Management of Residues from Fruit Tree Pruning: A Trade-Off between Soil Quality and Energy Use

Round 1

Reviewer 1 Report

Dear Authors,

In general, a very interesting article, an elegant approach to deal with the trade of between PtE and PtS. Below there are a number of minor suggestions and questions. In general, especially the introduction, the writing style is a bit over-complicated. Please keep it simple. The english language needs some improvement, a (native speaker) proof reader would help here.

In the intro, you might add something on the scale of the problem (how much pruning residues are available, where). Also, in ref. 41 it is shown, that considering the environmental aspects, PtE is better than PtS, provided the soil allows for it (and the allowing of the soil is actually what your article is about). If you would need an article for an example (rather than a project report):

DOI: 10.3390/en13112734

DOI: 10.3390/su11061604

Line 36-39.

Fruit production, climate change mitigation (by reducing GHG emissions, fossil fuel consump-tion and increasing carbon sequestration), soil nutrient recovery and cycling, improving water use efficiency and water regulation (run-off and erosion control), pest and disease biological control, pollination, and many others.

First of all, this is actually not a sentence. The fact, that fruit tree plantations reduce fossil fuel consumption, recover soil nutrients and other claims should be proven or linked to references.

Line 46-48. Mayby I am not into the theme, but it is unclear what is expressed here. 

Line 50: 'Soil ecosystem' lacks an article

Line 73-80: why pruning to soil cannot be considered as 'providing', as it provides an increase of soil quality?

Line 91-92: renewable energy is 'remarkable'? Please express this in a more scientific way.

Line 102: 'mineral nutrients are cycled' I think 'cycling' is not the proper wording. Returning to soil, recycling eventually or something thelike.

Line 124: 'significant impact on soil quality', perhaps change in 'significant negative impact on soil quality'

Line 163: the abbreviation SOC should be given in full

Line 196: insert white line

Line 198: article lacking before 'Carbon fraction'

Line 204-206: please refrase

Table 1: it would be a lot easier to make one column for each soil, with e.g.:

Sandy Soils

0-0.8

0.8-1.4

1.4-2

>2

Formula (1): what is the meaning of 'MIN [3;'

Formula (4): what is 'S'? Why the soil properties (K) have an influence on the slope inclination?

Figure 3 seems not to add too much to the article

Table 3: SOM iIntegrated strategy: maybe rather 'SOM integration strategy'?

Chapter 2 overall question: it seems that a programme is used for the analysis, however (as far as I see), it is nowhere mentioned what that is. Your own application, or something else? Maybe provide some screenshots...

Table 4: please explain why the mean value is lower than the minimum value

Figure 4 and table 6 are part of chapter 3.1, but located in 3.2. This does not enhance readibility. 

Table 6 is hardly explained, abbreviations are not provided.

Line 492-501: reference needed

Line 520-525: does regular mowing limit the water consumption of the green cover (e.g. grass)? A green cover consumes water, but also prevents evaporation. This is lacking in the discussion as well as a reference.

Line 563-567: It can be argued, that the energy substituted by Pruning-to-Energy is rather fossile energy. In practice, a coal or gas boiler will be replaced by a biomass boiler. Or biomass is used as a co-fuel replacing coal for electricity generation. It is unlikely that other renewable sources are shut down to open up a PtE plant. So, not the energy mix is replaced, but rather the worse components of it (e.g. coal, gas or oil). See also ref. 41

Line 568-577: only a few % of carbon in the PtS strategy is sequestered, wherease in PtE all carbon is used for energy production and therefore (partly) substitutes fossil emissions. At higher SOM scores the PtE strategy is anyway the better choice. In addition, the sequestration effect of PtS dimishes, so in my opinion, this does not effect the advise provided by your tool.

Reference 

General comment: consider the advising of a partial removal of prunings for the PtE in case of the scores between 1,5 and 2,5. E.g. only 50% removal, or every second year.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have posited a model to create a simple decision matrix for orchard producers to decide whether to divert prunings to bio-energy, or recycle through the orchard. The decision tree essentially uses SOM as the key soil health indicator to determine whether soils are 'healthy' enough to minimise the harm associated with non-residue return.  The model incorporates the main drivers of SOM accumulation, (texture and rainfall/temperature) and to a lesser extent slope.  Slope may not be the most ideal and only measure of erosion risk, as in orchards, cover, as indicated in their management options, may also usefully be included in that term.

The main weakness in the manuscript concerns the lack of comparison with other methods to determine soil 'health'.  The authors have done a rudimentary sensitivity analysis on their own model, but there is little to no interaction with others models that may exist to assess soil health.  Were they solving a problem that already had a solution? There is little way to determine that considering the absence of comparison with other models or assessments of soil health. 2-3 paragraphs that compare and contrast their modeled outcomes with other methods of determining soil 'health' should be considered.

It was clearly a conscious decision to have a quantitative free assessment of the decision tree as there were no indications of the magnitude of C lost/gained under any of their scenarios and how mineralisation of composted prunings is in turn affected, post-soil application, by the same factors used to assess SOM/soil 'health'. The authors could usefully direct readers to sources that have quantified some of these parameters, simply to acknowledge they are aware that it can, and perhaps should, be quantified.

Author Response

Please see the attachment

Author Response File: Author Response.pdf