Effects of Catch Crops Cultivated for Green Manure on Soil C and N Content and Associated Enzyme Activities

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Effects of catch crops cultivated for green manure on soil C and N content and associated enzyme activities

The study investigated the impacts of catch crop management, specifically field pea used as green manure, on soil organic carbon (C), total nitrogen (N), mineral nitrogen, microbial biomass C and N (MBC, MBN), and the activity of five soil enzymes associated with C- and N-cycling. The research was conducted over a three-year period with the hypothesis that catch crop application would enhance these soil properties compared to control soil without catch crops. The research indicated that adding field pea biomass to the soil notably raised the mineral nitrogen levels and improved both microbial and enzymatic activity when compared with the control soil. Nonetheless, the timing of the catch crop’s addition—whether in autumn or spring—did not consistently affect the properties under examination. Moreover, the levels of total organic carbon and total nitrogen remained largely unchanged regardless of the catch crop management practices or the time of year when samples were taken. This manuscript is well written. However, there are additional points that need to be addressed by the author.

 

 

1.      figure 1, there are significant differences between A.I. treatment and S.I. treatment in year 2010 for Corg and Nt. What is the reason for these results? Significant levels of the comparison should be added in Figs.

2.      Fig 2, there is great variances between years of this experiment, what could be the reason. Considering the huge difference between year, the results would be greatly influence by random errors?

3.      The format of Table 1 and Table 3, Table 4 should be improved to improve the clarity.

4.      Table 5-7, in the caption, the author mentioned that data of 2009-2011. However why only one year data was presented?

5.      There were too many tables I suggest to use figures to show the data of enzyme activities.

Author Response

Dear Reviewer

We would like to thank you for your thoughtful comments and efforts towards improving our manuscript. Below, we address all comments and suggestions in a point-to-point manner. Appropriated changes have been introduced to the manuscript and changes have been highlighted in green font color.

 

Reviewer 1

Comments and Suggestions for Authors

Effects of catch crops cultivated for green manure on soil C and N content and associated enzyme activities

The study investigated the impacts of catch crop management, specifically field pea used as green manure, on soil organic carbon (C), total nitrogen (N), mineral nitrogen, microbial biomass C and N (MBC, MBN), and the activity of five soil enzymes associated with C- and N-cycling. The research was conducted over a three-year period with the hypothesis that catch crop application would enhance these soil properties compared to control soil without catch crops. The research indicated that adding field pea biomass to the soil notably raised the mineral nitrogen levels and improved both microbial and enzymatic activity when compared with the control soil. Nonetheless, the timing of the catch crop’s addition—whether in autumn or spring—did not consistently affect the properties under examination. Moreover, the levels of total organic carbon and total nitrogen remained largely unchanged regardless of the catch crop management practices or the time of year when samples were taken. This manuscript is well written. However, there are additional points that need to be addressed by the author.

 

1. Figure 1, there are significant differences between A.I. treatment and S.I. treatment in year 2010 for Corg and Nt. What is the reason for these results? Significant levels of the comparison should be added in Figs.

Authors' response:

Although the difference between A.I. and S.I. was  2.1 g.kg for C_ORG and 0.14 g/kg for Nt, these differences were not statistically significant. That is why no results of analysis of variance were presented. The data that are not statistically different usually are not interpreted and discussed.

2. Fig 2, there is great variances between years of this experiment, what could be the reason. Considering the huge difference between year, the results would be greatly influence by random errors?

Authors' response:

As regards the MBC/C_ORG ratio mean differences between years were as follows: 2009 - 2.04, 2010 – 1.82 and 2011 – 1.75. Such differences (mean for catch crop management was 11% and 14% between years, as well as 10% for A.I. between years, 18% for S.I. between years and 30% for C between years) in the case of soil biological properties/indicators/ratios are not usually considered to be great. The obtained differences could be caused by the of random errors, mainly changes in  the environmental conditions such as soil temperature and moisture as well as resulted from the spatial variability of soil, which is sometimes high even on the small areas.

3. The format of Table 1 and Table 3, Table 4 should be improved to improve the clarity.

Authors' response: Table 1, 3 and 4 were reworked to be more readable.

4. Table 5-7, in the caption, the author mentioned that data of 2009-2011. However why only one year data was presented?

Authors' response:

Since the activity of invertase, β-glucosidase and urease (there were tables 5-7, now are

Figure 3a-c) was not significantly affected by the catch crop management in individual years

of the study, the results for the entire study period (mean value for 2009, 2010 and 2011) were

only presented.     

 

5. There were too many tables I suggest to use figures to show the data of enzyme

activities.

Authors' response:

The activity of urease, invertase and b-glucosidase was presented on figure as was suggested

by the Reviewer. We have tried to do the same as regards the activity of cellulase and nitro

reductase but without the success. Because of many results (separately for subsequent years

and the average for 2009-2011) the figures were not readable and the content was difficult to

follow. That is why we have decided to leave the data in the tables.

Reviewer 2 Report

Comments and Suggestions for Authors

line 154, 156, 170, 188, 191,202,204, 275, 358-360, 392 and 417 There are no correct chemical formulas.

line 110 m2 superscript is not set

Line 142 The method citation is missing.

Line 159-194 Absorbance was measured! Please use this word not Optical density or extinction

What type was the spectrophotometer and what was the cuvette (10 mm)?

I recommend measuring the total nitrogen and carbon content of the samples by CN elemental analyzer. I recommend the measure that way. How was the soil's pH and how was measured the TOC? It was not mentioned (Figure 4.)

Remove these (TN, TBC, TOC) parameters from the correlation analysis or remeasure it.

 

Please carefully check the manuscript.

Author Response

Dear Reviewer

We would like to thank you for your thoughtful comments and efforts towards improving our manuscript. Below, we address all comments and suggestions in a point-to-point manner. Appropriated changes have been introduced to the manuscript and changes have been highlighted in green font color.

Comments and Suggestions for Authors

line 154, 156, 170, 188, 191,202,204, 275, 358-360, 392 and 417 There are no correct chemical formulas.

 

Authors' response:

All superscript and subscripts in the given above lines were corrected.

 line 110 m2 superscript is not set

Authors' response:

Corrected: “250 m² each…”

Line 142 The method citation is missing.

Authors' response:

We have added the following reference: Jackson, M.L. 1979. Soil chemical analysis – advanced course: a manual of methods useful for instruction and research in soil chemistry, physical chemistry of soils, soil fertility, and soil genesis. Publisher Madison Wi. 2^nd edition]

Line 159-194 Absorbance was measured! Please use this word not Optical density or extinction

Authors' response:

We have used the term “absorbance” instead of “optical density or extinction” in all enzymatic methods as was suggested by the Reviewer.

What type was the spectrophotometer and what was the cuvette (10 mm)?

Authors' response:

We have used a spectrophotometer UV Vis Evolution 220 (Thermo Scientific) with cuvette (10 mm). The following sentence was added in M&M section” The absorbance was measured using a spectrophotometer UV Vis Evolution 220 (Thermo Scientific) with cuvette 10 mm.

 

I recommend measuring the total nitrogen and carbon content of the samples by CN elemental analyzer. I recommend the measure that way. How was the soil's pH and how was measured the TOC? It was not mentioned (Figure 4.)

 

Authors' response:

Since we have no soil samples from the experiment anymore, we are not able to determine carbon and nitrogen by CN elemental analyser. However, we will remember to use the analyses while determining these properties in other experiments. C_ORG should be instead of TOC - corrected. We did not assess the soil pH and we have removed it from Figure 4a (currently Figure 5a)

Remove these (TN, TBC, TOC) parameters from the correlation analysis or remeasure it.

Authors' response:

TN, TBC and TOC was removed the PCA figure.

 Please carefully check the manuscript.

Authors' response:

The manuscript was checked carefully as regards other mistakes and shortcomings.

Reviewer 3 Report

Comments and Suggestions for Authors

The Abstract and Introduction are well written, with a clear presentation of the research ideas, hypotheses, and objectives. 

I suggest the authors shorten the second paragraph by splitting it into two paragraphs. Too much information to just one...

All the introduction the authors mention 'catch crops' in a very general way, not specifying which crops other studies used... Also, I miss a bit of why the authors chose pea as the catch crop for this study... one obvious reason is because it is a legume... but I've seen many other legumes being used for that...    

Line 91-93: "Recently, however"... the study is from 14-16 years ago... is this still recently? There were not other studies assessing the short-term during these years? I suggest the authors to rethink about this sentence. 

Line 93: I suggest: "Therefore, the present study evaluated the effect of pea (Pisum sativum L.) as a catch crop in a 3-year experiment..." Also, always remember to use italics when using scientific names.

 This sentence in lines 93-94 really made things a bit confusing "carried out in a different site each year"... Maybe you could make this a bit more clear: now I understand that the authors used 3 different fields in three consecutive years? Or let it to be described in more details in the M&M. 

Please, correct K2SO4 in line 154.

Sentence in Lines 173-174 in a bit confusing. Please, improve it. 

Results: well written and presented. It is not clear for me what Plot b on Figure 4 

 

Discussion: 

Second paragraph is too long, maybe split into 2. 

Conclusions: should be more concise and conclusive. Now it seems more like a summary of the main findings. 

 

Comments on the Quality of English Language

Fine

Author Response

Dear Reviewer,

We would like to thank you for your thoughtful comments and efforts towards improving our manuscript. Below, we address all comments and suggestions in a point-to-point manner. Appropriated changes have been introduced to the manuscript and changes have been highlighted in green font color.

Comments and Suggestions for Authors

The Abstract and Introduction are well written, with a clear presentation of the research ideas, hypotheses, and objectives. 

I suggest the authors shorten the second paragraph by splitting it into two paragraphs. Too much information to just one...

Authors' response:

The second paragraph was divided into two parts as was suggested by the Reviewer.

All the introduction the authors mention 'catch crops' in a very general way, not specifying which crops other studies used... Also, I miss a bit of why the authors chose pea as the catch crop for this study... one obvious reason is because it is a legume... but I've seen many other legumes being used for that...    

Authors' response:

The specific catch crops were detailed throughout the introduction (ryegrass, chicory, mixtures of ryegrass and chicory, white clover, mixtures of ryegrass and various clover species, rye, legume-rye mixture, winter rye, summer sorghum) (lines…..)

Of course, we completely agree with this opinion. There are many legume crops to choose and some of them are suitable for cultivation as stubble catch crop. The basis for the selection of this plant were the results of previous research, in which field pea was characterized by greater yield reliability than serradella and yellow lupine (Skinder et al. 2007). The amount of biomass produced, as well as the impact of this plant on cereal yield, was satisfactory even under sowing conditions in the time from  8th to 9th of August.

(Skinder Z., Lemańczyk G., Wilczewski E., 2007. Wartość wybranych roślin motylkowatych uprawianych w międzyplonie ścierniskowym na glebie lekkiej Cz.I. Wydajność biomasy i zdrowotność roślin. Acta Sci. Pol., seria Agricultura, 6(1), 23-33.)

Line 91-93: "Recently, however"... the study is from 14-16 years ago... is this still recently? There were not other studies assessing the short-term during these years? I suggest the authors to rethink about this sentence. 

Authors' response:

The sentence was reworked as was suggested by the Reviewer: “In the last decade both long-term benefits and short-term advantages of catch crops (e.g. rye, legume-rye mixture, ryegrass, chicory, winter rye, summer sorghum) application have been studied [22-26].”

Line 93: I suggest: "Therefore, the present study evaluated the effect of pea (Pisum sativum L.) as a catch crop in a 3-year experiment..." Also, always remember to use italics when using scientific names. This sentence in lines 93-94 really made things a bit confusing "carried out in a different site each year"... Maybe you could make this a bit more clear: now I understand that the authors used 3 different fields in three consecutive years? Or let it to be described in more details in the M&M. 

Authors' response:

That’s right, the present study they did not concern the cumulative multi-year impact, but assessed only the effect of one-year impact, typical in agricultural practice, whereas subsequent years were only repetitions. According to this suggestions the appropriate corrections have been made in the Introduction (lines 94-96) and in M&M section (lines 113-114) .

Please, correct K2SO4 in line 154.

Authors' response: Corrected: K₂SO₄

Sentence in Lines 173-174 in a bit confusing. Please, improve it. 

Authors' response:

Corrected as follows: “The soil samples were incubated for 24 h (for endo-cellulase) and 3 hours (for invertase) at 50°C with the acetate buffer (2 M, pH 5.5) and substrate (0.7% carboxymethyl cellulose sodium salt for endo-cellulase and 10% sucrose for invertase)”.

Results: well written and presented. It is not clear for me what Plot b on Figure 4 

Authors' response:

The PCA of cases revealed the significant differences in soil variables in individual study years and it was presented to show that most of the studied properties revealed the clear differences between the study years. It was observed that variables in soil samples collected in 2009 were positively correlated with PCA1, while variables in soil samples taken in 2010 and 2011 were negatively related to this component. In turn, the PCA2 distinguished variables determined in soil samples collected in 2010 (positively correlated) from those evaluated in 2011 (negatively correlated).

 Discussion: 

Second paragraph is too long, maybe split into 2. 

Authors' response:

The second paragraph was divided into two parts as was suggested by the Reviewer. We have added the sub-chapter 4.3. Autumn vs. spring incorporation of field pea.

Conclusions: should be more concise and conclusive. Now it seems more like a summary of the main findings. 

Authors' response:

Conclusion were reworked according to the suggestions of the Reviewer.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

OK