Nitrogen Use Efficiency of Quality Protein Maize (Zea mays L.) Genotypes

Round 1

Reviewer 1 Report

MDPI - Agronomy

Manuscript Number: agronomy-1639982

Title: «Nitrogen use efficiency of quality protein maize (Zea mays L.) genotypes».

As requested, I have reviewed the revised version of the above-titled paper for potential publication in the Agronomy - MDPI Journal. The topic of the article is very relevant for modern science in the field of nitrogen.

The presented topic is interesting and well prepared in terms of organization and selection of literature. The authors focused on aspects nitrogen use efficiency (NUE) of different QPM inbred lines at various levels of nitrogen (N) fertilizer application.

The conducted study and analyzes are extensive and aimed at achieving the assumed goals. The methodological and statistical side is correct.

 

Author Response

REVIEWER 1

There were no corrections made as there were none suggested by the reviewer.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors,

As a whole, I like your manuscript titled "Nitrogen use efficiency of quality protein maize (Zea mays L.) genotypes". Apart from minor exceptions in the results section, it is really enjoyable to read. The writing is quite clear. The description of the methods deserves special appreciation. However, I have a few comments that may help you improve this manuscript. I will post them below as they appear in the text.

In the introduction, you cite FAO data from 2003 and 2007. Why? The most recent data from 2020 are available. I suggest you use them. 

In your material description you indicate that you tested 32 inbred lines but in Table 1 there are only 21. Please complete it with the missing genotypes. 
Table 2 should be moved to the supplement. It is unnecessary in the manuscript main body. 

Section 3.3 of the results needs to be rewritten. As it stands, it records exactly what is in Table 5. This section reads very badly. Furthermore, you list lines here that are missing from Table 1. 
I suggest moving Tables 5,6,7 and 8 to the supplement. 
Figure 2 is completely unreadable. I suggest you move the legend under the chart so that the chart area is wider. You need to widen data bars, decrease distance between lines, error bars cannot be black, they blur everything, you can also draw them with thinner line. 
In table 9 please remove non significant values and leave only "ns". The abbreviation "ns" must be explained in the footer. 
Conclusions should be shortened. It should be the essence itself. 

Best regards,

M.

Author Response

REVIEWER 2

• Reviewer: the results are clearly presented but can be improved.

Response: the results presentation was improved as necessary.

• Reviewer: In the introduction, you cite FAO data from 2003 and 2007. Why? The most recent data from 2020 are available. I suggest you use them. 

Response: Most recent data from FAO was included in the introduction of the manuscript.

“As at 2011, an increase in regional average maize yields of 1.7 t/ha in West Africa, 1.5 t/ha in East Africa, but a decline to 1.1 t/ha to <1.8 t/ha in Southern Africa was recorded [8], which is far below the ~5 t/ha global average maize yield [8].”

The most recent data that stated maize yield in South Africa was used and it was from FAOSTAT (2015) and FAS (2018) [8].

• Reviewer: in the material description, it was indicated that 32 inbred lines were tested but in Table 1 there are only 21. Please complete it with the missing genotypes. 

Response: The 32 inbred lines tested in this study are all listed in Table 1. The remaining ones are in the second table directly below the first table of Table 1. They were separated based on sources and designated as Table 1(a) and 1(b).

• Reviewer: Table 2 should be moved to the supplement. It is unnecessary in the manuscript main body. 

Response: Table 2 was moved to the supplement, it was earlier inserted in the main body of the manuscript to show the nutrient status of the soil on which the trial was conducted as it is a NUE study.

• Reviewer: Section 3.3 of the results needs to be rewritten. As it stands, it records exactly what is in Table 5. This section reads very badly. Furthermore, you list lines here that are missing from Table 1. 

Response: This section was recast as shown below:

“From the thirty - two inbred lines evaluated, the top ten QPM inbred lines   with high harvest indices (HI) across N levels were L25, L30, L9, L23, L32, L14, L29, L5, L12 and L13 (Figure 1). However, performance of these inbred lines varied across N levels considering the indices REN, AE, NUE and NUtE. Genotype L25 ranked 1^st for HI but ranked 14^th for REN, 26^th for AE while 4^th and 5^th for NUE and NUtE respectively. It ranked 4^th for yield. On the other hand, L30 ranked 2^nd for HI but ranked 29^th, 4^th, 18^th and 22^nd for REN, AE, NUE and NUtE respectively. L9 performed quite well as it ranked 3^rd, 2^nd, 13^th, 8^th, and 3^rd in estimation of HI, REN, AE, NUE, and NUtE respectively. It ranked 5^th for yield. Genotype L9 had 0.11 kg grain/ kg N-fertilizer of NUE, 0.005 kg N-uptake/kg N fertilizer of REN, 37.32 kg grain/kg N-fertilizer of AE, 2.02 kg grain/ total N of NUtE and 6.57 t/ha across N levels (see the Supplementary Material S2). L14 ranked 6^th for HI but ranked 7^th, 23^rd, 21^st and 7^th for REN, AE, NUE and NUtE respectively. However, L29 ranked 7^th, 31^st, 22^nd, 6^th, and 4^th in estimation of HI, REN, AE, NUE, and NUtE respectively. It ranked 3^rd for yield with 6.72 t/ha of yield across N levels (see the Supplementary Material S2). These inbred lines were top performing across the different N application rates.”

No missing inbred lines. All inbred lines are presented in Table 1(a) and 1(b).

• Reviewer: I suggest moving Tables 5,6,7 and 8 to the supplementary materials. 

Response: Tables 5, 6, 7 and 8 were moved to the supplementary materials, as suggested.

• Reviewer: Figure 2 is completely unreadable. I suggest you move the legend under the chart so that the chart area is wider. You need to widen data bars, decrease distance between lines, error bars cannot be black, they blur everything, you can also draw them with thinner line. 

Response: The Figure 2 was adjusted as suggested by the reviewer.

• Reviewer: In table 9 please remove non-significant values and leave only "ns". The abbreviation "ns" must be explained in the footer. 

Response: In table 9, non-significant values were removed and only "ns" were left. The abbreviation "ns" was explained in the footer. 

(9) Reviewer: Conclusions should be shortened. It should be the essence itself. 

Response: Conclusions was shortened as suggested.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Manuscript Agronomy-1639982 - Nitrogen use efficiency of quality protein maize (Zea mays L.) genotypes

 

The manuscript is about the identification of the best maize QPM genotypes regarding the nitrogen use efficiency and, the determination of the appropriate rate of fertilizer application.

Overall the manuscript is well done, with valuable results for a more sustainable use of mineral N fertilizers in degraded soils. The discussion, the presentation of the results and the conclusions are consistent with the data obtained during the experiment and are also appropriate for the audience.  Nevertheless, to be accepted for publication the manuscript needs to be improved in the following items

 

 

Abstract

The phrase “These genotypes can be considered …. under low N soils” is repeated, pleae remove it from the abstract.

 

Introduction

 When the authors refer that the maize yield in East Africa is of 1,33 t/ha it seems that it should be changed for 1.33 t/ha.

Please clarify what is the meaning of “low N stress”. In the context of the work it seems that the authors used the term “low N stress” instead of “ow N soil content”.  In this case in soils with low N content, the crops should suffer a “high N stress”.

 

Material and Methods

2.1.

The authors should refer the duration of the maize growth cycle.

In the phrase “The fertilized plots received basal compound fertilizer…” what is the meaning of (N:P:K ratio (30))?  (30) is a bibliographic reference? If so, it must be placed within square brackets.

 

 Table 2 – The units of the exchangeable bases should be: cmol_c/kg

The soil pH should be indicated as: pH (KCl)

 

Results

 

The authors should place the units in the parameters of the tables and in the Figures (e.g. Table 3, Table 4, Figure 1 YY axis…)

 

Discussion

In lines 107, 112 and 117 the meaning of the terms “low-nitrogen stress conditions”, “under low soil N stress” and “low soil N conditions” are confused, please clarify taking into consideration the N level in the soil.

 

 

Comments for author File: Comments.docx

Author Response

REVIEWER 3

• Reviewer:

Abstract

The phrase “These genotypes can be considered …. under low N soils” is repeated, please remove it from the abstract.

Response: the repeated statement was removed as suggested.

 

• Reviewer:

Introduction

(a) When the authors refer that the maize yield in East Africa is of 1,33 t/ha it seems that it should be changed for 1.33 t/ha.

Response: 1,33 t/ha was changed to 1.33 t/ha.

(b) Please clarify what is the meaning of “low N stress”. In the context of the work it seems that the authors used the term “low N stress” instead of “low N soil content”.  In this case in soils with low N content, the crops should suffer a “high N stress”.

Response: Lines 107 …..”…..low nitrogen stress conditions” and 112”………. low nitrogen stress” were changed to “……low soil nitrogen conditions” and “…..low soil N conditions…” respectively.

• Reviewer:

Material and Methods

2.1.

(a) The authors should refer the duration of the maize growth cycle.

Response: The growth stages in which the fertilizer application was done was included, that is ….. “1/3 at 4 WAS (3 leaf stage, V3 stage), 1/3 at 6 WAS (growing point stage, V6), and 1/3 at 8 WAS (rapid top growth stage, V9)). At harvest, the entire row of each inbred line per nitrogen level was harvested

(b) In the phrase “The fertilized plots received basal compound fertilizer…” what is the meaning of (N:P:K ratio (30))?  (30) is a bibliographic reference? If so, it must be placed within square brackets.

Response: The fertilized plots received basal compound fertilizer (N:P:K ratio 2:3:4(30)) The (30) is not a bibliographic reference.

(c) Table 2 –

(i)The units of the exchangeable bases should be: cmol_c/kg

Response: The units of the exchangeable bases was labelled as cmol_c/kg as suggested.

(ii)The soil pH should be indicated as: pH (KCl)

Response: The soil pH was indicated as: pH (KCl) as suggested.

• Reviewer:

Results

The authors should place the units in the parameters of the tables and in the Figures (e.g. Table 3, Table 4, Figure 1 YY axis…)

Response: The units in the parameters of the tables Table 3, Table 4 and in the Figures 1 YY axis were included as suggested. The units in the parameters of the Tables 3 and 4 were placed at the footnotes of each table. The legend was moved under the Figure 2.

(5 Reviewer:

Discussion

In lines 107, 112 and 117 the meaning of the terms “low-nitrogen stress conditions”, “under low soil N stress” and “low soil N conditions” are confused, please clarify taking into consideration the N level in the soil.

Response: Lines 107 …..”…..low nitrogen stress conditions” 112 and 117”………. low nitrogen stress” were changed to “……low soil nitrogen conditions” and “…..low soil N conditions…” respectively.

 

Author Response File: Author Response.docx