Although crop residues constitute an enormous resource, actual residue management practices in ricebased
systems have various negative side effects and contribute to global warming. The concept of a
combined bioenergy/biochar system could tackle these problems in a new way. Rice residues would be
used for energy production, thereby reducing field burning and the use of fossil fuels, and the biochar byproduct
could help to improve soils, avoid methane emissions, and sequester carbon in soils. To examine
some of these promises,weconducted field experiments from 2005 to 2008 in three different rice production
systems. Objectives were to study the effect of biochar from rice husks on soil characteristics, assess
the stability of carbonized rice residues in these different systems, and evaluate the agronomic effect of
biochar applications. The results showed that application of untreated and carbonized rice husks (RH and
CRH) increased total organic carbon, total soil N, the C/N ratio, and available P and K. Not significant or
small effects were observed for soil reaction, exchangeable Ca, Mg, Na, and the CEC. On a fertile soil, the
high C/N ratio of CRH seemed to have limited N availability, thereby slightly reducing grain yields in the
first three seasons after application. On a poor soil, where the crop also suffered from water stress, soil
chemical and physical improvements increased yields by 16–35%. Together with a parallel study including
methane and CO2 emission measurements at one site, the results strongly suggest that CRH is very
stable in various rice soils and systems, possibly for thousands of years. However, the study also showed
that CRH was very mobile in some soils. Especially in poor sandy soil, about half of the applied carbon
seemed to have moved below 0.30min the soil profile within 4 years after application.Weconcluded that
biochar from rice residues can be beneficial in rice-based systems but that actual effects on soil fertility,
grain yield, and soil organic carbon will depend on site-specific conditions. Long-term studies on biochar
in field trials seem essential to better understand biochar effects and to investigate its behavior in soils.
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