Using Biochar in Coffee Agroforestry Management to Store Soil Carbon and Produce Biomass Energy in Puerto Rico

Abstract

Anthropogenic climate change is disrupting ecological and human systems worldwide, particularly across the tropics. A complete transformation of our energy and food systems is necessary. We must aggressively phase out fossil fuels and dramatically reduce the current levels of atmospheric CO2 to avoid disaster. The 2018 IPCC Report acknowledges that to stay under the 1.5 degrees of warming target, carbon dioxide removal (CDR) must be employed. Unfortunately, most proposed CDR projects center around expensive and energy-intensive industrial-chemical processes. Instead, we hope that this research can contribute to the growing amount of scholarly research of biological carbon sequestration through smallholding agricultural management and energy microgrids. The motivation behind this research is to understand the potential between coffee agroecosystems, smallholder farming, and climate change mitigation. Current research shows evidence that smallholder management of coffee agroecosystems is linked to increased biodiversity (Richard & Mendez, 2013; Perfecto et al., 2014; Goodall et al., 2015). However, the results are mixed for its potential for carbon sequestration and climate change mitigation (Schmitt-Harsh et al., 2012; Richard & Mendez, 2013; Goodall et al., 2015; Tumwebaze & Byakagaba, 2016). This study explores the sustainable management of coffee agroforests using biochar and biomass energy to store soil carbon and provide decentralized energy in rural and farming communities in Puerto Rico. This work is divided in two chapters. In Chapter 1, we examine the relationship between shade management in coffee agroforestry, and the availability of downed woody material (DWM), and its potential as feedstock for energy production. We estimate total biomass of DWM from sampling twenty coffee farms across a shade gradient in the central mountains of Puerto Rico using line transects. We then compare the average amount of DWM found in each farm and the amount of shade measured at two levels (at breast height and above the highest coffee bush). Using the data obtained in the field survey, we estimate the potential for electricity generation per year using DWM from coffee agroforests in Puerto Rico and the potential for reduction in carbon emissions from the production of biochar. In Chapter 2, we study a greenhouse experiment using biochar to understand its effects on plant growth of coffee (Coffea arabica). Using coffee seedlings grown in different mediums consisting of compost, soil, and biochar mixtures, we track height, number of leaves, and length of the longest leaf of each seedling for three consecutive months to understand the potential effect of biochar as a soil amendment. This study was the first part of a broader project with our local partner Casa Pueblo. This self-management organization owns a small coffee farm where the seedlings were transplanted for the next phase of this project.