[Terrapreta] Wardle: "indirect effects" of biochar most important?

[Laurens Rademakers]

Hello again,

Don't the Wardle et al findings bring us back to biochar's original potential and its quite specific geographical origin? Where was TP discovered? In soils with very low native SOM contents: the highly weathered, acidic, nutrient-poor soils of the Amazon. The soils investigated by Steiner, Lehmann and the others.

If you were to apply biochar in humus-rich soils, I can well imagine the "Wardle effect" to take place, and cancel out some of the carbon sequestration capacity of biochar (SOM decomposes and releases CO2, thus counteracting the C locked up in char). 

This is why I think the guys over at the Biochar Fund (to which I'm affiliated), might be on the more interesting track: they look at the many *indirect effects* of biochar, in very particular contexts (again: the nutrient-poor, acidic oxisols at the tropical forest frontier, where slash-and-burn agriculture is practised).

These indirect effects are of a social and economic nature. It is these indirect effects which help make biochar a true carbon sequestration concept:

-by making the poor tropical soils far more fertile, farmers can slow down deforestation: the C contained in the aboveground biomass of a tropical rainforest is large; avoiding the destruction of this stock is very important; biochar "indirectly" protects these C-stocks, by altering the slash-and-burn cycle.  In our own backyards here in Europe or the US, we don't have these large C-stocks that must be protected - no tropical rainforests over here.
-because of biochar's nutrient holding capacity, the use of mineral fertilizers becomes worthwile (without biochar, fertilizers would probably be too expensive to be applied onto these tropical soils); remember Steiner's findings: an 880% increase in crop yield when fertilizers were applied on plots of charchoal-amended soil, as compared with a non-amended but fertilized soil.
-as fertilizers are introduced in this scenario, biochar's N2O-offsetting potential becomes quite important too
-because of the use of highly optimized slow pyrolysis plants which yield both char and electricity, local communities can use their field-residues as a biomass feedstock for energy instead of wood. Field residues are currently not used to cook and heat, instead, these communities use wood, which they often gather by cutting down trees (again a C-stock that should be protected); or they use the ubiquitous diesel-genset, which means fossil fuels. So again, the use of the optimized pyrolyser results in an indirect CO2-offsetting effect: tree-cutting and/or the use of fossil fuels is avoided

In short, biochar/TP might not work elegantly as a carbon-sequestration method in soils with normal or high native SOM-contents. The concept might only work because of its multiple indirect socio-economic effects in the very particular context of the tropical forest frontier, where agricultural communities use slash-and-burn farming. 

I'm not sure. But I think the Wardle findings must be taken very seriously: just dumping char in our own backyards here in Europe or the US might not be a planet-saver.

What do you think?
Regards, 
Lorenzo/Laurens
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