Soil organic carbon losses following conversion of natural forests into agriculture: Insights from Eritrea

Conversion of natural forests into conventional agricultural lands may lead to significant soil organic carbon losses. Soil organic carbon stock assessment for such land use changes is very crucial for appropriate land use management, soil fertility improvement, ecosystem restoration and climate-change mitigation measures. However, information on the status of soil organic carbon stocks for such land use types is limited in Eritrea and in the Horn of Africa. Thus, the study aimed to assess soil organic carbon stocks for natural forests, continuous cropping, shifting cultivation, and grazing land use types. Fifty-one surface soil samples were collected from these four types of land use around Adi Hakin, Laelay Gash, Eritrea, and analysed. One-way analysis of variance (ANOVA) test results showed that land use changes had highly significant effect on soil organic carbon stock (p < 0.001). The natural forest and continuous cropping land use types recorded the highest (51.69 Mg·ha-1) and lowest (21.23 Mg·ha-1) mean soil organic carbon stocks, respectively. Grazing and shifting cultivation had 22.74 and 23.57 Mg·ha-1 soil organic carbon stocks, respectively. Conversion of natural forest into continuous cropping, grazing, and shifting cultivation in the study area in the long run resulted in losing 58.93, 56.00 and 54.40% of soil organic carbon stocks, and emitting 111.79, 106.25 and 103.20 Mg·CO2 ha-1, respectively, to the atmosphere. Thus, the study concludes that conventional agriculture contributes to the atmospheric CO2 concentration through soil carbon emission. On the contrary, conservation of natural forests is crucial for soil carbon sequestration and atmospheric CO2 mitigation endeavors.