Soil carbon to go: Agroforestry practices including coffee sequester the highest amounts of soil C in mountainous Southern Ethiopia

Abstract

Agroforestry (AF) systems are considered more sustainable than conventional agriculture because high production and cover enhance carbon sequestration and water and nutrient retention. However, above- and below-ground carbon stocks in different traditional agroforestry systems and in relation to adjacent land use types remain poorly understood, especially in East Africa. This study evaluates the carbon sequestration potential of three agroforestry systems—coffee, enset, and khat—in the Sidama region of southern Ethiopia compared to cropland and eucalyptus woodlots. Ten plots per land use type were selected, and carbon stocks were assessed by estimating woody biomass using allometric equations, and soil organic carbon (SOC) stocks by soil sampling to 60 cm depth. AF systems store significantly higher SOC than cropland and partially woodlots, with coffee-based AF systems sequestering the most carbon. In AF practices, approximately 79% of total carbon stocks were found in the soil, while woody biomass accounted for the remaining 21%. The study highlights a decreasing trend in total carbon stocks from AF-Coffee to cropland, with similar values in woodlots compared to AF practices. The higher SOC levels in these agroforestry plots are attributed to greater plant species diversity and minimal soil disturbance. Our results indicate that AF systems, particularly those based on coffee and enset, are key to enhancing soil carbon storage and promoting sustainable land use practices across the region. The study provides important insights into carbon mapping and climate change mitigation strategies.