the CA crops used less water. This appears to be a one-word error, but MUST be fixed, because this is an important finding. In many cases, the increased yields from CA *do* cause an increase in total water demand, even though water productivity still ultimately increases. 

The paper reads well, although there are some places where the English can be improved in a minor way - unusual use of verb tenses, verb/subject disagreement, and punctuation. More importantly, the paper mentions several aspects of the system that are somewhat outside the scope of the paper: ecosystem services, soil aggregates, microorganisms, weed and disease pressure, soil evaporation, nutritional content of crops, cash crops - without quantifying any of these facets. The experiment does not attempt to demonstrate which conservation practices are contributing to yields and water productivity, although several physical mechanisms are suggested. A lot of the soil benefits of no-till that are mentioned, like soil aggregates and microorganisms, are generally not observed for several seasons after the last tillage, so are less likely to have made a difference within the timespan of the study compared with mulching. The qualitative observations are very valuable, like noting that the mulch prevented tomatoes from coming into direct contact with soil. I would like the authors to move these factors into an expanded discussion section, and talk a little bit more about next steps and needs for further research. Some of this stuff is really hard to measure (like nutritional outcomes and evapotranspiration and loss due to pest pressure) and it's OK to say that; treat the suspected mechanisms for improved yield and water productivity, and knock-on effects like improved soil, nutrition, and ecosystem services, as hypotheses rather than findings. 

Please be sure to go through my comments on the attached PDF - nearly all the edits in the PDF have written comments associated, and I've had experiences with other authors not spotting these suggestions. Thank you for a pleasurable read on a very important topic. 

Comments for author File: Comments.pdf

Author Response

Thank you for your valuable comments.

Author Response File: Author Response.docx

Reviewer 3 Report

Review comments on water-449160

Dear Editor,

This study has merit but I’m afraid the paper still requires thoroughly editing to reach the level of international publications and before publication is granted. The main issue is convincing of the novelty of the research and discussing it in respect of the existing research on the subject. While this is partly done in the Introduction section, the performed statements are not adequately supported when the authors give general statements about trends and cite at the end of the sentences numerous references. Instead, it is recommended to further introduce the existing studies on the subject by citing the main site characteristics and values for instance CT and CA, i.e; quantitative information to support the presented trends in existing literature. This is missing in the present manuscript. Moreover, both the abstract and the introduction sections should better convince on the novelty of the work and this can only be done by (1) discussing the existing finding and identifying research gap(s); critically discuss these existing works to summarize research advances and gaps in knowledge of the subject ; (2) clearly state the research objectives, which should be in accordance with the identified gaps. Finally, the discussion section should compare the obtained results with the existing literature (the ones cited in the introduction section but not only). How do the obtained results compare to these obtained in similar regions or elsewhere? on other objects? What are the possible explanations of the trends? What do we learn from the results?

Finally, the structure of the different parts should follow standards. The abstract as it stands bellow does not contain important aspects an abstract is supposed to display such as:

A.        Topic sentence (s) on the subject (its importance) and research question(s): what is(are) the research gaps in this field of research?

B.        Objectives of the study

D.        Main results (with quantitative information, tests of significance)

E.         Conclusions:  how these results respond to the objectives; general implications of the research

 

As it stands, the abstract starts with materials and methods. Results should indicate WUE data in kg per litre of water.

 

“A field-scale experimental study was conducted in Sub-Saharan Africa (Ethiopia and Ghana) to examine the effects of conservation agriculture (CA) with a drip irrigation system on water productivity in vegetable home gardens. A total of 28 farmers (13 farmers in Ethiopia and 15 farmers in Ghana) participated in this experiment. The experimental setup was a paired ‘t’ design on a 100 m2 plot; where half of the plot was assigned to CA and the other half to conventional tillage (CT), both under drip irrigation system. Irrigation water use and crop yield were monitored for 3 seasons in Ethiopia and one season in Ghana for vegetable production including garlic, onion, cabbage, tomato, and sweet potato. Irrigation water uses were substantially increased under CA, 18 % to 45.6 %, with a substantial increase in crop yields, 9 % to about two-folds, when compared with CT practice for the various vegetables. Crop yields and irrigation water uses were combined, water productivity, for the statistical analysis on the effect of CA with drip irrigation system. One-tailed paired t-test statistical analyses on water use data found a significant improvement (α = 0.05) in irrigation water productivity under the CA practice; 100 %, 120 %, 222 %, 33 %, and 49 % for garlic, onion, tomato, cabbage, and sweet potato respectively. This could be due to the improvement of soil quality and structure due to CA practice, adding nutrients to the soil and stick soil particles together (increase soil pores). Irrigation water productivity for tomato under CA (5.17 kg m-3 in CA as compared to 1.61 kg m-3 in CT) is found the highest when compared to water productivity for the other vegetables. The mulch cover provided protection for the tomatoes from direct contact with the soil and minimize the chance to soil-borne diseases. Adapting to CA practices with drip irrigation in vegetable home gardens is, therefore, a feasible strategy to improve water use efficiency, and to intensify crop yield, which directly contributes towards the sustainability of livelihoods of smallholder farmers in the region.”

 

There are many different ways of writing an abstract and an Introduction. This depends on the academic subject involved, the journal itself and the specific topic of the article. It is important for the purpose of the research that authors can identify the patterns used in abstracts of comparable articles published in the same area, and for journals that authors might write for.

 

Introduction sections

A.        Presenting the background of the subject;

B.        Indicating the importance of the research on the subject;

C.        Acknowledging what has be done so far on the subject by referring to existing research studies and reporting ones; referring to methods and ideas associated with other researchers;

D.        Pointing to a gap in knowledge of the subject;

E.         Selecting research objectives

F.         Explaining the organisation of the research;

 

Discussion section may fulfil one or more of the following functions:

A         Presenting background information

B         Summarising what was (not) done

C         Explaining why it was (not) done

D         Evaluating the method(s) or model used

E          Statement of result(s)

F          Explanation of result(s) – why and how it happened

G         Implication of the result(s) – what it does, or does not, imply

H         Making reference to previous research

I           General statement of interpretation

J          Elaboration of interpretation

K         Discussing implication(s) of the interpretation

L          Rejection of interpretation

M        Acceptance of interpretation

N         Making a recommendation

O         Stating the limitations of the data

P          ……………………………….. (other)

 

 

Conclusions

A.        Remind of research objectives

B.         Statements of general findings

C.        Statements of specific and significant finding

D.        Statement of overall trends with respect to what was known prior to the study

E.         How well do results respond to initial gaps, research questions

F.         Making predictions; recommendations.

Author Response

Thank you for your suggestions. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I am very pleased with the revised manuscript.  Although you did not accept all of my suggestions (that is ok), you seriously considered all of the issues, and gave thoughtful responses.

Reviewer 3 Report

paper can be accepted as it is. Authors did a tremendous work to revise it