Assessment of Precise Land Levelling on Surface Irrigation Development. Impacts on Maize Water Productivity and Economics

Round 1

Reviewer 1 Report

Dear Authors, 

 

This study titled "Assessment of precise land levelling on surface irrigation development. Impacts on maize water productivity and economics" focuses on assessing the performance and the impacts of PLL on surface irrigation systems, focusing on the maize crop on the irrigation districts Hetao (China) and Lower-Mondego (Portugal). The experimental study at field scale assessed the PLL and evaluated the on-farm irrigation under 21 precise levelled fields and well management practices.

1. Introduction: Although the Introduction does a good job of defining what is PLL and what are its benefits and why it is important, the paper does not well define what is contribution this research is providing to the established literature evaluating different types of PLL techniques, what is the novel methodology or analysis that is different in this paper that provides a new argument or insights in terms of existing studies and literature in the field? Next, the authors do not rationalize well why China and Portugal are selected as case study sites for the analysis? Are Chinese farmers particularly water stressed or are they more prevalent or do they traditionally use land levelling techniques already - the Introduction does not explain why these two areas were of relevance for the novelty of the design and contributions of the findings of this study, which needs to be stated upfront in in the Introduction. 

Section 2: Materials and Methods

1. The following line "Sustainable water saving irrigation is being implemented in response to the referred global changes 141 occurring in the Yellow River basin" (pg. 3 lines 141-142) are not clear - what does sustainable water saving irrigation mean and what global changes to the Yellow River? This is not well cited or substantiated statement. 
2. Figure 2, there is no year or timeline provided for the data on climatic average trends nor is the source of the data specified, please correct. 
3. Section 2.2 - the sampling of the operators, who they were selected, how many and the methodology for who and how, how many were surveyed, please elaborate. 
4. 16 Field Experiments selected based on authors long field expertise (line 285-286, pg.8 is not sufficient or clear in terms of the methodology applied for which field sites were selected and why, in addition, as this is looking for an impact of the intervention on specified parameters of irrigation performance, it is not clear what is the counterfactual field site (farms that did no PLL interventions) and or a baseline over time when these points are collected against specific farms or field sites with PLL interventions and in a previous year (without PLL interventions) so the comparative across the field sites is missing and not well specified. This needs substantial clarity to further outline the novel contributions of this study. 
5. Lastly, in the methods section, it is positive that the authors describe two types of canal systems between China and Portugal study sites but some clarity on the starting condition of the overall irrigation system is needed, were the canals operating at full capacity and potential at the start of the field experiment? Or did some canals suffer from distribution or seepage channels - important to describe how canal system efficiency can also affect the parameters of irrigation water efficiency, and economic water efficiency (in spite of the PLL interventions). This needs to be elaborated and explained at the outset. 

Section 3 Results. 

1. On lines 370-374, pg. 12, the authors make a potentially important insight on the impacts of modernization of canal irrigation systems and how the combination of modernization + PLL measures which has positive responses on the BWUF indicator - however, what is not clear is what is the causal difference that the PLL mechanism is making as how can we differentiate the impact of the PLL vs. the modernization effect? Either the authors upfront state they are not trying to purely pull out the instrumental difference in irrigation parameters purely from PLL interventions (As that is how it is currently framed in the Introduction) but talk about how modernization efforts can then create the right enablers for farmers to begin adopting water saving and irrigation efficiency techniques (one of them being PLL) as it is widely recognized in the literature that PLL is not the only technique available to farmers for enhancing yield, efficiency, cost, and income gains  - this argument needs to be substantially sharpened and goes back to my original point - it is not well argued and grounded in the existing literature - what is the novel contribution of this analysis to the field? 

Section 4 Discussion. 

1 - This sentence "Therefore, the results of the 446 present study confirm the success of surface irrigation, showing that PLL had direct impact on maize 447 water productivity and economics. Values of BWUF of 80%-90%, IWP of 2.0-2.4 kg/m3, and EWPR of 448 6-8, were observed on Hetao and Lower-Mondego, which are similar to the good ones achievable by 449 sprinkler systems." (lines 446-450) reflect my comments above, we cannot isolate for the causal impact of PLL alone as these are combined with modernization of the canal system at a major or medium reservoir scale (or not, that is also not very clear) - so the authors need to nuance this point based on the results obtained because can we say the value of BWUF of 80-90% is purely due to the PLL interventions? This needs to be clarified and elaborated upon in the discussion. 

Section 5. Conclusions

1 - Overall, it is important to point out that land levelling maintenance is one of the various options available to farmers for on-farm development, other interventions (better inputs, technology adoption with respect to irrigation technologies, better crop and data services) can also achieve similiar objectives of enhanced water productivity and income growth for farmers where surface systems are modernized - this point needs to nuance and place the findings of this study in the wider literature that examines specific interventions for enhancing on-farm development in surface irrigated systems in Asia and the Mediterranean. 

 

Author Response

This study titled "Assessment of precise land levelling on surface irrigation development. Impacts on maize water productivity and economics" focuses on assessing the performance and the impacts of PLL on surface irrigation systems, focusing on the maize crop on the irrigation districts Hetao (China) and Lower-Mondego (Portugal). The experimental study at field scale assessed the PLL and evaluated the on-farm irrigation under 21 precise levelled fields and well management practices.

 

Comment about the number of fields: the field evaluation was carried out in six Hetao fields and four Lower-Mondego fields (Table 1); the irrigation projects considered eight fields in Hetao and eight field in Lower-Mondego (Table 5).  

 

Introduction - Question 1:

Although the Introduction does a good job of defining what is PLL and what are its benefits and why it is important, the paper does not well define what is contribution this research is providing to the established literature evaluating different types of PLL techniques, what is the novel methodology or analysis that is different in this paper that provides a new argument or insights in terms of existing studies and literature in the field?

Answer 1:

The “different types of PLL techniques” could be organized relatively to i) the operation objective: i) The references to the initial and maintenance operation are presented in lines 62-69, and 69-71, respectively; ii) the type of equipments used, usually drag scapers or leveling blades, referred in lines 50-51. The purpose of this article was not to focus on more detailed aspects of the types of equipment and their operating mode, which are well described in the bibliography, for example in Dedrick et al. (2007), but instead to assess the PLL on surface irrigation development. Relatively to the novelty of the methodology and analysis, some preliminar considerations:

1. the conventional method to analyse the PLL performance is to examine this operation itself - the design, planing, execution and assessment through the topographic results and the soil impacts. This approach allows a direct comparison with the traditional practices. It was adopted in some studies (examples: Naresh et al. 2014; Aryal et al. 2018; Jat et al. 2014; Aggarwal et al. 2010).
2. However, our experience in surface irrigation tell us that the unique improvement by PLL itself is not always significant and, that sometimes it is counter-productive: PLL has a relevant cost and the benefits could be insignificant, if other aspects of irrigation design and management do not improve in parallel, like for example, the irrigation scheduling and the right control of inflow. This situation contributes to the farmer misperception that surface irrigation and PLL are ineffective.

Therefore, the methodology we adopted assumes that PLL is a basilar operation to the development and modernization of surface irrigation systems, and that it requires the conjunction with other aspects, like those referred (irrigation scheduling and flow control), which are not dissociable. Although, this is not a conventional approach of this topic, we are convinced that this integrated vision of the surface irrigation process is more logic and effective to change the behavior and attitudes of technicians and farmers.

A merit of this research is that it allows obtaining a set of data, technical and economic (see Tables 6, 7 , 9, 10), which characterize PLL in the context of surface irrigation, which are useful for project and planning. Note that this data is not usually available for decision support tasks.

These ideas are explicit in the phrase (lines 38-46); to highlight the importance of considering together the development of these various aspects, a sentence is added:

 

The factors influencing the performance of these modern systems are multiple and refer to the design process, which in turn are related with the appropriateness of land levelling, field shape and dimensions, and inflow discharge. Moreover, they also depend on the farmer operative decisions, mainly regarding the land levelling maintenance, timeliness and time duration of every irrigation event, and the water supply uncertainties. Improving the irrigation performance requires a variety of measures and practices, acting together on the design and operation of the systems. To consider the conjunction of these development actions of surface irrigation systems, is a hallmark of methodology for analyzing these problems. In this context, the land levelling operation plays a determinant role in the pragmatic performance of these systems, namely on the reduction of water use and on the increasing of land and water productivity [1-5].

 

Introduction - Question 2:

Next, the authors do not rationalize well why China and Portugal are selected as case study sites for the analysis? Are Chinese farmers particularly water stressed or are they more prevalent or do they traditionally use land levelling techniques already - the Introduction does not explain why these two areas were of relevance for the novelty of the design and contributions of the findings of this study, which needs to be stated upfront in in the Introduction.

Answer 2:

Introduction refers in lines 110-114 “... to assess the water productivity and economics impact of precise land levelling practice by typical farmers on surface irrigation systems cropped with maize. It was carried out in the Hetao Irrigation District, China and in the Lower Mondego Irrigation District, Portugal, sites, where irrigated maize by surface methods is dominant, with high economic relevance.”.

These aspects are reinforced in lines 125-127 “These areas have in common the fact that the maize crop irrigated by surface methods is the most representative, with high economic and social regional relevance.”. Therefore, the relevance of these two areas is their representativeness of the surface irrigation problems and potential of development on water scarcity areas cropped by maize.

We agree that it is omitted the previous relationship between the researchers of both countries, from 2007. To clarify these aspects the following phrase is now inserted, in line 114: “This proximity to contexts of water saving requirement and the typology of irrigation problems has led the research teams of both countries to have worked together on projects and scientific cooperation, sharing knowledge and methodologies.”

 

 

Section 2: Materials and Methods - Question 1:

The following line "Sustainable water saving irrigation is being implemented in response to the referred global changes occurring in the Yellow River basin" (pg. 3 lines 141-142) are not clear - what does sustainable water saving irrigation mean and what global changes to the Yellow River? This is not well cited or substantiated statement.

Answer 1:

Hetao traditionally used 5,0x10⁹m³/year of irrigation water. Nowadays, due to increased demand for non-agricultural sectors, the Yellow River Commission is reducing the Hetao demand to a target of 4,0x10⁹m³/year (decrease of 20% from baseline). It requires an adaptation, including the adoption of various water-saving technologies, an objective that this paper is contributing to. The problem is aggravated during periods of drought and severe water scarcity, when the water use priority is given to non-agricultural uses. However, a heavy reduction in water supply for agriculture may have very important social consequences, making the agriculture non-sustainable. These aspects are described in lines 128-137.

 

To cleafy that sentence, we inserted anew reference and changed it to:

"Sustainable water saving irrigation, applying technologies and practices guaranteeing land productivity, soil conservation and farmers' income, is being implemented in response to the referred global changes occurring in the Yellow River basin" [Shi et al. 2020]

 

New reference:

Shi, H.; Yang, S.; Li, R.; Li, X.; Li, W.; Yan, J.; Miao, Q.; Li, Z. Soil Water and Salt Movement and Soil Salinization Control in Hetao Irrigation District: Current State and Future Prospect. J. of Irrig. and Drain. 2020, 39(8): 1-17 (In Chinese); doi：10.13522/j.cnki.ggps.2020156.

 

Section 2: Materials and Methods - Question 2:

Figure 2, there is no year or timeline provided for the data on climatic average trends nor is the source of the data specified, please correct.

Answer 2:

The caption of Figure 2 was changed, to include this information:

Figure 2. Average monthly climatic data, maximum, medium and minimum air temperature, precipitation and reference evapotranspiration: (a) Hetao (Linhe county, period 1981-2012, source: Linhe Weather Station); (b) Lower-Mondego (Montemor-o-Velho county, period 1971-2000; source: www.ipma.pt).

 

Section 2: Materials and Methods - Question 3:

Section 2.2 - the sampling of the operators, who they were selected, how many and the methodology for who and how, how many were surveyed, please elaborate.

 

Answer 3:

These inquiries tried to survey all the operators actually (2020) active in each one of the sites. We got answers of nine operators in Lower-Mondego and seven in Hetao. The questions were centered in the most usual field parcel where they have operated recently. The questions are presented in lines 186-190. We think that the sentence of line 190 (These inquiries were posed to the maximum number of operators available.) is not clear, whereby is was changed: These inquiries were posed to the operators active in each of the sites, having obtained answers from seven operators in Hetao, and from nine operators in Lower-Mondego, who answered by referring to the most common field parcels recently operated.

 

Section 2: Materials and Methods - Question 4:

16 Field Experiments selected based on authors long field expertise (line 285-286, pg.8 is not sufficient or clear in terms of the methodology applied for which field sites were selected and why, in addition, as this is looking for an impact of the intervention on specified parameters of irrigation performance, it is not clear what is the counterfactual field site (farms that did no PLL interventions) and or a baseline over time when these points are collected against specific farms or field sites with PLL interventions and in a previous year (without PLL interventions) so the comparative across the field sites is missing and not well specified. This needs substantial clarity to further outline the novel contributions of this study.

 

Answer 4:

This component of the study refers to “16 irrigation projects”, corresponding to design projects of modernized systems developed by simulation (explanation in lines 272-281), applied to fields described in Table 5. In Hetao, the longest fields (particularly 200 m length) correspond to scenario of field reshaping; in Lower-Mondego all fields correspond to the actual condition. PLL is considered in all these projects, using the parameters presented in lines 368-372. A previous study (Miao et al. 2015) assessed the traditional practices of land levelling and irrigation management in Hetao. To clarify this, a sentence was added in line 288:

“A set of 16 irrigation projects were considered in this study, through a simulation process, being selected based on the authors experience, applying the irrigation methods and the on-farm distribution systems with more potential and feasibility for each one of the study sites (Table 5): ...”

Section 2: Materials and Methods - Question 5:

Lastly, in the methods section, it is positive that the authors describe two types of canal systems between China and Portugal study sites but some clarity on the starting condition of the overall irrigation system is needed, were the canals operating at full capacity and potential at the start of the field experiment? Or did some canals suffer from distribution or seepage channels - important to describe how canal system efficiency can also affect the parameters of irrigation water efficiency, and economic water efficiency (in spite of the PLL interventions). This needs to be elaborated and explained at the outset.

 

Answer 5:

The on-farm distribution systems considered are explained in lines 295-297 and first three lines of Table 4. For Hetao, the solution was the non-lined canal, due to the high charge of water sediments of Yellow River, the unique solution that allows an efficient maintenance to clean those sediments. The lined canal would be possible, but is very expensive and only is used in the collective conveyance system. The seepage in the on-field canal is not significant, because the use of those canal is reduced to the irrigation event time. Therefore, this seepage was not considered. For Lower-Mondego, the distribution system in by pipe, being the layflat tubing the usual. The solution of rigid gated pipe is not feasible because it is not tradable.

To clarify this option, the text of lines 295-297 was changed:

The on-farm water distribution system considered was: i) for Hetao, the non-lined canal equipped with modern field gates, well-adjusted to the high charge of sediments of irrigation water which does not allow a pipe distribution system, a low cost solution, well practiced by farmers; ii) for Mondego, the lay-flat tubing with manual valves to adjust each single gate, the most usual solution, with a reduced cost and well managed by farmers.

 

Section 3 Results - Question 1:

On lines 370-374, pg. 12, the authors make a potentially important insight on the impacts of modernization of canal irrigation systems and how the combination of modernization + PLL measures which has positive responses on the BWUF indicator - however, what is not clear is what is the causal difference that the PLL mechanism is making as how can we differentiate the impact of the PLL vs. the modernization effect? Either the authors upfront state they are not trying to purely pull out the instrumental difference in irrigation parameters purely from PLL interventions (As that is how it is currently framed in the Introduction) but talk about how modernization efforts can then create the right enablers for farmers to begin adopting water saving and irrigation efficiency techniques (one of them being PLL) as it is widely recognized in the literature that PLL is not the only technique available to farmers for enhancing yield, efficiency, cost, and income gains - this argument needs to be substantially sharpened and goes back to my original point - it is not well argued and grounded in the existing literature - what is the novel contribution of this analysis to the field?

 

Answer 1:

The first aspect of this answer was referred in Answer 1.

The beneficial impact of the PLL as well as the irrigation management are well known and taken for granted. In this study, we did not aim to assess the PLL impact versus the irrigation management impact. Instead, our study focused on the integrated management of those aspects in two case studies. This goal was set, because our experience in the development of surface irrigation systems show that to achieve acceptable and good results three conditions should be satisfied: PLL, irrigation scheduling and inflow adjustment and control. Their relative importance is variable, depending on the local conditions. When looking for the modernization, saving water, labor, energy and cost, the systems need the best condition relative to those three factors.

A current problem in several regions is that surface irrigation systems is the devaluation of PLL, postponing the maintenance operation and reducing its accuracy. In fact the impacts of loss of quality of the land leveling are gradual in time and go unnoticed. Frequently, farmers have the perception that a good irrigation performance could be obtaining just with a timely and an optimal inflow control. This study highlighted the importance of PLL and gave the technical and economic data, useful for project and planning.

To clarify this question, the phrase of lines 377-378 was changed: “It should be noted that these results combine the effects of PLL with adequate irrigation scheduling, inflow rates and cut-off control, it is not possible to differentiate the isolated effects of each of these factors.”

 

Section 4 Discussion - Question 1:

1 - This sentence "Therefore, the results of the present study confirm the success of surface irrigation, showing that PLL had direct impact on maize water productivity and economics. Values of BWUF of 80%-90%, IWP of 2.0-2.4 kg/m3, and EWPR of 6-8, were observed on Hetao and Lower-Mondego, which are similar to the good ones achievable by sprinkler systems." (lines 446-450) reflect my comments above, we cannot isolate for the causal impact of PLL alone as these are combined with modernization of the canal system at a major or medium reservoir scale (or not, that is also not very clear) - so the authors need to nuance this point based on the results obtained because can we say the value of BWUF of 80-90% is purely due to the PLL interventions? This needs to be clarified and elaborated upon in the discussion.

 

Answer 1:

To clarify this question, the phrase of lines 451-455 was changed: “Therefore, the results of the present study confirm the success of surface irrigation, showing that PLL, combined with adequate irrigation scheduling and control of inflow rates and cut-off, had direct impact on maize water productivity and economics. Values of BWUF of 80%-90%, IWP of 2.0-2.4 kg/m3, and EWPR of 6-8, were observed on Hetao and Lower-Mondego, which are similar to the good ones achievable by sprinkler systems.”

 

Section 5. Conclusions - Question 1:

1 - Overall, it is important to point out that land levelling maintenance is one of the various options available to farmers for on-farm development, other interventions (better inputs, technology adoption with respect to irrigation technologies, better crop and data services) can also achieve similiar objectives of enhanced water productivity and income growth for farmers where surface systems are modernized - this point needs to nuance and place the findings of this study in the wider literature that examines specific interventions for enhancing on-farm development in surface irrigated systems in Asia and the Mediterranean.

 

Answer 1:

We agree with this perpsective that other actions (beyond PLL) are determinant to achieve good results. Pertinent references have been inserted in the article: Abdullaev et al. [3] for Tajikistan, Gonçalves and Pereira [22] for Portugal, Bai et al. [9] for China, Playan et al. [2] for Spain. To highlight it, the paragraph of lines 550-556 was changed:  

 

Land levelling maintenance is an important issue to guarantee a high effectiveness of irrigation performance. It should be highlighted that the its effectiveness requires the adoption of other improvement measures, namely those related with the irrigation management, or with the agronomic inputs and practices. The optimization of PLL appeals the application of better soil tillage practices and the monitoring of soil surface elevations with newer information technology tools to support decisions about the land levelling maintenance. Efficient operational guidelines to support the PLL planning, schedule, and operation are key factor to its improvemente, such as well trained operators, carefully adjusted equipment, and informed farmers. Appropriate extension and training services for farmers and equipment operators, as well as institutional and economic incentives, are also determinant.

 

Reviewer 2 Report

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Comments for author File: Comments.pdf

Author Response

Note: this reviewer did not present questions.

Reviewer 3 Report

Dear authors:

This paper is well organized, structured and written. Offers scientific robustness.

From my point of view it is a publishable paper, without a doubt. Technically, it is an excellent paper.

However, perhaps the authors could improve it. Some suggestions are as follows:

• To Introduce in the introductory section more basic and theoretical information.
• To Add cartography of the zones or specific areas of analysis.
• Agregar fotografías de las áreas de estudio que faciliten la comprensión de los resultados.

On the other hand, perhaps the authors should mention, in addition to the pernicious effects of using these techniques for fertile soils (increased erosion, etc.), and that their formation requires a process of many years, the negative effects on the traditional landscape. Traditional irrigated landscapes sometimes constitute a cultural identity. With the leveling of the land, homogeneous landscapes are generated, also with the concentration of parcels, losing that landscape diversity that characterizes traditional irrigated landscapes.

Clearly, there are economic and environmental benefits in terms of improved irrigation efficiency and lower water consumption, but sometimes other social and environmental aspects not related to the economy must be valued.

Best regards,

CE

Author Response

Question 1:

To Introduce in the introductory section more basic and theoretical information.

Answer 1:

Our idea relative to the writing the Introduction include the general presentation of the problem, the state of the art of technologies to solve it, and the objectives of the study. More details with basic and theoretical aspects have been placed in Material and Methods chapter. The question that we do not understand is if these aspects are not properly developed in this chapter.

 

Question 2:

To Add cartography of the zones or specific areas of analysis.

Answer 2:

This question is very pertinent, an issue that we pondered before. To include this cartography demanded more two figures of the studied areas, of Lower-Mondego and Hetao. It seems that those maps do not input an effective value to the manuscript. Therefore, think that the relevant information of the experimental plots is presented on Table 1.

 

Question 3:

Agregar fotografías de las áreas de estudio que faciliten la comprensión de los resultados.

Answer 3:

Analogous to question 2, this one is also very pertinent. Photographs could be interesting illustration of equipments and crops, but we concluded that in practice the photographs that we have available from the field work do not have additional values compared with the typical land levelling equipment published.

 

Question 4:

On the other hand, perhaps the authors should mention, in addition to the pernicious effects of using these techniques for fertile soils (increased erosion, etc.), and that their formation requires a process of many years, the negative effects on the traditional landscape. Traditional irrigated landscapes sometimes constitute a cultural identity. With the leveling of the land, homogeneous landscapes are generated, also with the concentration of parcels, losing that landscape diversity that characterizes traditional irrigated landscapes.

Clearly, there are economic and environmental benefits in terms of improved irrigation efficiency and lower water consumption, but sometimes other social and environmental aspects not related to the economy must be valued.

Answer 4:

The significant impacts of land levelling on rural landscape occur when big changes are made during the processes of land reshaping or the installation of a new irrigation district. This question is undoubtedly important, so a reference will be made in the Discussion. The phrase of lines 466-470 was changed:

Therefore, reparcelling of land is determinant in several regions to increase the plot size for better production efficiency. Another advantage of reparcelling and PLL in small land areas is the enhance of the cultivable area due to removal of extra bunds and channels in the field: Jat et al. [15] and Sidhu et al. [52] reported increased average areas of 3.2% and 9%, respectively. These changes of the rural environment should be carefully analysed to consider its impacts on landscape, livelihood, social, traditional culture and heritage [Groenfeldt 2006].

New reference:

Groenfeldt, D. Multifunctionality of agricultural water: looking beyond food production and ecosystem services. Irrig. and Drain. 2006, 55: 73-83; doi: 10.1002/ird.217.