Yields and Yield Gaps in Lowland Rice Systems and Options to Improve Smallholder Production

Round 1

Reviewer 1 Report

The manuscript entitled “Yields and yield gaps in Ugandan lowland rice system and options to improve smallholder production” authored by Awio et al. is interesting for minimizing yield gaps of Uganda. However, a number of improvements are required before accepting this paper.

1. There many sentences which are not very clear or hard to follow throughout the manuscript. Please consider rephrasing them, like comment number 12.
2. The abstract has 277 words, but according to journal, the abstract should be a total of about 200 words maximum.
3. Line 115: “policy makers” ---> “policymakers”
4. Line 79, 173, 196, 536: “levelling” ---> “leveling”
5. Line 189: “Forty one” ---> “Forty-one”
6. Line 199: “water-release” ---> “water release”
7. Line 224: delete “respectively”
8. Line 226: Is the grain yield really adjusted at 0% moisture, or it will be 14%? In following sentence (Line 228), it is already mention 14% moisture.
9. Line 520: delete “that there is”.
10. Line 520: “famers” ---> “farmers”
11. Line 557: “thereby to reducing” ---> “reduces”
12. Line 559: “For farmers these rates, therefore, do not pay-off at current rice and fertilizer prices” ---> “Therefore, these rates do not pay off at farmers' current rice and fertilizer prices”

Author Response

Response to Reviewer 1 Comments

1. There many sentences which are not very clear or hard to follow throughout the manuscript. Please consider rephrasing them, like comment number 12.

We thank the reviewer for pointing out this. We have revised the manuscript where we spotted sentences that might not have been fully clear – in Line 47 - 50, 72 – 74, 96 – 98, 249 – 251, 272 – 273, 273 – 276, 302 – 305, 408 – 410, 426 – 428, 444 – 448, 557 – 559 of the revised manuscript.

2. The abstract has 277 words, but according to journal, the abstract should be a total of about 200 words maximum.

The abstract has been revised to 230 words. We feel this is within the agreeable limit of an abstract without over-summarizing information that the reader may not understand.

3. Line 115: “policy makers” ---> “policymakers”

Revised to “policymakers” as suggested by the reviewer (Line 115 of the revised manuscript).

4. Line 79, 173, 196, 536: “levelling” ---> “leveling”

“Levelling” revised to “leveling” as observed by the reviewer (Line 79, 174, 196, and 538 of the revised manuscript).

5. Line 189: “Forty one” ---> “Forty-one”

“Forty one” revised to “Forty-one” as suggested by the reviewer (Line 189 of the revised manuscript).

6. Line 199: “water-release” ---> “water release”

“Water-release” changed to “water release” as noted by the reviewer (Line 199 of the revised manuscript).

7. Line 224: delete “respectively”

“Respectively” deleted from Line 229 of the revised manuscript as suggested by the reviewer.

8. Line 226: Is the grain yield really adjusted at 0% moisture, or it will be 14%? In following sentence (Line 228), it is already mention 14% moisture.

Grain yield reported in this manuscript was adjusted to 0% moisture content as mentioned in Line 231 - 232 of the revised manuscript. However, in calculating net income from paddy, grain yield adjusted to 14% moisture content was used, as grain weight at 14% moisture content is the commercial basis for pricing rice not weight at 0% moisture content. This is stated in Line 232 – 234 of the revised manuscript.

9. Line 520: delete “that there is”.

Deleted “that there is” from the revised manuscript as observed by the reviewer (Line 522).

10. Line 520: “famers” ---> “farmers”

“Famers” corrected to “farmers” in Line 522 and 474 of the revised manuscript after verification in other places.

11. Line 557: “thereby to reducing” ---> “reduces”

Replaced “thereby to reducing” with “reduces” as suggested by the reviewer (Line 558 of the revised manuscript).

12. Line 559: “For farmers these rates, therefore, do not pay-off at current rice and fertilizer prices” ---> “Therefore, these rates do not pay off at farmers' current rice and fertilizer prices”.

Revision made in the manuscript as suggested by the reviewer (Line 560 – 561 of the revised manuscript).

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

The paper entitled “Yields and yield gaps in Ugandan lowland rice system and options to improve smallholder production” by Thomas Awio et al. investigates yields and yield gaps under different management levels, factors contributing to variation in on-farm yield, and possible options available for low- land rice farmers in Uganda to intensify their production. I consider that the topic covered by this manuscript is suitable for Agronomy journal. The paper submitted is generally well written and organized. I have two questions concerning this manuscript:

1. How you set the fertilizer doses for RAP + NPK (100, 50 and 50 kg^-1)? Or these doses are generally used by farmer in the Doho, Butaleja District?
2. Why did you chose for yield the expression in g m^-2and not in kg ha^-1 in tables 1 and 2.(the same for figures 1,2 and 3)?

Author Response

1. How you set the fertilizer doses for RAP + NPK (100, 50 and 50 kg-1)? Or these doses are generally used by farmer in the Doho, Butaleja District?

The fertilizer doses of 100, 50 and 50 kg^-1 N, P and K used in this study were doses used in a previous study in the same location, with which substantial yield gains were observed, mentioned in Line 138 – 142 of the revised manuscript. This study being a follow-up of the previous study, we used NPK doses of the previous study to check response in different farmers’ fields. Farmers in the study site use varied rates usually much lower than these rates as can be observed from farmers’ fertilizer rates in Table 1 Line 208 of the revised manuscript. 

2. Why did you chose for yield the expression in g m^-2 and not in kg ha^-1 in tables 1 and 2.(the same for figures 1,2 and 3)?

Yield expression of g m^-2 we chose to use is the preferred SI unit expression, easier to interpret for a reader, and one can easily convert it to kg ha^-1, if needed.

Author Response File: Author Response.docx

Reviewer 3 Report

I reviewed the above manuscript with great interest. It seeks to assess the contribution of specific management regimes to current yield levels of smallholder rice farmers in the Doho Rice Irrigation Scheme using experimental designs set up on farmers fields. Overall, the study was well-designed and carried out and the findings are well-presented.

1. Introduction seems too long; authors should consider having two or three subheadings.
2. The use of the concept of economic attainable yields is quite problematic. Authors should refer to van Dijk et al., (2017) for detailed economic yield gaps and associated concepts such as feasible yield levels, technical yield levels, etc https://doi.org/10.1016/j.agsy.2017.03.004. Should economically-attainable yields not be the maximum yield s farmers can profitably produce? Conceptualizing it as the average of the top decile yields is thus problematic as farmers could be producing at such levels even if they are using inordinate fertilizer levels, making it unprofitable and uneconomic. Perhaps authors might stick to exploitable yields?
3. Line 153: Experimental design: Given that the study sites used both fully irrigated and partially irrigated fields, it would be important for authors to clarify how they computed potential yields. The definition and determination of potential yields for rain-fed and irrigated fields is obviously different.
4. What do authors mean by the net plot? Is this the subplot? Line 164
5. Section on treatment and management: A table summarizing the treatment and associated management practices would have been helpful.
6. Line 229-231: In considering the cost of producing rice, is there any reason why rental for the fields was excluded? I would think payments for land would be important here unless the parcels of land are given out free of charge to interested farmers. Additionally, was the price reported for rice in 2019 the average or farm gate price at the time of harvest?
7. Line 369: Is it whether fertilizers were applied or not or authors are reporting the quantity and timing of fertilizer application? Would have been refreshing to demonstrate at what fertilization levels yields are optimal, profit wise, for farmers. Also, what is the recommended rate of fertilizer application? (Lines 83-84).
8. Authors should report the cost of fertilizer when discussing net income.
9. The discussion section did not adequately deal with the implications of the status quo. I was hoping to see a discussion of the high fertilizer prices and the consequences for reducing the exploitable yield gap under current fertilizer prices.
10. In the concluding section, there is copious reference to ‘proper timing of weeding’ but what does this really mean. Each field would have different weed infestation level and so will have to be weeded at different stages with some (depending on flooding regimes and other management activities prior to planting) may not need to be weeded during the 120 days of rice growth at all.

Some more minor points to note:

Line 40: should have either ‘crops’ or ‘cereal’ before the word yields.

Line 47: Insert the word ‘ideal’ between under and growth.

Line  84: delete ‘soils termed’. Also, the phrase non-responsive soils should not have quotation marks.

Lines 96-98: Sentence is long but incomplete, please revise.

Line 122: Prefix the noun Doho Rice Irrigation Scheme with the article The.

Line 570: Replace timelier with more ‘in a timely manner’ or ‘timeously’

Author Response

1. Introduction seems too long; authors should consider having two or three subheadings.

We agree with the reviewer. The manuscript has been revised to include three subheadings: 1.1 Food demand in sub-Saharan Africa, 1.2 Crop yield gap concept, and 1.3 Rationale of the study, in Line 33, 43, and 75 of the revised manuscript, respectively.

2. The use of the concept of economic attainable yields is quite problematic. Authors should refer to van Dijk et al., (2017) for detailed economic yield gaps and associated concepts such as feasible yield levels, technical yield levels, etc https://doi.org/10.1016/j.agsy.2017.03.004. Should economically-attainable yields not be the maximum yields farmers can profitably produce? Conceptualizing it as the average of the top decile yields is thus problematic as farmers could be producing at such levels even if they are using inordinate fertilizer levels, making it unprofitable and uneconomic. Perhaps authors might stick to exploitable yields?

Economically attainable yield by definition is the optimum yield farmers can profitably achieve, taking into account risks and existing institutions (Fischer, 2015 and Stuart et al., 2016), as defined in Line 51 – 55 of the revised manuscript. In rice production systems, economically attainable yield has been measured as the average of the top decile of farmers’ yields (Laborte et al., 2012; Senthilkumar et al., 2020; Stuart et al. 2016; Tanaka et al., 2015, 2017), stated in Line 55 – 56 of the revised manuscript. The top decile yield is what peer farmers reach in the same climatic, edaphic, irrigation scheme management and socio-economic environment. This top decile yield is considered what farmers could profitably attain in these conditions when economically optimal practices and input levels are used, and effects of market prices considered. Using the top decile yields to estimate exploitable yield gap has been identified as practical and robust, and highly relevant at the local level because it takes into account what is achievable given local bio-physical and socio-economic conditions, as mentioned in Line 265 – 268 of the revised manuscript. The approach has also been used in other rice studies reporting on yield gaps, for instance, by Stuart et al. (2016), Tanaka et al. (2017), and Senthilkumar et al. (2020). We have retained the top decile approach as an estimate of economically attainable yield.

3. Line 153: Experimental design: Given that the study sites used both fully irrigated and partially irrigated fields, it would be important for authors to clarify how they computed potential yields. The definition and determination of potential yields for rain-fed and irrigated fields is obviously different.

The study site (Doho rice irrigation scheme) is a fully irrigated environment where farmers grow rice throughout the year (Line 124 – 125 of the revised manuscript), depending fully on irrigation water during dry season, while during the rainy season rainfall is supplemented with irrigation. As this was not clear from the earlier text, we have revised the sentences to “The January crop was the first crop, planted in the dry season, mostly irrigated with little rainfall. March and April planting was the second crop, planted in the first rainy season of the year, fully utilizing the rainfall with supplementary irrigation. August planting was the third crop planted in the second rainy season, also using rainfall with supplementary irrigation” (Line 157 – 161 of the revised manuscript). So, for fields that were planted during dry season, the crop relied fully on irrigation water, while fields planted during rainy season received irrigation water, based on water release schedule for the different blocks, in addition to the rainfall (stated in Line 198 – 200 of the revised manuscript).

Regarding potential yield, we did not compute potential yield for the study environment rather we use attainable yield (defined in this study as average of the top decile of farmers’ yields) to determine the exploitable yield gap; described in Line 55 – 59 and 260 – 271 of the revised manuscript.

4. What do authors mean by the net plot? Is this the subplot? Line 164

A net plot is an area marked from the center of each treatment plot to determine grain yield. To make it clear to the readers, we named it ‘harvest area’ with the plot dimensions, in Line 164, 221 and 227 of the revised manuscript.

5. Section on treatment and management: A table summarizing the treatment and associated management practices would have been helpful.

We agree with the reviewer’s suggestion, and  Table 1 below, summarizing the treatments and associated management practices, has been included in the revised manuscript (Line 208).

 Table 1. Summary of treatments and associated management practices

Treatment	Management practices
Farmers’ practice (FP, n = 114)	Farmers implemented different management practices: transplanting time (21 – 39 DAS), transplanting method (random or line), weeding time (15 – 48 DAT)  , and N rate (13.8 – 46 kg ha-1), no P and K.
Recommended agronomic practices without fertilization (RAP, n = 114)	Transplanting time (21 – 33 DAS), line transplanting, timely weeding (14 – 25 DAT), and no fertilization.
Recommended agronomic practices with NPK fertilization (RAP+NPK, n = 19)	Transplanting time (25 – 33 DAS), line transplanting, timely weeding (15 – 22 DAT), and 100, 50 and 50 kg ha-1 N, P and K.
Farmers’ intensification practice (FIP, n = 55)	Farmers implemented different management practices: transplanting time (23 – 39 DAS),  transplanting method (random or line), weeding time (15 – 40 DAT), and N (6.8 – 46 kg ha-1), P and K (0 – 27.2 kg ha-1).

Field tillage, bunding, leveling and number of weeding operations were identical across treatments. DAS = days after sowing, DAT = days after transplanting, n refers to the number of farmers who implemented the different treatments. Under farmers’ intensification practice, improved management practices implemented by these farmers were different from their farmers’ practice.

6. Line 229-231: In considering the cost of producing rice, is there any reason why rental for the fields was excluded? I would think payments for land would be important here unless the parcels of land are given out free of charge to interested farmers. Additionally, was the price reported for rice in 2019 the average or farm gate price at the time of harvest?

In the study site, farmers own the land since land was allocated to them on a 99-year lease basis after construction of the scheme was completed in 1989. During our study, no case of a farmer hiring land was recorded, the reason cost of land hire was not included in calculating net income. A sentence “Land is farmer owned under a leasehold basis, so land rental was not included in the calculations” has been added to the revised manuscript (Line 237 – 238). We thank the reviewer for notifying us to mention what we considered too obvious mentioning.

Regarding price, the reported price for rice in 2019 was the average price. The sentence has been revised to include “average” (Line 236 of the revised manuscript).

7. Line 369: Is it whether fertilizers were applied or not or authors are reporting the quantity and timing of fertilizer application? Would have been refreshing to demonstrate at what fertilization levels yields are optimal, profit wise, for farmers. Also, what is the recommended rate of fertilizer application? (Lines 83-84).

Fertilization timing, and N, P and K fertilization, when fertilizers were applied, contributed to yield variation among fields. The sentence has been revised to include “when fertilizers were applied” to clarify on this (Line 375 of the revised manuscript).

We agree that it would have been nice to demonstrate at what fertilization levels yields are optimal, profit wise, for farmers, however, our experiments were not set-up to do this, so analysis focused on showing yield gains from every extra kg of fertilizer investment, which can guide on whether investing in fertilizers would be profitable based on output per kg input. The analysis assumed a linear relation, however, to establish fertilizer levels where optimal yields are realized, the experiment would need more nutrient levels on a single field which data were not obtained.

The sentence referring to recommended fertilizer rates is now revised to show that SSA farmers use very low fertilizer rates compared with Latin America and Asia, for instance (Line 82 – 84 of the revised manuscript).

8. Authors should report the cost of fertilizer when discussing net income.

Fertilizer cost during the study period was US$1.0 kg^-1 for urea (46% N) and US$1.1 kg^-1 for NPK blend (17:17:17). The fertilizer cost during the period is now reported in the discussion of net income (Line 496 of the revised manuscript).

9. The discussion section did not adequately deal with the implications of the status quo. I was hoping to see a discussion of the high fertilizer prices and the consequences for reducing the exploitable yield gap under current fertilizer prices.

We agree we did not delve deeper into this issue; however, in our discussion, we did highlight the possible implications of the high fertilizer costs on fertilizer use and the resultant yield gain, and how the challenge could be addressed (Line 494 – 504 of the revised manuscript). We believe this is adequate to give the reader a sense of how high fertilizer costs can be addressed at the government level, as observed in other areas of SSA.

10. In the concluding section, there is copious reference to ‘proper timing of weeding’ but what does this really mean. Each field would have different weed infestation level and so will have to be weeded at different stages with some (depending on flooding regimes and other management activities prior to planting) may not need to be weeded during the 120 days of rice growth at all.

We agree with the reviewer that what is proper will depend on weed infestation levels and competitive power of those weeds. Yet our data show that earlier weeding than farmers currently do improved yields as application of recommended practices mainly implied earlier weeding. So better timing than current practice remains a major step forward. To clarify on this, a sentence has been added in the revised manuscript (Line 563 – 564).

Some more minor points to note:

Line 40: should have either ‘crops’ or ‘cereal’ before the word yields.

“Cereal” included before the word “yields” and other “cereal” in the sentence deleted to avoid repetitions (Line 38 – 39 of the revised manuscript). 

Line 47: Insert the word ‘ideal’ between under and growth.

The word “ideal” added between under and growth, in the revised manuscript Line 46, as proposed by the reviewer.

Line  84: delete ‘soils termed’. Also, the phrase non-responsive soils should not have quotation marks.

Sentence revised as suggested by the reviewer (Line 84 of the revised manuscript).

Lines 96-98: Sentence is long but incomplete, please revise.

The sentence has been revised as advised by the reviewer, Line 96 – 98 of the revised manuscript.

Line 122: Prefix the noun Doho Rice Irrigation Scheme with the article The.

“The” added to precede Doho Rice Irrigation Scheme, Line 122 of the revised manuscript.

Line 570: Replace timelier with more ‘in a timely manner’ or ‘timeously’

Timelier replaced with “in a timely manner” as suggested by the reviewer (Line 573 of the revised manuscript).

References

1. Fischer, R.A. Definitions and determination of crop yield, yield gaps, and of rates of change. Field Crops Research 2015, 182, 9-18. DOI: 10.1016/j.fcr.2014.12.006
2. Stuart, A.M.; Pame, A.R.P.; Silva, J.V.; Dikitanan, R.C.; Rutsaert, P.; Malabayabas, A.J.B.; Lampayan, R.M.; Radanielson, A.M.; Singleton, G.R. Yield gaps in rice-based farming systems: Insights from local studies and prospects for future analysis. Field Crops Research 2016, 194, 43-56. DOI: 10.1016/j.fcr.2016.04.039
3. Laborte, A.G.; de Bie, K.; Smaling, E.M.A.; Moya, P.F.; Boling, A.A.; van Ittersum, M.K. Rice yields and yield gaps in Southeast Asia: Past trends and future outlook. European Journal of Agronomy 2012, 36(1), 9-20. DOI: 10.1016/j.eja.2011.08.005
4. Senthilkumar, K.; Rodenburg, J.; Dieng, I.; Vandamme, E.; Sillo, F.S.; Johnson, J.M.; Rajaona, A.; Ramarolahy, J.A.; Gasore, R.; Abera, B.B.; Kajiru, G.J.; Mghase, J.; Lamo, J.; Rabeson, R.; Saito, K. Quantifying rice yield gaps and their causes in Eastern and Southern Africa. Journal Agronomy and Crop Science 2020, 206, 478–490. DOI: 10.1111/jac.12417
5. Tanaka, A.; Diagne, M.; Saito, K. Causes of yield stagnation in irrigated lowland rice systems in the Senegal River Valley: Application of dichotomous decision tree analysis. Field Crops Research 2015, 176, 99-107. DOI: 10.1016/j.fcr.2015.02.020
6. Tanaka, A.; Johnson, J.M.; Senthilkumar, K.; Akakpo, C.; Segda, Z.; Yameogo, L.P.; Bassoro, I.; Lamare, D.M.; Allarangaye, M.D.; Gbakatchetche, H.; Bayuh, B.A.; Jaiteh, F.; Bam, R.K.; Dogbe, W.; Sékou, K.; Rabeson, R.; Rakotoarisoa, N.M.; Kamissoko, N.; Mossi, I.M.; Bakare, O.S.; Mabone, F.L.; Gasore, E.R.; Baggie, I.; Kajiru, G.J.; Mghase, J.; Ablede, K.A.; Nanfumba, D.; Saito, K. On-farm rice yield and its association with biophysical factors in sub-Saharan Africa. European Journal of Agronomy 2017, 85, 1-11. DOI: 10.1016/j.eja.2016.12.010

Author Response File: Author Response.docx