Biomass and soil carbon stocks of Rhamnus prinoides based agroforestry practice with varied density in the drylands of Northern Ethiopia

Agroforestry plays a significant role in climate change mitigation through improved sequestration and storage of carbon in farmlands. However, quantitative information on above and belowground carbon inputs in agroforestry systems practiced is limited in the drylands is limited. This study estimated biomass and soil carbon stocks of Rhamnus prinoides based agroforestry practices in Ahferom and Ganta-Afeshum districts of Tigray region. Inventory was conducted on farms with R. prinoides intercropping of varied density. Destructive method was used to develop allometric models for estimating above and belowground biomass carbon. Undisturbed and composite soil samples were taken from farms with and without R. prinoides plants (open). The model based on diameter at stump height (r = 0.91) and height (r = 0.83) presented good fit (0.86 < R2 < 0.93, P < 0.01) with lower mean predicted error (MPE) values for estimating the aboveground (AGB) and belowground (BGB) biomass. Compared to existing models our model produced lower MPE (− 0.05) in predicting observed R. prinoides AGB. Overall, 8.3 Mg ha−1 and 5.5 Mg ha−1 carbon stocks were found in AGB and BGB, respectively. The carbon stock in AGB and BGB increased as tree density increases. Soil organic carbon (SOC) stock in farms with R. prinoides intercropping (121.9 ± 29 Mg ha−1) significantly increased as density increased, and it was significantly higher than nearby open farms (93.2 ± 25.6 Mg ha−1) (P < 0.05). SOC stock was not significantly decreasing from upper to lower soil depth in farm plots with R. prinoides of varied density. While significantly decreased in the open farms (P < 0.05). R. prinoides annual leaves harvest increased as tree density increased. While annual production of associated crop Wheat decreased. Farm plots with medium tree density and with large size were optimal for carbon accumulation, R. prinoides leaves and crop production. The higher amount of carbon stock in farms with R. prinoides agroforestry compared to open farms indicates the possibility of increasing carbon stock in farming systems through scaling up similar practices.