Biochar – a potential component of a new green revolution

Biochar is a product of biomass that is subjected to pyrolysis, which is the process of charring biomass under absence of oxygen. Adding biochar to degraded cropland soils in the African tropics has significant potential to enhance soil fertility and crop productivity. Biochar-based farming can also mitigate climate change, through soil carbon sequestration.

– In a study involving nine smallholder farms in eastern, central, and western Kenya, we examined the response of non-fertilised and fertilised maize monoculture to realistic dosages of biochar at sites differing in fertility status, says Thomas Kätterer, professor in ecosystem ecology at the Swedish University of Agricultural Sciences.

Study design and results

Commonly available biomass wastes in each agro-ecosystem were used as feedstock for biochar production in gasifier stoves on smallholder farms. The biochar was applied at 1, 5, and 10 tons/hectar at the start of the field experiments. Across seasons and fertiliser treatments, maize grain yield showed consistently positive responses over four growing seasons studied, with an average increase of 1.1, 2.6, and 4.1 tons/hectar, respectively, above the local control for the three biochar application rates. Grain yields in the unfertilized control were below 1 ton/hectar. Responses of maize grain yield to specific biochar doses were similar across seasons and farms, and uncorrelated to yield in control treatments. Here we show for the first time that yield gain per ton biochar added decreased with increasing application rate, indicating that it may be better to spread a given amount of biochar over a large area rather than concentrating it to a smaller area.

Biochar production for food security in a changing climate

Biochar production in gasifier stoves and its application to soil may be implemented as climate mitigation technology in many rural areas in the world similar to those investigated here in Kenya, which also would increase food security in a changing climate. For this potential to be realized, it is important to reach also the households with lower capacity for uptake of new technology. This requires careful planning and implementation of policy and projects supporting uptake of this technology.

However, before large-scale implementation of this practice, its benefits and drawbacks must be thoroughly evaluated in system analyses considering food security and economic, social and environmental dimensions. These analyses should also consider potential effects on the long-term sustainability of soil nutrient cycling.  

Publication

Kätterer, T., Roobroeck D., Kimutai G., Karltun E., Nyberg G., Sundberg C., Röing de Nowina K. 2022. Maize grain yield responses to realistic biochar application rates on smallholder farms in Kenya. Agronomy for Sustainable Development 42:63 https://doi.org/10.1007/s13593-022-00793-5

Funding

The work was supported by the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (FORMAS), through grant number 942-2015-1648.