Optimizing Soil Fertility Management Strategies to Enhance Banana Production in Volcanic Soils of the Northern Highlands, Tanzania

Round 1

Reviewer 1 Report

I believe authors have satisfactorily addressed issues mentioned in my prior review.

Reviewer 2 Report

The responses provided to the reviewers' comments are subject to conceptual and formal limitations. In some occasions, the response to the comments has been represented by the elimination of the sentence. In others by adding unsolicited and not useful information for a better understanding of the results.

Although the manuscript has been revised, it has not been improved to the point that it can be accepted for publication on Agronomy.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Title: ok, but primarily deals with N, residue & organic input management. Issues related to other specific nutrients are not really addressed directly.

 

General: This is a useful and interesting study of some practical N, manure, & residue management issues that are relevant to the study region as well as other banana production areas. The manuscript is well organized and easy to understand. It could be improved by a few clarifications:

-was recycling of pseudostems & leaves practiced in this study, or were they removed at harvest. What are the consequences of this decision for smallholder nutrient management & livestock feeding, if applicable?

-are there any general socioeconomic factors or constraints involved in smallholder management decisions, i.e. feasibility of purchasing fertilizer inputs, demand for crop residues as fodder, availability of manure?

- Throughout the manuscript the authors should use appropriate numbers of significant digits for all quantities (inputs, yields, etc.). It is unusual in this type of field study for 4 or more significant digits to be appropriate. (i.e. N rate of 153 kg N/ha/yr rather than 153.3; fruit yield of 33.8 t/ha/cycle rather than 33.76).

 

Intro

This covers relevant issues with clearly stated objectives. An area that could be expanded on for a more general readership not familiar with smallholder farming in Tanzania: Are these commercial-scale operations that typically have access to funds for fertilizer inputs? Are there any typical knowledge resources utilized by these farmers (local farm traditions, internet/print/radio/agricultural advisors/etc.)?

 

M&M

Unclear if total Kjeldahl N is expected to be useful as a management tool. Perhaps it is just indicative of soil organic matter as a general site quality correlate.

 

Were pseudostems & leaves removed from plots at harvest, or allowed to recycle? Explain relevance, especially for 2^nd season nutrient management measurements.

 

Results

Rainfall appears to be a major factor in productivity in this study, with close correlations to soil properties & plant productivity measurements.

 

15, l. 353-354: This statement regarding total nutrient distribution patterns appears to be true for N & P, but not necessarily for the other nutrients.

 

 

 

Discussion

19, l. 445-448: It is unclear if the primary effect of cattle manure would be associated with nutrient supply or with its influence on soil moisture holding capacity.

 

20, l. 477: Are tissue N interpretation guidelines accurate since T. 3 indicates all treatments had N% exceeding the published sufficiency range yet N responses were measured?

 

21, l. 508-510: I did not note description of whether or not pseudostems & leaves were allowed to recycle, or we removed, in this experiment.

 

Conclusions

 

22, l. 553: There has been no prior mention of costs, or other socioeconomic indicators of the relevance of fertilizer costs, for this production system. Due to the highly variable nature of agriculture across banana producing regions, it is difficult for readers not familiar with this specific region to interpret this statement.

 

Reviewer 2 Report

Dear Authors

The paper was done to optimize soil fertility manage in order to enhance Banana production in Tanzania. The general idea of the manuscript is good. However, my first impression is that the authors tend to promote the use of synthetic N fertilizer instead of promoting the renewable resources of nitrogen such as green manure, compost and plant residue management for sustainable production. The soil at the three sites seem to have good fertility (OM ≥ 3%) according to the analysis the authors carried out. The authors justify the use of synthetic N fertilizer by stating that animal manure has become a scarce resource but they did not mention why and how manure has become a scarce source. Manure and other organic sources of nitrogen are known as slow release nitrogen fertilizer and for their ability to provide the plant with sufficient nutrients in a long run. In my opinion, the problem could be that manure application did not provide sufficient nutrients, especially nitrogen, to the plant in a given time because of its slow release. In this regard, soil management strategies can be optimized in order to improve the decomposition process of these organic matters, which therefore enhance the availability of the utilizable nitrogen. Moreover, in the frame of sustainability criteria, available raw organic materials in the country could be processed through composting to make the nutrients more available for the plant. This strategy can be both economically viable and environmentally friendly, and authors should introduce these aspects in rewriting the paper.    

In addition, in their objective, the authors tested the addition of cattle manure and haulms to evaluate the contribution of organic N fertilizer to improve the use efficiency of mineral N applied. In my opinion, the concept is wrong. Usually, the contrary is correct. In agricultural soils, the application of mineral nitrogen is usually performed to improve the use efficiency of organic N fertilizers because mineral N has the ability to stimulate the activity of soil microorganisms and as a consequence higher decomposition process of the organic matter and therefore higher available nitrogen. I think that the authors should rewrite the manuscript with this idea in mind.

 

General observation/comments

English is sometimes confusing and there is a use of unsuitable words in many places. Therefore, English editing by professional English scientist is required. Abstract to be rewritten. The current abstract concentrate more to describe material and methods with few lines regarding the results. The best is to balance between important parts such introduction, material and methods, results and conclusion in brief. Keywords are too many. Please minimize them in accordance with author guidelines of the journal. Introduction need to expanded highlighting important aspects. Please eliminate the dots all throughout the manuscript when you write the measurement unit (t.ha^-1; kg.ha^-1….etc.). Some figures and tables can be unified in order to minimise their number. For example, Figure 1 and 2 can be presented in one figure ……

Here are some specific observation/comments:

Abstract: The authors highlighted that “Animal manure has become a scarce resource” why? scarce as a raw material? Last report from FAO (2018) indicated a significant increase in the production of meat, eggs and milk in the last 10 years in the country which surely come as a result of an increase in animal production…… or as a source of N because it is slow N release fertilizer and does not provide sufficient N? The concept should be clarified in both abstract and the introduction. Reasons for not including other organic N sources such as poultry manure (as low cost and available organic material that can be managed as a good source of N) should be mentioned. “which do no longer meet crop nutrient requirements”? English structure is not correct. Cattle manure (76.7 and 38.4 t.ha-1 as, respectively, sole and in combination with urea) was applied once a year at the onset of the 25 long rainy season for 2 consecutive years. It is not clear and rather confusing. I do not understand if the amount (Numbers) refer to cattle manure or urea. If urea is involved, is the quantity refer to ton of urea or tone of nitrogen? Are you sure about this high amount?

 

Introduction The introduction is short. Important aspects related to crop cycle, cultivation time and local crop management practices need to be highlighted. In addition, the authors need to quantify other available (at country level) sources of organic nitrogen and how small farmers can benefit from these low-cost environmentally-friendly raw materials for sustainable production. Augmented? Substitute the word with more suitable word (i.e. improve, enhance and increase).

 

Material and methods Subsection 2.3. why you consider 153.3 kg N from urea as optimum level? Based on what? As the study is dealing with strategies for soil fertility management, the authors should report the characteristics of both organic fertilizer (bean haulms and cattle manure) such as total N and other microelements. It is not clear if the eight fertilization treatments were present each year in the three locations. Fertilization treatments are a bit confusing. Mineral N and K were applied in three splits per year for two consecutive years. What was the quantity of mineral fertilizer in each split and when it was applied during the crop cycle? ….. Mineral P and K were applied to some treatments, while in T5-T6 these nutrients were supplied from cattle manure. Again, characteristics of both organic fertilizer should be reported. In addition, it would be much better if you report fertilization treatments in a simple table indicating the particularity of each treatment, and to minimize extensive text regarding the treatments. I think table 1 belongs to the material and method section. Therefore, it needs to be replaced in proper place and then referred to in the text. In addition, the table reports some physio-chemical properties of the surface soil. It should be mentioned however, the depth (cm) from which soil was sampled and respective analysis was done. H₂O not H₂0, substitute the zero with O. Line 76. You mentioned that Soil samples were collected for bulk density and physio-chemical properties determination. However, no bulk density data were reported in table 1 for the different site. Line 82. Available P (avail. P). The name should be mentioned as for other microelements reported after. Subsection need to be reorganized re-titled avoiding excessive information. For example, experimental design should go with site description. In addition, the information reported in subsection 1.1 should be belonging to a new subsection (for example, soil characterization and analysis). Line 90-91 Profile analytical data were 90 used for soil classification using soil classification guidelines provided in the USDA Soil Taxonomy. Soil classes according to the texture should be reported in Table 1 or eliminate this paragraph. Subsection 2.7 should be statistical analysis.

 

Results Again, some subsections need to be renamed, reorganized. Subsection 3.3 is too long and need to be minimized. In addition, subsection 3.1 (Site characteristics) should be renamed to weather conditions where mean annual and monthly temperature has to be presented for the different locations. Moreover, lines 216-238 should be removed and integrated in the material and method section as data represented in Table 1 are not results and data were obtained before the start of your experiment as you indicated in the title of the table (properties of the surface soil in the study sites prior the establishment of experimental treatments). Similarly, N use efficiency, N recovery efficiency and N utilization efficiency should be grouped in one subsection (i.e. N efficiency). Results are badly presented and sometimes is difficult to understand. For example, in Table 4c and 4d there is no sign of treatments as well as location effects.

 

Discussion Crop cycle should be discussed in relation to weather conditions (i.e. precipitation and temperatures) as the latest has a noticeable impact on crop maturity and therefore crop cycle. Lines 420-430. As the subsection titled by Effects of site characteristics on crop performance, the discussion should include all the site characteristics … what about the soil conditions in highest produced site? To be rewritten in accordance to the previous comments.

 

Conclusions

To be rewritten in accordance to the previous comments.

 

Comments for author File: Comments.pdf

Reviewer 3 Report

 

 Abstract:

L21-L24 “To evaluate the contribution of organic N fertilizer to improve the use efficiency of mineral N applied, … cattle manure and haulms from common bean… were applied in the respective plots.

This sentence is not clear. It is better to use more specific one.

Do the authors are sure that they are evaluating the use efficiency of mineral N instead of other effects because “The internal efficiency of a fertilizer nutrient is assumed to be the same for all nutrient-sources”(Jimenez et al., 1993) and therefore, instead of desired they can be measuring:

Differences on water availability
L237 Banana plants grown in Lyamungo produced higher 237 yield than Tarakea and Tengeru (Table 2). L 382-L383 total contents of the investigated nutrient elements in the above ground plant biomass at harvest correlated strongly and positively with rainfall and,… L421 partly can be linked to  satisfactory soil moisture in most part of the year, a result of more and better distributed precipitation…

L524 … and water holding capacity as well.
L541show that nutrient uptake by plants grown in Tarakea and Tengeru sites was constrained by low soil moisture coined by smaller precipitation volumes
differences in nutrient uptake during early plant growth,

nutrient absorption imbalance due to a possible short supply of another plant nutrient
L276-279 Banana leaves in cattle manure only (T6) or in combination with urea (5) contained adequate concentrations of K while those in urea only (T2-T4), bean haulms only (T8) or in combination with urea (T7) contained this nutrient below the sufficiency range as in the control (T1).

 

the improvement in soil physical properties related to clay content and organic matter content or addition (Lyamungo soils have less clay and more total C and N, Table 1)
L229 Soil total C contents ranged between 16 and 22.2 g.kg-1 with  soils of Tengeru and Tarakea containing smaller amounts than the proposed critical value of  230 g.kg-1.
L 382-L383… and, initial soil total (C and N).
L524 increased quantities of total C in the soil would increase the concentration of total N while improving soil physical properties viz. aeration…

Therefore, it is better to eliminate this concept and use:

-(L53-55): This paper aims to improve our knowledge on the proper use of mineral N fertilizer viz. application rate and strategy as an alternative approach to manage soil N or

 

- L430 aimed to explore the possibility of improving banana production through the use of 430 mineral N fertilizer.

N recovery efficiency is well defined. Just use it

L29-L30 Mineral N fertilization at 153.3 kg.ha-1.year-1 resulted in substantial significant (p < 0.001) yield increases in all soil types. Perhaps it would be better to say: in all experimental plots.

L-30 But, superior results were obtained with the same N dose when combined with cattle  manure, with the N derived from both sources at 50 per cent each and similar to cattle manure alone.

The above sentence is not clear. Define superior and similar: significant higher than ... significant same yield than obtained using ...

Introduction

L 56 (ii) understand the additive effect of integrating mineral and organic N resources on nutrient use efficiency and banana fruit yield The authors do not really evaluate the N use efficiency. It is better to delete this part of the sentence.

It is necessary to improve introduction and complete with more references

 

Materials and Methods

L75 Soil colour was 74 identified by the use of standard Munsell soil colour charts. From each horizon… define how many horizons were found and its depth. Include soil characterization in mat-met: L419-420 Nitisol in Lyamungo, followed by the values obtained on Andosol in Tarakea and on Phaeozem in Tengeru.

L103-L104 The field experiment was arranged in a randomized complete block design (RCBD) with three replications. Each replication was planted with 200 banana plants? L95-L96 Each experimental plot (10 x 15 m) contained 25 banana plants

L160 Yield (t.ha¯1.cycle¯1) = Bunch weight x number of bunches (2). It is necessary to use number of bunches per surface unit and cycle.

To compare different sources of fertilization, the authors should calculate relative agronomic effectiveness (see Jimenez et al., 1993)

L161 N use efficiency = [Yield (N fert)-Yield (control)] ÷ N applied (3) This formula do not express N use efficiency because other factors are implied as how much quantity of N is derived from mineralization of soil N

L187 N recovery efficiency = [N uptake (N fertilizer plot) - N uptake (zero N plot)] ÷ N applied (4) It is more clear to denominate this concept as: the percent of N fertilizer utilization

L188 N utilization efficiency = [Yield (N fertilizer plot) - Yield (zero N plot)] ÷ N uptake (5) This concept was previously mentioned as internal efficiency by (Khasawneh and Doll, 1979)

L 193 were checked using error bars of the 193 standard error of the mean generated by histogram. The sentence is not clear.

L369 When N recovery efficiency by the plants was compared among the fertilization strategies, the sole cattle manure treatment (T6) or cattle manure in combination with urea recorded higher values than This should be also interpreted using water availability and N lixiviation

 

Discussion

The authors obtained very good results that make their work valuable:

L445 application of N at 153.3 kg.ha-1.year-1 through cattle manure in combination with urea (T5) resulted in an extra yield increment

L463-465 The findings of this study substantiate the need to supplement cattle manure with mineral fertilizers for improved production and sustainability of the existing banana-based farming systems.

L472 legume residues should be supplemented with mineral fertilizer to maintain high soil fertility and crop yield.

L479 inclusion of B, Cu and Zn in fertilizer programs should be given special attention to enhance banana 479 production.

L508-509  the management decision to remove or leave pseudostem and leaf residues in the field is crucial as it can play a significant role in recycling nutrients to the soil stock  following decomposition…. L 512 recycling nutrients, especially for smallholder farmers without cattle, is hardly possible.

Conclusions

The authors obtained very useful conclusions:

L 550 the combined use of inorganic and organic fertilizer is an excellent alternative to reduce the reliance/dependence on cattle manure which is in short supply

L 554 Organic/inorganic interactions will in turn, contribute towards improved soil fertility, increased crop production and sustainable banana-based farming systems.

 

To be consulted:

Jimenez, E. I. et al. (1993) ‘City refuse compost as a phosphorus source to overcome the P-fixation capacity of sesquioxide-rich soils’, Plant and Soil, 148(1), pp. 115–127. doi: 10.1007/BF02185391.

Khasawneh, F. E. and Doll, E. C. (1979) ‘The Use of Phosphate Rock for Direct Application to Soils’, Advances in Agronomy. Academic Press, 30, pp. 159–206. doi: 10.1016/S0065-2113(08)60706-3.

 

Comments for author File: Comments.pdf