Changes in soil organic carbon and total nitrogen contents in three adjacent land use types in the Bale Mountains, south-eastern highlands of Ethiopia

Abstract

Improper cultivation practices are seriously and considerably degrading native forest ecosystems in the Bale Mountains of the south-eastern highlands of Ethiopia. This study investigated the effects of land use change on the contents of soil organic carbon (SOC) and total nitrogen in three adjacent land uses: native forest, cropland and grazing. A total of 108 soil samples (3 replications × 3 treatments × 4 profiles × 3 soil depth layers—0–0.2, 0.2–0.4 and 0.4–1.0 m) were collected for laboratory analyses. Results showed that organic carbon and total nitrogen contents of soils were significantly lower in cropland ( p < 0.001) compared to the contents in grazing and native forest. Conversion of a forest ecosystem into cropland during a 15-year period has significantly reduced the original amount of soil organic carbon and total nitrogen in the top 1 m soil layer by 30.9 and 32.1%, respectively. The findings suggested that conversion of native forest and the subsequent cultivation had resulted in a distinct decrease in the amount of SOC and total N of the surface soil due to the lower supply and return of organic matter to the soil system. Soil carbon content and total nitrogen can be protected and maintained through improving existing land use practices and proper cropland management.