Optimizing Nitrogen Fertigation Rates for Young Southern Highbush Blueberry

Round 1

Reviewer 1 Report

A study was conducted to assess the implications of N fertilization rates on the vegetative and reproductive development of young Southern Highbush blueberry plants. An aim was to identify the optimal N requirements suitable for cultivating these plants. The authors conclude that greater N application advanced the reproductive development cycle, in addition to increasing vegetative growth and fruit yield. High N application rates also corresponded with nitrate leaching. Finally, they found that maximum fruit yields were achieved when the plants received around 200 to 220 kg.ha^-1 N per year.

The manuscript is well-written, concise, has clear outcomes and would contribute to the literature in a novel fashion. Below are a few minor suggestions for the authors to consider:

Abstract: This section is well-written, and clearly outlines the objectives and key results and conclusions.

Introduction: This section has an excellent structure and contains clear, informative paragraphs. A few specific comments below:

Line 45: You could elaborate a little more on the “large storage of N” – if you are referring to the N reserves stored in the woody plant tissues, you could describe a bit more in relation to the utilization of these reserves and how this may have affected the differences among your N treatments.

Line 56: Can you name the major goals/objectives for the study here. For example, one objective was perhaps to assess the implications of the treatments on N leaching, another objective was to evaluate the impact of N application on vegetative development, etc.

Material and methods: This section is thorough, and the methods clearly described. However, some additional information may be beneficial:

Lines 92-112: Can you include a short description of the growth stages in relation to these sampling dates somewhere? For example, the leaf samples were collected on 13 Oct 2015, and 21 Apr, 1 Jun and 22 Aug 2016, while photographs for canopy ground cover assessments were taken on 14 Nov 2015 and 27 Oct 2016 – Where possible, a brief description of the growth stages would be beneficial to clearly understand when these samples and photographs were taken. The same applies for the soil sample collection dates. Perhaps you could also include some of this information about growth stages within the Figures and Tables (e.g. Fig 1 and Table 1).

Lines 93-94: I would rephrase - “…micronutrient concentrations were analyzed from samples collected on 13 Oct. 2015 and 1 June 2016.”

Lines 96-98: Can you provide more details regarding the model and manufacturer details for the N gas analyzer and spectrophotometer?

Lines 111-112: Can you provide details regarding the make and model of the flow injector analyzer?

Lines 116-121: Can you include a short description of how berry maturity was assessed prior to harvesting? For example, were the berries harvested when they have reached a target TSS level?

Line 127: “Total soluble solid content” should be “Total soluble solid concentration”.

Lines 134-140: Information regarding the linear plateau model used to assess the regression between N rates and yield seems lacking here. Can you include this here in the data analysis section?

Results and discussion: This section is mostly clear and well-written, a few additional comments below:

Lines 145-147: It is likely that mobilization of N reserves stored in woody tissues including the roots and stems additionally occurred. These reserve may have contributed to the similarities you observed in leaf N concentration (at least at some stages of the season). 

Lines 151-152: As mentioned earlier, if you include a brief description of the plant growth stages relevant to your sampling dates, it would be easier to follow why “other plant tissues also demanded a high amount of N” after Apr 2016. In fact, can you briefly elaborate here on the developmental activities in relation to the other plant tissues demanding a high amount of N?

Lines 152-155: Can you add a short description of why leaf N are likely translocated to other sinks later in the season? For example, are the leaf N exported to ultimately contribute towards growth and reserve storage in these other tissues?

Figure 1: It would still be beneficial to include the leaf N concentrations for Farthing in this figure. You could split the Figure into A) and B) if applicable.

Line 177: I would replace “symptoms” with “sign” in the context of this sentence.

Table 1: It would still be interesting and thorough if you include the data for Farthing here as well.

Lines 206-214: You may add to the discussion here that a possible flush in root growth and root activity during the post-harvest period may have contributed to an increase in plant N uptake during this period. It is, for example, often described for at least some other crops, such as grapevines, that a flush in root growth and activity, including nutrient uptake, occurs after fruit maturity. For example, check:

Comas, L. H., Bauerle, T. L., & Eissenstat, D. M. (2010). Biological and environmental factors controlling root dynamics and function: effects of root ageing and soil moisture. Australian Journal of Grape and Wine Research, 16, 131-137.

Bates, T. R., Dunst, R. M., & Joy, P. (2002). Seasonal dry matter, starch, and nutrient distribution in'Concord'grapevine roots. HortScience, 37(2), 313-316.

Van Zyl, J. L. (1984). Response of Colombar grapevines to irrigation as regards quality aspects and growth. S. Afr. J. Enol. Vitic, 5(1), 19-28.

Lines 218-220: This sentence needs a rewrite, perhaps: “…plant canopy size, was significantly larger in the 336N treatment compared to the 0N, 42N and 84N plants for both cultivars…”

Lines 247-249: Can you clarify and elaborate a little on this statement? Do you mean that there is likely a cumulative effect caused by the higher N rates, thus inducing higher N reserve levels in woody tissues and also increased N remobilization the next season? Then effectively causing earlier reproductive development? The current sentence/statement is a little vague.

Line 249: Can you check the reference here “[23]” – this seems to be the incorrect reference number; the peach reference seems to be number 24. In fact, can you check throughout the manuscript – some of the citations appear to have the wrong citation number next to it (for example, also lines 351 and 353, citations 29 and 30, should be 30 and 31 it seems.

Lines 272-275: This sentence appears a bit loose. Can you link this better to your results, otherwise it’s hard to see the point for the presence of this final sentence in this paragraph.

Line 281: As mentioned earlier, can you include information in the material and methods section regarding the linear plateau model?

Figure 3 and the discussion of these results: can you clarify if the ground cover data in this figure is for only the first or second assessment date, or for a combination of the two?

Line 314: Change “Figure3” to “Figure 3”

Line 314: Remove “For” at the start of the sentence.

Lines 324-325: Can you clarify this sentence? What exactly do you mean by a reduced fruit size was likely due to insufficient source supply in relation to the high fruit sink demand, following the high N rate? The meaning of this sentence is unclear and should be rephrased. For example, when you mention sources and sinks, are you referring to sources and sinks for N, sources and sinks for carbon, or both?

Figure 4: This figure has a A) and B) component, please indicate this within the figure as well.

Line 343-344: It may still be beneficial to include the Emerald data in Table 5, if you cannot include this data, you should at least indicate that this data is not shown. Also, “early” and “middle” season is a bit vague, can you define these dates here?

Line 354-356: The comment above applies to this sentence as well.

Line 364: “more carbohydrate source” should be rephrased. Do you mean that these plants had a greater total leaf area and therefore higher whole-plant photosynthesis, or do you mean that the plants had higher photosynthesis rates per individual leaves?

Line 365: “…and/or a longer fruit development…”

Conclusions: This is well-written, concise and easy to follow.

Author Response

A study was conducted to assess the implications of N fertilization rates on the vegetative and reproductive development of young Southern Highbush blueberry plants. An aim was to identify the optimal N requirements suitable for cultivating these plants. The authors conclude that greater N application advanced the reproductive development cycle, in addition to increasing vegetative growth and fruit yield. High N application rates also corresponded with nitrate leaching. Finally, they found that maximum fruit yields were achieved when the plants received around 200 to 220 kg.ha^-1 N per year.

The manuscript is well-written, concise, has clear outcomes and would contribute to the literature in a novel fashion. Below are a few minor suggestions for the authors to consider:

Abstract: This section is well-written, and clearly outlines the objectives and key results and conclusions.

Introduction: This section has an excellent structure and contains clear, informative paragraphs. A few specific comments below:

Line 45: You could elaborate a little more on the “large storage of N” – if you are referring to the N reserves stored in the woody plant tissues, you could describe a bit more in relation to the utilization of these reserves and how this may have affected the differences among your N treatments.

Response: two sentences are added in L45-49:

However, N rates did not affect yield, possibly because stored N reserves in mature plants compensated for low N fertilizer rates during the 2-year study. [3]. Our previous work has shown that reserve N contributes to fruit development in blueberry [4].Line 56: Can you name the major goals/objectives for the study here. For example, one objective was perhaps to assess the implications of the treatments on N leaching, another objective was to evaluate the impact of N application on vegetative development, etc.

Response: revised in L67-69:

The objectives of this study were to (1) determine the effect of N rates on growth and yield of young SHB and (2) optimize N application rates for commercial blueberry production in Florida.

Material and methods: This section is thorough, and the methods clearly described. However, some additional information may be beneficial:

Lines 92-112: Can you include a short description of the growth stages in relation to these sampling dates somewhere? For example, the leaf samples were collected on 13 Oct 2015, and 21 Apr, 1 Jun and 22 Aug 2016, while photographs for canopy ground cover assessments were taken on 14 Nov 2015 and 27 Oct 2016 – Where possible, a brief description of the growth stages would be beneficial to clearly understand when these samples and photographs were taken. The same applies for the soil sample collection dates. Perhaps you could also include some of this information about growth stages within the Figures and Tables (e.g. Fig 1 and Table 1).

Revised accordingly in L107-108:

These dates correspond to initiation of fall leaf coloration, beginning of fruit harvest, end of fruit harvest, and initiation of flower buds, respectively.

Lines 93-94: I would rephrase - “…micronutrient concentrations were analyzed from samples collected on 13 Oct. 2015 and 1 June 2016.”

Revised accordingly in L108-110:

Leaf P, K, Ca, Mg, S and micronutrient concentrations were analyzed from leaf samples collected on the 13 Oct. 2015 and 1 June 2016 sample dates.

Lines 96-98: Can you provide more details regarding the model and manufacturer details for the N gas analyzer and spectrophotometer?

Revised accordingly in L114-115:

using LECO-Nitrogen Gas Analyzer (FP 628, Model#: 622-000-200, St. Joseph, MI 49085)Lines 111-112: Can you provide details regarding the make and model of the flow injector analyzer?

Revised accordingly in L133-134:

by flow injection analyzer (Shimadzu model 6AV spectrometer, Kyoto, Japan).Lines 116-121: Can you include a short description of how berry maturity was assessed prior to harvesting? For example, were the berries harvested when they have reached a target TSS level?

Revised accordingly in L139:

Berries are considered ripe at color break from red to blue.

Line 127: “Total soluble solid content” should be “Total soluble solid concentration”.

Revised accordingly in L150: Lines 134-140: Information regarding the linear plateau model used to assess the regression between N rates and yield seems lacking here. Can you include this here in the data analysis section?

Revised accordingly in L165:

The linear and quadratic regressions between variables except yield and N rates were analyzed if the ANOVA indicated a significant N treatment effect on the variable [14]. The regressions mentioned above, linear plateau regression between yield and N rates, and linear correlations among each pair of traits (berry number, berry diameter, berry weight, yield, and ground cover percent) were all analyzed using R studio with the ‘nlstools’ and ‘easynls’ packages.

Results and discussion: This section is mostly clear and well-written, a few additional comments below:

Lines 145-147: It is likely that mobilization of N reserves stored in woody tissues including the roots and stems additionally occurred. These reserve may have contributed to the similarities you observed in leaf N concentration (at least at some stages of the season). 

Revised accordingly in L180-181:

[11]. Additionally, mobilization of N reserves stored in the roots and stems may have contributed to the similarities in leaf N concentration for 2016.Lines 151-152: As mentioned earlier, if you include a brief description of the plant growth stages relevant to your sampling dates, it would be easier to follow why “other plant tissues also demanded a high amount of N” after Apr 2016. In fact, can you briefly elaborate here on the developmental activities in relation to the other plant tissues demanding a high amount of N?

Revised accordingly in L107-108:

These dates correspond to initiation of fall leaf coloration, beginning of fruit harvest, end of fruit harvest, and initiation of flower buds, respectively.Lines 152-155: Can you add a short description of why leaf N are likely translocated to other sinks later in the season? For example, are the leaf N exported to ultimately contribute towards growth and reserve storage in these other tissues?

Response: added two sentences in L190 to 191:

From late Aug. to early winter, N is remobilized from leaves prior to leaf abscission, and accumulates as reserves in the perennial parts of the plant.

Figure 1: It would still be beneficial to include the leaf N concentrations for Farthing in this figure. You could split the Figure into A) and B) if applicable.

Response: added in Figure 1

Line 177: I would replace “symptoms” with “sign” in the context of this sentence.

Response: added L214.

There were no signs of Fe or Cu deficiency in plants.

Table 1: It would still be interesting and thorough if you include the data for Farthing here as well.

Response: The data for ‘Farthing’ are very similar to those for ‘Emerald’. We believe using ‘Emerald’ data can support our findings clearly and don’t want to simply repeat a similar dataset in this table. Thus, we didn’t include the data for ‘Farthing’.

Lines 206-214: You may add to the discussion here that a possible flush in root growth and root activity during the post-harvest period may have contributed to an increase in plant N uptake during this period. It is, for example, often described for at least some other crops, such as grapevines, that a flush in root growth and activity, including nutrient uptake, occurs after fruit maturity. For example, check:

Response: added one sentence in L260 to 261:

Additionally, there was likely a flush of root growth after berry harvest [4], which increased N uptake in the postharvest period.

Comas, L. H., Bauerle, T. L., & Eissenstat, D. M. (2010). Biological and environmental factors controlling root dynamics and function: effects of root ageing and soil moisture. Australian Journal of Grape and Wine Research, 16, 131-137.

Bates, T. R., Dunst, R. M., & Joy, P. (2002). Seasonal dry matter, starch, and nutrient distribution in'Concord'grapevine roots. HortScience, 37(2), 313-316.

Van Zyl, J. L. (1984). Response of Colombar grapevines to irrigation as regards quality aspects and growth. S. Afr. J. Enol. Vitic, 5(1), 19-28.

Lines 218-220: This sentence needs a rewrite, perhaps: “…plant canopy size, was significantly larger in the 336N treatment compared to the 0N, 42N and 84N plants for both cultivars…”

Response: revised in L265 to 267:

The percent ground cover in 2015 indicates that relative plant canopy size was significantly larger in the 336N treatment than in the 0N, 42N, and 84N treatments for both cultivars, but was similar to the 168N treatment (Table 2).Lines 247-249: Can you clarify and elaborate a little on this statement? Do you mean that there is likely a cumulative effect caused by the higher N rates, thus inducing higher N reserve levels in woody tissues and also increased N remobilization the next season? Then effectively causing earlier reproductive development? The current sentence/statement is a little vague.

Response: one sentence added in L296 to 299:

The advancement in bloom at the greater N rates may be due to increased accumulation of N reserves at the higher compared with the lower N rates, and therefore increased allocation of stored N from the previous season to flower buds in those treatments, as described by [24] for peach.ine 249: Can you check the reference here “[23]” – this seems to be the incorrect reference number; the peach reference seems to be number 24. In fact, can you check throughout the manuscript – some of the citations appear to have the wrong citation number next to it (for example, also lines 351 and 353, citations 29 and 30, should be 30 and 31 it seems.

Response: Revised thoroughly. All tracked.

Lines 272-275: This sentence appears a bit loose. Can you link this better to your results, otherwise it’s hard to see the point for the presence of this final sentence in this paragraph.

Response: Revised accordingly in L323-327.

Similarly, plants with 168N advanced 50% harvest one week earlier than those with 42N and 0N. This advancement of fruit harvest at greater N rates is similar to the results from Wilber and Williamson [25], who reported an advancement in fruit ripening at medium (20.1 g/plant/year) and high N rate (30.0 g/plant/year) compared to low N rate (10.5 g/plant/year) for SHB ‘Misty’ but not for ‘Star’.Line 281: As mentioned earlier, can you include information in the material and methods section regarding the linear plateau model?

Response: Yes, added L165-169

Figure 3 and the discussion of these results: can you clarify if the ground cover data in this figure is for only the first or second assessment date, or for a combination of the two?

Response: the following sentence is added in L352-356.

Figure 3. Correlations among N rate, berry number, berry weight, berry diameter, yield, and ground cover percent for ‘Emerald’ (A) and ‘Farthing’ (B). The numbers are the correlation coefficient (R) between variables. The ground cover percent data are from the first year (2015) and the yield data (2016) are from the second year when the first harvest occurred. Asterisks (*) indicates the correlation is significant at *P £ 0.05, **0.01, or ***0.001.

Line 314: Change “Figure3” to “Figure 3”

Response: Changed in L369

Line 314: Remove “For” at the start of the sentence.

Response: removed in L369.

Lines 324-325: Can you clarify this sentence? What exactly do you mean by a reduced fruit size was likely due to insufficient source supply in relation to the high fruit sink demand, following the high N rate? The meaning of this sentence is unclear and should be rephrased. For example, when you mention sources and sinks, are you referring to sources and sinks for N, sources and sinks for carbon, or both?

Response: added carbon in L380

Figure 4: This figure has a A) and B) component, please indicate this within the figure as well.

Response: changed accordingly in Figure 4.:Line 343-344: It may still be beneficial to include the Emerald data in Table 5, if you cannot include this data, you should at least indicate that this data is not shown. Also, “early” and “middle” season is a bit vague, can you define these dates here?

Response: added “data not shown at L399. Revised at L147:

At each of the early (‘Emerald’ 2 May 2016; ‘Farthing’ 9 May 2016), mid (‘Emerald’ 9 May 2016; ‘Farthing’ 16 May 2016), and late (‘Emerald’ 16 May 2016; ‘Farthing’ 23 May 2016) seasonLine 354-356: The comment above applies to this sentence as well.

Response: Revised at L147:

At each of the early (‘Emerald’ 2 May 2016; ‘Farthing’ 9 May 2016), mid (‘Emerald’ 9 May 2016; ‘Farthing’ 16 May 2016), and late (‘Emerald’ 16 May 2016; ‘Farthing’ 23 May 2016) season

Line 364: “more carbohydrate source” should be rephrased. Do you mean that these plants had a greater total leaf area and therefore higher whole-plant photosynthesis, or do you mean that the plants had higher photosynthesis rates per individual leaves?

Response: revised as shown in L417-421:

This may be attributed to: (1) more carbohydrate source from leaf photosynthesis due to more leaves in late season and (2) the smaller berry size later in season with possibly greater concentration of photosynthates.Line 365: “…and/or a longer fruit development…”

Response: deleted

Conclusions: This is well-written, concise and easy to follow.

Reviewer 2 Report

Overall, this is a good study and contributes important information about highbush blueberry fertility. The quality of the writing is decent and I had areas where I indicated more details should be provided in the attached document. The introduction and methods sections, in particular, need more description. 

I recommend this paper be published with revision. 

Comments for author File: Comments.pdf

Author Response

Lines 38-40: Wow - these are extremely high N rates! However, these two sentences are a bit unclear to me. How did irrigation influence the response to the high rates? Please describe. Also, could immobilization be an issue with pine bark, leading higher N rates to be benefical to avoid competition with microorganisms? This needs to be better explained in the introduction to set up the justification.

Revised accordingly line 39-40.

However, they explained the high fertilizer requirement was due to the considerable nutrient leaching as a result of low water and nutrient holding capacity of pine bark and high frequency of irrigation.

Response to the second part of question: Pine bark immobilization may be not an issue here since pine bark was applied at year 2000 which was 3 years ahead of experiment start (year 2003).

 Lines 46-49: Sound mention that the reduced yield in these studies was likely due to accumulation of salts from the fertilizer. Also, should mention how the plants in these two studies were fertilized (i.e., drip vs. dry) and source, as this could influence the different responses in these two studies.

Response: revised as shown in L55-58:

The fertilizer in both studies was manually broadcasted under plant canopies and evenly split into thirds. The inconsistency between the two studies may be due to cultivar differences in susceptibility to salt stress and/or the absence of overhead irrigation after fertilizer application in the former study.

 

Lines 50-51: This is too general. I think you should explain this more in the introduction and responding to the two comments above will help.

Response: revised as shown in L59-63:

Blueberry plants response to N rate is also influenced by N application method [78]. These studies reported fertigation reduced salt accumulation and changed N use efficiency as compared with dry granular fertilization [7, 8]. Hanson [9] reported that soil conditions such as soil texture and nitrifier populations affected N dynamics and uptake by blueberry plants, resulting in additional variability in blueberry response to N rate.

Lines 59: Specify nursery.  Also, what was the planting density?

Response: Added nursery in L73; planting density added in line 83.

Line 63: Did you do any baseline soil tests of the site? Those would be interesting to see. Also, I can tell it was a sand. Was it a coarse or fine sand?

Response: We did the soil test in Mehlich I before planting: P, 65 ppm; K, 38; Ca, 347, magnesium, 45.5 mg/kg. The bed was soil with 97% fine sands mixed with pine bark of 787.5 m³ ha^-1.

The sandy soil was mixed with 787.5 m3 ha-1 of pine park incorporated into the top 20 cm soil as shown in L78.

Line 73: Why just two?  Also, how big were the plots? It would be good to show the scale of the experiment by reporting plot size, buffer between plot, etc. 

Response: The plot consisted of six plants, and two end plants were used as buffer. It would be too much work to measure all of the plants.

Plot scale mentioned in L86-88

Line 76: What percentage of the ammonium nitrate was NH4 vs NO3? Is this standard for FL? I would be worried about the NO3 given it is metabolically not used and leaching.

Response: 3:1. 50% N from urea and 50% N from NH4NO3. Added in L90-91.

Lines 79-80: This is quite a bit of change in initiating and ending fertilizer applications between the years. Please explain why this was done.

Response: We planted in March, 2015. So the fertilization started in April, 2015 later than the second year.

Line 81: Good that all plants received equivalent water. Did this volume of water represent standard grower practices or recommended guidelines? Given this adjustment in volume to accommodate higher rates, I worry that too much water will be applied overall and favor leaching.

Response: We adjust the irrigation rate as plants’ need. Leaching was likely happened due to the low water holding capacity of sandy soil and pine bark.

Line 92-94: Do these timings allow you to compare with know sufficiency standards?  If so, that would be good to cite.

Also, did you sample from shoots and whips or were you more restrictive. Specify please.

Response: In literature, sufficiency standards for SHB are only available for summer (June-Aug.). We measured on 1 June and 22 Aug. 2016 and also include Apr sampling date because we would like to know leaf N during reproductive stage.

Only recently fully expanded leaves from shoots were sampled.

Line 101 - how was the camera mounted? Did you worry about ground cover and how did you separate that out during post image processing? Overall, I'd like to see more description on post image processing and how you managed to account for ground cover and isolate a single plant (I see plants growing into each other).

Response: Revised in L118-121:

A digital camera (Canon PowerShot SX50 HS with a resolution of 12.1 megapixels) (Canon, Tokyo) was mounted 130 cm above the center of each plant to take the pictures of the plant canopies. Plants that were adjacent to the data plants were separated by hand while taking pictures if canopies were touching or overlapping.  

Section 105: How far was the auger from emitters? Was that consistent?

Response: There was a tubing on each side of plants. We took the samples from the middle of two tubings, which was consistent for all the samples. To further reduce the effects from irrigation, we turned off the irrigation system during the sampling day.

Lines 128-129: What were the operating parameters of the FirmTech (E.g. minimum deflection and max compression)?

Response: Added line 151-152:

Berry diameter and fruit firmness were measured with a firmness tester (FirmTech 2, BioWorks, Wamego, KS) at a minimum force setting of 50 g and a maximum setting of 350 g on the day of harvest.

Lines 126-132: Were berries frozen for fruit quality analysis for later re-testing or not? Also, please describe how juice was extracted for SSC and TA. 

Response: Added in line 153-156:

After firmness measurements, berries were sealed in ziploc bags and frozen in a -20 °C freezer for later TSS and TTA analyses. The thawed berries were ground with a blender (Chefman immersion blender, Model#: RJ19-MS-PBG-CA). After centrifuging (ThermoFisher Scientific, Model# Sorvall Legend XTR Centrifuge) and filtering with cheese cloth, juice TSS

15. Lines 137-138: What do you mean "were followed"? You need to explain your linear-plateau modeling process, as well as other modeling processes.

Response: Revised and added line 165-170:

The linear and quadratic regressions between variables except yield and N rates were analyzed if the ANOVA indicated a significant N treatment effect on the variable [14]. The regressions mentioned above, linear plateau regression between yield and N rates, and linear correlations among each pair of traits (berry number, berry diameter, berry weight, yield, and ground cover percent) were all analyzed using R studio with the ‘nlstools’ and ‘easynls’ packages.

Statistics - did you evaluate for year effects and/or interactions? You should explain how you handled year effects and their interactions.

Response: We analyzed variables in each year separately and didn’t evaluate the year effects and interactions because the objective to this project was to evaluate the N rates effects.

Line 147: Do you have data that pine bark decomposition contributed to N release? If not pine bark, literature for another organic amendment showing what you are inferring would strengthen your discussion.

Response: Added in L180

The similar leaf N concentration of the 0N plants with the plants receiving N fertigation was likely due to the pre-plant N and N release from pine bark decomposition [11].

Line 177: If there were no symptoms, does this indicate these standards may need to be re-vised?

Response: Added in L215-216

These results suggest that leaf nutrient standards for young SHB may need to be improved.

Line 179: It would be really nice to see the 2015 soil nitrate data. Can you please just report averages with SE?

Response: added in L.220-225:

There was a tendency for greater soil nitrate concentrations in the 336N treatment than in the other treatments. For example, in the ‘Emerald’ field, the respective soil nitrate concentrations throughout the year for 336N averaged 15.20 ± 1.01 and 7.43 ± 1.43 mg kg^-1 at the 30 cm and 76 cm depths, respectively. Conversely, all the other treatments averaged 3.34 ± 0.35 and 4.02 ± 0.36 mg kg^-1 at the aforementioned depths.Table 1. You reported collecting at different depths in cm, but here in meter. Keep consistent with units, please.

Response: revised Table 1

Line 190 - why do you think July was different than your other sampling dates? It would be nice to have a mechanistic explanation to explain these results. ...I see you kind of do this below, but remind the reader when harvest ends and how that relates to this specific July period.

Response: Added inL235 and L250:

In July (after harvest when plants were at vegetative growth stage), there were no significant differences among the treatments at any depth.

However, after fruit harvest and through fall of 2016 when plants were in a vigorous vegetative growth stage

Line 204 - peach species name should be in italics.

Response: Revised L249

Lines 230-232 -the lower efficiency was primarily due to young plants having smaller root  systems, but efficiency increased when plants got older and root volume increased. Therefore, plant age has lots to do with it and you may want to consider specifying that in the last sentence of this paragraph.

Response: In this paper, we focused on young plants. Revised in L260-261:

Additionally, there was likely a flush of root growth after berry harvest [4], which increased N uptake in the postharvest period.

 

Lines 287-291: I'm glad you mentioned this here, but still think it should be brought up in the introduction.

Response: Added in L55:

The fertilizer in both studies was manually broadcasted under plant canopies and evenly split into thirds.

Figure 3 - Nice way to show these relationships! Asterisks are hard to see. Can you place them below or above the coefficient to make clearer?

Response: Revised Figure 3

Lines 302-303: Could your sandy soils also influence this response?

Response: Revised in L358: especially in sandy soil and pine bark with low water holding capacity.

Line 308 - check your figure and compare with these values. It looks like it explains more variability to me.

Response: The numbers showed in figure 3 were correlation coefficient (R) while the variability explained should use R²

Line 316: Where are the berry weight data?

Response: Berry weight data was not presented in tables to reduce the number of tables but we present the average values in the context. See L372-374

Line 325 - specify what you mean by "source supply'. Also, remind the reader about berry number to highlight how that sink represented as berry number differed across the treatments.

Response: Revised L381:

Reduced berry size from the highest N rate may be due to insufficient carbon source supply for the high sink demand from heavy fruit loads

30. Line 350 - would be good to remind the reader that diameter was reduced at higher rates.

Response: Added line 429:

Plants with 336N had the smallest berries throughout the season.

31. Line 377- this is still a very high rate! Perhaps suggest monitoring to avoid leaching?

Response: Added L437-438:

Adjusting N application rates based on plants’ need, avoiding over irrigation to reduce nutrient leaching may result in a lower N requirement.