Abstract: There is limited understanding of the effects of rice residue biochar, particularly when applied in combination with nitrogen (N) fertilizer on soil fertility, soil C sequestration and crop productivity. A one-year pot experiment was established to examine effects of rice residue biochar (0, 10, 20 and 40 t ha-1) and N (0, 60, 90, 120 and 150 kg N ha-1) in soils with contrasting texture (loamy sand and sandy clay loam) in a wheat(maize cropping sequence. Biochar was only applied once before sowing wheat. Biochar alone or in combination with N did not significantly increase wheat biomass in both soils, whereas biomass of maize (next crop) was significantly increased from the residual effect of biochar, alone or in combination with N fertilizer. In both soils, electrical conductivity (EC) and pH, oxidisable organic carbon (OC), microbial biomass carbon (MBC), dissolved organic carbon (DOC) and available nutrients (NPK) increased with increasing rates of biochar addition. However, addition of N with biochar (cf. biochar alone) did not change pH and oxidisable OC values but increased EC significantly. After one year, the soil organic carbon (SOC) stocks increased beyond the input of biochar-C, that is, by 0.1-2.1 t ha-1 and 1.8-4.8 t ha-1 in loamy sand and sandy clay loam, respectively, across all treatments. It may be concluded that the potential benefits of rice residue biochar to soil functions and crop production may encourage growers to minimise open field burning of straw, which is a common practice in the region.

O "biochar" tem potencial para dar uma importante contribuição para a mitigação das mudanças climáticas e para o aumento da produção vegetal. No entanto, para que o "biochar" possa atender a esta expectativa, a indústria e os organismos reguladores devem seguir alguns passos para gerenciar as potenciais ameaças ambientais e abordar as percepções negativas. As ameaças potenciais à sustentabilidade dos sistemas de "biochar", para cada estágio de seu ciclo de vida foram revisadas. Nós propomos que a estrutura da sustentabilidade para o "biochar" poderia ser adaptada de estruturas já existentes, desenvolvidas para a bioenergia. Políticas de uso sustentável da terra, combinadas com a regulação efetiva das instalações de produção do "biochar" e incentivos para a utilização eficiente de energia, além do conhecimento aperfeiçoado dos impactos do "biochar" na saúde e na produtividade do ecossistema, poderiam fornecer uma estrutura robusta para o desenvolvimento de uma indústria sustentável de "biochar". A certificação de sustentabilidade poderia ser introduzida, para proporcionar confiança aos consumidores de que práticas sustentáveis foram empregadas ao longo da cadeia de produção, particularmente onde o "biochar" é comercializado internacionalmente.

Biochar has the potential to make a major contribution to the mitigation of climate change, and enhancement of plant production. However, in order for biochar to fulfill this promise, the industry and regulating bodies must take steps to manage potential environmental threats and address negative perceptions. The potential threats to the sustainability of biochar systems, at each stage of the biochar life cycle, were reviewed. We propose that a sustainability framework for biochar could be adapted from existing frameworks developed for bioenergy. Sustainable land use policies, combined with effective regulation of biochar production facilities and incentives for efficient utilization of energy, and improved knowledge of biochar impacts on ecosystem health and productivity could provide a strong framework for the development of a robust sustainable biochar industry. Sustainability certification could be introduced to provide confidence to consumers that sustainable practices have been employed along the production chain, particularly where biochar is traded internationally.