Soil organic carbon and associated soil properties in Enset (Ensete ventricosum Welw. Cheesman)-based homegardens in Ethiopia

Abstract

Enset (Ensete ventricosum Welw. Cheesman)-based homegardens have long been practiced as central elements of agricultural land management and food security in south and southwest Ethiopia. In contrast to the homegardens’ biodiversity and role in food security, soil quality has received little attention. Objective of this study was to assess soil quality parameters in typical homegardens in comparison with adjacent croplands, both under continuous management for >30 years. The study was undertaken at high (2200–2330 masl), mid (1799–1849 masl), and low (1349–1381 masl) elevation in the central Omo-Gibe basin, southwest Ethiopia. Through interviews of 49 randomly selected farm households, and soil sampling at six paired sites at high and mid elevations, and five paired sites of low elevation, we found that homegardens received the majority of household waste and manure and were less frequently tilled. By contrast, some, but not all, croplands occasionally received inorganic fertilizer. Homegarden soil had significantly greater (P < 0.05) soil organic carbon (SOC) concentrations than croplands. At 0–20 cm depth, SOC concentrations in homegardens (22.4–26.4 mg g−1 soil) were twice as high as in croplands (11.5–12.7 mg g-1 soil). Most likely the lower content of SOC in cropland was due to the limited input of organic matter and intensive tillage. The top 60 cm of homegarden soils stored 21–32 Mg ha-1 more SOC than adjacent croplands. Homegardens at high elevation had a significantly greater SOC stock (P < 0.05) than at low elevation. Hot water extractable (labile) organic carbon levels at 0–20 cm in homegardens (540–649 μg g-1 soil) were three to five times greater than in croplands (106–207 μg g-1 soil) and was strongly correlated with the SOC concentration (R2 = 0.85, in homegardens). The fraction of water-stable macro-aggregates (>0.5 mm) was positively correlated with the SOC concentration and significantly greater in homegardens than in cropland. Our results show that traditional homegardens represent a sustainable form of land management and cropping system, enhancing SOC concentration, soil structure and fertility.