"Global climate models enable the prediction of warming/cooling effects of albedo changes, but realistic scenarios can only be built on the basis of field-scale measurements," Lorenzo Genesio of the Institute of Biometeorology at Italy's National Research Council told environmentalresearchweb. "This is because the net biochar effect on surface albedo is the result of a complex biophysical interaction involving soil type and amendment effects on crop development."

Some estimates indicate that biochar could mitigate as much as 12% of current man-made carbon dioxide emissions. But there are still concerns regarding its long-term stability in soil, safety for human health and impact on radiative balance. Both charcoal production sites and burnt regions of savannah have shown lower albedo.

Genesio believes that new crop varieties that increase surface albedo could be combined with biochar applications "as a sort of 'thermostat' that we may use to adjust the local climate".

He and colleagues from FoxLab and Consorzio LaMMA treated a field near Pistoia in central Italy with a commercial horticultural charcoal pyrolysed from coppiced beech, hazel, oak and birch in the UK. The biochar was added by hand to 25 m2 plots of bare soil at a concentration of either 30 or 60 tonnes per hectare, and was then ploughed in to the top 10 cm of soil.

The wheat was sown in December 2009 and harvested in July 2010. The albedo of the treated plots decreased significantly before the crop emerged and during its initial growth, on average to about one-third of the value for the control plot. The concentration of biochar did not appear to affect the amount of albedo change. Later in the season all the plots exhibited similar reflectivities. But after harvest the albedo of the biochar-treated areas was again lower. The following year the biochar affected the reflectivity of the surface to a much lesser extent.

"We believe that this work has interesting implications in different disciplines: for climate modellers and geoengineers to produce realistic climate scenarios under different land-use change options, for agronomists to further study the impact of biochar on early crop development and for soil scientists to better understand the impact of biochar on soil respiration," said Genesio.

The team also used the Simultaneous Heat and Water model to simulate the changes in soil temperature that they measured. The model indicated that the biochar-treated plots were warmer than the control at a soil depth of 5 cm from January to March. From April the treated plots were cooler, indicating that the increased biomass above ground was boosting evapotranspiration. After harvest the soil in the treated plots was again warmer than the control.

"Our paper is just a first attempt to provide an experimental assessment of the changes in surface albedo deriving from biochar applications on a key crop for the Mediterranean environment and evaluating, at the microscale, the feedbacks on the radiative balance," said Genesio. "We hope we are paving the way to more profound and extensive studies and experimentation."

The team coordinates the EuroChar project, which aims to assess the impact of large-scale biochar agricultural application. One aspect of the work uses a sensitivity experiment that forces the albedo parameter in a regional climate model.

"But we want to go beyond that and eventually test the modelling results in a more realistic framework, where biochar applications and crops with higher albedo properties will be combined in different ways," said Genesio. "We hope that the new EU Programme 'Horizon 2020' will offer opportunities for that. Climate modellers, agronomists, plant scientists and micrometeorologists will have the chance to work together. The Call for Partnership is open..."