Nitrogen Hotspots on the Farm—A Practice-Oriented Approach

Round 1

Reviewer 1 Report

This paper proposes nitrogen (N) budgeting for on-farm assessment of N flows and identification of N hotspots.

This review is lengthy and often somewhat verbose. In general, relatively simple concepts seem to be written in an overly complex manner. It also appears that a lot of facts about relevant topics are presented, but not necessarily synthesized or put into the context of this review (i.e., N flow and hotspots). Certainly, discussion on N budgets and hotspots – at the bottom in Section 4 – should be be placed first in the manuscript, as it is a lot more relevant to the title and abstract, and seemingly, the aim of the paper. The other sections could include a lot less detail on the processes themselves and instead focus more on how those processes relate to N flow and or potential formation of hotspots.

Some more specific comments are provided below, and detailed comments are supplied as comments in the attached PDF.

·         The Introduction primarily focuses on a lot of factors that aren't really relevant to the topic under review, viz. on-farm N flows and identification of potential hotspots. I suggest the Introduction section is considerably re-worked to reduce the focus on the broad challenges faced by agricultural production and instead increase the focus on N-relevant issues.

·         Clear definitions of N budgeting and hotspot should be included early in the manuscript. These are the key terms in the review title and abstract.

·         There seems to be the introduction of varying terms/names when referring to the same thing. For example, manures, organic sources, fresh organic matter, recycled sources of N, seem to have all been used interchangeably to refer to the same “pool” of N (i.e., organic amendments). This needs to be made consistent.

·         Table 2: Explain the differences between "real" and "common" ranges. Also, is this data only collected from a single source?  If so, I'm not sure that you can present this unless you have express permission from the authors and possibly the original article publisher. Please check this.

Overall, I think the concept of this paper is nice but in terms of execution, this manuscript needs considerable re-structering and thought needs to be given to how each of the sections/processes relate to N flows and hotspots.  

Comments for author File: Comments.pdf

Author Response

Review 1

This sentence is a little difficult to follow.  I think what you're trying to explain is why N-fertilizers are purchased and applied?  It doesn't need to be this complicated. The reality is, without N-fertilization, farm yields will be severely penalized. Perhaps you could re-word to this effect?

The issue raised is now of key importance for the farmer, as the price of natural gas has increased in Europe 5(7) times. In many regions of the world, the use of fertilizers will fall, and thus the production of food will be reduced. This makes this sentence relevant.

It can be clearly stated that the time of cheap fertilizers is over.

This sentence has been corrected.

Clarify that you are talking about "on-farm resources" here. Otherwise, the reader might wonder why fertilizers aren't mentioned.

These N resources are clearly defined in the abstract.

The so-called "on-farm N resources" are of a secondary nature, as they come from the recycling of N  previously used in the form of nitrogen fertilizers. Another “on-farm N resource”, in fact, the primary one, is the symbiotically fixed nitrogen. It cannot be neglected, as shown by the production of soybean, for example in Brazil (one the main exporter in the world).

I would use 'resources' here, as this is the word you've previously used to refer to them. Keep it consistent.

This term is used throughout the text.

Why is this more realistic? I would avoid including this unless you have some evidence to support it.

The number of articles on alternative ways to reduce food consumption is huge, but food consumption trends are increasing anyway.

This sentence has been corrected.

Reference?

It has been added.

Le Mouël, C.; Forslund, A. How can we feed the world in 2050? A review of the responses from global scenario studies. Eur. 896 Rev. Agric. Econ. 2017, 44, 541–591.

This sentence doesn't make sense.

It has been removed from the text.

The increasing use of mineral fertilizer is the key option to cover the food gap in coming 30 years.

Conijn, J.G.; Bindraban, P.S.; Schröder, J.J.; Jongschaap, R.E.E. Can our global food system meet food demand within planetary  boundries? Agric. Ecosys. Environ. 2018, 251, 244–256.

I think you are contradicting yourself here.

There is no contradiction in this sentence. Nitrogen cannot replace water, because it does not work (moving towards the root surface of the plant) without water in the soil solution. Both factors interact each other in crop production. There are thousands scientific articles supporting this conclusion.

The Introduction up until this point focuses on a lot of factors that aren't really relevant to the topic under review, viz. on-farm N flows and identification of potential hotspots. I suggest the Introduction section is considerably re-work to reduce the focus on the broad challenges faced by agricultural production and increase the focus on N-relevant issues.

The part defining nitrogen hotspots on the farm has been added to the introduction. Their significance for both crop production and environmental protection is discussed.

insert comma here

It has been added.

I think you should use organic amendment here, it is not only manures that can be used as alternative N sources.

This article discusses the various sources of nitrogen. The term “organic amendment” can only be used in the case of generalization of organic N sources. In specific cases, it is necessary (obligatory) to clearly distinguish between them.

This term was used when necessary throughout the text.

Delete this word

It has been delated.

I have never heard of this before for maize N nutrition. If it is such a thing, I think it would only be used in a very specific sense. I would delete from this discussion... unless it is relevant further down.

In the USA, one of the terms, used for diagnosing the nitrogen nutritional status of maize is the 5th leaf stage. This stage is crucial for the formation of leaves and inflorescences by maize. In cereals the stage BBCH 30/31 is crucial for formation of yield components (number of ears per unit area).

Luce, M.St.; Whalen, J.K.; Ziadi, N.; Zebarth, B.J. Nitrogen dynamics and indices to predict soil nitrogen supply in humid 943 temperate soils. Adv. Agron. 2011, 112, 55–102.

Subedi, K.; Ma, B. Nitrogen uptake and partitioning in stay-green and leafy maize hybrids. Crops Sci. 2005, 45, 740–747.

Chen, Z.; Miao, Y.; Lu, J; Zhou, L.; Li, Y.; Zhang, H.; Lou, W.; Zhang, Z.; Kusnierek, K.; Liu, Ch. In-season diagnosis of winter wheat nitrogen status in smallholder farmer fields across a village using unmanned aerial vehicle-based remote sensing. Agronomy 2019, 9, 619.

This is confusing. You earlier defined N(f) as nitrogen fertilizers. But here, you immediately go on to mentioned other processes of N input (i.e., atmospheric N2 fixation and BNF). Are these part of N(f)? If so, you could be clearer in your definition earlier. If not, then you need to clarify that you're talking about something else. In fact, this would probably be better placed in it's own section, or at least, after you've finished describing the three sub-pools.

This part has been corrected in accordance to your suggestion.

Clarify that you are talking about "on-farm resources" here. Otherwise, the reader might wonder why fertilizers aren't mentioned.

The so-called "on-farm resources" are of a secondary nature, as they come from the recycling of nitrogen previously used in the form of nitrogen fertilizers. Another “on-farm resource”, in fact, the primary one is the symbiotically fixed nitrogen. It cannot be neglected, as shown by the production of soybean, for example in Brazil (the main exporter in the world).

This should be really written as a paragraph or two, so the concepts flow logically. It’s a little jarring to read in list format. In fact, I think you could probably remove this list, replace with a general introduction of N2 being very prevalent in the atmosphere. Then discuss how specific relationships with microorganism and plants can exploit this atmospheric N.

This part of the text has been reconstructed.

conditions necessary

It has been corrected.

successful

It has been corrected.

of a strictly

It has been corrected.

compatible?

It has been corrected.

What are the implications? Is this why it is not common for all plants to do?  You need to explain, or put into context, some of the facts you're mentioning.

The text was corrected, indicating the sources of energy consumption necessary for N₂ reduction by symbiotic plants.

The equation presented in this part of the article has been removed due to its detailed nature.

This discussion on nitrogenase probably belongs higher up in this section, after the first mentioned of it. It seems to pop up randomly here, after the reader has gone through some text on specific types of bacteria.

This article is not random, but each sentence or part has been placed according to a problem analysis scenario that is relevant to the farmer. Growing legumes is not only seeds and bacteria, but also a number of soil factors that determine the effectiveness of the N₂ reduction process. Statistical yearbooks – data on seed yields – do not indicate high efficiency of these processes.

This part has been moved to a more relevant place in this section.

Check this sentence makes sense and remove the full stop in the middle.

It has been corrected.

In response

It has been delated.

Explain the differences between "real" and "common" ranges. Also, is this data only collected from a single source?  If so, I'm not sure that you can present this unless you have express permission from the authors and possibly the original article publisher. Please check this.

When studying the world literature on the subject from 1975 to 2016 (examples below), the most frequently repeated ranges, considered optimal, were determined.

The results presented in the manuscript were presented at the conference and in conference proceedings in Poland and then partially in the Polish manuscript.

Waraczewska Z., Niewiadomska A 2017. Diazotrofia – charakterystyka układu symbiotycznego roślin motylkowatych – Rhizobia. W: Rośliny motylkowe w rolnictwie polskim: Genetyka, hodowla, uprawa i użytkowanie [Diazotroph – characteristics of the symbiotic legume – Rhizobium. In: Leguminous plants in Polish agriculture: Genetics, breeding, cultivating and using]. Scientific Conference Materials. Poznan. Publish by University of Life Science p.83–94.

And in:

Waraczewska, Z.; Niewiadomska, A.; Kosicka-Dziechciarek, D. The use of microorganisms with synergistic effects in the biological process of nitrogen bonding. Water-Environment-Rural Areas. 2017, 17(2); 157-168.

Ranges of N fixation in various ecosystems¹, kg N ha^-1.

Forest

Boring, Lindsay R., et al. "Sources, fates, and impacts of nitrogen inputs to terrestrial ecosystems: review and synthesis." Biogeochemistry 6.2 (1988): 119-159.

Granhall, U., and T. Lindberg. "Nitrogen fixation in some coniferous forest ecosystems." Ecological Bulletins (1978): 178-192.

Granhall, U., and T. Lindberg. "Nitrogen fixation in some coniferous forest ecosystems." Ecological Bulletins (1978): 178-192.

Rice and Azola

Roger, Pierre-Armand, and J. K. Ladha. "Biological N 2 fixation in wetland rice fields: Estimation and contribution to nitrogen balance." Biological nitrogen fixation for sustainable agriculture. Springer, Dordrecht, 1992. 41-55.

Kanungo, P. K., et al. "Nitrogenase Activity and Nitrogen‐Fixing Bacteria Associated with Rhizosphere of Rice Cultivars with Varying N Absorption Efficiency." Journal of the Science of Food and Agriculture 73.4 (1997): 485-488.

Ladha, J. K., and P. M. Reddy. "Extension of nitrogen fixation to rice—necessity and possibilities." GeoJournal 35.3 (1995): 363-372.

Prasanna, Radha, et al. "An improvized technique for measurement of nitrogen fixation by blue green algae and Azolla using moist soil cores from rice fields." Experimental Agriculture 39.2 (2003): 145-150.

Fodder legumes

Iannetta, Pietro PM, et al. "A comparative nitrogen balance and productivity analysis of legume and non-legume supported cropping systems: the potential role of biological nitrogen fixation." Frontiers in Plant Science 7 (2016): 1700.

Ghosh, P. K., et al. "Legume effect for enhancing productivity and nutrient use-efficiency in major cropping systems–an Indian perspective: a review." Journal of Sustainable Agriculture 30.1 (2007): 59-86.

Seed legumes

Rennie, R. J., and G. A. Kemp. "N2‐Fixation in Field Beans Quantified by 15N Isotope Dilution. II. Effect of Cultivars of Beans 1." Agronomy Journal 75.4 (1983): 645-649.

Taylor, J. D., J. M. Day, and C. L. Dudley. "The effect of Rhizobium inoculation and nitrogen fertiliser on nitrogen fixation and seed yield of dry beans (Phaseolus vulgaris)." Annals of applied biology 103.3 (1983): 419-429.

Kumar, Kuldip, and Kuan M. Goh. "Biological nitrogen fixation, accumulation of soil nitrogen and nitrogen balance for white clover (Trifolium repens L.) and field pea (Pisum sativum L.) grown for seed." Field Crops Research 68.1 (2000): 49-59.

Legumes as catch crop

Sanginga, Nteranya. "Role of biological nitrogen fixation in legume based cropping systems; a case study of West Africa farming systems." Plant and soil 252.1 (2003): 25-39.

Li, Xiaoxi, et al. "Quantifying biological nitrogen fixation of different catch crops, and residual effects of roots and tops on nitrogen uptake in barley using in-situ 15N labelling." Plant and Soil 395.1 (2015): 273-287.

Tonitto, C., M. B. David, and L. E. Drinkwater. "Replacing bare fallows with cover crops in fertilizer-intensive cropping systems: A meta-analysis of crop yield and N dynamics." Agriculture, Ecosystems & Environment 112.1 (2006): 58-72.

Madhanzi, Bothwell. Effect of various multipurpose tree prunings and their placement methods on root development in rape (brassica napus). Diss. BUSE, 2015.

This section has provided a reasonable overview of the key factors which impact BNF, but doesn't discuss the role of this process in N-flows and hotspots, to any great detail.

This part has been considerably expanded, pointing to the multiple and complex role of legumes in the N flow on the farm.

This section should start with how crop residues become incorporated into SOM. Then go into the specific of SOM.

This part has been preceded by a section on the effects of organic amendments on SOM.

And unquestioned

This phrase has been deleted.

This is a very untidy way to present this. Can you remove the grey background? Also, I would suggest just showing the final equation. Readers don't need to be shown the re-arranging process.

This part has been moved to the supplement.

Treated

This phrase has been deleted.

This information is what you need to have all equations / reactions presented. Whether in a list like this, or in the text intermediately before/after.

The presented set of equations was selected in such a way that the farmer, on the basis of raw data, could independently calculate the N resources obtained from livestock production. His challenge is to maintain the initial amount of n during manure storage and application.

Again, please find a way to remove the grey background.

This part has been moved to the supplement.

If you have already defined the N-NH4 abbreviation earlier in the text, then you don't need to do it again.

This term is used throughout the text.

I would give the range of losses in a single column, and list the references (with the number notation) below the table.

It has been corrected.

I'm not sure if it's the formatting of the supplied graphic or in the manuscript, but this is not tidy.

It has been corrected.

Should this be section 2.2.3 ?

It has been corrected.

Are you talking about the organic amendments/fertilizers discussed earlier? If so, please don't introduce a new term for these. Is is extremely confusing to read. At the very least, explain what you a referring to, if you must use a new term.

It has been corrected throughout the text.

Is there a reason these are so far aligned to the left?

It has been corrected throughout the text.

Isn't the yield plateauing at around 150 kg N / ha in Figure 3?

This is a classic quadratic regression model as indicated by the well-defined N_f optimum and responsible Y maximum.

Explain the abbreviations used in the figure.

The abbreviations used in the figure has been explained in a legend.

This sections discuses relevant factor of N for crop production but still largely fails to link to how this drives N flows and may potentially create hotspots.

The crop requirement for N during the growing season is the top N hotspot on the farm. The flow of N is quite clearly presented in all three sections of this chapter. Figure 6 summarizes the authors’ view of the crop’s  demand for N, thus determining N flow. In this case, it refers to the amount of Nf applied. This amount depends on the inorganic N stock in the soil that the farmer should quantify, using available diagnostic tools. Moreover, this N stock depends to a large extent on the farmer’s management of the on-farm N resources.

This section needs to be placed first in the manuscript, as it is a lot more relevant to the title and abstract.

The organization of a conceptual research article is key for presenting and discussing the issues raised. The authors had two options:1) present the balance of nitrogen and then discuss its components;2) present potential N hotspots on a standard farm and then provide a diagnostic tools.

Both ways of presenting the concept are not mutually exclusive.

43% of what??

It refers to the total N input into agricultural production, regardless the source.

A definition of hotspots might be useful.. and certainly should be included at the very start of this manuscript.

The definition of the hotspots is presented in the Introduction.

Equation number?  And explanation of the terms?

All equations used in the manuscript are numbered. All terms appearing in equation No xx are  explained in table 6.

This may true for farms in some areas or systems, but I would say applicaiton of inorganic N-fertilizers is the primary N input for most farms.

I fully agree with this conclusion, but it is limited only to market-oriented farms, where fertilizer N is the main, but not the primary form of N used in crop production.

Nitrogen budgeting has certainly has not been the focus of this paper.  I also think I need a more convincing case that this is the most practical approach for identification of hotspots. For example, while a farmer may be able to identify is he/she has a net gain or loss of N, in such an "open" system, it would be difficult to determine exactly where the losses might be occurring, without extensive investigation. 

Forecast of fertilizer prices, including N, are not optimistic for any farmer, regardless of his place in the world. By using simple diagnostic tools and using a set of simple methods of the N flow control on the farm, the farmer can reduce the amount of N fertilizers used. Farmers know the N hotspots on the farm, but the challenge is to exploit them to the maximum. The diagnostic tools given in the manuscript are simple, requiring to use data about the yield and the applied N fertilizer rate for a given crop.

Author Response File: Author Response.pdf

Reviewer 2 Report

In line 322, the equation is missing the units of daily urine production.

In line 371, in subparagraph A) the sentence is unfinished.

In photo 1, the caption is out of place, the sections A and B are placed before the caption of the figure. Maybe they should be included in the caption of the figure.

The text written between lines 380 and 402 is outside the indentation, too far to the left, it does not fit well, it should be at the same level as the general text. It happens as well in lines from 432 to 434 and there are more cases later the text.

In photo 2 is the same as in photo 1, the caption should include the text below the photo named A and B.

The SD of figures 7 and 8 are very large, there is a high variability

Author Response

Review No. 2 – response

In line 322, the equation is missing the units of daily urine production.

The unit missing from the equation No 3 (L 322) has been filled in.

In line 371, in subparagraph A) the sentence is unfinished.

This part has been corrected.

In photo 1, the caption is out of place, the sections A and B are placed before the caption of the figure. Maybe they should be included in the caption of the figure.

Captions under the photos No. 1 and 2 have been corrected and placed under the caption for a given photo.

The text written between lines 380 and 402 is outside the indentation, too far to the left, it does not fit well, it should be at the same level as the general text. It happens as well in lines from 432 to 434 and there are more cases later the text.

This is an error that occurred while transferring the text to the Agronomy text template. All such errors have been corrected.

In photo 2 is the same as in photo 1, the caption should include the text below the photo named A and B.

Captions under the photos No. 1 and 2 have been corrected and placed under the caption for a given photo.

The SD of figures 7 and 8 are very large, there is a high variability

In the current version of the manuscript this comment applies to Fig. 6 and 7. Nitrogen balance on the farm, averaged for all fields, presented in Fig. 6, was negative (- 5 kg N ha^-1). This state indicates that natural N resources are depeleted, albeit slight, A slight excess of N as shown in Fig. 7, indicates excess N introduced into the soil/plant system. The analysis of the variability in the N balance in the years for individual fields, allowed for the identification of reference fields in relations to N management and those requiring correction. Both aspects of N management in the farm are explicitly mentioned in the text of the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors, I am reviewing your manuscript "Nitrogen does not end on the farm - a practice-oriented approach", which is a particularly relevant topic for this period. The efficient use of nitrogen on the farm is the best way to protect the environment from N pollution. The main precondition for sustainable agricultural production is the efficient use of non-renewable means of production on the farm. In this sense, the manuscript should be published in a journal. However, I have a few remarks to help emphasize the importance of the results of these studies:

The results are presented in Table 3. Losses of nitrogen from manure in dependence on the method of fresh manure fermentation from 50 to 27 years ago. They do not fully reflect the current situation. Manure storage technologies are improving, and nitrogen losses are decreasing. Also the units did not listed in the table: is it fermentation time? Is this a percentage loss of gas?

Abbreviations are abundant throughout the text, but lack explanations: DW, GD, ED, GE, RLD, YEP, etc., should be reviewed throughout the text.

Author Response

Review No. 3 – response

Dear authors, I am reviewing your manuscript "Nitrogen does not end on the farm - a practice-oriented approach", which is a particularly relevant topic for this period. The efficient use of nitrogen on the farm is the best way to protect the environment from N pollution. The main precondition for sustainable agricultural production is the efficient use of non-renewable means of production on the farm. In this sense, the manuscript should be published in a journal. However, I have a few remarks to help emphasize the importance of the results of these studies:

The results are presented in Table 3. Losses of nitrogen from manure in dependence on the method of fresh manure fermentation from 50 to 27 years ago. They do not fully reflect the current situation. Manure storage technologies are improving, and nitrogen losses are decreasing. Also the units did not listed in the table: is it fermentation time? Is this a percentage loss of gas?

The authors are fully informed about specialized methods of fermentation of farmyard manure or slurry. These methods are mainly used in livestock farms. On farms with mixed production, as a rule of medium size, these methods are too expensive. The essence of good, i.e. both pro-productive and pro-environmental management of animal excreta is to limit the access of oxygen to the fermenting mixture of manure with bedding or water. This effect can be obtained by systematically pressing the manure heap or pouring liquid manure or water over the manure. This method are simple and cheap and accessible to every farmer over the world.

The losses in the Table 3, refer to the percentage losses of C and N content in the manure after a 3-month fermentation in relations to the initial content.

Abbreviations are abundant throughout the text, but lack explanations: DW, GD, ED, GE, RLD, YEP, etc., should be reviewed throughout the text.

In accordance to the rules for writing scientific texts, when a compound feature is  first used, the full name is given and then only the abbreviation is used. All abbreviations used in the text have been described and checked throughout the text. Its pity that Agronomy does not have a separate section for description of the used abbreviations. This method of a scientific text editing facilities the work of the author and the reader.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Thanks to the authors for their answers, but I am of the opinion that the article have too many abbrevations and some of the phrases could be written in full terms. There may be an explanation of all abbrevations at the beginning of the article, but this is only valid when authors use only few abbreviations of the terms. In this case, all reading in general was difficult.