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Unprecedented insight into ‘miraculous’ biochar

This is a field experiment in Switzerland, with setup of compost windrows from mixed manure before adding the biochar. Credit: Nikolas Hagemann/University of Tübingen
This is a field experiment in Switzerland, with setup of compost windrows from mixed manure before adding the biochar. Credit: Nikolas Hagemann/University of Tübingen

An international team has looked into what it labels ‘the miraculous properties of biochar’, revealing that the charcoal-like substance’s carbon coating explains its carbon storage and fertilising capabilities.

The team’s unprecedented insights could help boost more widespread commercialisation of biochar fertilisers. This would in turn reduce global dependence on inorganic nitrogen fertilisers.

Made from oxygen-deprived plant or other organic matter, biochar stores nutrients and promotes plant growth, acting as a non-toxic fertiliser. In addition, it can store carbon, contributing to reductions in greenhouse gas emissions.

Led by the University of Tuebingen in Germany, and involving researchers from the US Colorado State University, the new research published in the journal Nature Communications has provided a mechanistic understanding of biochar’s properties. The research revealed how the composting of biochar creates a very thin organic coating that significantly improves biochar’s fertilising capabilities.

Advanced analytical techniques confirmed that the coating strengthens the biochar’s interactions with water its ability to store soil nitrates and other nutrients.

"This organic coating makes the difference between fresh and composted biochar," said Andreas Kappler, leader of the study from the University of Tuebingen. "The coating improves the biochar's properties of storing nutrients and forming further organic soil substances."

According to Hagemann, the coating also developed when untreated biochar was introduced into soil, but much more slowly. Composting experiments were carried out on a small commercial scale at the Ithaka Institute in Switzerland.

Mineral nitrogen fertilisers and liquid manure have an adverse impact on the environment, causing the emission of nitrous oxide and resulting in nitrates leaching into the groundwater. Adding biochar as a nutrient carrier in the soil has long been heralded as an eco-friendly alternative, however its use on a large scale has been restricted because little was known about how it stores and releases nitrates.

"In agricultural crop production, higher yields usually only occur when biochar is applied together with nutrients from non-charred biomass such as liquid manure," Hagemann said. "Using biochar without adding nutrients or with pure mineral nutrients has proved to be far less successful in many experiments."

This is a field experiment in Switzerland, with setup of compost windrows from mixed manure before adding the biochar. Credit: Nikolas Hagemann/University of Tübingen