Biochar crop boost "found only in the tropics"

A new international study has cast doubt on biochar's ability to boost crop yields in temperate areas.

Image: Oregon Department of Forestry (CC BY 2.0)
Image: Oregon Department of Forestry (CC BY 2.0)

The research, by Dr Simon Jeffery of Harper Adams University along with colleagues in the Netherlands, Portugal, the USA and Canada, analysed data from more than a thousand trials conducted around the world, each measuring the effect of biochar on crop yield.

This found that biochar only improves crop growth in the tropics, with no yield benefit at all in the temperate zone.

"Location, location, location: it really matters for biochar," said Jeffery. "Biochar had a huge benefit in the tropics - a 25% increase in yield. But in the temperate zone, there was just no effect at all. We were really surprised."

The idea of biochar was inspired by the terra preta – Portuguese for "black earth" – a soil rich in black carbon, the partially burned remains of old plants, which is more fertile, and with a more favourable pH, than typical tropical soils.

"Our study was the first to test whether geography matters, and we were able to do this because of the very large dataset we assembled," said Professor Jan Willem van Groenigen of Wageningen University & Research.

"Our findings confirm that biochar can benefit farms in low-nutrient, acidic soils such as in the tropics, but in more fertile soils, such as those in the temperate zone, obtaining yield increases through biochar application is much less certain."

The study, published in Environmental Research Letters, did not evaluate other potential benefits from biochar such as managing waste or locking up carbon in the soil.


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