Reduced Nitrogen Fertilizer Rates Maintained Raspberry Growth in an Established Field

Round 1

Reviewer 1 Report

Dear authors,

Thank you for the opportunity to meet the manuscript entitled: "Nitrogen Fertilizer Rate Had Minimal Impact on Floricane Raspberry Growth, Yield, Fruit Quality". The pressure to reduce the doses of industrial fertilizers in relation to environmental protection is constantly increasing. For this reason, I rate the article as beneficial. The manuscript is written at a good level, the individual chapters are clearly processed, although I also have a few comments and questions:

I consider the absence of harvest and subsequent analyses in 2019 to be a lack of research. From this point of view, it is difficult to consider the experiment as multiannual, as the harvest and quality of raspberry were main goals of the experiment.

I recommend simplifying the table names. The methodology is clearly described in Chapter MM, so it is unnecessary to include it in the tables. In addition, I recommend incorporating measurable units into the tables to the parameters (not in the title), this will increase clarity.

I am not an expert in growing raspberries, but can the authors explain why the photosynthetic parameters (Chapter 2.5) were measured on August 26, when, as they claim (L183), July 28 is already considered a late harvest? In my opinion, it has a better rationale to measure photosynthetic parameters during periods of primary growth and crop production.

In Table 3, the yield data are presented in kg plant^-1, although in the manuscript text, the authors evaluate the data in g plant^-1. I recommend unifying this.

L355 You state: "However, fertilized plants had greater primocane lengths than unfertilized plants in the second year, but plants fertilized with either low or high N fertilizer rates had similar primocane lengths". No data from individual years are given. I recommend either adding them to the supplementary files or evaluating only the averages, similar to the ones listed in Table 5.

In addition, the authors did not evaluate or discuss at all that all values ​​presented in Table 5 were higher on the control variant. This is an important finding and needs to be addressed.

I recommend also presenting the results in chapter 3.4 in the table or in the figure.

Author Response

Reviewer #1

Dear authors,

Thank you for the opportunity to meet the manuscript entitled: "Nitrogen Fertilizer Rate Had Minimal Impact on Floricane Raspberry Growth, Yield, Fruit Quality". The pressure to reduce the doses of industrial fertilizers in relation to environmental protection is constantly increasing. For this reason, I rate the article as beneficial. The manuscript is written at a good level, the individual chapters are clearly processed, although I also have a few comments and questions:

We extremely appreciate the reviewer’s support and thank you for the comments and suggestions.

I consider the absence of harvest and subsequent analyses in 2019 to be a lack of research. From this point of view, it is difficult to consider the experiment as multiannual, as the harvest and quality of raspberry were main goals of the experiment.

We appreciate the reviewer’s comment. We are aware of these issues and would have liked to include these variables. Unfortunately, we had to omit 2019 yield and fruit quality data due to the malfunction of our machine harvester. However, please consider the following:

1. The objective of this study was to evaluate the response of raspberry (mainly leaf tissue N concentrations) to N fertilizer rates because the application of N fertilizer is based on leaf tissue nutrient analysis results according to the existing nutrient management guide, such as Hart et al. (2006) (full reference provided below for your convenience).
2. Given the unique physiology of floricane-fruiting raspberry, Rempel et al. (2014) reported that the fertilizer applied in the current year was mainly used to fuel vegetative growth in the current year and reproductive growth in the next year, which means the impact of N fertilizer applied in 2019 on raspberry yield and fruit quality should manifest in 2020 rather than 2019. Thus, collecting 2019 yield and fruit quality data would actually have reflected nutrient practices in 2018, before the study was implemented.

References

Hart, J., Strik, B., Rempel, H., 2006. Caneberries. Nutrient management guide. Ore. State Univ. Ext. Serv., EM8903-E.

Rempel, H.G., Strik, B.C., Righetti, T.L., 2004. Uptake, partitioning, and storage of fertilizer nitrogen in red raspberry as affected by rate and timing of application. Journal of the American Society for Horticultural Science. 129, 439–448. https://doi.org/10.21273/JASHS.129.3.0439.

I recommend simplifying the table names. The methodology is clearly described in Chapter MM, so it is unnecessary to include it in the tables. In addition, I recommend incorporating measurable units into the tables to the parameters (not in the title), this will increase clarity.

We thank the reviewer for the comment. This has been changed.

I am not an expert in growing raspberries, but can the authors explain why the photosynthetic parameters (Chapter 2.5) were measured on August 26, when, as they claim (L183), July 28 is already considered a late harvest? In my opinion, it has a better rationale to measure photosynthetic parameters during periods of primary growth and crop production.

We thank the reviewer for this observation. The rationale of measuring leaf photosynthesis on August 26 are as follows:

1. Leaf photosynthesis is one of the indicators of leaf N concentration sufficiency. It was reported that ‘Meeker’ raspberry primocanes actively take up N until the end of September (Rempel et al., 2014; full reference provided below for your convenience). Given this, August 26 is within a good time range of observing overall primocane leaf N concentration sufficiency and N fertilizer rate effect as current growth stage is approaching final uptake of nutrients from soil.
2. Floricane raspberry can continue fruiting until early September although the intensive commercial fruit harvest period is concentrated in July. So, the plant growth and plant productivity was still very active on August 26, particularly for the vegetative primocanes that we measured (note – floricane raspberry has biennial canes and we did not measure photosynthesis from fruiting floricanes, but vegetative primocanes that differ in growth and physiology). Additionally, the date of measurement was in accordance with Zhang at el. (2019), who measured primocane leaf photosynthesis of floricane raspberry planted in the similar area on the similar date. Thus, there is precedence for this sampling time and allows us to make comparisons with other published literature.
3. Leaf photosynthesis is highly influenced by weather conditions, such as solar radiation. Where the experiment was carried out, the total solar radiation in August was similar to July (WSU AgWeatherNet, 2022), which further validates the feasibility to measure leaf photosynthesis in August.

References

Rempel, H.G., Strik, B.C., Righetti, T.L., 2004. Uptake, partitioning, and storage of fertilizer nitrogen in red raspberry as affected by rate and timing of application. Journal of the American Society for Horticultural Science. 129, 439–448. https://doi.org/10.21273/JASHS.129.3.0439.

Washington State University AgWeatherNet, 2022. Weather Data for Mount Vernon Station. https://weather.wsu.edu/index.php?page=station_details&UNIT_ID=100090/ (accessed 10 March 2022).

Zhang, H., Miles, C., Ghimire, S., Benedict, C., Zasada, I., DeVetter. L., 2019. Polyethylene and biodegradable plastic mulches improve growth, yield, and weed management in floricane red raspberry. Scientia Horticulturae. 250, 371–379. https://doi.org/10.1016/j.scienta.2019.02.067.

In Table 3, the yield data are presented in kg plant^-1, although in the manuscript text, the authors evaluate the data in g plant^-1. I recommend unifying this.

We thank the reviewer for this observation. This has been addressed.

L355 You state: "However, fertilized plants had greater primocane lengths than unfertilized plants in the second year, but plants fertilized with either low or high N fertilizer rates had similar primocane lengths". No data from individual years are given. I recommend either adding them to the supplementary files or evaluating only the averages, similar to the ones listed in Table 5.

We thank the reviewer for the comment. The sentence the reviewer stated above was the summary of the results in Rempel et al. (2014), we had the appropriate citation at the end of the sentence in the manuscript. We would like to clarify that this sentence was NOT the result of our study.

In addition, the authors did not evaluate or discuss at all that all values ​​presented in Table 5 were higher on the control variant. This is an important finding and needs to be addressed.

We appreciate the observation from the reviewer. We are aware that all variables in Table 5 had numerically greater values in control, however, the difference is insignificant given all the p-values were more than 0.05. However, to address this point for Table 5 data we have added a sentence stating where variables are numerically greater with the control.

I recommend also presenting the results in chapter 3.4 in the table or in the figure.

We thank the reviewer for this observation. Data presented in chapter 3.4 are from one of our manuscripts, which is in review by another journal. We did not present the data neither in table nor figure to eliminate the data duplication problem.

Author Response File: Author Response.pdf

Reviewer 2 Report

I have reviewed this manuscript. The topic is replica of past researches. However, well tuned with the journal scope. I include my comments and questions. I would love to hear from authors. 

The authors decalre, no effect of fertilization rates on plant yiield and growth p[arameters, how come various levels results in same traits, without differences? I am confused.

Ok, can the authors suggest any critical limit where, the N use is minimum but the yield level is same for different levels? This is something on the basis of which you can sayyour approach reduce the input costs for plant production. 

line 35, italicize the family name, check other places too

The citations are not matched with the journal requirements. 

To me, the introduction section is wordy and lack of focus is crucial. 

So, the obtained results could not support the study hypothesis? Need a double check. Or should be taken into account in discussion. 

I suggest converting table 2 to a figure

How many plots were there for soil and plant sampling.?

Line 208, you mean the plant pjysiology was only tested in 2020? and not in 2019?

Well, the results obtained does not match with the study objectives, i suggest authors double check this and redraw the objectives. 

The limitation of study should be highlighted. 

Finally, the outline of the study is difficult to follow, which should be rearranged.

Author Response

I have reviewed this manuscript. The topic is replica of past researches. However, well tuned with the journal scope. I include my comments and questions. I would love to hear from authors. 

We appreciate the hard work of the reviewer and the valuable suggestions. We will try our best to address the comments proposed by the reviewer and looking forward to the future feedback from the reviewer. The topic of the experiment may be similar to past research but the work has never been done in the western Washington, which highlights the necessity of the experiment given western Washington is the No. 1 producer of processed raspberry nationwide and also an important global producer. Any information regarding utilizing N fertilizer at the appropriate rate is important to local raspberry growers and may also justify other fertilizer studies where raspberry is grown and fertilizer rates should be re-evaluated given the huge variations in soil type and climates.

The authors decalre, no effect of fertilization rates on plant yiield and growth p[arameters, how come various levels results in same traits, without differences? I am confused.

We appreciate the reviewer’s suggestion. We understand the reviewer is shocked to see the lack of fertilizer response in this study. However, this is what we get from the field experiment, we have explained the lack of plant response to applied fertilizer (lines 309–319, 380–382, 408–422) in the discussion. Basically, the lack of plant response was due to the utilization of nutrients from plant nutrient reserves and soil organic matter mineralization. This is an important finding and also mirrors other work Dr. DeVetter is co-authoring in northern highbush blueberry (Vaccinium corymbosum; manuscript is in preparation). Furthermore, a recent study in northern highbush blueberry found no effect of nitrogen fertilization rate on yield in a long-term study conducted from 2003-2018 (Vance and Strik, 2022; full reference provided below for your convenience). This study was done in Oregon, which is adjacent to Washington. While northern highbush blueberry is different than raspberry, these combined findings from the Pacific Northwest region highlight that established berry plants are less sensitive to fertilizer rate and there may be benefits to reducing fertilizer rates.

References

Davis, A. J., and B.C. Strik. 2022. Long-term Effects of Pre-plant Incorporation with Sawdust, Sawdust Mulch, and Nitrogen Fertilizer Rate on ‘Elliott’ Highbush Blueberry. HortScience 57(3): 414-421.

Ok, can the authors suggest any critical limit where, the N use is minimum but the yield level is same for different levels? This is something on the basis of which you can sayyour approach reduce the input costs for plant production. 

We appreciate the reviewer’s suggestion. We are aware that our research is lacking a critical value. We are unable to give the critical limit where the N use is minimum but the yield level is same for different N levels based on this experiment due to the lack of fertilizer response. This would be an important next step for the research. However, please note based on our findings, plant growth and productivity variables did not differ across N fertilizer rate and therefore we concluded that adjusting fertilizer rates based on these characteristics COULD reduce fertilizer costs and the potential for environmental pollution from excess fertilizers (lines 479–481). We use the word COULD to manifest the potential suggestion.

line 35, italicize the family name, check other places too

We thank the reviewer for the observation. We have all species names italicized. Botanical family names (e.g., Rosaceae) by convention are not italicized.

The citations are not matched with the journal requirements. 

We thank the reviewer for the suggestion. This has been addressed.

To me, the introduction section is wordy and lack of focus is crucial. 

We thank the reviewer for the suggestion. We have restructured the introduction to make the justification concise.

So, the obtained results could not support the study hypothesis? Need a double check. Or should be taken into account in discussion.

We thank the reviewer for the suggestion. We are sorry the reviewer was confused with the relationship between obtained results and study hypothesis. The study hypothesis and the rejection to the study hypothesis have been clarified in this manuscript. Please note, in the introduction we had the hypothesis that improved plant performance will be observed when plants receive high N fertilizer rates (lines 148–149). We clarified in the conclusion that based on our data we rejected our hypothesis (lines 469–472). The ensuing presentation of the results and discussion elaborates on why we rejected our hypothesis.

I suggest converting table 2 to a figure

We thank the reviewer for the suggestion. This has been addressed.

How many plots were there for soil and plant sampling.?

We thank the reviewer for the observation. There were12 experimental plots in total for soil and plant sampling and we have added this information to the manuscript (lines 161–163).

Line 208, you mean the plant pjysiology was only tested in 2020? and not in 2019?

We thank the reviewer for the question. The leaf photosynthesis was only measured in 2020 as stated in the manuscript. We were not able to measure in 2019.

Well, the results obtained does not match with the study objectives, i suggest authors double check this and redraw the objectives. 

We thank the reviewer for the suggestion but respectfully disagree. The objective of this research was to evaluate the response of ‘Meeker’ floricane red raspberry when treated with different N fertilizer rates in northwest Washington. This objective was tested with the raspberry being fertilized at different N rates and we used rates recommended for the region plus a no-fertilizer control, expecting we would see a decline in our variables within the control. A surprising yet very important finding is there was no response to the rates. Thus, our logic is that we evaluated response to fertilizer rates and observed no-to-minimal responses for most of our key production and nutrient assessment variables. We respectfully request the reviewer re-consider our rationale and objectives framing the work.  

The limitation of study should be highlighted. 

We thank the reviewer for the suggestion. We have evaluated the limitation of the study in the conclusion. This is the new sentence: it should be noted that the overall impact of N fertilizer rate on raspberry growth and productivity was limited in this experiment due to the lack of a fertilizer response despite application of a no-fertilizer control in addition to regionally recommended rates. Thus, further research with a measurable plant response to N fertilizer rates is warranted to better characterize the interplay of soils and plant reserves and to create more robust and localized nutrient management guidelines for raspberry growers in northwest Washington (lines 481–488).

Finally, the outline of the study is difficult to follow, which should be rearranged.

We are sorry to hear the outline of the study was difficult to follow. A previous reviewer felt the chapters were clearly processed and co-authors agree the organization is adequate for an agricultural journal. Thus, after careful consideration we decided to maintain the current organization/outline. Please note the flow of data presentation is consistent in order to enhance reader understanding. 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I am satisfied with the responses. The MS can be accepted now.