Biochar-Ca and Biochar-Al/-Fe-Mediated Phosphate Exchange Capacity are Main Drivers of the Different Biochar Effects on Plants in Acidic and Alkaline Soils

Round 1

Reviewer 1 Report

THis is a good paper, and a number of corrections to english grammar required. 

Figure S4 Day 41, day 60. these photos need to specify which treatment they belong to.

Figure S7 - the digital resolution of the imagery is not suitable for publication. Higher resolution photos are required. Also need to indicate which pots are alkaline and which are aciic soils.

Comments on the attached PDF

Comments for author File: Comments.pdf

Author Response

All the changes suggested by reviewer 1 have been included in the “Track changes manuscript” and they can check the changes made following their recommendations in this version.

Reviewer 2 Report

Biochar-Ca and Biochar-Al/-Fe mediated phosphate exchange capacity are main drivers of the different biochar effects on plants in acidic and alkaline soils

 Roberto Baigorri^#,*, Óscar Urrutia^#, Sara San Francisco and José María García-Mina

A very interesting paper providing new knowledge on causes of biochar effects under different soil conditions. This information is necessary for assessing the potential of biochar to improve soil functions. Generally, the paper is well written and require minor revisions following the comments below.

Abstract

Generally ok. Noted the following:

1.       Problem is clearly stated. However, the objective of the study is not clear.

2.       Line 18,- These fertilizers have been applied to wheat cultivated in pots containing an alkaline soil and grown for 60 days. ‘Have been’ could be replaced with ‘were’.

3.       Methods and results are ok.

4.       Line 23-25,- Desorption experiments showed that P and Fe/Al were no desorbed from the P- Fe/Al-biochar complex by water or the Olsen reactant, while partial desorption was observed when 24 HCl 0.1 M was used. No could be replaced with not.

5.       Missing concluding statement.

Introduction

Too broad/general. General information is important, but need to focus on the specific study. May include information on P forms in alkaline and acid soils, sorption processes, or possible interactions of biochar with nutrients based on biochar properties such as nutrient content, surface area, high pH and CEC.

Materials and Methods

2.5. Biochar integration on granulated fertilizers and Growth Chamber experiment.

1.       Treatments are clear, however, experimental design and number of replications are not stated.

2.       Line 91- Two PK (0-8-12) granulated fertilizer were carried out with a 1% (P-CHAR1) and 5 % (P-CHAR5) of biochar in w/w (Figure S1). Statement is not clear, need to recast.

3.       Line 97, Soil analysis is available in Table S1. May be written as ‘soil analysis results are’. May require citations for some standard methods.

4.       Line 101, Once analyzed the fresh matter production, shoots were dried in an oven at 40 °C for 3 days to determine dry matter (Figure S2). Statement need to be checked.

2.8. Greenhouse experiment.

Treatments are clear. However, the experimental design is not stated.

2.7. Biochar-Soil solution interactions

1.       Line 113, ‘Four different soils were used in the soil solution interaction experiment’. Need to state the soil type based on standard soil classification system.

2.       Line 122, Soils analysis is available in Table S2 and Table S3. May be written as ‘Soils analysis results are available in Table S2 and Table S3’.

Results

3.1. Biochar characterization

Line 142, ‘The temperature of manufacturing biochar was 400 °C’, Contradicts line 69 ‘manufactured by pyrolysis at temperature of 450 °C’.

3.2. Growth Chamber experiment

1.       Line 148, ‘The PK fertilizers were manufacturing with biochar previously to be applied on a growth chamber experiment in wheat.’ Need to check the statement.

2.       May need to shift Line 148 to 153 to materials and methods section. The focus in this section should be the results.

3.       Line 153 to 154, ‘P-CHAR5 treatment showed a statistically significant decrease in mass production, as shown in Figure 1. What was the alpha or level of significance under which this statement was made?

3.3. Biochar-Nutrients adsorption isotherm kinetics

Line 163-164, ‘The two last nutrients were adsorbed, being Al adsorbed at 60 min but Fe more rapidly at 5 min’. Check statement to give correct interpretation of the graph.  Normally aluminium is not considered as a plant nutrient though used by some plants. May need to check this.

3.4. Biochar-Soil solution interactions

1.       Line 186-188 should shift to materials and methods. Focus in this section should be the results.

2.       Line 191-192, ‘We want to indicate that Figure 4 doesn’t show the correct level of nutrients in soils. ‘doesn’t’ maybe replaced with ‘does not’.

3.5. Greenhouse experiment

1.       Line 202-203, ‘The greenhouse experiment carried out in both acidic and alkaline soils (Figure S7) yielded statistically significant differences among Control – and Control + treatments Figure 5. Statistically significant differences in what? May also need to specify the alpha level.

2.       Also check the error bars in Figure 5, not consistence with the letters a, b and c.

3.       Need to state what the letters a, b and c mean.

Discussion and conclusion

1.       A well written discussion. However, this section may require more scientific knowledge to support the obtained results.

2.       Line 258-260, ‘These relationships were supported by the results obtained in the greenhouse experiment with tomato (Figure S7), which showed positive results in acidic soils but any effect in alkaline ones in line with the results reported by other studies. This statement need to be checked.

3.       Conclusion is generally ok.

References

Relevant literature was cited.

 General observation

Some sentences are starting with abbreviations instead of being written in full.

 Supplementary materials

Page 2 of 9, Table S2; Analysis of acidic soil used in Greenhouse experiment- Authors must check the Cation Exchange capacity (28.1).

Author Response

All the changes suggested by reviewer 2 have been included in the “Track changes manuscript” and they can check the changes made following their recommendations in this version