Comparative Analysis of Energy and GHG Emissions Using Fixed and Variable Fertilization Rates
Round 1
Reviewer 1 Report
Review of Agronomy Article:
Comparative analysis of energy andGHG emissions using fixed and variable fertilization rates.
General comments:
Overall the study is not described very clearly and needs to be revised considerably. Minor details need to be shortened and the overall results need to be presented more clearly. This includes the calculations that translate soil and plant analysis into fertilizer application recommendations. The language needs to be revised by a native English speaker. Maybe that also clarifies a few points to the reader .
The author describes technical equipment and some calculations in great detail , but major explanations or comparisons are missing . For example from line 111 to line 152 the authors described technical details of performing soil analysis. However, there is no thorough explanation as to how analysis of soil parameters are transferred into fertilizer application recommendations. Also there is no list of the fixed fertilizer application rates. This comparison after all, appears crucial to me. In line 127, the authors mention a fertilizer plan, but this is not described or visualized. Also in line 147-152, no information about fertilization is given, only that the program calculates it.
To me it is unclear, where those 4 plots of different soil characteristics are (line 122). Or do the authors mean soil property classes, that are unevenly distributed across the field? This needs to be described in detail!!
In line 155, the “accurate N-uptake in plants was determined”. There is a difference between N-content, N-concentration and N-uptake. Presumably the N-concentration was measured at different times in the study. The wording here needs to checked and corrected if wrong.
Also line 158: “nitrogen fertilizer were spread in real time”. I assume fertilizers are always spread in real time. The authors probably mean “N-fertilizer rates were calculated in real time”.
I cannot understand line 171-174. Describe more clearly the fertilizer rates applied.
Line 192-2011 , this section describes small calculations. The wordings should be shortened considerably. However, the source of information described in the Table, the basis for translating the amount of fertilizer into energy or GHG-equivalents is not mentioned in the text and also not explained in detail.
Table 2: what does it mean ”Recommended interval” ?? There is a considerable difference in P concentration between the 4 samples. Difficult to use mean values, since sample 4 is dominating. Any reason for those high values ?
Figure 5 What does the letter D- or D+ stands for in the description “pH average D-“.
Probably would be more suitable to have the paired graphics next to each other, for example pH in 2015 next to pH in 2019
Line 250-256 , major results of the study are described. Probaly this should be described in clear details in a Table. Maybe outlined for each crop in each year. Sentence in line 252-253 is unclear or without information.
Line 275 is this fact true?? Not overly relevant for this study.
Figure 6 and 7 : Legend needs to be clearer. Seems to me juts the output of the N-sensor. There are no headings for the columns: “Percentage of field” . The word “legend” stands for 2 columns without explanation.
Line 299-302, threshing details are provided . However, there is no Table describing the yield of the different crops and the different years for the VRF and FRF fertilization strategies. Figure 8 gives some indication , but only for winter wheat.
Table 3 column: Reduction N-rate for total field area (kg field-1) is not necessary at all. Important information is in kg-1 ha .
Line 348-356 the authors need to point out the overall dominance of N fertilizer in respect to the energy use ha-1 , due to fertilizer application. Energy savings with reduced P or K application are generally less.
Line 369 do you mean greenhouse gas reductions due to VRF fertilization …
Line 381-392 Economic savings per field is not important, only confusing. Savings per ha are the important information. Would be good to have a table comparing economic savings to CO2 savings and this comparison for each crop.
Line 411 “ almost twice the greenhouse gas emissions” compared to what ????
Language:
The english still needs major revision. Some words are used in unusual situations, for example fertilization is not “performed” but ”applied” (line 16) and many times throughout the text. It is “mineral fertilizer” and not “chemical fertilizer”
Author Response
First of all, we would like to thank the Reviewer for valuable comments, detailed recommendations, and contributions to improving the quality of this manuscript.
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The objective of the article is to compare the effects of two fertilization strategies, fixed rates and variable fertilization rates stablished according to soil analysis and plant status. The study focus in the save in fertilizer and energy consumption, and in reduction in greenhouse gases emissions associated to both direct emissions and fertilizer production. The subject is of interest and fit in the scope of the Agronomy Journal
It is not clear the way that fixed fertilizer rates and variable fertilizers rates are stablished. It is clear the procedure of integration of the information but no the way the information is managed to obtain the fertilizer rates applied. Fixed and variables rates for each year are not given clearly although the average values appear in table 3.
I understand than for P and K four application rates are stablished based on the values of soil P and K concentrations given in Table 2. For Nitrogen, in years 2017 and 2018 variable rates are spread all over the field using the readings of Yara N-sensor. For years 2016 and 2019 fixed rates are used. But I have some doubts if this is correct.
The material and methods section is not clear in many aspects, and should be clarify. See more comments in detail below.
Introduction
There is a confusion between nitric oxide (NO) and nitrous oxide (N2O). see for instance lines 57, or 63
Lines 58-59
“The concentration of N2O in the atmosphere is 310 times higher than carbon dioxide (CO2)”
This phrase is not correct perhaps you want to refer than N2O has a 310 times higher warming potential than CO2? .
Line 65
“or evaporated into the atmosphere” better change to
“or emitted to the atmosphere
Line 80
of different fertilization methods using long-term crop rotation of 4 plants is still lacking.
Please eliminate 4 plants, change to
of different fertilization methods using long-term crop rotations is still lacking.
Materials and Methods
Need to be reorganize. Consider joining subsections 2.2 and 2.3 as soil sampling and adding a subsection to explain how fixed and variable fertilizer (N-P-K) rates are calculated
Lines 95-97
I suggest to rewrite to
Average (2016-29) annual precipitation was 505.7 mm and average annual air temperature was +8.0 °C (Lithuanian Hydrometeorological Service, meteo.lt).
Line 102
Figure 2. Dynamics of temperature and precipitation distribution in 2016–2019.
Better change to
Figure 2. Monthly air temperature and precipitation in the period 2016-2019.
Lines 112-117
With the EM38 MK-2 you don not measure soil electrical conductivity but apparent electrical conductivity. To obtain EC values is necessary to calibrate the readings versus soil samples.
Rewrite the paragraph to something similar to:
Prior to beginning the experiment, soil apparent electrical conductivity (ECa) at the 0-1.5m depth was measured using an EM-38 MK-2 (Geonics Ltd, Canada) in the vertical position to determine differences in the field soil’s properties and to establish an accurate soil sampling plan. EM-38 readings were performed while driving a Toyota off-road vehicle towing the EM38-MK2 mounted on plastic sledges at a speed of 10–15 km h-1 in parallel technological tracks separated 30 m, with a total of xx readings in the 11.37 ha field and stored in a computer Panasonic Toughbook CF 19 (Panasonic Corporation, Japan)
Need to add a figure with the 4 homogeneous areas delineated
Add the number of readings in the field or the density of EM38 reading (readings/ha)
Lines 118- 124
Rewrite the paragraph to something similar to:
ECa readings were converted to CSV file format using Convert EM38-MK2 software and subsequently, using the Open Source Geographic Information System (QGIS) program, a total of 4 areas with different ranges of ECa were delineated. The delineate plots in a digital shape (SHP) file were sent back to the field computer and soil samples were taken.
It is not necessary to specify the computer.
Lines 126-127
In order to apply the fertilizer at a variable rate, the fertilization plans were drawn up for a 126 period of 4 years according to the crop rotation, taking into account the expected crop yield (t ha-1) 127 and the available nutrients in the soil.
This should be in a specific subsection “Determination of fixed and variable fertilization rates”.
Lines 128-141
Rewrite to something similar to:
Soil (add soil depth) was sampled on 17 September 2015 and 2 September 2019 using an automatic soil sampling equipment (Figure 3) developed by Agricon (GmbH, Germany) and manufactured by Adigo (AS, Norway). Twenty samples were collected while driving non-stop (50% more efficient than sampling at a stop) in the trajectory of the letter Z, and combined in one sample in each of the 4 homogeneous areas delineated previously.
Lines 141-144
“A total of 4 samples were taken from plots formed according to different soil electrical conductivity into boxes containing 300–500 g of combined soil samples of different structure. After all the boxes were filled, the soil sample from each box was placed into separate plastic bags labelled with a bar code including the following information: 1) the coordinates of the sampling point; 2) information about the farm; 3) a name of the person who took the sample; 4) date and time of sampling”.
It is not clear how samples were collected, please explain better.
If each sample was a combination of 20 subsamples taken along the Z letter. You cannot label the coordinate of the sampling point, so there is something that is not clear.
I see in Figure 5 that there is more information than from 4 points. You should explain clearer how you manage soil sampling.
Lines 144-147
Rewrite to something as:
Samples were sent to the accredited laboratory Agrolab GmbH (Germany) and granulometric structure, magnesium (Mg) and pH (CaCl2 method) and potassium (K) and phosphorous (P) (CAL method) determined.
Lines 147-152
You need to explain how rates of P2O5 and K2O were stablished for each of the 4 Areas, giving the total crop needs during the four years and the amount provide for the soil and the fertilizer requirements for each area.
Lines 151-152
“There was no demand for pH and Mg elements”.
Change to
Magnesium was enough to satisfy crop demand in the whole rotation and was not supplied.
Delete pH
Lines 153 and on
Need to explain how N rates are calculated as a function of the N sensor readings for each crop.
Lines 169-174
The amount of different fertilizer products are average values? In the whole field, why not for areas?
Lines 176-190
It is not clear the reason to calibrate the ALS sensor versus Yara N-tester.
Lines 197- 198
“Another very important benchmark that has been identified is the reduction in energy 196 consumption of fertilizers per tonne of crop. This indicator was calculated by dividing the difference 197 between VRF and FRF by crop yield.”
You do not have crop yield for fixed fertilizer rates, how do you calculate this benchmark?
Line 203
GHG emissions calculated using the information of Table 1 is for fertilizers manufacture. You could also include in the balance the N2O emission from soil, based on emission factors (see IPCC 2019 guidelines)
https://www.ipcc-nggip.iges.or.jp/public/2019rf/pdf/4_Volume4/19R_V4_Ch11_Soils_N2O_CO2.pdf
Results
Lines 246-249
Please add information on Fixed and variable N-P-K rates for each crop in the rotation, and not only the differences between both approaches.
Lines 258 -260
You should explain what is the additional fertilization (in Material and methods).
Lines 286-288
“For the calculation of chemical fertilizer demand and energy and pollution indicators, the yield was determined for each crop in the crop rotation, which corresponded to the determined soil properties. “
The phrase is not clear, what do you mean by “which corresponded to the determined soil properties”.
Values of yields given later are for the whole field?
It is confuse
Lines 290-294
You should discuss the reason why the highest yield was obtained in the areas with lower N application rate and viceversa.
Lines 306-307
It is unclear in the manuscript the additional fertilizations
Line 380
Economic Benefits: This should be done not only considering savings in fertilizer but also considering crop yield. Some comment should be included on this.
Comments for author File: Comments.pdf
Author Response
Thank you very much for the reviewer for taking the time to review our manuscript and provide valuable comments.
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors have carried out a comprehensive comparison of fixed and variable fertilization rates on energy and GHG emissions. The results presented are sound and interesting, however I suggest a few changes below.
Point 1: L36-37 - explain why this is not beneficial for soil health or plant production. This is essential for the discussion.
Point 2: L61 - what does 'environmental quality' mean in this context?
Point 3: L78-79 - expand this statement with more specific facts – which kind of results has already been published
Point 4: L81-84 - The aim in these sentences is not clear enough – it is too weak just investigation. Re-write.
Point 5: L88-90 - was the cultivar of tested crops?
Point 6: L 202-211 – please describe GHG emission determination in more detailed and please include appropriate citation(s).
Point 7: L 213-215 – Since statistical analysis is a critical for formulation of conclusions, it would be advisable to include details about the mandatory data normality and homoscedasticity tests preceding the ANOVAs.
Point 8: Can you contribute more generally? At the end of the discussion we expect researchers to comment on how the alternative fertilization may have limited the conclusions that could be drawn. Also, they have the opportunity to recommend to their followers, about future needs and research.
Author Response
Thanks to the reviewer for reviewing the manuscript and providing valuable comments.
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The article “Comparative analysis of energy and GHG emissions
using fixed and variable fertilization rates“ describe the fixed and variable rate fertilization effects with energy and fertilizer consumption on spring barley, winter oilseed rape, winter wheat and faba bean crops based on 4 years crop rotation systems. The manuscript is quite well written and addressing the GHG emissions by using variable rate and fixed rate fertilization determined by sensors. The results presented and describe well both via tables and graphs. But some sentences were not clearly defined. Furthermore, some quires that need more attention by researchers which are given in the research paper.
Introduction
Introduction part is written good. Add some points related to nutrients measuring sensors with latest references.
Material and methods
Line 95 and 99_ Improve sentences structure
Line 211_Add standard reference for GHG calculation
Line 286_ Delete and between chemical fertilizer demand and energy and add comma here.
Page 4, Line 125, Did authors validate the results of automatic soil sampling equipment with ground?
Add planting time of crops, either sowing time for 4 years was different or same?
Results and discussions
Good explained
Conclusions
What are general findings for the farmers? Are these findings are farmer friendly and what authors say about the adoption of this technology by the farmers in the region.
Please discuss about general recommendations for future research.
Author Response
Thanks to the reviewer for reviewing the manuscript and providing valuable comments.
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
General
Still have the problem, that minor technical or other details are described in detail and major information is left out or is just mentioned in a few words aside. For example: line 154-157, Line 264-267 and line 300-305 and line 380-390, the details oft he table are just listed again. However, it would be important to point out major information. For example Table 2 that all Phosphate concentrations in the soil are in or above the optimum level. And that only K-levels are reduced significantly (?) over time.
As far as I understand , there was only 4our soil samples, consisting of 20 subsamples, taken at a given sampling time. Thus 1 sample for each of the four management areas. . How are the maps in Figure 6 created then ?
In line 162, the authors mention fertilization plans. Are they shown anywhere ? Would be good to see. Also line 169-172 is one long sentence that is unclear to me.
Is figure 5 necessary?
Cannot understand : in line 223 the authors mention that the Yara N-sensor-ALS can only collect data for uptake of N . I assume the sensor measures N concentration and Biomass. For waht reason ist he sensor Yara-N tester (line 2018) used. Presumably to calibrate the N-concentration in the wheat variety. If so that should be described correctly.
The text needs tob e structured much more. For example in section „2.3 Determination of fixed and variable fertilizer rates „ the nutrients N, P and K are discussed and in section „2.4 variable rate application of nitrogen fertilizer“ then again issues of N are discussed. Would be better to discuss N in one section and Pand K in another section, since the variable rate for P and K are determined differently than for N.
Also the section „2.5 Yara N-sensor ALS calibration in cereals“, should be discussed prior describing how it was applied. However, this section should be shortened considerably.
IN line 193 „an accurate N-uptake in plants „ was determined. IN line 175 the actual N-uptake has been determined. Was this not accurate?
Line 241 the authors state that „fixed and variable fertilizer rates were calculated for a predictable yield“ . What is a predictable yield ???? Ist hat the average yield oft he last 5 years or so ? Was the variable fertilizer rate, that was applied, whith known yield, recalculated for that „predictable yield?
If the comparison between VRF and FRF is based on recommended fertilizer rates and assumed yield for the FRF method, thatn this needs tob e discussed, because this is obviously a weak point in the study. How can we assume that the FRF treatment would achieve this yield ? Or maybe the yield would be higher. If those values are assumed, then the choice of those needs tob e explained carefully.
Statistical analysis is mentioned in line 256-261, but no information (sd or se or significant differences) are given in any table, also not in Table 1.
Line 265-267 , values of Table 2 are repeated . This happens a few times throughout the text. This is not necessary. Would be better to point out important trends. (also line 382-390)
Table 2 The „recommended interval“ should spell out the interval for what: optimum nutrient amount, as explained in line 272.
Are the maps in Figure 6 drawn on the basis of the four soil samples (line 151) ?? Or were all the 20 subsamples for one sample analysed separately
Section 3.2 could include the N-variable rate in the title, to differentiate from P,K variable rate.
Line 329 „ the average yield“ needs tob e explained (see comment above)
Line 340 unclear: „the N uptake map and the yield map were homogenous“ ??
The discussion is mainly repeating the numbers oft he Tables 4, 5 . It only states that there are savings. Are the changes considerable ? Also compared to other studies? A comparison with another study in line 440 states tha difference in crop yields in the other study. But this was nit even measured here. The authors should focus more on their main issue, analysing a crop rotation. The discussion needs to be streamlined to focus an a few important findings. Maybe it helps to differentiate bettter between N and the other two nutrients.
In Table 4, are the digits behind the comma necessary?? ( for example 1837.4)
Could Table 6 be showen as a bar graph since thisis a major comparison. And include Energy input?
Major fertilizer and energy savings are due to Phosphat fertilizer savings. This needs to be discussed on the basis of high P levels in the soil
Why are there so little savings in N-Fertilizers?
It needs to be pointed out in more detail, that the Fixed Fertilizer Application (FFA ) was not performed in the field as actual comparison. As far as I understand it the FFA fertilizer rate was assumed and the resulting yield was also assumed on the basis of average values. This needs tob e pointed out and also discussed in the Discussion.
Language
The writers tend to form long or very long sentences. Would help the readability to shorten those long sentences. The englisch of the manuscript has improved but still needs further improvement.
This woule improve the readability oft he manuscript significantly. A native speaker should edit the manuscript.
Quite often unusual words are used :
Line 251 „ environmental friendliness“, probably means environmental impact
Line 242 „ predictable yield“, probably means assumed average yield for the region
Sentences are never started with a number or otherwise the number needs tob e spelled out.
Author Response
Thank you very much for the reviewer for taking the time to review our manuscript and provide valuable comments. The manuscript has been corrected based on all the reviewer comments below. Each of the comments below helped to improve the quality of the individual sections and subsections and the overall manuscript.
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comparative analysis of energy and GHG emissions 2 using fixed and variable fertilization rates
Comments and Suggestions for Authors
Most of the comments and suggestions have been incorporated adequately in the manuscript. However there are some details that need to be clarified related mainly to the way that variable fertilizer rates are obtained and applied to the field.
Lines 204-216
It is clear that P and K rates are calculated taking into consideration soil analysis and potential yields of the whole rotation and in table 5 are the amounts of P and K applied to the whole field each year for the VRF. But it is not clear the total amount (whole rotation) of P and K applied to each of the 4 delimited areas for VRF. I recommend to add a table with this information other ways the reader only have the total amount for the whole field but no how this amount has been distributed on the field taking in consideration the information on soil properties given in table 2.
It is not clear how variable P and K rates are assigned to the field. Are they 4 different rates to be applied to the 4 different areas identified with electromagnetic sensor? . Perhaps you can add in the map in figure 3 the boundaries of the 4 delimited areas.
Line 264.
2.5 Yara N-Sensor ALS calibration in cereals
You calibrate Yara ALS versus N-tester. How do you use this calibration? You have added information but It is not clear for me reading the section. If you do not use the calibration this section should be deleted.
Figure 6
Only one sample is collected for each of the four delineated areas with the EM38. Each sample is composed of many soil samples taken in a transect within each area. At the end you have 4 analytical determinations, one for each area. Please could you explain how you manage the information to produce these maps, with their variability.
Author Response
We would like to thank the Reviewer for additional valuable comments, detailed recommendations, and contributions to improving the quality of this manuscript. All of the issues raised in the Reviewer comments were corrected and attached. All revisions are highlighted in the text.
Please see the attachment.
Author Response File: Author Response.pdf
