Grey water footprint reduction in irrigated crop production: effect of nitrogen application rate, nitrogen form, tillage practice and irrigation strategy

Chukalla, Abebe D.; Krol, Maarten S.; Hoekstra, Arjen Y.

doi:https://doi.org/10.5194/hess-22-3245-2018

Articles | Volume 22, issue 6

https://doi.org/10.5194/hess-22-3245-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-22-3245-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 22, issue 6

Research article

|

11 Jun 2018

Research article |

| 11 Jun 2018

Grey water footprint reduction in irrigated crop production: effect of nitrogen application rate, nitrogen form, tillage practice and irrigation strategy

Abebe D. Chukalla, Maarten S. Krol, and Arjen Y. Hoekstra

Download

Final revised paper (published on 11 Jun 2018)
Preprint (discussion started on 04 May 2017)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

- Printer-friendly version

- Supplement

RC1: 'Review', Anonymous Referee #1, 26 May 2017
- AC1: 'Reply to Referee #1', Abebe Demissie Chukalla, 30 Jul 2017
RC2: 'Comments for Grey Water Footprint Reduction in Irrigated Crop Production', Ann-Perry Witmer, 27 Jun 2017
- AC2: 'Reply to the comments from Ann-Perry Witmer', Abebe Demissie Chukalla, 30 Jul 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by Editor and Referees) (21 Aug 2017) by Nandita Basu

AR by Abebe Demissie Chukalla on behalf of the Authors (05 Sep 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Sep 2017) by Nandita Basu

RR by Anonymous Referee #3 (05 Jan 2018)

RR by Anonymous Referee #4 (23 Jan 2018)

Suggestions for revision or reasons for rejection

The authors tried to show the trade-off between crop yield, nutrient application rates, and nutrient loading to downstream waterbodies. However, I do not think the findings are new to the literature (please read Journal of Soil and Water Conservation and other relevant journals). In addition, the methodology including APEX model preparation and leaching-runoff fraction definition is unclear and questionable. Furthermore, the results are confusing, and they are not appropriately presented and explained in the manuscript. My specific comments are provided below.

Lines 21 to 22: Does this mean the crop yield decreases from 11.1 ton/ha to 3.7 ton/ha when the N application rate is reduced from 300 kg N/ha to 50 kg N/ha? Is so, I do not think this N application scenario is feasible and realistic since farmers will not apply this practice.

Lines 28 to 30: Applying manure can cause another water quality (phosphorus) issues such as algal bloom and eutrophication.

Lines 51 to 52: I do not follow this sentence. I do not understand why water pollution (or nutrient loads) is compared to the volume of crops produced. Is this a meaningful comparison?

Lines 49 to 73: What is the main idea of this paragraph?

Lines 180 to 182: I wonder if the authors had a chance to evaluate the applicability of the maximum acceptable N concentration (of 50 N mg/L) and natural concentration (of 0.5 mg N/L) to the study watershed. They must be highly varying depending on many factors.

Lines 204 to 220: I do not understand why the leaching-runoff fractions are less than 1.0. For instance, the N load to freshwater bodies can be greater than the N fertilizer applied or the N applied but not taken up by the plant. Please describe the mathematical relationship between the variables.

Lines 241 to 253: There is no information about the reliability of the assumptions made. I wonder if the authors had a chance to compare the assumptions with other reference values, statistics, and field observations.

Lines 282 to 290: I could not find information about how the other parameters (for flow, N cycle and transport) were determined. I believe they might be calibrated to measurements, but there is no description about the parameter calibration.

Line 361: Could you explain why the grey WF is minimized at the N application rate of 50 kg N/ha rather than 25 kg N/ha? In addition, the authors might be able to find an N application rate that minimizes grey WF between 50 and 100 kg N/ha. In addition, I wonder if these results can be applicable to other cases and watersheds.

Lines 373 to 392 and Figure 5: In Figure 5b, the largest consumptive WF (blue and green WFs) is found at the lowest nitrogen application rates (of 25 kg N/ha), and it rapidly decreases with increases in the application rates. When nitrogen application rates low, however, crop yields are also low, and ETs are low as well, as demonstrated in Figure 5a. Thus, consumptive WF should be low when the nitrogen application rates are low (rather than high like 3000 m3/ton, compared to 700 m3/ton). Please explain why the consumptive WF is high even though ET is low when nitrogen application rate is low.

Lines 402 to 447: I do not understand these descriptions and explanations.

Lines 464 to 464 and Table 2: I believe it is good to show three WFs separately rather than total WF so that the authors can effectively discuss the strengths and weaknesses of each scenario.

Lines 488 to 492: I think the findings mentioned are well known (not new to the literature). The authors just used different terms such as grey, blue, and green water footprint.

Hide

RR by Anonymous Referee #5 (02 Apr 2018)

Suggestions for revision or reasons for rejection

GENERAL COMMENTS
This manuscript details the results of a modeling exercise to assess the fate of nitrogen and grey water footprint size in agricultural systems under different management practices. The authors use the Agricultural Policy Environmental eXtender (APEX) model to assess crop yields and nutrient leaching/ runoff, and results are compared against a more simplistic, less-data intensive, expert-based approach for estimating N loads from agricultural areas. The assessments are based on climate and agricultural characteristics of a farming region in Spain. Results indicated that for low levels of nitrogen application, the simple approach yields approximately the same results as the more data-intensive modeling endeavor. At higher levels of nitrogen application, the simple method underestimates nitrogen leaching/runoff. The modeling results also explored multiple types and combinations of management practices, finding there are inevitable tradeoffs between crop yield and water pollution, and water pollution and water consumption.

SPECIFIC COMMENTS
This is an interesting paper with potential implications for applied agricultural management to reduce water pollution problems while minimizing negative impacts to crop yields. The following are a few comments that could help improve this work if incorporated.

- Lines 79-84 provide an overview of studies that have explored the impacts of crop yield and N management via various agricultural management practices. However, what would be more helpful to the reader is an overview of those study findings, and how these findings informed the present work.

- I realize that validating model results with field experiments is difficult, and the authors clearly explain why this is so (Lines 90-94). I also appreciate the author’s comparison of their model results with those of Berenguer et al 2009- particularly given that the APEX results are only really comparing Tier 1 and Tier 3 levels. Given the lack of field data available, this multi-model comparison is very important. However, I feel the discussion and comparison of model results is short and lacks depth. There is brief mention of modeling results based on EU studies, and research by Berenguer et al 2009, but digging in and really discussing the differences and similarities between these results would add greatly to this work.

- At the beginning of Section 2.3, the authors state that part of the reason for evaluating Tier 3 vs Tier 1 is to see if “the simpler estimation approach (Tier 1) as applied to previous studies” is an accurate measure. I’m not sure what these “other studies” are in particular, maybe they’re the ones I mention in the comment above, but either way, there could be much value added to explicitly showing the comparisons between Tier 1 results and Tier 3 results, if possible?

TECHNICAL COMMENTS

- In line 36, “fertilizer” should be “fertilizers”.

- The authors use the spelling “freshwater” and “fresh water” in this manuscript (see lines 38 and 39 for examples). One spelling version should be selected and used consistently throughout.

- In line 157, I suspect the authors meant “Phenological”, not “Phonological”.

- Equations 4 & 5 (Lines 220-223) reference work done by Franke et al 2013. In these equations, there is a variable s¬_i that is a “score for leaching runoff potential”, while I realize this is information from another paper, it would be helpful to discuss how these values are developed, even if briefly.

- In Figs 8 & 9, I assume the “calculated, tier-1” numbers (in blue) are mean values? Please specify in the body of the manuscript for clarity.

Hide

RR by Anonymous Referee #6 (07 Apr 2018)

ED: Publish subject to minor revisions (review by editor) (12 Apr 2018) by Nandita Basu

AR by Abebe Demissie Chukalla on behalf of the Authors (21 Apr 2018) Author's response Manuscript

ED: Publish as is (10 May 2018) by Nandita Basu

AR by Abebe Demissie Chukalla on behalf of the Authors (22 May 2018) Manuscript

Short summary

This paper provides the first detailed and comprehensive study regarding the potential for reducing the grey WF of crop production by changing management practice such as the nitrogen application rate, nitrogen form (inorganic N or manure N), tillage practice and irrigation strategy. The paper shows that although water pollution (grey WF) can be reduced dramatically, this comes together with a great yield reduction.