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Biochar reduces nitrous oxide emissions on farms

Bio-char, a type of vegetal coal, can reduce emissions of nitrous oxide, a greenhouse gas, and also the need for fertilizers. Scientists at the CSIC study their use and have demonstrated their benefits.

Nitrous oxide is a greenhouse gas mainly produced on agricultural soil. Compared to the emissions of CO2, the nitrous oxide emissions are small. Nevertheless, it has 300 times more warming potential than carbon dioxide and it has a lifetime of 114 years.

But nitrous oxide is generated by a natural process, the denitrification, caused by bacteria which transform nitrates from the soil. So, it has always been there. Then, why is it a problem? The reason is its growing tendency: year after year, more fertilizers are applied to larger fields which has increased the amount of nitrates in the soil and, therefore, the nitrous oxide emissions.

Scientists have recently started to study the use of vegetal carbon or (biochar) on agricultural land as a tool to reduce the nitrous oxide emissions. Although some preliminary studies have been successful, it is still a mystery why and how biochar reduces the nitrous oxide emissions.

Mari Luz Cayuela, Miguel Angel Sánchez-Monedero and Asunción Roig, CSIC scientists at the Centro de Edafologia y Biología Aplicada del Segura (CEBAS) are investigating the use of biochar. They have evaluated the application of biochar on 15 types of soils with different characteristics and from different places in Spain, the US and Brasil. The results, published recently, shown that biochar can minimize the nitrous oxide emissions by about 55% on average (reductions from 10% to 90%, depending on the soil).

Biochar can minimize the nitrous oxide emissions by about 55% on average (reductions from 10% to 90%, depending on the soil)

CSIC scientist Mari Luz Cayuela, main author of the work, explains that the study offers a scientific basis. “We have seen that biochar facilitates the transformation of  nitrous oxide into molecular nitrogen (N2), which is the form nitrogen is usually found in the atmosphere and it is not a warming gas.

The study, developed together with Cornell University shows that a small quantity of biochar added to the agricultural land (at a ratio of 2%) is enough to consistently mitigate the nitrous oxide emissions.

Good for the air and for the plants

Besides, in 10 out of the 15 soils analyzed, not only nitrous oxide emissions are reduced but also the total loss of nitrogen by denitrification, which  means that more nitrogen remains in the soil available for the plants and that there is less need for fertilizers.

As a next step, says scientist Mari Luz Cayuela, we are going to study if biochar can reduce warming emissions in other biotechnological processes in the treatment of organic waste and waste waters.

The study"Biochar and denitrification in soils: when, how much and why does biochar reduce N2O emissions?" is also co-authored by Johannes Lehmann, professor of soil science at Cornell University, and Cornell technicians Kelly Hanley and Akio Enders. It has been published in Scientific Reports (Nature press) and has been funded by the Organisation for Economic Co-operation and Development and the European Union Marie Curie Fellowship.

CSIC scientists at the Centro de Edafologia y Biología Aplicada del Segura are also involved on the European Project Fertiplus, aimed at finding out strategies to transform organic waste into all kinds of fertilizers to improve the agricultural soil.

"Biochar and denitrification in soils: when, how much and why does biochar reduce N2O emissions?". Scientific Reports | 3 : 1732 | DOI: 10.1038/srep01732

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