Enhancing Maize Yield and Resource Efficiency through Controlled-Release Nitrogen Fertilization on the Semiarid Loess Plateau

Round 1

Reviewer 1 Report

The study evaluated the impact of N use (CRU) on soil and plant variables to assess whether this N use is useful in the production of maize cultivated in China. The work was well executed, but the introduction and discussion need to be improved to indicate more clearly all published works involving N (CRU) and what would be the novelty of their study. This has to be clear the gap in the literature that your research will collaborate. Several other adjustments are necessary so that the manuscript has an excellent scientific foundation and that it justifies its disclosure to the scientific community. I leave other notes below.

It is not clear in the text how N treatments were applied and when N was applied in relation to plant emergence after maize sowing. The N dose used needs to include a reference. It is known that the response of plants to N application is very dependent on sulfur and it is not clear that this nutrient was applied or if the S content in the soil was adequate. Why was micronutrients not applied? I would have to detail that in the manuscript.

In figure 6 it indicates "relative chlorophyll content (SPAD)" and in the y axis the term SPAD is indicated and this is not correct as it is the name of a manufacturer of an indirect chlorophyll meter. Change to "green color index". It is important for the authors to improve the discussion, that is, to improve the defense of their results. For this, the multivariate analysis must indicate which analyzed variables have greater weight to explain the effects of treatments on crop productivity. This discussion will allow us to know if N (CRU) has a greater influence on which soil and plant variables.

Author Response

Reviewer 1:

• The work was well executed, but the introduction and discussion need to be improved to indicate more clearly all published works involving N (CRU) and what would be the novelty of their study. This has to be clear the gap in the literature that your research will collaborate.

Authors’ response: Thank you for this suggestion, which we have followed (line 72-90).

• It is not clear in the text how N treatments were applied and when N was applied in relation to plant emergence after maize sowing. The N dose used needs to include a reference. It is known that the response of plants to N application is very dependent on sulfur and it is not clear that this nutrient was applied or if the S content in the soil was adequate. Why was micronutrients not applied? I would have to detail that in the manuscript.

Authors’ response: Thank you for this suggestion. We revised this sentence to address this suggestion and provide clarity (lines 131–135). All N fertilizers were applied at once as base fertilizer and was manually distributed over the soil surface prior to sowing and then plowed into the soil [17], and the N treatments remained consistent in the same plots each year. As per standard farming practices in the region, we did not apply sulfur fertilizer in our experiment,

• In figure 6 it indicates "relative chlorophyll content (SPAD)" and in the y axis the term SPAD is indicated and this is not correct as it is the name of a manufacturer of an indirect chlorophyll meter. Change to "green color index". It is important for the authors to improve the discussion, that is, to improve the defense of their results.

Authors’ response: Thank you for this suggestion, which we have followed. Figure 6. Effect of controlled-release urea fertilization on green color index (SPAD) at different growth stages in 2020 and 2021. DAA, days after anthese. Shown is the mean value (n = 3). Vertical bars denote Fisher’s protected least significant difference at P ≤ 0.05.

Author Response File: Author Response.pdf

Reviewer 2 Report

Water limitations and nitrogen deficiency are the two primary factors restricting high-yield agriculture. The lack of water can limit the efficiency of nitrogen fertilizers, while the application of nitrogen fertilizers enhances the resistance of plants to drought. Moreover, reducing nitrogen fertilizer losses is crucial for achieving optimal efficiency. These complex two-way and multi-way relationships and effects have been extensively studied in recent years. The focus of the peer-reviewed article is on exploring ways to improve the efficiency of nitrogen fertilizers, particularly through the use of controlled-release nitrogen fertilizers (Controlled-Release Urea, CRU). This study has focused on determining the optimal application rate of CRU for maximizing corn productivity.

The research investigates the impact of different ratios of common urea and CRU on various aspects, including soil water content, soil enzyme activities, soil nitrogen content, biomass accumulation, grain yield, water use efficiency (WUE), and agronomic use efficiency of nitrogen fertilizer (AEN). The key finding of this study is that optimal controlled-release nitrogen fertilization increases both yield and WUE. Specifically, a combination of 70% CRU and 30% common urea is recommended as the appropriate application ratio for the semiarid western Loess Plateau of China. The manuscript presents novel findings with a comprehensive description of the results obtained. The research methodology employed is of high quality, making the article interesting and its results significant. The findings are expected to be valuable to a wide range of researchers and practitioners in the field.

One essential suggestion for the manuscript is to include calculations for two other indicators of nitrogen nutrition by plants: the Apparent Nitrogen Recovery (ANR) and the Physiological Use Efficiency of nitrogen (PhEN).

Apparent nitrogen recovery (%) can be calculated as follows: Apparent nitrogen recovery (%) = [(Total N uptake by plants in the variant with N fertilizer – Total N uptake by plants in the control variant without N fertilizer) / Applied dose of nitrogen fertilizers] x 100.

PhEN (kg kg-1) can be calculated as follows: PhEN = (Grain Yield in the variant with N fertilizer - Grain Yield in the control variant without N fertilizer) / (Total N uptake by plants in the variant with N fertilizer – Total N uptake by plants in the control variant without N fertilizer).

In addition to the content, there are a few specific comments on the text:

·         Line 24: In the annotation, the N rate is stated as 200 kg ha–1, while Table 1 indicates 225 kg ha–1. This inconsistency should be addressed and clarified.

·         Line 111: Regarding the "organic matter content of 12.1 g kg−1," it should be specified whether it refers to Corg or Organic matter (Corg x 1.724).

·         Line 114: Details about how the controlled-release urea (CRU) was produced should be included in the manuscript.

·         Line 120: The method for applying fertilizers to the soil needs to be described. It should be clarified whether the fertilizer was mixed into the soil or locally placed.

·         Lines 367-370: It is important to investigate whether AEN and WUE correlate with each other. This correlation should be discussed in the article.

Conclusion: The article can be accepted after minor revisions.

Author Response

Reviewer 2:

• One essential suggestion for the manuscript is to include calculations for two other indicators of nitrogen nutrition by plants: the Apparent Nitrogen Recovery (ANR) and the Physiological Use Efficiency of nitrogen (PhEN).

Authors’ response: Thank you for these suggestions. These issues were clarified by added a figure to the manuscript (Fig. 1) and by revising the text on lines 161–163.

 

• Line 24: In the annotation, the N rate is stated as 200 kg ha–1, while Table 1 indicates 225 kg ha–1. This inconsistency should be addressed and clarified.

Authors’ response: Thank you for this observation. It should be “225 kg ha^–1”.

 

• Line 111: Regarding the "organic matter content of 12.1 g kg−1," it should be specified whether it refers to Corg or Organic matter (Corg x 1.724).

Authors’ response: Thank you for this observation. It should be “Organic matter (Corg x 1.724)”.

 

 

• Line 114: Details about how the controlled-release urea (CRU) was produced should be included in the manuscript.

Authors’ response: Thank you for this suggestion. We revised this sentence for enhanced clarity (lines 135).

 

Polyethylene is used as a coating material for the production of CRU.

 

• Line 120: The method for applying fertilizers to the soil needs to be described. It should be clarified whether the fertilizer was mixed into the soil or locally placed.

Authors’ response: Thank you for this observation. We revised this sentence for enhanced clarity (lines 133).

 

All N fertilizers were applied at once as base fertilizer and was manually distributed over the soil surface prior to sowing and then plowed into the soil.

 

• Lines 367-370: It is important to investigate whether AEN and WUE correlate with each other. This correlation should be discussed in the article.

Authors’ response: Thank you for this suggestion, which we have followed.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript presents valuable research regarding nitrogen and water use efficiencies and I recommend publication after minor revisions. I have attached detailed suggestions. 

Comments for author File: Comments.pdf

Author Response

 

Reviewer 3:

• Abstract, Line 23: Change to ' Field treatments, including six N treatments, were investigated.....

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 2, Lines 66-68: Change ' averaging at 32% 'to ' averages 32%. Also, change ' resulting in negatively effect on the environment'to ' resulting in a negative effect on the environment'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 3, Line 123: The P2Os of triple superphosphate is listed as 16%. This is not correct. YTypically this is 46%.

Authors’ response: Thank you for this suggestion. The P2O5 of triple superphosphate is listed as 16%.

 

• Page 4, Lines 144-145: Change to ' The calculation of the DI followed data collected in previous studies'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 5, Line 212: Change ' were measured random factors' to ' were measured as random factors'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 10, Lines 300-301: Change ' did not significantly affected plant height' to' did not significantly affect plant height'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 11, Line 324: Change ' the rest treatments' to ' the other treatments'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 12, Line 340: Change'it was not significantly difference in the rest treatments'to' it was not significantly different in the other treatments'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 13, Line 351: Change ' others treatments' to ' other treatments'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 14, Lines 370-371: Change'was tends to increase' to 'tended to increase'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 15, Line 381: Change ' activities was greatly' to ' activities were greatly'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 15, Lines 386-387: Suggest to end sentence after the citation (37) and start a new sentence with ' It is very important.....

Authors’ response: Thank you for this suggestion, which we have followed.

 

• Page 16, Line 434: Delete ' was' before'should be regarded'.

Authors’ response: Thank you for this suggestion, which we have followed.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been improved and can be published.

Author Response

Thank you for your time and help with this manuscript.