Application of biochar to the soil has been shown to increase soil fertility and to decrease greenhouse gas emissions from the soil while also sequestering carbon. But what are the mechanisms behind such observed effects and how do they influence soil properties? Research undertaken in the soil physics lab aims to provide robust explanations that can help to maximise the benefits of biochar application to soil while minimising the potential risks.
What is Biochar?
Biochar is a charcoal like substance which is produced by heating organic “feedstocks” to temperatures in excess of 350°C in an oxygen free environment. This process is called pyrolysis. Biochar differs from charcoal in that it can be produced from a wide range of feedstocks including crop residues, manure and biosolids, as well as wood, which is the usual feedstock for charcoal production. It also differs from charcoal in its means of utilisation; biochar is produced with the specific aim of application to soil, while charcoal is mainly used as a source of fuel.
What makes Biochar useful?
Interest in biochar has been increasing in recent years due to its potential to sequester carbon in soils, thereby helping to mitigate climate change. When organic materials are pyrolysed, the carbon within the resulting biochar is much more recalcitrant (i.e. harder to decompose) than the carbon in the original feedstock. This means that when applied to soil, the carbon in biochar can remain locked up there for centuries to millennia. For comparison, organic matter that is applied to soil decomposes in years to decades at most, meaning the carbon is relatively quickly returned to the atmosphere in the form of carbon dioxide (CO2). Further to this, biochar has been shown to generally increase crop yields, particularly in highly weather, nutrient poor, tropical soils. It has also been shown to reduce fertilizer leaching and to reduce nitrous oxide (N2O) emissions from soils (an important greenhouse gas).
Understanding the Biochar-Soil mechanisms
Understanding the mechanisms behind observed effects following biochar application to soil will allow robust predictions to be made concerning the application of biochar to soils in novel areas. Such information is also necessary to allow the effective guidance of policy which will allow the potential benefits of biochar to be maximised, while the risks such as contamination, effects on soil erosion and potential priming of soil organic matter to all be minimised. Through use of the facilities in the soil physics lab of Wageningen University and Research Centre we are able to peer into the “black box” of the soil to help us understand the interactions between biochar and the soil and its effects on soil processes and functions. All results are now in and analysis is underway. The first publication is hoped for the first quarter of 2015; watch this space!
Simon Jeffery, Diego Abalos, Marija Prodana, Ana Catarina Bastos, Jan Willem van Groenigen, Bruce A Hungate and Frank Verheijen, 2017. Biochar boosts tropical but not temperate crop yields. Newport, Harper Adams University, Environ. Res. Lett. 12 (2017) 053001
Jeffery, S., M.B.J. Meinders, C.R. Stoof. M. Bezemer, T.F.J. van de Voorde, L. Mommer, J. van Groenigen, 2015. Biochar application does not improve the soil hydrological function of a sandy soil. Wageningen, Wageningen University, Geoderma 251–252: 47–54
Lehman J and Joseph S, 2009. Biochar for Environmental Management: Science and Technology. Earthscan Publishers Ltd (ISBN 978-1-84407-658-1)
Verheijen, F. G. A., Jeffery, S., Bastos, A. C. ., van der Velde, M,. and Diafas, I., 2010. ‘Biochar Application to Soils - A Critical Scientific Review of Effects on Soil Properties, Processes and Functions’,. EUR 24099 EN, Office for the Official Publications of the European Communities, Luxembourg.