Effect of Compound Biochar Substrate on the Root Growth of Cucumber Plug Seedlings
Round 1
Reviewer 1 Report
General comments
Biochar is reported to improve the porosity and surface area for adsorption of nutrient in selected soil types (such as sandy soils) and suitable substrates for seedling growth. Manipulating the existing substrates to improve the seedling health will improve crop growth and productivity. This manuscript investigated the effect of biochar addition at different proportion on the substrate strength and root growth and seedling growth parameters. The design and statistical analysis are appropriate. The content is relevant to the readership of the journal. The results of the investigation provide additional data to improve the understanding of biochar effect on the seedling substrate. Result and discussion are comprehensive and well detailed. However, the manuscript needs improvement. There are several grammatical errors. Few are detailed briefly in the comments below. However, authors need to revise the entire manuscript to improve the English standard.
Detailed comments
Few spelling errors are below, but authors need to look into the entire manuscript.
Line 18-21- The sentence is very long. Rephrase
Line 24- Revise keywords- plug seedling and biochar are already in the title. Use different keywords
Line 51- Thermal decomposition or pyrolysis
Line 54- what is the difference between soil density and soil bulk density?
Line 55- rephrase ‘exchange capacity of soil’ to ‘cation exchange capacity (CEC)’
Line 57- C/N ration improved? What does this mean increase or decrease?
Line 59-62- The sentences were contradicting in meaning. Line 59 suggest compost of peat is widely used as a substrate nowadays, but line 62 contradicts and suggest the same was not widely used. Pl rephrase and revise.
Line 117- Pl specify the period of time (e.g. minimum of two hours)
Line 140- an incubator for cultivation or germination?
Line 146-158- It is mentioned the 100 mL of distilled water was used for leaching. However, the biochar amendments will influence the volume of leachate. The N release will be a function of N concentration and leachate volume. So, what do authors mean by measuring N content using Kjeldahl azotometer? Do they multiply leachate volume and N concentration to calculate total N release? Pl elaborate.
Line 186- …. was used to collect the data or process the data?
Line 210- significantly difference between….. does read well. Pl rephrase
Line 216-217- … which resulted in a significantly increase for the porosity of the substrate doesn’t read well. Pl rephrase fix a grammatical error
Figure 7 needs to be improved for quality. Nitrogen release mg N /100 g of what?
Also, how the calculation for N release was made. Pl check the comments above for line 146-158
Line 275- nitrogen energy? Pl delete energy
Line 367- change Pervious to Previous
Line 402-405- Improve the discussion by incorporating a discussion on the energy cost and associated emission involved in biochar production (pyrolysis) process.
Author Response
Response to Reviewer 1 Comments
The authors thank the reviewer 1 for affirming the content of our manuscript, and also thank his/her comprehensive comments for improving the quality of this manuscript.
Point 1: Line 18-21- The sentence is very long. Rephrase
Response 1: According to your comment, we changed the sentence into ‘It was noticed that the strength of substrate with appropriate biochar proportion was enhanced as well. Under the interaction of strong root system and solid substrate, the compressive strength of the substrate with 20% and 10% biochar-treated was much better than others, especially that of 40% and 50% biochar-treated, which efficiently satisfied the requirements of automatic seedling picking.’ in line 19-23 (the new line number in the revised manuscript, the same below).
Point 2: Line 24- Revise keywords- plug seedling and biochar are already in the title. Use different keywords
Response 2: According to your comment, we changed the two keywords of ‘plug seedling’ and ‘biochar’ into ‘Substrate’ and ‘Tests’ in line 25.
Point 3: Line 51- Thermal decomposition or pyrolysis
Response 3: ‘Pyrolysis’ is more suitable for the method of biochar production in our manuscript, so we changed ‘Thermal decomposition’ into ‘pyrolysis’ in line 52.
Point 4: Line 54- what is the difference between soil density and soil bulk density?
Response 4: There is a clear distinction between them by definition, and we will explain it with some equations.
Figure M1. The measuring tools to determine the soil density and bulk density. (a) Ring cutter; (b) Pycnometer.
- Soil bulk density: it is generally determined by ring cutter (Figure M1a, standard method) in the natural state, and the pore volume (volume of air and water) in the soil is counted in the calculation.
Where BD means bulk density, g/cm3; m1 is the weight of ring cutter filled with the substrate, g; m2 is the weight of the ring cutter, g; V is the volume of ring cutter, cm3; ω is the mass water content of the substrate sample, g/kg.
- Soil density (also called soil particle density): it is generally determined by pycnometer (Figure M1b, standard method), and the pore volume in the soil is not counted in in the calculation.
Where ρD means soil density, g/cm3; mD is the weight of the substrate, g; mw is the weight of the spilled liquid, g; mt is the weight of the remaining water and the substrate in the pycnometer, g; ρw is the density of the liquid in pycnometer, g/cm3.
At present, most scholars [1-3] use bulk density to represent the physical parameters of soil.
Point 5: Line 55- rephrase ‘exchange capacity of soil’ to ‘cation exchange capacity (CEC)’
Response 5: According to your comment, we changed ‘exchange capacity of soil’ into ‘cation exchange capacity (CEC)’ in line 55-56.
Point 6: Line 57- C/N ration improved? What does this mean increase or decrease?
Response 6: What we want to express here in the introduction is that C/N ration increased, so we changed ‘so the C/N ration of soil will be improved’ into ‘so the C/N ration of soil will be increased’ in line 57-58 according to your comment.
Point 7: Line 59-62- The sentences were contradicting in meaning. Line 59 suggest compost of peat is widely used as a substrate nowadays, but line 62 contradicts and suggest the same was not widely used. Pl rephrase and revise.
Response 7: We are sorry to confuse you about that. According to your comment, we changed the sentence into ‘Nowadays, most of the substrate used for plug seedling raising were composed of peat, vermiculite and perlite, and previous research proposed that this kind of substrate had relatively good mechanical properties, but the cost of this substrate was high and some farmers were reluctant to use this substrate.’ in line 60-63.
Point 8: Line 117- Pl specify the period of time (e.g. minimum of two hours)
Response 8: According to your comment, we changed ‘period of time’ into ‘24 hours’ in line 115.
Point 9: Line 140- an incubator for cultivation or germination?
Response 9: The incubator we used in the experiment could provide constant temperature, illumination and humidity, so we used it to raise the plug seedlings, and the seed germination and subsequent growth were all carried out in the incubator. What we mentioned in line 139-140 ‘we put them into the incubator for cultivation’ just meant that we put the substrates without seeds in the same environment as the plug seedling raising, so we could get the accuracy water retention of different substrates to guide the cultivation of plug seedlings.
Point 10: Line 146-158- It is mentioned the 100 mL of distilled water was used for leaching. However, the biochar amendments will influence the volume of leachate. The N release will be a function of N concentration and leachate volume. So, what do authors mean by measuring N content using Kjeldahl azotometer? Do they multiply leachate volume and N concentration to calculate total N release? Pl elaborate.
Response 10: Because of the lacking of explanations about the process of leaching liquid digestion in the first manuscript, you may feel confused, so we added the necessary explanations in line 154-161. In a typical trial, we collected 25 mL leaching liquid into the centrifuge tube for total nitrogen determination after all the leaching liquid was collected and only 2 mL leaching liquid was needed to be digested according to standard digestion process.
Actually, the biochar amendments do influence the volume of leachate (before being saturated in water), but we used 50 mL distilled water to saturate the substrates in the leaching pipe and sealed the top of the pipe by polyethylene film before leaching, and the pipes with substrates were all under the condition of constant temperature and humidity, so we found that volume of the leaching liquids were almost the same (between 90 mL and 95 mL) when we collected them. Besides, we also measured the density of the leaching liquid. As shown in Figure M2, we measured the weight of 25 mL leaching liquid in the centrifuge tube (in order to ensure the accuracy of the density, the pipette was used to collect the leaching liquid), and then calculated the density as
Where ρL means density of the leaching liquid, g/mL; m1 is the weight of the leaching liquid with the centrifuge tube, g; m2 is the weight of the centrifuge tube, g; V1 is the volume of the leaching liquid in the centrifuge tube, mL.
Figure M2. The determination of the leaching liquid density.
In indoor environment (the temperature is 28 ℃), we measured the density value of different leaching liquids was almost the same (between 1.021 g/mL and 1.052 g/mL).
At first, we directly used the values (unit: mg/100g) measured by the automatic Kjeldahl azotometer to represent the total nitrogen release, but the total nitrogen release from the substrate should be the results of multiplying the volume of the leaching liquid by the nitrogen concentration, so we recalculated the total nitrogen release from the substrate as
Where m means the weight of the total nitrogen release from the substrate, g; ρL is the density of the leaching liquid, g/mL; C is the nitrogen concentration of the leaching liquid measured by automatic Kjeldahl azotometer, mg/100g.
According to the new calculation results of the total nitrogen, we changed some data and modified Figure 1b (line 245, the new Figure number in the revised manuscript, the same below) in the revised manuscript.
Point 11: Line 186- …. was used to collect the data or process the data?
Response 11: According to your comment, we changed ‘collect the root data’ into ‘process the root data’ in line 185.
Point 12: Line 210- significantly difference between….. does read well. Pl rephrase
Response 12: According to your comment, we changed ‘significantly difference’ into ‘remarkable difference’ in line 207.
Point 13: Line 216-217- … which resulted in a significantly increase for the porosity of the substrate doesn’t read well. Pl rephrase fix a grammatical error
Response 13: According to your comment, we changed ‘which resulted in a significantly increase for the porosity of the substrate’ into ‘which resulted in a significant increase for the porosity of the substrate’ in line 213-214.
Point 14: Figure 7 needs to be improved for quality. Nitrogen release mg N /100 g of what?
Also, how the calculation for N release was made. Pl check the comments above for line 146-158
Response14: According to your comment, we changed ‘Nitrogen release’ into ‘Nitrogen release of different substrates’ in Figure 1b (line 245). And the calculation method of nitrogen release was explained in detail in comment 10.
Point 15: Line 275- nitrogen energy? Pl delete energy
Response 15: According to your comment, we changed ‘nitrogen energy’ into ‘nitrogen’ in line 269, and we also changed ‘nitrogen energy’ into ‘nitrogen’ in line 58.
Point 16: Line 367- change Pervious to Previous
Response 16: We changed ‘Pervious’ into ‘Previous’ in the whole text.
Point 17: Line 402-405- Improve the discussion by incorporating a discussion on the energy cost and associated emission involved in biochar production (pyrolysis) process.
Response 17: Thank you for your precious comments! In the present study, we mainly focused on the effects of biochar on the growth of plug seedlings, however, the accurate energy cost and associated emission during the process of biochar production, and the effects pyrolysis condition on the properties of derived compound biochar substrate and plant growth will be explored in details for our further study in the near future. We deleted this paragraph in order to ensure the accuracy of the experimental data in the manuscript.
We gratefully acknowledge your comments and suggestions, which are very valuable in improving the quality of our manuscript.
- Tracy, S. R.; Black, C. R.; Roberts, J. A.; Mooney, S. J. Exploring the interacting effect of soil texture and bulk density on root system development in tomato (solanum lycopersicum L.). Environmental and Experimental Botany 2013, 91 (7), 38-47.
- Qu, P.; Cao, Y.; Wu, G.; Tang, W.; Xia, L. Preparation and properties of coir-based substrate bonded by modified urea formaldehyde reinsnfor seedlings. Bioresources 2018, 13 (2): 4332-4345.
- Matt A.; Malcolm C. Mapping soil profile depth, bulk density and carbon stock in Scotland using remote sensing and spatial covariates. European Journal of Soil Science 2020,71(4).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
All comments are in the pdf file.
Comments for author File: Comments.pdf
Author Response
Response to Reviewer 2 Comments
First of all, the authors would like to express our heartfelt gratitude to reviewer 2 for his/her comments for improving the quality of this manuscript. Some specific responses under your comments are as follows:
Point 1: Line 10-23- Incomplete. Results showed that high ratios of biochar applied (30%, 40% and 50% and probably 20%) are clearly negatives for seedling's growth. Please, add this conclusion in Abstract as well as in Conclusion.
Response 1: We added the effect of the substrates with 40% and 50% biochar-treated on the seedling growth in line 18-19 (the new line number in the revised manuscript, the same below).
Point 2: Figure 1-Figure 6- Fit better in Suplementary Information. Not in the main article.
Response 2: According to your comment, we deleted Figure 1-Figure 6 in our revised manuscript, and used them as the supplementary information. We also added some explanations in line 427-430.
Point 3: Line 214- ‘Pervious’ should be changed to ‘Previous’.
Response 3: We changed ‘Pervious’ into ‘Previous’ in the whole text.
Point 4: Line 218- ‘common peat’ should be changed to ‘in common peat’.
Response 4: According to your comment, ‘common peat’ has been changed into ‘in common peat’ in line 215.
Point 5: Line 254- slope data missing
Response 5: We added the slope data in line 248.
Point 6: Line 261- Line 268- Very confuse. Please, explain better this paragraph.
Response 6: We are sorry to confuse you about the sentence, we have modified the paragraph to be ‘As shown in the enlarged part of Figure 1a (the new Figure number in the revised manuscript, the same below), the first substrate that dropped to 8 g was T5, and the last was T1, indicating that the substrate with T1 treatment had the best water retention in comparison with the substrates with other treatments. Besides, the substrate’s weight from the lightest to the heaviest on the 21th day was T0, T1, T2, T3, T4, T5 in sequence, which meant initial moisture content of peat was much better than biochar, so the content of biochar in the substrate was not the more the better. To sum up, adding a certain proportion of biochar in the substrate significantly increased the water retention of the substrate.’ in line 256-262.
Point 7: Line 269- This affirmation in incorrect. Only, ammonium is directly analyzed by Kjeldahl. Nitrate and organic nitrogen need to be transformed and/or digested.
Response 7: We are sorry that we brought the confusion to you because of the vague expression about the method which we measured the nitrogen. In order to determine the total nitrogen in the leaching liquid by the automatic Kjeldahl azotometer, the leaching liquid must be digested before determination. In a typical trial, we collected 25 mL leaching liquid into the centrifuge tube for total nitrogen determination after all the leaching liquid was collected and only 2 mL leaching liquid was needed to be digested according to standard digestion process. We used an inappropriate word ‘decocted’ in line 158 (in the first manuscript) to represent the process of leaching liquid digestion, so we changed the word ‘decocted’ into ‘digested’. Besides, we added some professional description to represent the whole process of total nitrogen determination in the revised manuscript in line 154-161.
Point 8: Line 275- The ‘nitrogen energy’ is bad expressed.
Response 8: We changed ‘nitrogen energy’ into ‘nitrogen’ in line 269.
Point 9: Line 282- The ‘Figure 10a’ should be changed to ‘Figure 8a’.
Response 9: According to your comment, we changed ‘Figure 10a’ into ‘Figure 2a’ in line 304.
Point 10: Line 316-Line 318- These results are as important as growth improvement by T1 treatment is. But in text authors only commented in a secondary way. Please remark in text this results.
Response 10: We are sorry that we omitted some discussions about the seedlings raised in the substrates with 40% and 50% biochar-treated in the first manuscript, so we added necessary discussions about the substrates with 40% and 50% biochar-treated inhibited the seedling growth in the revised manuscript. For example: line 18-19 in the abstract, line 277-280, line 332-334, line 349-352, line 418-419 and line 422-424 in the conclusion.
Point 11: Line 329-Line 331- Please, rewrite this paragraph in Figure 9a we observe length differences. Then these words (Figure 9a) are more appropriate in the second sentence.
Response 11: According to your comment, we changed the order of these two paragraphs, and we rewrote the paragraph to be ‘The total length of the root and the weight of root dry matters were two important parameters to judge root growth [33], so we selected these two parameters in order to better describe the effect of substrates with different biochar treatment to root systems. The root systems of the 19-day-old seedlings were washed carefully, and finally the roots were put on the paper after excess water of them was absorbed (Figure 3a). We found that the seedling raised in the substrate with T1 treatment got the strongest root system, and the root system of the seedlings raised in the substrate with T0 and T2 treatment were almost the same which were weaker than that of T1 treatment. However, the root system of the seedlings raised in the substrate with T4 and T5 treatment were the worst in comparison with that of other treatments’ in line 326-334.
Point 12: Line 337- Line 348- Include in Figures 9b and 9c statistical significance for all treatments and not only for T1. Probably T3, T4 and T5 showed differences statistically significant that are missing and that indicated the decrease in root growth when applying these biochar rates.
Response 12: We are sorry that we just marked the significance of T1 in Figures 3b and 3c (line 341), so we used significant letter marking method in single factor analysis of SPSS to remark the significance about all treatments, and the significance in Figure 2c and 2d (line 304) was also remarked. Besides, we added some explanations about the effect of the substrates with 40% and 50% biochar-treated to enrich the discussion of our manuscript. ‘However, the weight of root dry matter raised in T4 and T5 treatment was the lightest in comparison with that of other treatments, especially on 19th day, which indicated that the substrates with 40% and 50% biochar-treated would inhibit the growth of seedling roots’ (in line 349-352).
Point 13: Line 406- Results showed that high ratios of biochar applied (30%, 40% and 50% and probably 20%) are clearly negatives for seedling's growth. Please, add this conclusion.
Response 13: According to your comment, we added the results about the growth of the seedlings raised in 40% and 50% biochar-treated in the Conclusion. ‘but the substrate would inhibit the growth of the seedlings with the increase of biochar proportion, especially when the biochar proportion reached 40% and 50%’ (line 418-419); ‘However, the compressive strength of the substrates with 40% and 50% biochar-treated were the worst in comparison with that of other treatments’ (line 422-424).
Finally, the authors are extremely grateful for the reviewer and his/her constructive and rigorous comments aimed at improving the quality of our manuscript.
Author Response File: Author Response.pdf
