This is obviously a very important contribution, simply by bringing up the issue of modelling the impact of biochar on C-stocks. The main goal was to evaluate the C sequestration potential of using biochar from the pyrolysis of sugarcane trash and bagasse compared to their current use of these feedstocks (bagasse is used for CHP and trash is mostly left in the field). Additionally, different intensities of positive priming of biochar on native SOC decomposition is investigated.
I would add the following notes about the publication:
(1) While the baseline scenario is accurate (although I guess much less than 30% of sugarcane trash is currently used for CHP), there are some issues with the other ones, which do not reflect management practice in the sugarcane industry of the state São Paulo (and I don’t believe they will change much upon a possible adoption of biochar):
a. Mills use bagasse for process heat and energy generation – the excess of which is sold to the grid in most cases.
b. Bagasse is not an ideal pyrolysis feedstock because of its large moisture content (about 50%) a consequence of the sugar extraction procedure.
c. No bagasse is or will be brought back to the field because of cost issues (scenarios 2 and 3).
(2) Negative priming of biochar on the decomposition of native SOC is also reported in the literature – it would have been interesting to see such a simulation or at least a note why it was not considered.
(3) The authors statements "We have not allowed for possible increases in sugarcane yield over time with biochar incorporation” because “… the management of sugarcane plantations in São Paulo is such that yields are already apparently optimized and there is little room left for improvement. According to the IBGE (Instituto Brasileiro de Geografia e Estatística), yields stabilized around 2007.” are wrong – sugarcane crop management is far from optimized yields:
a. Sugarcane is one of the crops with the largest gap between potential (> 350 t/ha) and realized yields (averages somewhere between 75 and 85t/ha/crop). Dias and Sentelhas, 2018 (https://www.sciencedirect.com/science/article/abs/pii/S0048969718316498?via%3Dihub).
b. The yield plateau identified in the IBGE data has various explanations:
i. The commodity boom (starting somewhen around 2005) triggered the expansion of sugarcane to new areas which showed rather poor yields – it took the sugarcane wills quite a time to get used to these new areas.
ii. Around 2010 burning sugarcane fields before harvest started to be phased out why two important consequence: substitution of manual by mechanical harvest. Existing varieties were not adapted to this changing management – sugarcane harvesters are heavy machines increasing the problem of soil compaction. Additionally, the mechanical stress of the machine damages the sugarcane clumps and negatively impacts the ratoon yields.
iii. Over the last years there were repeatedly seasons with below average rainfall – you will see in the Dias and Sentelhas (2018) publication that water supply is the main yield limiting factor in sugarcane crops (irrigation is not common in the state São Paulo).
c. I guess there is plenty of scope to increase sugarcane yield and I am quite confident biochar can give its contribution.
Here I am adding comments and links to data about biochar effects on sugarcane yield:
(1) I am looking forward to have details beyond those shown in the Isabel Lima’s presentation at the USBI conference 2019 - the biochar effects on sugarcane yields reported there are quite impressive – according to slide 24 the best treatment increased sugar yield by 12’480 kg over the four years of the experiment compared to the control – this is more than one extra crop. And this effect was achieved with only 800 kg biochar/ha. Such a yield increase will make biochar highly profitable.
(2) The other publication by Isabel Lima mentioned by Ron is not very realistic for practical applications:
a. This was a pot experiment with rather small pots for a plant like sugarcane.
b. Biochar application rates were way to large – there will not be sufficient feedstock to produce such large amounts of biochar.
(3) Here is a list of additional publications about biochar effects on sugarcane yield (or growth) I am aware of:
g. https://doi.org/10.1071/SR10011 [There is an issue with the figures in this publication.
About reasons why sugarcane is little studied:
(1) Sugarcane is a perennial crop – does not fit well into the academic life cycle.
(2) Brazil is the most important sugarcane producer worldwide – research is not a primary concern of our governments and companies are not used to do research on their own.
Hope this helps.
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