Does Increasing the Diversity of Small Grain Cropping Systems Improve Aggregate Stability and Soil Hydraulic Properties?

Round 1

Reviewer 1 Report

Review report of MS ID: agronomy-2428159

The manuscript entitled “Does Increasing Diversity of Small Grain Cropping Systems 2 Improve Aggregate Stability and Soil Hydraulic Properties?” has been reviewed.

Authors tried to highlight the impact of crop rotation on soil aggregates and soil carbon concentration. The MS is well organized and the statistical analysis and materials and methods are appropriately stated.

However, few concerns on the MS before publication in the journal.

Comment: 1: The scientific name of field pea is wrongly mentioned in Line 9 and 32. Please check the scientific name and correct accordingly.

Comment: 2: The introduction section is poorly written. I suggest to authors to highlights need of cropping system diversification. Wheat are problems that are compelling to diversify cropping systems in the studied regions. Also, it is important to highlights the problems of existing cropping systems in the regions. It will help readers to find the novelty of the study.  

Comment: 3: Line number 64-65: “However, little is known about the effects of rotating oilseed crops with wheat and barley on soil physical properties.” – Sentence is not clear whether to diversify oilseeds crop or to diversify wheat/barley crop? The immediate next is telling different things. Objectives can be reframed with alignment with title and results presented.

Comment 4: Soil organic carbon estimation method is missing in materials and methods.

Comment 5: Line 79: make italic of scientific name.

Comment 6: Figure 1: Error bars for standard deviation in few bar graphs are larger size that indicates a larger variation in data among replications. Please check data and correct accordingly.

Comment 7: Figure 2: Same comment as given for Fig.1 .

Comment 8: My major concern in discussion is that authors must highlight the previous studies on the effect of crop rotations on soil properties. There are many studies in this line. Accordingly, author should highlight previous studies and their agreements/disagreement with previous studies.

Comment 9: In conclusion, the best cropping should be highlighted in respects to different soil properties to have an idea of readers for designing cropping systems. 

There are typological and grammatical errors in MS that need to be addressed before publications.

Author Response

Dear Reviewer,

We appreciate the comments that you provided on our manuscript. I have read through your comments and made the changes to the manuscript. I have included our responses to your comments below.

Comment: 1: The scientific name of field pea is wrongly mentioned in Line 9 and 32. Please check the scientific name and correct accordingly.

Response: I changed it to Pisum Sativum L. on lines 9 and 32

Comment: 2: The introduction section is poorly written. I suggest to authors to highlights need of cropping system diversification. What are problems that are compelling to diversify cropping systems in the studied regions. Also, it is important to highlights the problems of existing cropping systems in the regions. It will help readers to find the novelty of the study.  

Response I added this on lines 30-31 Growing continuous wheat or barley can lead to weed and disease issues and reduced grain yield over time in the NGP.

I also added this on lines 36-54

Crop rotations are important for maintaining agricultural sustainability. Diversifying cropping systems has many benefits ranging from improving environmental quality to increasing grain yields [8-9]. One important reason for having a diverse crop rotation is to control weeds, pests and diseases [9]. Also, increasing the diversity of cropping systems can improve nutrient use efficiency and reduce the needed fertilizer inputs to optimize grain yields [8-10]. Crops such as field pea and soybean (Glycine max L.) can fix nitrogen from the atmosphere and convert it into organic nitrogen in plant biomass, which can be mineralized into useable nitrogen for the following crop and reduce the inorganic nitrogen fertilizer needs [9]. Reducing the need for inorganic chemicals such as herbicides, pesticides and inorganic fertilizers in cropping systems benefits the environment by reducing the amount of chemicals applied that can become pollutants in ground and surface waters [11-13]. Additionally having more diverse cropping systems can be more resilient to changing climatic conditions such as droughts [11, 13]. In addition, more diverse cropping systems can have a higher water use efficiency [9,11]. Also, more diverse cropping systems can increase crop grain yields [10-13]. Additionally, having more diverse cropping systems provide multiple sources of income for agricultural producers. Also, increasing crop rotational diversity may improve soil health [13]

Comment: 3: Line number 64-65: “However, little is known about the effects of rotating oilseed crops with wheat and barley on soil physical properties.” – Sentence is not clear whether to diversify oilseeds crop or to diversify wheat/barley crop? The immediate next is telling different things. Objectives can be reframed with alignment with title and results presented.

Response: I change the sentences in lines 88-94 to this However, little is known about the effects of adding oilseed crops to wheat and barley cropping systems on soil physical properties. The objective of this study is to determine whether diversifying wheat or barley small grain cropping systems by adding field pea, camelina and canola improves soil dry and wet aggregate stability, bulk density, water retention, hydraulic conductivity and soil carbon concentration compared to continuous wheat or barley cropping systems on a loam textured soil.

Comment 4: Soil organic carbon estimation method is missing in materials and methods.

Response: I added this reference for method used to measure soil inorganic carbon concentration. Sherrod, L.A.; Dunn, G.; Peterson, G.A.; Kolberg, R.L. Inorganic carbon analysis by modified pressure-calcimeter method. Soil Sci. Soc. Amer. J. 2002. 66, 299-305. https://doi.org/10.2136/sssaj2002.2990

We only measured total carbon on these samples that we collected by dry combustion. I changed section 2.5 to this.

In figure 5 the y axis title was supposed to say soil carbon not soil organic carbon. I made this fix.   I added this on lines 221-231

Samples were then run on a LECO (LECO, St Joseph Michigan) total C/N analyzer using dry combustion at 1300°C to determine soil carbon concentration [35]. Previous sampling at this location in 2015 and 2021 found no carbonates in the 0-15 cm depth so total carbon concentration is primarily soil organic carbon [Chloe Turner, Personal Communication 2021 and 25]. Inorganic carbon was determined in these samples using the calcimeter method [36]. Organic carbon can be estimated by subtracting the inorganic carbon concentration from the total carbon concentration. The results presented as total carbon concentration in section 3.4 for the 0-7.5 and 7.5-15 cm depths is essentially the same as soil organic carbon concentration due to samples previously collected from these plots having no inorganic carbon in the 0-15 cm depth.

Comment 5: Line 79: make italic of scientific name.

Response: I changed the scientific name to Italics

Comment 6: Figure 1: Error bars for standard deviation in few bar graphs are larger size that indicates a larger variation in data among replications. Please check data and correct accordingly.

Response I included p value in text on line 253-254 for replication effect and in the updated table 2. I checked all the data in this manuscript to see if replication had an effect on the soil properties that I measured. I also added p value for replication interaction for soil carbon on line 353

Comment 7: Figure 2: Same comment as given for Fig.1.

Response I added on line 305-307 Replication did not affected fraction of water stable aggregates of any aggregate size or GMD and MWD of aggregates between 4.75- 8mm and greater than 8 mm (Appendix Table 2).

Comment 8: My major concern in discussion is that authors must highlight the previous studies on the effect of crop rotations on soil properties. There are many studies in this line. Accordingly, author should highlight previous studies and their agreements/disagreement with previous studies.

Response I added this to the discussion on lines 412-460 comparing our study to previous studies.

Our study agrees with other studies that found no differences in wet aggregate stability, bulk density, hydraulic conductivity and soil water retention when comparing different small grain cropping systems [18, 19, 25]. Chang and Lindwall [18] compared a continuous winter wheat to a winter wheat-fallow and a winter wheat- barley-fallow cropping system in Alberta after 8 years in a loam textured soil at depths between 0-120 cm. They found no differences in water retention, saturated hydraulic conductivity and bulk density, which agrees with our study. Also, Arshad et al., [19] measured soil organic carbon, wet aggregate stability, water infiltration and bulk density after 11 years comparing a continuous spring wheat to a spring wheat- spring wheat-canola, spring wheat- spring wheat- pea and spring wheat- spring wheat- fallow rotation in a silt loam in Alberta Canada. They also found that increasing the diversity of wheat cropping systems had no effect on these four soil properties. Hammel [25] measured bulk density after 10 years when comparing a winter wheat-spring pea to a winter wheat-spring barley-spring pea cropping system on a silt loam textured soil in Idaho, USA in the 0-60 cm depth and generally found no differences in bulk density between the two cropping systems. Pikul et al., [20] measured bulk density, dry aggregate stability and infiltration rate at 8 locations across the Great Plains region of USA and Canada. This study found infiltration was higher under winter wheat- fallow rotation than a winter wheat-corn (Zea mays L.)-millet (Cenchrus americanus L.) cropping system on a silt loam in Colorado, USA, and higher in a spring wheat-winter wheat-sunflower (Helianthus annuus L.) rotation than a spring wheat-fallow rotation in North Dakota, USA on a silt loam but no  differences at other locations [20]. Additionally, this study found no differences in bulk density between cropping systems at 3 of the locations but found a lower bulk density under a continuous winter wheat cropping system than a winter wheat-sorghum (Sorghum bicolor L.)-fallow rotation in Texas, USA on a silty clay textured soil, a lower bulk density in a spring wheat-winter wheat-sunflower rotation than a spring wheat-fallow rotation in a silt loam in North Dakota, USA, a lower bulk density in corn-soybean-sorghum-oat (Avena sativa L.)+ clover (Trifolium repens L.) than continuous corn in Nebraska, USA on a silty clay loam and a lower bulk density in a spring wheat-fallow than continuous spring wheat rotation in a loam textured soil in Montana, USA [20]. Also, this study found MWD of dry soil aggregates was not affected by cropping system at most of the locations but found higher MWD in a continuous spring wheat than a winter wheat-sorghum-fallow rotation in Texas, USA in a silty clay loam [20]. Although this study found some effects or cropping system diversity on soil properties that they measured, some of the studies found increasing cropping system diversity had improved soil physical properties the others found the opposite effects. Additionally, a study conducted in Ontario, Canada found that wet aggregate stability was higher in a soybean-winter wheat rotation than a continuous corn, soybean-corn and continuous soybean rotation but there was no differences water retention and soil organic matter in the 5 rotations that were compared in this study after 14 years in a clay loam soil [22]. This study was conducted in a climate with greater precipitation and had different crops than in our study. When comparing our study with other previously published studies in most of the cases diversifying wheat and barley cropping in the Great Plains region of the United States and Canada does not improve soil organic carbon, aggregate stability, hydraulic conductivity and water retention in a variety of soil textures and mean annual temperatures. In the minority of cases where there were differences there were differences cropping systems were different than our study [20]. However, our study compared how 10 different cropping systems affected soil physical properties at a location compared to 5 or less analyzed at a given location in these previous studies [18-25].

I also added this on lines 477-484

No-till can lead to better soil quality in these studies than conventional tillage [18,22, 46]. Van Eard et al [22] found wet aggregate stability and soil organic matter was higher in no tillage than conventional tillage in their cropping system study. Chang and Lindwall [18] found water retention was higher under no-till than conventional tillage at – 75, -500 and -1500 kPa water potentials and bulk density was less under no till near soil surface, but saturated hydraulic conductivity was not affected in 0-30 cm depth in their cropping system study. Also, Mahli et al.,[46] found no tillage reduced bulk density but increased the MWD of dry soil aggregates and saturated hydraulic conductivity in their cropping system study near the soil surface.

Comment 9: In conclusion, the best cropping should be highlighted in respects to different soil properties to have an idea of readers for designing cropping systems. 

Response I added this to the conclusion on lines 495-500

This finding is important because diversifying wheat or barley cropping systems by adding canola, camelina and field pea does not have negative effects on important indicators of soil physical quality. Our finding shows having more diverse cropping systems that can provide a more sustainable source of income and be better for environmental quality will not cause negative effects to soil physical properties and soil organic carbon concentration. 

I feel that the reviewer wants us to suggest growing one of the 4-year cropping systems. Our study and most of the previous studies have found diversifying wheat or barley cropping systems does not improve but does not harm soil carbon and physical properties. These findings are beneficial to producers in the NGP region showing that adding canola, camelina of field peas to cropping systems have previously continuous wheat or wheat-fallow will not negatively affect important soil quality indicators. Our study does not show that there is a best rotation for increasing soil carbon or improving soil physical properties. There are additional manuscripts that are going to be written from this study analyzing grain yields, water use and nitrogen use efficiency which may provide more insight into which of these rotations may be best for producers in the NGP.

Comments on the Quality of English Language

There are typological and grammatical errors in MS that need to be addressed before publications.

Response I fixed many typological and grammatical errors throughout the manuscript.

Reviewer 2 Report

Some articles missing in the abstract (a higher, the cropping), and further in the text. Make the paragraph uniform.

line 38, 40, 41 - important is mentioned three times in three consecutive sentences - find an adequate word, a synonym

Table 1 – “NH means not harvested” should be as a table footer (NH - not harvested)

line 147, 148, 151, 159, 160 - “-um” to μm

line 187 – “pF is the log base 10 of -water potential in cm” to base 10 logarithm of the water potential in centimeters of water

line 196 – “#40 sieve” make the markings uniform

line 238- “aggregates greater than 19 mm” – where is fraction >19mm in the table? Also, shorten the title.

In Table 1 line Fraction of Dry Soil Aggregates should be above fraction size, same for Appendix Table 1.

line 248 – “lowercase letters following numbers indicate statistical difference for Cropping System x Depth effect” – this is unclear, what is the depth effect in one soil layer? If there is no statistical significance it should be indicated in the table.

line 224-237 - what do the numbers in parentheses represent since they are not in Table 2?

line 263 – “Supplemental” to Appendix

Figure 3A and B – Please check the data for pF

line 324 –“ was” to were

line 325-326 – “Also, θs (r=-0.78 and P<0.0001) and α (r=-0.53 and 325 P<0.0001) parameters and Ks” – unclear

line 375 - can

line 389-393 – this is not the conclusion, delete

 Minor editing of the English language required

Author Response

Dear Reviewer,

We appreciate the time that you spent reviewing our manuscript and the comment that you provided. We have made changes to the manuscript based upon the comments that you provided. I hope that we have adequately addressed your concerns about this manuscript. We have included the response to your comments below.

Reviewer 2

Some articles missing in the abstract (a higher, the cropping), and further in the text. Make the paragraph uniform.

Response: I added the before cropping system on line 18 and 21. I added a on line 19.

line 38, 40, 41 - important is mentioned three times in three consecutive sentences - find an adequate word, a synonym

Response: I changed important to essential on line 57, and to meaningful on line 62

Table 1 – “NH means not harvested” should be as a table footer (NH - not harvested)

Response: I made this a Table footer

line 147, 148, 151, 159, 160 - “-um” to μm

Response: I made these changes

line 187 – “pF is the log base 10 of -water potential in cm” to base 10 logarithm of the water potential in centimeters of water

Response: I made this change on line 212

line 196 – “#40 sieve” make the markings uniform

Response I am unsure what the reviewer wants. I changed it to this to be consistent with earlier sections of the manuscript 0.425 mm sieve (No. 40) on line 221

line 238- “aggregates greater than 19 mm” – where is fraction >19mm in the table? Also, shorten the title.

Response I forgot to fix the table caption after combining soil aggregate sizes together. The caption on the table should read

Effect of cropping system on fraction size of dry soil aggregates greater than 8 mm (>8 mm), 4.75-8mm, 2-4.75 mm, 0.25-2mm and less than 0.25 mm (<0.25 mm), mean weight diameter of dry soil aggregates (MWD) and geometric mean diameter of dry soil aggregates (GMD) at the 0-7.5-cm and 7.5-15-cm soil depths.

In Table 1 line Fraction of Dry Soil Aggregates should be above fraction size, same for Appendix Table 1.

Response I added fraction size of dry soil and aggregates to Table 2. In appendix table 1 I measured fraction water stable aggregates. This is the fraction of aggregates of the four sizes used 0.25-2mm (0.25mm), 2mm-4.75mm (2mm) , 4.75mm- 8mm and >8mm (8mm). The aggregates were placed on top of a sieve and wetted then wet sieved for 10 minutes. The numbers are fraction of aggregates that were retained on top of sieves 0.25 mm and larger after wet sieving. The methods are described in section 2.3

line 248 – “lowercase letters following numbers indicate statistical difference for Cropping System x Depth effect” – this is unclear, what is the depth effect in one soil layer? If there is no statistical significance it should be indicated in the table.

Response I added the statistical interactions to Table 2. If there is a cropping system x depth effect it means that cropping system had a larger effect on the property in one depth than the other depth. It essentially undoes the cropping system or depth interaction. The was no differences in the fraction of aggregates <0.25 mm in the 7.5-15 cm depth between the 10 cropping systems. However, there were differences in the fraction of aggregates <0.25mm in the 0-7.5 cm depth. That is why there are letters after numbers for the 0-7.5 cm depth but not for the 7.5-15 cm depth for fraction of aggregates<0.25 mm. 

line 224-237 - what do the numbers in parentheses represent since they are not in Table 2?

Response: The values are averaged between the 0-7.5 and 7.5-15 cm depths. I added averaged between 0-7.5 and 7.5-15 cm depths after the fraction of the aggregate sizes in parenthesis. On lines 264-275

line 263 – “Supplemental” to Appendix

 Response: I made this change.

Figure 3A and B – Please check the data for pF

Repsonse The pF should be correct. pF can be between -2 and 0 if -cm of water potentials in data is between 0 and 1. The evaporation method measures water the water retention curve between water potentials of -0cm to about -600-800 cm when the tensiometers cavitate. That is from a pF range of approximately -2- 2.8. 

line 324 –“ was” to were

Response: I made this change

line 325-326 – “Also, θs (r=-0.78 and P<0.0001) and α (r=-0.53 and 325 P<0.0001) parameters and Ks” – unclear

Response: I changed the sentence to Additionally the soil hydraulic properties of Ks (r=-0.35 and p=0.0124) and van Genuchten α (r=-0.53 and P<0.0001) and θ_s (r=-0.78 and P<0.0001) were negatively correlated to soil bulk density. On lines 375-377

line 375 – can

Response: I made this change on line 476

line 389-393 – this is not the conclusion, delete

Response: I made this change on lines 501-504