Organic coating on biochar explains garden-greening power

Biochar fertilizers

Biochar, a carbon-rich, charcoal-like substance made from oxygen-deprived plant or other organic matter, has both delighted and puzzled scientists. As a soil additive, biochar can store carbon and reduce greenhouse gas emissions, and it can release nutrients to act as a non-toxic fertilizer.

But the precise chemistry by which biochar stores nutrients and promotes plant growth has remained a mystery.

Now, Colorado State University experts, has illuminated unprecedented detail and mechanistic understanding of biochar’s seemingly miraculous properties. The study demonstrated how composting of biochar creates a very thin organic coating that significantly improves the biochar’s fertilizing capabilities.

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

Biochar fertilizers

This improved understanding of biochar’s properties could trigger more widespread commercialization of biochar fertilizers. Such a change could reduce global dependence on inorganic nitrogen fertilizers that have served as modern food-production workhorses for more than a century.

Source: Colorado State University

To characterize a super-thin carbon coating on a carbon substrate is nearly impossible, Borch said. Our international team used many different advanced techniques to perform the analyses. Robert Young led our group’s contribution of ultra-high resolution mass spectrometry to investigate the coating and probe its elemental makeup.

The authors set out to investigate biochar before and after composting with mixed manure. Using a combination of microscopic and spectroscopic analyses, the researchers found that dissolved organic substances played a key role in the composting of biochar and created the thin organic coating.

This organic coating makes the difference between fresh and composted biochar. The coating improves the biochar’s properties of storing nutrients and forming further organic soil substances. The coating also developed when untreated biochar introduced into the soil only much more slowly.

Excessive use of mineral nitrogen fertilizers or liquid manure in agriculture has serious impacts on the environment. Such fertilizers cause the emission of nitrous oxide and result in nitrates leaching into the groundwater. As an eco-friendly alternative, scientists suggested adding biochar as a nutrient carrier into the soil. But, the use of biochar on a large scale has not viable economically because how it stores and releases nitrates.

Using biochar without adding nutrients or with pure mineral nutrients has proved to be far less successful in many experiments.

More information: [nature communications]