6 June 2024

Here is how biochar promotes the sequestration of organic carbon

,

Biochar promotes the formation of soil aggregates and, with them, carbon sequestration, a research explains. In some Chinese farmland, the presence of the substance has increased by 60 per cent

di Matteo Cavallito

 

Biochar, an organic product widely used in agriculture as a soil amendment, can promote carbon sequestration by improving soil aggregation. This is supported by a study by a group of researchers from Shanxi Agricultural University in Taigu and South China Normal University in Guangzhou.

This soil amendant “has been widely applied in agricultural ecosystems to improve soil physicochemical properties,” the study explains.“However, the underlying mechanisms of soil organic carbon (SOC) sequestration by soil aggregation with biochar addition are not well understood at a large scale”.

Biochar

Biochar results from the thermochemical conversion of biomass through so-called slow pyrolysis. In short, when the material is heated at low temperatures, it decomposes and turns into the finished product. This product, in particular, is characterised by a higher carbon content and a lower oxygen and hydrogen content than the original material.

The substance, especially when integrated with the traditional composting process, can be used to increase soil fertility. But also, in certain cases, to reduce the presence of heavy metals in the soil.

Its use, in other words, helps reduce dependence on the use of fertilisers and synthetic chemicals in agriculture. In addition to the general improvement of soil characteristics. Its positive impact on carbon sequestration, on the other hand, is particularly linked to its ability to strengthen soil aggregation.

A meta-analysis of 45 previous studies

To verify this point, the authors conducted a meta-analysis by collecting 2,335 measurements from 45 studies. This made it possible to quantify the impact of the addition of the soil improver on the formation of aggregates in the soil, their stability and carbon concentration. Indeed: the use of the substance, the researchers explained, had clear and measurable positive consequences.

“Biochar addition markedly enhanced the proportions of macro-aggregates and aggregate stability,” the study states.

Moreover, “Biochar overall stimulated macro-aggregate proportions (14.1%–21.9%). Soil aggregate-associated organic carbon (OC) indicated a significantly increasement by biochar addition, which was attributed to direct and indirect inputs of OC from biochar and organic residues, respectively.”

Biochar increases carbon sequestration

The effects on aggregate concentration are reflected in increased sequestration. “Collectively, our synthetic analysis emphasized that biochar promoted the SOC sequestration by improving soil aggregation in agricultural ecosystems of China,” the authors explain. The amendant “generally increased OC content in aggregates by 5.2%–60.5%.”

Climate and atmospheric conditions, i.e. average annual temperature and rainfall frequency, specific characteristics of the substance used (such as the ratio of carbon to nitrogen content as well as pH), the practices used in adding the soil conditioner, and different agronomic conditions including soil, intensity of cultivation, fertilisation methods, and type of crop, would also affect the sequestration of the element.