Abstract:

Biochar (pyrogenic organic matter) has emerged as an innovative way to improve soil fertility, increase soil carbon sequestration and reduce emission of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from agricultural soils. However, several questions remain as to the mechanisms responsible for the biochar effect and whether practical benefits for farmers are achievable under field conditions on low-fertility tropical soils. This study aimed at improving understanding of two broad questions: 1) By what mechanisms does biochar affect emission of GHG? 2) Canbiochar contribute practical benefits for farmers on low-fertility tropical agricultural soils? The specific research questions addressed in this thesis include; (i) To what extent does biochar quality (feedstock, production temperature, and biochar pretreatment) affect fluxes of CO2, N2O and CH4? (ii) How does biochar quantity affect nitrogen
transformation pathways and hence nitrous oxide emission in contrasting tropical agricultural soils? (iii) Since fluxes of GHGs are known to respond to physical properties such as aeration, is there a linkage between biochar and soil physical properties such as aggregation? (iv) By how much biochar application to soil contributes to low-emission agriculture in tropical environments? and (v) How long does the residual effect of biochar last in the soil under field conditions.