Abstract

The purpose of this study was to evaluate how different soil amendments, such as biochar, compost, a combination of biochar and compost mix, and inorganic fertilizer, affect crop productivity, soil health, and carbon dioxide (CO2) emission in the cobbly clay soils of northern Guam. The soil under the study had an average total carbon (TC) range of 8% to 12% and a total nitrogen (TN) range of 0.3% to 0.7% throughout each cropping season. The compost-only and compost/biochar mix plots had the highest carbon (C) levels, with biochar-treated plots surpassing both the fertilizer and control treatments. Despite the lower nitrogen levels in compost and compost/biochar mix during soil testing, both produced similar crops during most of the cropping season, comparable to the plots treated with fertilizers. The fertilizer-treated plots however had lower yields during the wet season, likely due to the lack of soil organic matter (SOM) or the leaching caused by intense rainfall. During the dry season, the compost/biochar mix had significantly lower CO2 emissions compared to compost-only plots. However, during the wet season, the emissions of CO2 were similar in compost/biochar mix as well as the compost only. Furthermore, compost and compost/biochar mix treatments had the highest response in basal (biological) soil response (BSR) as tested.

Keywords: Biochar, Carbon sequestration, Soil fertility, Climate resilience, Carbon dioxide.