Effect of Tillage, Previous Crop, and N Fertilization on Agronomic and Economic Performances of Durum Wheat (Triticum durum Desf.) under Rainfed Semi-Arid Environment

Round 1

Reviewer 1 Report

This paper deals with a very interesting and important topic which is agronomic and environmental performances of cropping systems, among which conservation agriculture, also called no-tillage here, except at the end… Hence, you have to be precise in the terms, and if the three pillars of CA are respected, you have to use the terminology ‘conservation agriculture’ everywhere.

The problematic is clear, and the experimental design and data analysis are clear as well, except one point: we do not know if we are facing to a real CA system or not (re. the three pillars), nor the age of it (which has to be given).

The discussion is very well carried out and documented, but would gain of being enriched with elements and thoughts about the importance of arbuscular mycorhizal fungi. These latter are abundant in CA systems and strongly support plant hydro-mineral nutrition. Doing so, how could they have influenced NUE and WUEg values?...

Hereafter, I only give some very minor recommendations to improve the article’s form, since in substance the work looks to me to have been very well done (just improve the points seen above).

Specific comments

1. Abstract:

• line 25: write “Semi-arid Environment” without capitals
• line 28: “Our results show that…” (show without s)
• line 29: delete “than”
• line 30: add “was”: “when DW was grown using…”
• line 33: delete N and put n at “No-tillage”
• line 34: delete “support of” and replace with “provide”
• line 38: idem as line 25

1. Introduction:

• line 43: “covers” and not “covering”
• line 59: add soil before “erosion control”
• line 72: adoption and not adoption
• line 75: what do you want to say? Is it “…and costs, would result in the continued erosion of crops’ gross margin” ?
• line 116: Bourabia or Bourbiaa ? (as in lines 84 and 85)

1. Materials and methods

• line 116: Bourabia or Bourbiaa ? (as in lines 84 and 85)
• line 155: Glyphosate without G but g
• lines 158-159: in lines, 97-98, you gave N rates from N4 to N0; hence, you should give them in the same order here.
• line 165: did you want to write “We assessed the agronomic and…” ? I suggest you to replace “analyzed” with “studied”
• line 174: R3.4.2 and not r3.4.2
• lines 198-201: change the text formatting
• line 208: “No differences were observed for other combinations…”
• lines 206, 211, 217, 218, 223, 241: “…had no significant…”
• line 217: delete “,” and  “.”  Respectively after “PC” and “N_grain”
• line 227: write “…more efficient for nitrogen use and water” instead of the reverse
• line 230: “increasing” without I but i

[new line numbering from page 9 to the end]

• line 20: “Our results show that…” (show without s)
• line 21: two spaces between words missing
• line 25: However (not Howerver)
• line 26: with (not whith)
• line 33: what do you mean with “CT-NT” between brackets? I guess that you wanted to write “CT-N4”, but better to entirely delete, as you never give the combination before the TND value in the other brackets

1. Discussion

• line 64: “…the highest yield, whereas without N-fertilization, NT had the lowest one.”
• line 88: durum and not drurum
• line 89: delete “than” and add “was”: “…higher when DW was grown using…”
• line 103: “CA" has never been defined in the article. Either you write in full words “conservation agriculture”, or you write NT
• line 104 : “…the importance of crop diversification for the success of conservation…”
• line 126 : “becomes” or “became”?
• lines 127-129: the sentence “Under water-limited… resource-use efficiency” is not understandable since both water and nitrogen are renewable resources. Please, be clearer and explain
• lines 129-130: why “their” (twice), since the subject is “DW growing” ?... Are you sure that “growing” is the appropriate term?
• line 132: similar and not “smiliar”
• line 135: add “wheat” after “bread”

1. Conclusion

• line 150: affected ; delete “than”
• line 151: add “was” before “grown”
• line 151: delete a space before “nitrogen use”
• line 152: “becomes” or “became”?
• line 159: lowercase n at “No-tillage”
• line 160: add “cultivation” after DW
• line 161: delete a space before “N-use efficiency”
• line 163: add “cultivation” after “wheat”

Author Response

Response to Reviewer 1 Comments

Point 1: line 25: write “Semi-arid Environment” without capitals

Response 1: It has been changed.

Point 2: line 28: “Our results show that…” (show without s)

Response 2: It has been changed.

Point 3: line 29: delete “than”

Response 3: It has been changed.

Point 4: line 30: add “was”: “when DW was grown using…”

Response 4: It has been changed.

Point 5: line 33: delete N and put n at “No-tillage”

Response 5: It has been changed.

Point 6: line 34: delete “support of” and replace with “provide”

Response 6: It has been changed.

Point 7: line 38: idem as line 25

Response 7: It has been changed.

Point 8: line 43: “covers” and not “covering”

Response 8: It has been changed.

Point 9: line 59: add soil before “erosion control”

Response 9: It has been added.

Point 10: line 72: adoption and not adoption

Response 10: It has been changed.

Point 11: line 75: what do you want to say? Is it “…and costs, would result in the continued erosion of crops’ gross margin” ?

Response 11: We delete this reference

Point 12: line 116: Bourabia or Bourbiaa ? (as in lines 84 and 85)

Response 12: It has been modified to Bourabia.

Point 13: lines 158-159: in lines, 97-98, you gave N rates from N4 to N0; hence, you should give them in the same order here.

Response 13: It has been changed.

Point 14: line 165: did you want to write “We assessed the agronomic and…” ? I suggest you to replace “analyzed” with “studied”

Response 14: It has been changed to The agronomic and economic variables were analyzed…

Point 15: line 174: R3.4.2 and not r3.4.2

Response 15: It has been changed.

Point 16: lines 198-201: change the text formatting

Response 16: It has been changed.

Point 17: line 208: “No differences were observed for other combinations…”

Response 17: It has been changed.

Point 18: lines 206, 211, 217, 218, 223, 241: “…had no significant…”

Response 18: It has been changed.

Point 19: line 217: delete “,” and  “.”  Respectively after “PC” and “Ngrain”

Response 19: It has been changed.

Point 20: line 227: write “…more efficient for nitrogen use and water” instead of the reverse

Response 20: I mean water- and nitrogen-use.

Point 21: line 230: “increasing” without I but i

Response 21: It has been changed.

 [new line numbering from page 9 to the end]

Point 22: line 20: “Our results show that…” (show without s)

Response 22: It has been changed.

Point 23: line 21: two spaces between words missing

Response 23: It has been changed.

Point 24: line 25: However (not Howerver)

Response 24: It has been changed.

Point 25: line 26: with (not whith)

Response 25: It has been changed.

Point 26: line 33: what do you mean with “CT-NT” between brackets? I guess that you wanted to write “CT-N4”, but better to entirely delete, as you never give the combination before the TND value in the other brackets

Response 26: It has been changed.

Point 27: “line 64: “…the highest yield, whereas without N-fertilization, NT had the lowest one.”

Response 27: It has been changed (line 63).

Point 28: line 88: durum and not drurum

Response 28: It has been changed (line 87).

Point 29: line 89: delete “than” and add “was”: “…higher when DW was grown using…”

Response 29: It has been changed.

Point 30: line 103: “CA" has never been defined in the article. Either you write in full words “conservation agriculture”, or you write NT

Response 30: It has been changed.

Point 31: line 104: “…the importance of crop diversification for the success of conservation…”

Response 31: It has been changed.

Point 32: line 126: “becomes” or “became”?

Response 32: It has been changed (became).

Point 33: lines 127-129: the sentence “Under water-limited… resource-use efficiency” is not understandable since both water and nitrogen are renewable resources. Please, be clearer and explain

Response 33:  ”non-renewable” has been deleted.

Point 34: lines 129-130: why “their” (twice), since the subject is “DW growing” ?... Are you sure that “growing” is the appropriate term?

Response 34: It has been changed. Yes, ”growing” is the appropriate term.

Point 35: line 132: similar and not “smiliar”

Response 35: It has been changed.

Point 36: line 135: add “wheat” after “bread”

Response 36: It has been changed.

Point 37: line 150: affected; delete “than”

Response 37: It has been changed.

Point 38: line 151: add “was” before “grown”

Response 38: It has been changed.

Point 39: line 151: delete a space before “nitrogen use”

Response 39: It has been changed.

Point 40: line 152: “becomes” or “became”?

Response 40: It has been changed to ‘’became’’ (simple past tense).

Point 41: line 159: lowercase n at “No-tillage”

Response 41: It has been changed.

Point 42: line 160: add “cultivation” after DW

Response 42: It has been changed.

Point 43: line 161: delete a space before “N-use efficiency”

Response 43: It has been changed.

Point 44: line 163: add “cultivation” after “wheat”

Response 44: It has been changed.

Point 45: The discussion is very well carried out and documented, but would gain of being enriched with elements and thoughts about the importance of arbuscular mycorhizal fungi. These latter are abundant in CA systems and strongly support plant hydro-mineral nutrition. Doing so, how could they have influenced NUE and WUEg values?

Response 45: This idea has been added

This latter could be also attributed to the enhancement of soil biological health including the abundance of arbuscular mycorhizal fungi (AMF) in no-tilled soils (Schalamuk et al. 2006), these mycorrhizae strongly enhance plant hydro-mineral nutrition through higher both water and nitrogen-use efficiency. These AMF are most effective in increasing yield and nutrient uptake of durum wheat as reported by Schutz et al. (2018).

Schütz L, Gattinger A, Meier M, Müller A, Boller T, Mäder P, Mathimaran N (2018) Improving crop yield and nutrient use efficiency via Biofertilization, a global meta-analysis. Front Plant Sci 8:2204

10. Schalamuk, S. Velazquez, H. Chidichimo & M. Cabello (2006) Fungal spore diversity of arbuscular mycorrhizal fungi associated with spring wheat: effects of tillage, Mycologia, 98:1, 16-22, DOI: 10.1080/15572536.2006.11832708

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper analysis the effect of tillage, previous crop, N fertilization on agronomic and economic performances of durum wheat under rainfed semi-arid environment.

The paper is well written but there are some improvements needed:

+ Suggestion for keywords: durum wheat, crop yield, nitrogen use efficiency, water use efficiency, gross margin, tillage systems, semi-arid environment

Formal improvements:

+ Title should be written with small letters, Include also Triticum durum in the title

+ be consistent with agronomic. At present there is a mixture of agronomic and biophysical.

+ Harmonize of the factors: Season, tillage, pre-crop (instead of PC), N rate

Line 25: semi-arid instead of Semi-arid

Line 71: adoption

Line 93: 1500 kg ha-1 of crop residues

Line 169: model tillage

Content comments:

+ Line 148-163, Section 2.8: What does (See Annex for detail) mean.

Explain the constant factors (1052 and 1040) in the equation.

+ For table 3: The source of variance caused by season is missed. This data of the two growing seasons 2013/14 and 2014/15 with different rainfall will support the interpretation of the results. What is the effect of a wet growing season (2013/14) and dry growing season (2014/15) on the analysed parameters?

+ Check the significance of interactions: e.g. For the variable WUEg it is not traceable, why the interaction tillage*season is significant, although the main effects of season and tillage are not significant. 

+ Line 63-69 on page 11: I cannot see the nitrogen immobilization effect in NT on grain yield in your data.

+ Figure 2: Are the inserted letters in d´) correct? The bars with SE would expect statistically significant differences between different N rate.

Author Response

Response to Reviewer 2 Comments

Point 1: Suggestion for keywords: durum wheat, crop yield, nitrogen use efficiency, water use efficiency, gross margin, tillage systems, semi-arid environment

Response 1: It has been modified according to the suggested keywords.

Point 2: Title should be written with small letters, Include also Triticum durum in the title

Response 2: It has been modified.

Point 3: be consistent with agronomic. At present there is a mixture of agronomic and biophysical.

Response 3: It has been modified to ‘agronomic’.

Point 4: Harmonize of the factors: Season, tillage, pre-crop (instead of PC), N rate

Response 4: It has been modified.

Point 5: Line 25: semi-arid instead of Semi-arid

Response 5: It has been modified as requested.

Point 6: Line 71: adoption

Response 6: It has been modified.

Point 7: Line 93: 1500 kg ha^-1 of crop residues

Response 7: It has been changed to 1500 kg ha^-1.

Point 8: Line 169: model tillage

Response 8: This comment is not clear.

Point 9: Line 148-163, Section 2.8: What does (See Annex for detail) mean. Explain the constant factors (1052 and 1040) in the equation.

Response 9: "1052" and "1040" are the total of charges of variable costs (TND ha^-1) under two tillage systems NT and CT, respectively.

I put a table in the annex for detail to explain the constant factors (1052 and 1040) in the equation.

Point 10: For table 3: The source of variance caused by season is missed. This data of the two growing seasons 2013/14 and 2014/15 with different rainfall will support the interpretation of the results. What is the effect of a wet growing season (2013/14) and dry growing season (2014/15) on the analysed parameters?

Response 10: Tillage*season effect has been added in the result part.

Point 11: Check the significance of interactions: e.g. For the variable WUEg it is not traceable, why the interaction tillage*season is significant, although the main effects of season and tillage are not significant.

Response 11: We checked and this is right.

Point 12: Line 63-69 on page 11: I cannot see the nitrogen immobilization effect in NT on grain yield in your data.

Response 12: In figure 2, we can see the nitrogen immobilization effect in NT on grain yield (Grain yield in N0-NT is significantly lower than that recorded in N0-CT).

Point 13: Figure 2: Are the inserted letters in d´) correct? The bars with SE would expect statistically significant differences between different N rate.

Response 13:  After verification the inserted letters in d´) are correct.

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript describes an experiment assessing the effect of two tillage practices, two preceding crops and five rates of N fertilization on the yield and monetary return of a durum wheat crop in a semi-arid climate. This study is interesting and reports valuable results for application in such production area. In my own perspective, it would deserve to be published but a lot of changes will be needed at first to bring this paper to a good standard of publication. Here are my principal considerations and suggestions after a first reading. I just take a look at the scientific aspects.

1. First, it may be too short to define benefits of using NT vs. CT with a study that lasted only 2 years. Usually, several years of implementation of a tillage practice are required to see the real effects. Please take into account this aspect.
2. The authors should reduce the number of abbreviations. There are too many which make the reading very difficult to follow. Keep CA, NT, CT, NUE and WUE and use the complete words such as wheat, grain yield, straw yield, grain N otherwise.
3. It looks to me that there are too many references in this paper (68). Many references are only listed in the introduction and others only in the discussion. A part of references should be listed in both sections to make a good link throughout the text.
4. L74: The authors reported the study of Mhiri that said damage in term of trade affects the profitability of margin gross. Explain longer as there is an important feature of this study. Also, it is important to cite other studies on economic aspects of NT, in northern Africa or elsewhere. This part is little elaborated in the introduction while the other aspects, more agronomic, have been well brought.
5. One aspect not mentioned in the material and methods is the difference between the season 1 and the season 2. The same plots were used or a different site, because there was the factor ‘previous crop’ in the experimental design?
6. Did the vetch serve only as a cover crop or was there any economic benefit in the year of cropping? With the bread wheat, there is a benefit with grain selling. Keeping in mind this when evaluating the whole economic aspect of NT vs CT.
7. I find something special that variable costs with NT was higher than with CT whereas it is generally reported that NT allows a reduction in operation costs. Here, differences seem attributed to glysophate application and seeding operation, which reduced the profitability of NT.
8. Statistical analysis demonstrated a tillage x season very significant and this aspect was not taken into account. Analysis should be redone by season at a first time before discussing the other factors.
9. Analysis of N rate should be done by contrast (linear, quadratic). It would be more appropriate and the results will be easier reported.
10. Improvement in the presentation of results. The sentences (and paragraphs) are too short and needed to be regrouped and better synthesized. Right now, this is just a launch of raw idea.
11. There are many grammatical errors in the gross margins section. Please correct.
12. Fig 3 on the relationship between NUE and WUE has not really been exploited in the discussion (difference between slope and Y-intercept with N rate).

Author Response

Response to Reviewer 3 Comments

Point 1: First, it may be too short to define benefits of using NT vs. CT with a study that lasted only 2 years. Usually, several years of implementation of a tillage practice are required to see the real effects. Please take into account this aspect.

Response 1: I took it into account. I nuanced this aspect in the conclusion and in the abstract part.

Point 2: The authors should reduce the number of abbreviations. There are too many which make the reading very difficult to follow. Keep CA, NT, CT, NUE and WUE and use the complete words such as wheat, grain yield, straw yield, grain N otherwise.

Response 2: It has been changed as requested.

Point 3: It looks to me that there are too many references in this paper (68). Many references are only listed in the introduction and others only in the discussion. A part of references should be listed in both sections to make a good link throughout the text.

Response 3: We deleted 9 references and we are obliged to add 4 new references: 2 for economic aspects (as response to reviewer 3 comment).

and 2 for AMF benefits (as response to reviewer 2 comment).

Point 4: L74: The authors reported the study of Mhiri that said damage in term of trade affects the profitability of margin gross. Explain longer as there is an important feature of this study. Also, it is important to cite other studies on economic aspects of NT, in northern Africa or elsewhere. This part is little elaborated in the introduction while the other aspects, more agronomic, have been well brought.

Response 4:

Mhiri (2018) reference has been removed from the introduction part.

We added “In this vein, conservation agriculture is prone to reduce production costs and increase profitability, often attributed to decreases in energy and labor consumption compared to conventional systems (Erenstein et al., 2012). Economic benefits associated with reduced soil erosion are considered as the main reasons to adopt no-tillage system (Derpsch et al., 2010).”

Point 5: One aspect not mentioned in the material and methods is the difference between the season 1 and the season 2. The same plots were used or a different site, because there was the factor ‘previous crop’ in the experimental design?

Response 5: Same site were used but other plots since respecting the rotation pattern.

Point 6: Did the vetch serve only as a cover crop or was there any economic benefit in the year of cropping? With the bread wheat, there is a benefit with grain selling. Keeping in mind this when evaluating the whole economic aspect of NT vs CT.

Response 6: In the trail, vetch is served as previous crop.  For this study, we evaluate only the gross margins of durum wheat (as strategic crop) and not the gross margins of the cropping systems.

Point 7: I find something special that variable costs with NT was higher than with CT whereas it is generally reported that NT allows a reduction in operation costs. Here, differences seem attributed to glyphosate application and seeding operation, which reduced the profitability of NT.

Response 7: Differences is low 12 TND ha^-1 ≃ 4 USD ha^-1 and is attributed to glyphosate application and seeding operation (direct seeding operation is slightly higher than that of conventional seeding).

Point 8: Statistical analysis demonstrated a tillage x season very significant and this aspect was not taken into account. Analysis should be redone by season at a first time before discussing the other factors.

Response 8: For tillage x season, we have added a sentence as requested by reviewer 2.

Point 9: Analysis of N rate should be done by contrast (linear, quadratic). It would be more appropriate and the results will be easier reported.

Response 9: We followed the methodology of Dalal et al., (2013).

Dalal, R.C.; Strong, W.M.; Cooper, J.E.; King, A.J. Relationship between water use and nitrogen use efficiency discerned by 13C discrimination and 15N isotope ratio in bread wheat grown under no-till. Soil Tillage Res. 2013, 128, 110–118, doi:10.1016/j.still.2012.07.019.

Point 10: Improvement in the presentation of results. The sentences (and paragraphs) are too short and needed to be regrouped and better synthesized. Right now, this is just a launch of raw idea.

Response 10: it has been improved.

Point 11: There are many grammatical errors in the gross margins section. Please correct.

Response 11: It has been corrected.

Point 12: Fig 3 on the relationship between NUE and WUE has not really been exploited in the discussion (difference between slope and Y-intercept with N rate).

Response 12:

The observed positive correlation between NUE and WUE (Fig. 3) is confirmed by Cabrera et al (2007) and Dadal et al (2013) for durum wheat and bread wheat, respectively. As the NUE is negatively correlated to N rate, the high N rates have less available water per N unit. In fact, under these conditions, plants become more efficient in WUE and less efficient in N use. The y-intercept is higher under NT than under CT which signifies that when WUE is very low, the NUE is higher under NT than under CT. Dalal et al (2013) explained this trend by the improvement of the NUE under NT compared to CT over 5-year period.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

This manuscript describes an experiment assessing the effect of two tillage practices, two preceding crops and five rates of N fertilization on the yield and monetary return of a durum wheat crop in a semi-arid climate. This version has been improved compared with the preceding one and several comments have been addressed. I did not make comments on the English writing at that stage but I provided general appreciation of the manuscript and how it can be improved to achieve a good standard for publication. Here are other considerations and suggestions before acceptance.

1. L24: … variability in climatic conditions that impact durum …
2. L25: … to assess the effects …
3. L25: … … practice, previous crop, …
4. L27: delete ‘tested in the paper’ … included …
5. L29: … on a 2-yr experiment, …
6. L30: grain N
7. L31: … when wheat was …
8. L32: N content
9. L34: available N.
10. L34: Our results highlight the …
11. L35: … vetch on enhanced yields, …
12. L44: … and meets about …
13. L45: … year, closely linked to …
14. L53: no-tillage (NT)
15. L58-60: this paragraph needs to be documented a little bit more or re-organized, with the references already cited. This is too short.
16. L62: conventional tillage (CT)
17. L64: NT
18. L68: CT
19. L72: new paragraph?
20. L75: where is reference [12]? Deleted? It is still present in the reference section. Please make a careful revision of the references, in order of appearance in the text and does it match correctly.
21. L87: The soil type for the field trial was a …
22. L88: clayey texture. The …
23. L93: evaluated
24. L96: delete ‘for the main crop: Durum Wheat’
25. L96: … -crop): a common … and a bread …
26. L99: The N fertilizer
27. L101: begin a new paragraph with ‘A Tunisian durum …
28. L102: … wheat, cv. Maali, was …
29. L111: replace ‘during the experimental period’ by ‘monitoring’
30. L116: was considered
31. L118: Then, 2014-2015 growing season was relatively dry.
32. L128: I do not understand this part. Grains were mechanically separated from the straw with this apparatus? Were the grains oven dried and cleaned before weighed?
33. L131: for total N content using …
34. L149: delete ‘expressed in TND ha-1- See’
35. L154: Note: herbicide also in post-seeding to all
36. L156 and L157: costs of N fertilizer
37. L159 and L160: minus straw yield x price. It reduces the variable cost unless the straw is harvested and thrown away.
38. L164: … using the MIXED procedure of …
39. L166: … separation were assigned …
40. L167: All factors are fixed except replicates which are random?
41. L178: This first sentence is not true because there is a very significant interaction between tillage and season. Begin with the interaction before going with the effect of tillage. Maybe, one year had a very high response and the other not.
42. L180: Also, interaction here between tillage and previous crop. The authors cannot conclude too rapidly on the effect of previous crop.
43. L178, L179, L196, L200, L204, L214, L224, L225 and other lines: grain N
44. L182: … with an average of …
45. L185: … (conventional and no-till) … and fertilizer N rate …
46. L186 and L191: … N content in grains, N use …
47. L194: … all treatments in each item
48. L196: Note: As mentioned in my first revision, the authors miss an important aspect of the study by not using the contrast analysis or at less a regression in the response curve of wheat yield to N rate. This also can serve in the economic analysis to determine the optimum N rate to be used in such field conditions in function of tillage practice and pre-crop. However, the N response did not show a plateau and therefore it will be difficult to determine an optimum N rate.
49. L196: N rate application
50. L201: However, grain N was similar among other N rates with an average of …
51. L203: The statistical analysis showed a significant Tillage x Season interaction on …
52. L204: … over the two …
53. L205: Note: by looking at these results, it seems to me that there was strong interactions that lead to overall no tillage effect on crop yield. In the first year, CT > NT and in second year CT < NT. This must be mentioned at the beginning of the results section but not later as this is the case now. And usually, interaction is shown with their respective values (as in Fig. 2) but not just an average of the treatments. Please revise.
54. L214: … interaction was …
55. L216: delete ‘on grain yield’
56. L216: Correct: Vetch pre-crop increased grain N in CT but decreased that in NT.
57. L218: Pre-crop did not interact with N rate to affect grain and straw yields (Table 2).
58. L220: On the other hand, Tillage and N rate showed a significant interaction on grain …
59. L221: Table 2
60. L221: treatment
61. L225: … grain N with 2.45%.
62. L226-230: The last sentence is the only to keep in this paragraph but move this to L219.
63. L232: The statistical analysis indicated that growing …
64. L233: also here, talk about the interaction before going to main treatment. The effect is more important and deserves to be mentioned.
65. L244: … over the two …
66. L248: By contrast, WUE significantly decreased under CT of …
67. L253: combinations
68. L255: Tillage by N rate significantly affected WUE but not NUE (Fig. 2).
69. L257: Note: the only difference is for N2. There is no difference between N1—N4 under NT and N1, N3 and N4 under CT.
70. L259-261: paragraph to delete
71. Figure 2: delete (Grain N). … all treatments in each item
72. L1: 3.1.3. Relationships between NUE and WUE
73. L2: merge the two paragraphs
74. L5: delete ‘(WUE and NUE)’
75. L7: … lines were significantly …
76. L7: The slope for N1 … than for higher N rates (4.0 vs. 1.8).
77. L9: different from what? N1?
78. L9: On the other hand, the slopes under CT was also significantly different with higher value for N1 (6.1) than for higher N rates (2.3-4.8).
79. L12: … for N2 vs. N3 and N2 vs. N4 (or N1+N2 vs N3+N4)?
80. L20: significant
81. L28: … over the two …
82. L38: … as they averaged 874 TND ha-1.
83. L39-41: delete this paragraph.
84. L45: … all treatments in each item
85. L54: The objectives of this study were to examine …
86. L59: delete ‘research’
87. L61: concluded at a best …
88. L68: … kg fertilizer N ha-1 applied, …
89. L70: However, …
90. L71: delete ‘mineral fertilizer’
91. L72: N fertilization
92. L79: Note: there is a significant tillage x season effect. I suggest to change significantly by remarkably. The difference in grain N was low.
93. L82: … observed after vetch compared to bread wheat.
94. L85: … with increasing N rates, …
95. L87: … demonstrated that NUE …
96. L97: by an increase …
97. L101: delete this portion of the sentence ‘this is mainly … [45].
98. L104: this paragraph needs to be re-written to be fitted with the preceding one (also merge the two paragraphs). Higher NUE was reported with wheat following vetch in NT than with any other combination. This was due to the more favorable environmental conditions for N uptake related to better …
99. L104: stages?
100. L109: … soils [47]. These …
101. L117: delete ‘as previous crop’
102. L120: delete ‘based’
103. L123: delete ‘level’
104. L124: .. in the no N …
105. L124: delete ‘research’
106. L135: replace ‘over 5-year period’ by ‘with long-term implementation’
107. L137: delete ‘than N1=75 kg N ha-1’
108. L141: growth
109. L145: This result supports …
110. L149: … legume were higher …
111. L155: … highest gross margins in durum …
112. L161: Based on a 2-yr experiment, …
113. L162: grain N concentration
114. L163: … mineral N application rate …
115. L169: conditions
116. Conclusion: the authors concluded that their findings support adoption and success of the conservation agriculture for durum wheat in Mediterranean. However, their studies have only two years. This may be enough for evaluating pre-crop and N rate but not for tillage practices that usually need 5 and even 10 years to see a real and constant effect. The absence of effect might be due to the short duration of the study. Please add this aspect to the conclusion.

Author Response

Response to Reviewer 3 Comments

Point 1: L24: … variability in climatic conditions that impact durum

Response 1: it has been modified as required.

Point 2: L25: … to assess the effects

Response 2: it has been modified as required.

Point 3: L25: … … practice, previous crop, …

Response 3: it has been modified as required.

Point 4: L27: delete ‘tested in the paper’ … included …

Response 4: it has been deleted.

Point 5: L29: … on a 2-yr experiment, …

Response 5: it has been modified as required.

Point 6: L30: grain N

Response 6: it has been modified as required.

Point 7: L31: … when wheat was …

Response 7: it has been modified as required.

Point 8: L32: N content

Response 8: it has been modified as required.

Point 9: L34: available N.

Response 9: it has been modified as required.

Point 10: L34: Our results highlight the …

Response 10: it has been modified as required.

Point 11: L35: … vetch on enhanced yields, …

Response 11: it has been modified as required.

Point 12: L44: … and meets about …

Response 12: it has been modified as required.

Point 13: L45: … year, closely linked to …

Response 13: it has been modified as required.

Point 14: L53: no-tillage (NT)

Response 14: it has been modified as required.

Point 15: L58-60: this paragraph needs to be documented a little bit more or re-organized, with the references already cited. This is too short.

Response 15: CA is effective in improving soil infiltration and thus reducing surface runoff and soil erosion as well as greater soil moisture-holding capacity. In addition, CA improves nutrient cycling, carbon sequestration, and biological soil health [6–8] . So, In dry rainfed areas, wheat yields under CA exceeded those under conventional tillage (CT) due to improved soil water conservation [9].

Point 16: L62: conventional tillage (CT)

Response 16: it has been modified as required.

Point 17: L64: NT

Response 17: it has been modified as required.

Point 18: L68: CT

Response 18: it has been modified as required.

Point 19: L72: new paragraph?

Response 19: it has been modified as required.

Point 20: L75: where is reference [12]? Deleted? It is still present in the reference section. Please make a careful revision of the references, in order of appearance in the text and does it match correctly.

Response 20: it has been modified as required.

Point 21: L87: The soil type for the field trial was a …

Response 21: it has been modified as required.

Point 22: L88: clayey texture. The …

Response 22: it has been modified as required.

Point 23: L93: evaluated

Response 23: it has been modified as required.

Point 24: L96: delete ‘for the main crop: Durum Wheat’

Response 24: it has been modified as required.

Point 25: L96: … -crop): a common … and a bread …

Response 25: it has been modified as required.

Point 26: L99: The N fertilizer

Response 26: it has been modified as required.

Point 27: L101: begin a new paragraph with ‘A Tunisian durum …

Response 27: it has been modified as required.

Point 28: L102: … wheat, cv. Maali, was …

Response 28: it has been modified as required.

Point 29: L111: replace ‘during the experimental period’ by ‘monitoring’

Response 29: it has been modified as required.

Point 30: L116: was considered

Response 30: it has been modified as required.

Point 31: L118: Then, 2014-2015 growing season was relatively dry.

Response 31: it has been modified as required.

Point 32: L128: I do not understand this part. Grains were mechanically separated from the straw with this apparatus? Were the grains oven dried and cleaned before weighed?

Response 32: Grains are separated from straw using a laboratory thresher (Wintersteiger LD 350).

Grain yield and straw yield were measured using a high capacity precision balance.

Point 33: L131: for total N content using …

Response 33: it has been modified as required.

Point 34: L149: delete ‘expressed in TND ha-1- See’

Response 34: it has been deleted.

Point 35: L154: Note: herbicide also in post-seeding to all

Response 35: agro-chemicals (i.e. pre-seeding use of glyphosate to NT, post-seeding use of herbicide to the both systems)

Point 36: L156 and L157: costs of N fertilizer

Response 36: it has been modified as required.

Point 37: L159 and L160: minus straw yield x price. It reduces the variable cost unless the straw is harvested and thrown away.

Response 37: I corrected it.

If NT then Variable costs (TND ha^-1) =

If CT then Variable costs (TND ha^-1) =

Point 38: L164: … using the MIXED procedure of …

Response 38: it has been modified as required.

Point 39: L166: … separation were assigned …

Response 39: it has been modified as required.

Point 40: L167: All factors are fixed except replicates which are random?

Response 40: Yes, all effects are fixed except replicates which are random.

Point 41: L178: This first sentence is not true because there is a very significant interaction between tillage and season. Begin with the interaction before going with the effect of tillage. Maybe, one year had a very high response and the other not.

Response 41: Remarque taken into account

Point 42: L180: Also, interaction here between tillage and previous crop. The authors cannot conclude too rapidly on the effect of previous crop.

Response 42: Remarque taken into account

Point 43: L178, L179, L196, L200, L204, L214, L224, L225 and other lines: grain N

Response 43: it has been modified as required.

Point 44: L182: … with an average of …

Response 44: it has been modified as required.

Point 45: L185: … (conventional and no-till) … and fertilizer N rate …

Response 45: it has been modified as required.

Point 46: L186 and L191: … N content in grains, N use …

Response 46: it has been modified as required.

Point 47: L194: … all treatments in each item

Response 47: it has been modified as required.

Point 48: L196: Note: As mentioned in my first revision, the authors miss an important aspect of the study by not using the contrast analysis or at less a regression in the response curve of wheat yield to N rate. This also can serve in the economic analysis to determine the optimum N rate to be used in such field conditions in function of tillage practice and pre-crop. However, the N response did not show a plateau and therefore it will be difficult to determine an optimum N rate.

Response 48:

We compared the linear regression with quadratic regression curves, the results showed (figure below) that the coefficients of determination (R²) are slightly higher in quadratic model (0.33 and 0.46) than in linear model (0.28 and 0.36), under CT and NT respectively. At this stage, we think to keep the linear one result because it is simply linked to the theory in order to understand the relationship between WUE and NUE.

Figure linear regression: Simple linear regressions relating nitrogen use efficiency (NUE) to water-use efficiency (WUE) used at four N rates individually (solid lines), and for the pooled data (dashed black line) for each tillage practices (CT and NT). Nitrogen rates (N rate) are represented with different symbols  (N1:green cercle; N2: purple triangle; N3: red square; N4: blue plus).

Figure quadratic regressions. Quadratic regressions relating nitrogen use efficiency (NUE) to water-use efficiency (WUE) used at four N rates individually (solid lines), and for the pooled data (dashed black line) for each tillage practices (CT and NT). Nitrogen rates (N rate) are represented with different symbols  (N1:green cercle; N2: purple triangle; N3: red square; N4: blue plus).

Point 49: L196: N rate application

Response 49: it has been modified as required.

Point 50: L201: However, grain N was similar among other N rates with an average of …

Response 50: it has been modified as required.

Point 51: L203: The statistical analysis showed a significant Tillage x Season interaction on …

Response 51: it has been modified as required.

Point 52: L204: … over the two …

Response 52: it has been modified as required.

Point 53: L205: Note: by looking at these results, it seems to me that there was strong interactions that lead to overall no tillage effect on crop yield. In the first year, CT > NT and in second year CT < NT. This must be mentioned at the beginning of the results section but not later as this is the case now. And usually, interaction is shown with their respective values (as in Fig. 2) but not just an average of the treatments. Please revise.

Response 53: Remarque taken into account, season effect was added in the first part of the result section

Point 54: L214: … interaction was …

Response 54: it has been modified as required.

Point 55: L216: delete ‘on grain yield’

Response 55: it has been deleted.

Point 56: L216: Correct: Vetch pre-crop increased grain N in CT but decreased that in NT.

Response 56: it has been corrected.

Point 57: L218: Pre-crop did not interact with N rate to affect grain and straw yields (Table 2).

Response 57: it has been modified as required.

Point 58: L220: On the other hand, Tillage and N rate showed a significant interaction on grain …

Response 58: it has been modified as required.

Point 59: L221: Table 2

Response 59: it has been modified as required.

Point 60: L221: treatment

Response 60: it has been modified as required.

Point 61: L225: … grain N with 2.45%.

Response 61: it has been modified as required.

Point 62: L226-230: The last sentence is the only to keep in this paragraph but move this to L219.

Response 62: it has been modified as required.

Point 63: L232: The statistical analysis indicated that growing …

Response 63: it has been modified as required.

Point 64: L233: also here, talk about the interaction before going to main treatment. The effect is more important and deserves to be mentioned.

Response 64: interaction are taken into account with and shown with their respective values

Point 65: L244: … over the two …

Response 65: it has been modified as required.

Point 66: L248: By contrast, WUE significantly decreased under CT of …

Response 66: it has been modified as required.

Point 67: L253: combinations

Response 67: it has been modified as required.

Point 68: L255: Tillage by N rate significantly affected WUE but not NUE (Fig. 2).

Response 68: it has been modified as required.

Point 69: L257: Note: the only difference is for N2. There is no difference between N1—N4 under NT and N1, N3 and N4 under CT. (L270)

Response 69: it has been added “No differences were observed between N1—N4 under NT and N1, N3, and N4 under CT”.

Point 70: L259-261: paragraph to delete

Response 70: This paragraph has been deleted.

Point 71: Figure 2: delete (Grain N). … all treatments in each item

Response 71: It has been deleted.

Point 72: L1: 3.1.3. Relationships between NUE and WUE

Response 72: it has been added.

Point 73: L2: merge the two paragraphs

Response 73: They have been merged.

Point 74: L5: delete ‘(WUE and NUE)’

Response 74: It has been deleted.

Point 75: L7: … lines were significantly …

Response 75: it has been modified as required.

Point 76: L7: The slope for N1 … than for higher N rates (4.0 vs. 1.8).

Response 76: it has been modified as required.

Point 77: L9: different from what? N1?

Response 77: …,the slopes of the lines were significantly different from each other’s

Point 78: L9: On the other hand, the slopes under CT was also significantly different with higher value for N1 (6.1) than for higher N rates (2.3-4.8).

Response 78: it has been modified as required.

Point 79: L12: … for N2 vs. N3 and N2 vs. N4 (or N1+N2 vs N3+N4)?

Response 79: the y-intercepts for these four N rates were significantly different only for (N2 vs. N3) and (N2 vs. N4).

Point 80: L20: significant

Response 80: it has been modified as required.

Point 81: L28: … over the two …

Response 81: it has been modified as required.

Point 82: L38: … as they averaged 874 TND ha-1.

Response 82: it has been modified as required.

Point 83: L39-41: delete this paragraph.

Response 83: This paragraph has been deleted.

Point 84: L45: … all treatments in each item

Response 84: it has been modified as required.

Point 85: L54: The objectives of this study were to examine …

Response 85: it has been modified as required.

Point 86: L59: delete ‘research’

Response 86: it has been deleted.

Point 87: L61: concluded at a best …

Response 87: it has been modified as required.

Point 88: L68: … kg fertilizer N ha-1 applied, …

Response 88: it has been modified as required.

Point 89: L70: However, …

Response 89: it has been modified as required.

Point 90: L71: delete ‘mineral fertilizer’

Response 90: it has been deleted.

Point 91: L72: N fertilization

Response 91: it has been modified as required.

Point 92: L79: Note: there is a significant tillage x season effect. I suggest to change significantly by remarkably. The difference in grain N was low.

Response 92: it has been modified as required.

Point 93: L82: … observed after vetch compared to bread wheat.

Response 93: it has been modified as required.

Point 94: L85: … with increasing N rates, …

Response 94: it has been modified as required.

Point 95: L87: … demonstrated that NUE …

Response 95: it has been modified as required.

Point 96: L97: by an increase …

Response 96: it has been modified as required.

Point 97: L101: delete this portion of the sentence ‘this is mainly … [45].

Response 97: it has been deleted.

Point 98: L104: this paragraph needs to be re-written to be fitted with the preceding one (also merge the two paragraphs). Higher NUE was reported with wheat following vetch in NT than with any other combination. This was due to the more favorable environmental conditions for N uptake related to better …

Response 98: it has been modified as required.

Point 99: L104: stages?

Response 99: Combinations

Point 100: L109: … soils [47]. These …

Response 100: it has been modified as required.

Point 101: L117: delete ‘as previous crop’

Response 101: it has been deleted.

Point 102: L120: delete ‘based’

Response 102: it has been deleted.

Point 103: L123: delete ‘level’

Response 103: it has been deleted.

Point 104: L124: .. in the no N …

Response 104: it has been modified as required.

Point 105: L124: delete ‘research’

Response 105: it has been deleted.

Point 106: L135: replace ‘over 5-year period’ by ‘with long-term implementation’

Response 106: it has been replaced.

Point 107: L137: delete ‘than N1=75 kg N ha-1’

Response 107: it has been deleted.

Point 108: L141: growth

Response 108: it has been modified as required.

Point 109: L145: This result supports …

Response 109: it has been modified as required.

Point 110: L149: … legume were higher …

Response 110: it has been modified as required.

Point 111: L155: … highest gross margins in durum …

Response 111: it has been modified as required.

Point 112: L161: Based on a 2-yr experiment, …

Response 112: it has been modified as required.

Point 113: L162: grain N concentration

Response 113: it has been modified as required.

Point 114: L163: … mineral N application rate …

Response 114: it has been modified as required.

Point 115: L169: conditions

Response 115: it has been modified as required.

Point 116: Conclusion: the authors concluded that their findings support adoption and success of the conservation agriculture for durum wheat in Mediterranean. However, their studies have only two years. This may be enough for evaluating pre-crop and N rate but not for tillage practices that usually need 5 and even 10 years to see a real and constant effect. The absence of effect might be due to the short duration of the study. Please add this aspect to the conclusion.

Response 116: Therefore, these findings, even coming from two-year experiment, support the adoption and the success of conservation agriculture for durum wheat cultivation under such semi-arid Mediterranean conditions. Furthermore, it is important that medium to long term studies on CA and nutrient management need to be conducted to improve the references and better guide local farmers to successful CA adoption.

Author Response File: Author Response.pdf