Analyzing the effectiveness of gasifier-produced biochar as a soil amendment in the humid tropics

Abstract

Biochar is the solid, carbonaceous byproduct from thermal treatment of biomass that is produced specifically for application to soils. Studies have shown that when biochar is added to soils it is able to increase yields, prevent erosion, and effectively store carbon for hundreds to thousands of years. Sizeable research has been conducted using biochar from traditional charcoal kilns as this is the method that maximizes biochar production. Biochar from gasification, however, has been relatively unexamined. The intent of this research, therefore, was to determine if gasifier-produced biochar would act as an effective soil amendment. The motivation behind this study was to create a valuable byproduct from gasification that would also allow the entire process to be considered “carbon-negative.” This investigation was designed to analyze the effectiveness of gasifier-produced biochar through a comparison with kiln-produced biochar. Two types of biomass – maize cobs and eucalyptus wood chunks – were used in the creation of biochar from a gasifier and traditional charcoal kiln. The biochar samples were combined with undisturbed soil from the Makerere University Agricultural Research Institute at Kabanyolo in a 45 day pot experiment to compare effects on plant growth. The experimental results show that, on average, soils amended with gasifier-produced biochar have higher yields than soils amended with kiln-produced biochar. The magnitude of this increase, however, was varied, and this variance was indicative of the sample‟s composition. Biochar composition varied across feedstocks, production methods, and even within samples from the same feedstock and production method. Results indicated that the characteristic with the greatest influence on soil productivity was the soluble ash content in the biochar. Soluble ash, when introduced to soils, helped to increase pH levels. Ugandan soils, like most soils in the humid tropics, are strongly acidic, and this increase in pH allowed for more favorable growing conditions and higher nutrient availability. This study indicates that gasifier-produced biochar has significant potential for use as a soil amendment in the humid tropics. However, further research