Evaluation and Mitigation of Greenhouse Gas Emissions from the Smallholder Coffee Supply Chain in Kenya

Abstract

Coffee is an important crop to the Kenyan export portfolio yet little information exists on the carbon footprints of the Kenyan coffee supply chains. This especially with regards to small holder coffee production which contributes 66% of the total coffee produced in Kenya. This study sought to assess how small holder coffee production systems in Kenya contribute to climate change and how this can be mitigated. The study was carried out in Kiambu County where a smallholder cooperative society was selected. The selected cooperative society had three primary coffee processing factories from which 108 smallholder farmers were selected using a two-way stratified random sampling approach. Stratification was based on farmer production level in kilogram of cherry per tree and the processing factory to which they delivered the cherry. The farmers’ yields were classified as 5kg/tree and above, 3-4.9 kg/tree and 0-2.9kg/tree for high, medium and low production levels, respectively. To quantify the GHG emissions, the Cool Farm Tool (CFT) was selected. Above ground carbon stock values for the selected coffee farms were computed using allometric models obtained from literature. The use of pumice and charcoal in mitigating greenhouse gases from the wastewater from coffee processing was as well investigated. The results of this study show that coffee product carbon footprints among small holder producers were dependent on the yield level and decreased with increase in production. The mean product carbon footprints obtained were 0.05kg CO2e/kg cherry, 0.27kg CO2e/kg cherry and 0.58 kg CO2e/kg cherry for high, medium and low producers respectively. ANOVA results showed that at 99% confidence level there were highly significant differences in product carbon footprints for the production levels (p<0.001; Fcalculated =19.35; Fcritical=3.09) and a highly significant difference in emissions per acre of land for the production levels (p<0.001; Fcalculated=4.702; Fcritical=3.09). The main source of emissions at farm level was fertiliser use which accounted for 94% of the overall farm footprint. At processing level, the main source of emissions was coffee processing wastewater which accounted for 93% of the total processing emissions at the factory. The carbon footprint at the primary processing stage ranged from 2.4 kg CO2e/kg parchment to 2.62 kgCO2e/kg parchment. Soil carbon formed the largest stock in the farms (15.28Mg/Ha), followed by shade tree biomass (9.32Mg/Ha) and finally coffee tree biomass (2.19Mg/Ha). Pumice and charcoal reduced the BOD levels in wastewater from coffee processing by 71.3 and 62.8% respectively.