Effect of biochar and biodigester effluent on growth of maize in acid soils

Conclusions:
Biochar produced as a byproduct of the gasification of sun-dried, sugar cane bagasse (the cane stalks were passed two times through a 3-roll mill traditionally employed for making “panela”), contained 35% ash.
Application of the biochar (50 g/kg of soil) to a fertile soil (from a shaded coffee plantation) increased above ground biomass growth five-fold with no additional benefit from simultaneous application of biodigester effluent. When applied to a sub-soil, there was a synergistic effect of the biochar and the biodigester effluent; the biochar alone increased yield eight-fold but combined with biodigester effluent the increase was twenty-fold. Effects on the root biomass were similar.
The initial pH of both soils was in the range of 4.0-4.5 and was increased to 6.0-6.5 by addition of the biochar. Effluent application did not affect soil pH.
Application of ash from a wood-burning stove at 50g/kg soil also increased maize yield but to a level of only one third of that achieved with biochar. The increase in soil pH was double that observed with biochar reaching levels of between 9 and 10.