Kiln biochar doesn't raise ph

I found this study to be interesting because it looks at areas where they made biochar decades ago and looked at the results. Quite positive!

John S
PDX OR

https://link.springer.com/article/10.1007/s42773-024-00378-3

Thanks for sharing this interesting study on long term charcoal sites. I've always suspected that ash content of the biochar was a bigger contributor for PH, since various methods of charcoal production result in different ash content. Overtime it makes sense leeching will still have an effect on biochar, despite a high cation exchange. But my immediate take away from this study is that biochar itself is not a complete substitute for organic matter created by plants. Also, sandy acidic soils is where we typically see bigger results of biochar as they mention themselves in the discussion.

'It should be noted, however, that the greatest positive effects of biochar are found in tropical soils poor in nutrients and organic carbon (Jeffery et al. 2017; Schmidt et al. 2021). In this case, instead, forest soils are particularly rich in organic carbon and the main nutrients, possibly masking biochar-positive effects. However, the use of both sterile and non-sterile soil suggests that the microbiome present in the kiln has a greater beneficial effect than that of external forest soil.'

The long term fungal and bacterial results are very positive too. Excellent read.

Yes, I always use biochar in conjunction with organic material in the soil.  They are symbiotic. They both improve drainage and moisture retention, allowing for much more biology in the soil.   Both seem to have been occurring naturally in many soils before industrialization kicked in.  Obviously, we don't want our houses and businesses to burn down, so we can't let those earlier fires go through our areas like before, even if it did improve the soil.

I don't go out and biochar the forest, either. I biochar my yard.  Suburban area.  Almost completely lawn.   The previous owners added nothing to the soil except pesticides and synthetic fertilizers. Then they covered a lot of it with 6 inches of gravel, and then finally black plastic.  It was not good soil at all.  I have really improved the quality of the soil through both biochar and organic material over the years.  Of course, I removed the black plastic and redistributed the gravel.  

John S
PDX OR

I had a look at the abstract, and sentence one is: "Charcoal kilns, old structures used for charcoal production in the forest, preserve a charcoal-enriched topsoil representing a suitable proxy for studying the long-term effect of biochar addition to soil."

My 2c: I am not sure these broad assumptions are worth a bucket of warm piss. These sites were businesses producing charcoal for fuel. Not fully cooked biochar. The best stuff was carted away and sold. Lots of uncooked odds and ends were cast aside, ready to be oxidized or broken down by decomposers. I think if you start with bad assumptions your conclusions may be up for debate. /grumpy

Doesn't it sound like the original terra preta, though, Douglas?  They weren't probably originally trying to make soil amendments in the Brazilian rainforest.  Charcoal and other stuff left for a long time, gradually becoming part of the soil and staying there.  Improving the fertility of the soil?

John S
PDX OR

Fair enough, John. I will give this study another look tomorrow with fresh eyes and an open mind.

I would bet that the plants growing in the biochar enriched soils are going to have symbiotic feedback loops with the microbes to steer the ph in their rhizosphere toward their preferred range. If they could not coevolve with the soil micro biome, due to ph being too extreme for them or otherwise, those plants were replaced with those that out competed them, whether in the wild or weeds in agriculture fields. In forests, feedback loops of rainfall and resulting acidity suitable for trees likely was facilitated by the biochar microbes, even if the char itself was alkaline.