Clinoptilolite Zeolite on Tropical Peat Soils Nutrient, Growth, Fruit Quality, and Yield of Carica papaya L. cv. Sekaki

Round 1

Reviewer 1 Report

The authors reviewed the manuscript according to the reviewer comments.

Author Response

Dear Reviewer,

In this revised manuscript, we have corrected the paper to the best of our ability by addressing all the points made by the reviewers. Corrections to the revised manuscript were highlighted in blue, and these minor revisions include additional information in the abstract (Line 24), and changes to table caption (Table 4) (Lines 309 to 311) and amendments to unify the y-axes scales for ammonium and nitrate graphs in Figure 2 (Line 317).

Thank you.

Reviewer 2 Report

Abstract, line 23: Please add "A one-year field experiment was conducted..."

Figure 2: Please unify the y-axis scales in each line (figures for Ammonium, figures for Nitrate). Or add "note different scales on y-axes for figures showing exchangeable ammonium as well as available nitrate" to the figure caption.

Table 4, line 309: Change to: Mean exchangeable ammoium, available nitrate, available phosphorus, and exchangeable potassium over all treatments (T1-T5 and control) in a peat soil....

The authors stated that the second trial year commenced in April 2020 and will be completed in February 2021. It would make more sense to wait for the new results and write the publication about both experimental years.

Author Response

Dear Reviewer,

In this revised manuscript, we have corrected the paper to the best of our ability by addressing all the points made by the reviewers as follows:

Point 1: Abstract, line 23 – Please add “A one-year field experiment was conducted…”

Response 1: The word ‘one-year’ was included in the abstract at Line 24 as follows “A one-year field experiment was conducted to determine the effects of CZ on: (i) soil ammonium, nitrate, P, and K, and (ii) growth, yield, and fruit quality of papaya grown on a peat soil”. Corrections have been made to the abstract (Lines 23 to 25).

Point 2: Please unify the y-axis scales in each line (figures for Ammonium, figures for Nitrate). Or add “note different scales on y-axes for figures showing exchangeable ammonium as well as available nitrate” to the figure caption”.

Response 2: Corrections have been made to unify the y-axis scales in Figure 2 (Line 317) for ammonium (y-axes scales from 0 to 1200 mg kg^-1) and nitrate (y-axes scales from 0 to 700 mg kg^-1).

Point 3: Table 4, line 309 – Change to: Mean exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium over all treatments (T1-T5 and control) in a peat soil….

Response 3: Corrections have been made to the table caption for Table 4 (Lines 309 to 311). The table caption for Table 4 was changed to “Table 4. Mean exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium over all treatments (T1 to T5 and control) in a peat soil at different soil depths and growth stages of papaya plants treated with different amounts of CZ and NPK fertilizer”.

Point 4: The authors stated that the second trial year commenced in April 2020 and will be completed in February 2021. It would make more sense to wait for the new results and write the publication about both experimental years.

Response 4: The authors agreed and acknowledged that results from a one-year field experiment for papaya cultivation might not be conclusive enough to confirm the findings on the effect of clinoptilolite zeolite. The authors also agreed that it would be practical to include the results of the upcoming field trials. However, due to uncertainties in regards to the COVID-19 pandemic and climatic factors particularly, flooding and heavy rainfall during the wet monsoon season from October to January (at the experimental site and farmers’ farm at different locations) may affect the outcome of the study. Thus, the authors believed that presenting preliminary results based on short-term measures is beneficial to provide reliable data in a timely manner so farmers can engage and sustainably manage peat soils without reducing peat soil and papaya productivity. This is important as papaya is mostly planted in limited areas as a small-holder crop in Malaysia.  

Thank you.

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

Line 126 : Table 1, please precise how was done the sampling of the soil and its characterization

Figure 2 : the legend is not visible, authors should put it in the figure caption

Table 4 : please specify that it is the control soil, without amendments. I would put this table before figure 2 which shows amendment effects

Table 7 : please specify the meaning of TSS in the table caption

Lines 282-284 : « higher concentrations of soil exchangeable ammonium and K for the treatments with CZ (T1 to T4) was because of the adsorption and absorption of these ions onto and within the lattices of the CZ ». authors did not evaluate the adsorption and absorption of ions on CZ, therefore this explanation is only a hypothesis and not an affirmation.

Author Response

Response to Reviewer 1 Comments

Dear Reviewer,

In this revised manuscript, we have corrected the paper to the best of our ability by addressing all the points made by the reviewers (revisions were highlighted in yellow). Please refer to the attached file.

Point 1: Line 126 – Table 1, please precise how was done the sampling of the soil and its characterization.

Response 1: Methodology on the soil sampling and analysis (bulk density, moisture, pH, cation exchange capacity, total organic carbon, total nitrogen, ammonium-nitrogen, nitrate-nitrogen, available phosphorus, and exchangeable potassium) have been included in the text and explained in detail from Lines 161 to 176. The sampling was carried out systematically in 16 points over a 10 x 10 m grid, and peat soil samples were collected at depths of 0 to 10 cm and 20 to 40 cm. Soil bulk density was determined using the core method (Lim, 1991) whereas soil pH was measured based on a 1:5 soil to water suspension (Ismail et al., 2007). Soil moisture and CEC was determined using the method of Lim (1991) and Harada and Inoko (1980), respectively. Total organic carbon was determined using Walkley and Black method (Nelson and Sommers, 1982) whereas total nitrogen was determined using the Kjeldahl method (Bremner and Mulvaney, 1982). Soil exchangeable ammonium-nitrate and available nitrate-nitrogen were determined using steam distillation method (Bremner and Keeney, 1966). Soil available phosphorus and exchangeable potassium were determined using the method of Olsen and Sommers (1982) and Knudsen et al. (1982), respectively. Additional information on the description of the experimental area was also included namely on the history of cultivation, date of land clearing prior to the soil sampling, and water table fluctuation at the study site. The physical and chemical characteristics of the peat soil used for the experiment were also described in detail from Lines 178 to 187. All the cited references as mentioned above are listed in the reference section of the manuscript.

Point 2: Figure 2 – the legend is not visible, authors should put it in the figure caption.

Response 2: The authors’ acknowledged the lack of visibility of the legend. Amendments have been made to the lettering for the legend in Figure 2 by using larger font size. Legend has also been included and explained in the figure caption (Lines 317 to 323). 

Point 3: Table 4 – please specify that it is the control soil, without amendments. I would put this table before figure 2 which shows amendment effects.

Response 3: The authors would like to clarify that the results presented in Table 4 is based on the mean soil exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium for all treatments (T1 to T5 including control) at different soil depths and growth stages of the papaya plants. Statistical analysis was carried out to compare the mean soil macronutrients content from all treatments using the sorting and by procedures (SAS 9.1 – ANOVA: Proc sort and By) at depths of 0 to 20 cm, and 20 to 40 cm according to the respective growth stages. Generally, the results in Table 4 indicated the mobilization of nutrients for all treatments, where mean soil ammonium, nitrate, available P and exchangeable K were higher at depth of 20 to 40 cm which could be attributed to the high preferential flow of peat soil water as demonstrated and explained in Section 4.1 from Lines 412 to 416. For this, amendments have been made to the manuscript to rephrase the sentences in Section 3.2 (Results) (Line 305) and to include the word “Table 4” to indicate the mean soil nutrient contents for all treatments at different depths and growth stages (Line 413). Also, figure caption for Table 4 has been rephrased accordingly to “Table 4. Mean exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium in a peat soil at different soil depths and growth stages of papaya plants treated with different amounts of CZ and NPK fertilizer” (Lines 309 to 311).

Point 4: Table 7 - Please specify the meaning of TSS in the table caption

Response 4: The abbreviation and meaning of TSS (total soluble solid) has been amended and specified in the table caption (as a footnote) for Table 7 (Line 359). The caption for Table 7 has been amended to “Table 7. Fruit quality and yield of papaya cv. Sekaki cultivated on a tropical peat soil treated with different amounts of CZ and NPK fertilizer” (Line 356 to 357). The meaning of TSS (fruit sweetness) was also included in Table 7. 

Point 5: Lines 282-284 - << higher concentrations of soil exchangeable ammonium and K for the treatments with CZ (T1 to T4) was because of the adsorption and absorption of these ions onto and within the lattices of the CZ >>. Authors did not evaluate the adsorption and absorption of ions on CZ, therefore this explanation is only a hypothesis and not an affirmation.

Response 5: The authors confirm that no evaluation was carried out on the adsorption and absorption of ions on clinoptilolite zeolite (CZ). However, various studies have clearly demonstrated that the higher concentration of nutrients such as ammonium and potassium in soil treated with CZ is because of the mechanism of adsorption and absorption of ion within the open-three dimensional structure of CZ that is made-up from hydrated aluminosilicates with interconnected pores and void linked by shared oxygen atoms (Bernal and Lopez-Real, 1993; Hernández-Espinosa et al., 2018; Jakkula and Wani, 2018; Mumpton, 1999; Murkani et al., 2015; Ramesh and Reddy, 2011; Sangeetha and Baskar, 2016; Zwingmann et al., 2011). This property of CZ provides large internal microporous area for nutrients to be retained or passed through CZ’s surface via ion adsorption and absorption, cation exchange, and catalytic activity. Thus, the results of the present study corroborate previous works by Ahmed et al., 2017; Ahmed et al., 2010; Latifah et al., 2017; Millán et al., 2008; Rabai et al., 2013, who reported that higher retention of ammonium and potassium in soil amended with CZ was because of the adsorption and absorption of ions on the surface or within the lattices of CZ. For this, amendments have been made to the manuscript by rephrasing the sentence to explain the results obtained in the study (Line 363). Also, improvements have been made to the manuscript by adding more information to better explain the mechanism of nutrient retention by CZ that support the results of the present study (Lines 364 to 368). All the cited references as mentioned above are listed in the reference section of the manuscript.

Reviewer 2 Report

Introduction

Lines 60-61: delete „compelled“; reword this sentence

81-89: add additional information on CZ, its usage in agriculture, especially in the tropics, more examples of crops that were evaluated for the effect of CZ.

Add data on actual use of CZ in agriculture/Malaysia.

Is the use of CZ regulated?

94: US $?

Add information on the distribution of peat soils and their share in agriculturally used land in Malaysia. To which extend is papaya cultivated on peat soils in Malaysia? What are the main problems for farmers using peat soils in Malaysia?

Materials & Methods

128: add parentheses

131-138: add information on origin of CZ used in this study. Is it a commercially available product?

147: replace uniformed by uniform

162: Specify the phrase: was the CZ/fertilizer mixture applied on the soil?

163: replace within by below (if the CZ was applied on the soil)

167-176: How many soil samples were taken per plot/repetition?

179: Were samples taken from each plant, i.e. 4 per plot?

181: change to Kjeldahl

Overall: Field trials should be repeated for at least two years and/or preferably be conducted at different sites. This study was conducted on a relatively small scale with just 3 replicates. This is the largest shortcoming of the present work. The results should be verified in a further trial year.

Results

Figure 2: Change figure caption to: Exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium in a peat soil treated with different amounts of CZ and fertilizer throughout papaya plants growth stages, (a) flowering stage; (b) fruiting stage; and (c) harvesting stage.

Figure 2: Figures in first line, Ammonium: There were just 3 replicates. Is there really a significant difference between T2 and T3/T4 (first figure, flowering), T3 and T4 (second and third figure, fruting/harvesting)? Please check again.

Figure 2: Unify the y-axis labels for each line (e.g. Ammonium).

Table 4: Data were obtained from which variant?

Figure 3: Change figure caption to: Leaf nitrogen (a), phosphorus (b) and potassium (c) contents during flowering of papaya cv. Sekaki cultivation on a tropical peat soil treated with different amounts of CZ and fertilizer.

Table 6: Change table heading accordingly: Vegetative growth of papaya cv. Sekaki cultivation on tropical peat soil treated with different amounts…

Table 7: Change heading to: fruit quality and yield of papaya cv. Sekaki cultivated on a tropical peat soil…

Table 7 and line 349: Explain the meaning of °Brix.

Discussion

How do the results compare to the average papaya yields on peat soils in Malaysia?

T1 yields as well as fruit quality are very high compared to the control (T5). Please discuss these results.

Conclusion might contain recommendations for Malaysian papaya-growers.

Author Response

Response to Reviewer 2 Comments

Dear Reviewer,

In this revised manuscript, we have corrected the paper to the best of our ability by addressing all the points made by the reviewers (revisions were highligthed in yellow). Please refer to the attached file. 

Point 1: Introduction – Lines 60 – 61: delete compelled; reword this sentence

Response 1: The word ‘compelled’ has been deleted and the sentence has been rephrased to “This results in N immobilization because soil microbes use inorganic N from N fertilizers for decomposition of organic matter before being utilized by plants” (Lines 78 to 80).

Point 2: Introduction – add additional information on CZ, its usage in agriculture, especially in the tropics, more examples of crops that were evaluated for the effect of CZ

Response 2: Additional information on CZ have been included in the manuscript (Lines 100 to 107). This information include the application of CZ in agriculture to improve the soil physico-chemical properties of marginal soils namely acidic, sandy and clayey soils. The application of CZ improved soil physical and chemical conditions such as soil acidity, water holding capacity, nutrient retention, uptake and use efficiency for nitrogen, phosphorus, and potassium. The types of crops that have been evaluated for the effect of CZ are barley, maize, potatoes, wheat, strawberry, and sunflowers.  

Point 3: Introduction – Add data on actual use of CZ in agriculture/Malaysia.

Response 3: Amendments have been made to the manuscript to include the data on the use of CZ in Malaysia particularly for agriculture (Lines 110 to 118). Amending CZ with inorganic fertilizers on acid soils significantly minimized ammonia loss from urea, reduced nutrient leaching, improved soil chemical properties, nutrient uptake and use efficiency, and increased yields of lowland rice (cv. MR 219) and maize (Zea mays L.) cultivation in Malaysia. Also, the application of CZ effectively mitigated P fixation in acid soils besides reducing the need for chemical fertilizers namely Egypt Rock Phosphate in maize cultivation.

Point 4: Introduction – Is the use of CZ regulated?

Response 4: Amendments have been made to the manuscript to explain the regulation of CZ (Lines 110 to 111). In Malaysia, there are no regulations on the utilization of CZ as a soil amendment by the Department of Agriculture Malaysia (the authorization body responsible in monitoring the country’s agricultural development, services, and resources.

Point 5: Introduction – Line 94: US $?

Response 5: The authors acknowledged the typo error made in Line 94. Corrections have been to the manuscript to include the dollar symbol “$” (Line 125) because the export value for papaya production is calculated using the US dollar.

Point 6: Add information on the distribution of peat soils and their share in agriculturally used land in Malaysia. To which extend is papaya cultivated on peat soils in Malaysia? What are the main problems for farmers using peat soils in Malaysia?

Response 6: Amendments have been made to the manuscript to include information on tropical peat soils in Malaysia. Information on the coverage and distribution of peat soils, acreage of agricultural areas on peat soils, definition of tropical peat soils, types of crops cultivated on peat soils including their planted areas, and agronomic challenges in managing peatlands in Malaysia have been included (Lines 37 to 54). Papaya is mostly cultivated in small-scale on peat soils under mixed cropping systems. Fruit cultivation on peat soils, namely papaya, pineapple, banana, coconut, ciku, rambutan, and durian, accounts for 16% of the total agriculture fruit area in Malaysia (Lines 49 to 51). Also, papaya cultivation covers a total planted area of 3, 267 hectares (Line 124).

Point 7: Materials and methods – Line 128: add parentheses

Response 7: The authors acknowledged the error made in Line 128. Corrections have been made to the manuscript to include parentheses to represent standard error the mean for the respective soil properties in Table 1 (Lines 199 to 200).

Point 8: Materials and methods – Line 131 – 138: Add information on origin of CZ used in this study. Is it a commercially available product?

Response 8: The origin of the CZ used in the study have been included in the manuscript (Section 2.2) (Lines 203 to 204). The CZ used in the study is commercially available natural zeolite that originated from Indonesia.

Point 9: Materials and methods – Line 147: replace uniformed by uniform

Response 9: The authors acknowledged the grammatical error made in Line 147. Corrections have been made to the manuscript (Section 2.3) (Line 219) by replacing the word “uniformed” with “uniform”.

Point 10: Materials and methods – Line 162: Specify the phrase: was the CZ/fertilizer mixture applied on the soil?

Response 10: Corrections have been made to the manuscript in Section 2.4 by rephrasing the sentence to clearly explain the application method of CZ and NPK fertilizers onto the peat soil (Lines 234 to 236). The sentence has been rephrased to “The mixture, consisting of CZ and NPK fertilizers (T1 to T5) were applied circularly onto the soil (approximately 20 cm) from the collar of the papaya plants below the canopy of the plants to ensure they were not injured”.

Point 11: Line 163 – replace within by below (if the CZ was applied on the soil)

Response 11: The authors acknowledged the grammatical error made in Line 163. The mixture containing CZ and NPK fertilizers were applied onto the soil and the word “within” have been replaced with “below” (Line 235).

Point 12: Lines 167-176: How many soil samples were taken per plot/repetition?

Response 12: The experimental design used in the study was a randomized complete block design with three blocks and five treatments. Each of the five treatments within a block had four papaya plants (giving a total of 60 papaya plants for the experiment). For each treatment, the peat soil sampling was carried out systematically at a distance of 30 cm from the collar of the papaya plants. The peat samples were taken at depths of 0 to 20 cm and 20 to 40 cm from each plant, giving a total of forty soil samples per block. Amendments have been made to the manuscript to include the number of soil samples taken per block (Lines 244 to 246). 

Point 13: Line 179: Were samples taken from each plant, i.e. 4 per plot?

Response 13: For this, leaf samples were collected from the bottom fourth or fifth leaf, including midrib from each plant for each treatment, giving a total of twenty leaf samples per block. Amendments have been made to the manuscript to include the number of leaf samples taken per block (Lines 252 to 253).  

Point 14: Line 181 – change to Kjeldahl

Response 14: The authors acknowledged the typo error made in Line 181. Corrections have been made to the manuscript in Section 2.6 (Line 255) by using the right spelling for Kjeldahl.

Point 15: Overall – Field trials should be repeated for at least two years and/or preferably be conducted at different sites. This study was conducted on a relatively small scale with just 3 replicates. This is the largest shortcoming of the present work. The results should be verified in a further trial year.

Response 15: The authors acknowledged that results from one cycle of papaya cultivation may not be conclusive enough to confirm the findings obtained from the study. Actual effects of clinoptilolite zeolite in improving peat soil properties and papaya growth and yields require more time. However, a second field trial for papaya cultivation treated with clinoptilolite zeolite is currently on-going, which commenced in April 2020 and will be completed by February 2021. At the moment, the authors are only able to present the interim findings on the effect of clinoptilolite zeolite on peat soil properties and papaya growth and fruit quality based only on the first trial. Also, the authors are embarking on field trials in farmers’ farm at different locations in Sarawak and Peninsula Malaysia to verify and confirm the findings from the study because climatic factors such as temperature and rainfall distribution between planting cycles may affect the outcome of the study. Papaya was chosen as the test crop of the study because papaya is mostly planted as a small-holder crop throughout the country. Moreover, papaya cultivars such as Sekaki and Eksotika have good potential for commercialization and export due to its high-quality fruit characteristics that can significantly contribute to the Malaysian economy. Amendments have been made to the manuscript to explain the limitation of the present study in the conclusion section (Lines 478 to 482).

Point 16: Figure 2 – Change figure caption to: Exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium in a peat soil treated with different amounts of CZ and fertilizer throughout papaya plant growth stages, (a) flowering stage; (b) fruiting stage; and (c) harvesting stage.

Response 16: Corrections have been made to Figure 2 (Lines 317 to 323). The figure caption for Figure 2 was changed to “Figure 2. Exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium in a peat soil treated with different amounts of CZ and NPK fertilizer throughout papaya plants growth stages, (a) flowering stage; (b) fruiting stage; and (c) harvesting stage”.

Point 17: Figures in first line, Ammonium: There were just 3 replicates. Is there really a significant difference between T2 and T3/T4 (first figure/flowering), T3 and T4 (second and third figure, fruiting and harvesting)? Please check again.

Response 17: We confirm that there are significant differences between treatments (T1 to T5) at the flowering, fruiting, and harvesting stage for ammonium. Each of the five treatments within a block had four papaya plants (giving a total of 60 papaya plants for the experiment). For each treatment, the peat samples were taken at depths of 0 to 20 cm and 20 to 40 cm from each plant, giving a total of forty soil samples per block. Means of the treatments were compared using Tukey’s test at P ≤ 0.05 using the Statistical Analysis System (SAS) Version 9.1. The results for ammonium at different growth stages is as follows:

Values (mean ± standard error) with different letters within the same column are significantly different by Tukey’s test at P ≤ 0.05.

Point 18: Figure 2 – Unify the y-axis labels for each line (e.g. Ammonium)

Response 18: Corrections have been made to unify the y-axis labels for ammonium, nitrate, phosphorus, and potassium (Line 317).

Point 19: Table 4 – Data were obtained from which variant?

Response 19: The authors would like to clarify that the results presented in Table 4 is based on the mean soil exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium for all treatments (T1 to T5 including control) at different soil depths and growth stages of the papaya plants. Statistical analysis was carried out to compare the mean soil macronutrients content from all treatments using the sorting and by procedures (SAS 9.1 – ANOVA: Proc sort and By) at depths of 0 to 20 cm, and 20 to 40 cm according to the respective growth stages. Generally, the results in Table 4 indicated the mobilization of nutrients for all treatments, where mean soil ammonium, nitrate, available P and exchangeable K were higher at depth of 20 to 40 cm which could be attributed to the high preferential flow of peat soil water as demonstrated and explained in Section 4.1 from Lines 412 to 416. For this, amendments have been made to the manuscript to rephrase the sentences in Section 3.2 (Results) (Line 305) and to include the word “Table 4” to indicate the mean soil nutrient contents for all treatments at different depths and growth stages (Line 413). Also, figure caption for Table 4 has been rephrased accordingly to “Table 4. Mean exchangeable ammonium, available nitrate, available phosphorus, and exchangeable potassium in a peat soil at different soil depths and growth stages of papaya plants treated with different amounts of CZ and NPK fertilizer” (Lines 309 to 311).

Point 20: Figure 3 – Change figure caption to: Leaf nitrogen (a), phosphorus (b) and potassium (c) contents during flowering of papaya cv. Sekaki cultivation on a tropical peat soil treated with different amounts of CZ and fertilizer.

Response 20: Corrections have been made to Figure 3 (Lines 338 to 343). The figure caption for Figure 3 was changed to “Figure 3. Leaf nitrogen (a); phosphorus (b); and potassium (c) contents during flowering of papaya cv. Sekaki cultivation on a tropical peat soil treated with different amounts of CZ and NPK fertilizer”.

Point 21: Table 6 – Change table heading accordingly: Vegetative growth of papaya cv. Sekaki cultivation on tropical peat soil treated with different amounts….

Response 21: Corrections have been made to Table 6 (Lines 344 to 345). The table heading for Table 6 was changed to “Table 6. Vegetative growth of papaya cv. Sekaki cultivation on tropical peat soil treated with different amounts of CZ and NPK fertilizer”.

Point 22: Table 7 – Change heading to: fruit quality and yield of papaya cv. Sekaki cultivated on a tropical peat soil…

Response 22: Corrections have been made to Table 7 (Lines 356 to 357). The table heading for Table 7 was changed to “Table 7. Fruit quality and yield of papaya cv. Sekaki cultivated on a tropical peat soil treated with different amounts of CZ and NPK fertilizer”.

Point 23: Table 7 and line 349: Explain the meaning of °Brix

Response 23: Amendments have been in Table 7 (Line 359) to explain the meaning of °Brix (pure sucrose content) in the table caption as a footnote. Correction has been made to the manuscript in Section 4.2 to explain the meaning of TSS measured as pure sucrose content which is expressed in °Brix (Lines 432 to 434).

Point 24: Discussion – How do the results compare to the average papaya yields on peat soils in Malaysia?

Response 24: Papaya planted on peat soils treated with CZ significantly contributed to higher fresh fruit yield compared to control (without CZ and fertilized with compound NPK fertilizer).

Sekaki is a medium sized papaya fruit weighing between 1.5 to 2 kg/fruit. The higher fresh fruit weight of T1 to T4 (ranging between 2.2 to 2.6 kg/fruit) indicates good fresh fruit yield compared with control. Generally, papaya planted on peat soils bears fruit after 8 to 10 months with yields of about 30 tonnes per hectare for the first year of production. In comparison, amending peat soils with CZ is able to produce an average of 62.4 tonnes fresh papaya fruit yield per hectare in a shorter period of 6 months after planting. Additional information on the comparison between the results with CZ and average papaya yields on peat soils in Malaysia have been included in the manuscript from Lines 453 to 459.

Point 25: Discussion – T1 yields as well as fruit quality are very high compared to the control (T5). Please discuss these results.

Response 25: The discussion explaining the results of T1 contributing to higher fruit yield and improved fruit quality compared to the control treatment (T5) have been discussed from Lines 442 to 449. However, additional information explaining the effectiveness of T1 including T2 in improving fruit quality and fruit yields have been included in the manuscript from Lines 449 to 453. This information includes the temporary adsorption/absorption of ammonium, nitrate, P, and K ions within the lattices of CZ that allows these ions to leach out as water runs through the soil and be taken up in small amounts by papaya plants. Also, the effectiveness of T1 and T2 in improving papaya fruit quality and yield is consistent with the higher retention of ammonium, nitrate, P, and K in peat soils fertilized with CZ compared with other treatments including control (Figure 2).

Point 26: Conclusion might contain recommendations for Malaysian papaya-growers.

Response 26: Recommendations for Malaysian papaya growers have been included in the conclusion section from Lines 472 to 475. This recommendation includes the suggestion on monthly fertilization using compound NPK fertilizers in conjunction with 70 to 100% CZ might be applicable and useful to local farmers in improving soil acidity, macronutrients availability, fresh fruit yield and fruit quality of papaya grown on peat soils.