Soil–landscape relationships in the basalt-dominated highlands of Tigray,Ethiopia

Though knowledge about the distribution and properties of soils is a key issue to support sustainable land management, existing knowledge of the soils in Tigray (Northern Ethiopian Highlands) is limited to either maps with a small scale or with a small scope. The goal of this study is to establish a model that explains the spatial soil variability found in the May-Leiba catchment, and to open the scope for extrapolating this information to the surrounding basalt-dominated uplands. A semi-detailed (scale: 1/40 000) soil survey was conducted in the catchment. Profile pits were described and subjected to physico-chemical analysis, and augerings were conducted. This information was combined with information from aerial photographs and geological and geomorphologic observations. The main driving factors that define the variability in soil types found were: 1) geology, through soil parent material and the occurrence of harder layers, often acting as aquitards or aquicludes; 2) different types of mass movements that occupy large areas of the catchment; and 3) severe human-induced soil erosion and deposition. These factors lead to “red-black” Skeletic Cambisol–Pellic Vertisol catenas on basalt and Calcaric Regosol–Colluvic Calcaric Cambisols–Calcaric Vertisol catenas on limestone. The driving factors can be derived from aerial photographs. This creates the possibility to extrapolate information and predict the soil distribution in nearby regions with a comparable geology. A model was elaborated, which enables the user to predict soil types, using topography, geomorphology, geology and soil colours, all of which can be derived from aerial photographs. This derived model was later applied to other catchments and validated in the field.     

Vegetation cover density and disturbance affected arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest,northern Ethiopia

Arbuscular mycorrhiza fungi(AMF) are vital in the regeneration of vegetation in disturbed ecosystems due to their numerous ecological advantages and therefore are good indicators of soil and ecosystem health at large. This study was aimed at determining how the seasonal, vegetation cover density, edaphic and anthropogenic factors affect AMF root colonization(RC) and spore density(SD)in Desa'a dry Afromontane forest. AMF RC and SD in the rhizosphere of five dominant woody species, Juniperus procera, Olea europaea, Maytenus arbutifolia, Carissa spinarum and Dodonaea angustifolia growing in Desa'a forest were studied during the rainy and the dry seasons in three permanent study vegetation cover density plots(dense, medium, and poor). Each plot(160 x40 m~2) has two management practices(fenced and unfenced plots) of area. A 100 g sample of rhizosphere soil from moisturefree composite soil was used to determine spore density.Spore density ranged from 50 to 4467 spores/100 g soil,and all species were colonized by AMF within a range of 4–95%. Glomus was the dominant genus in the rhizosphere of all species. Vegetation cover density strongly affected SD and RC. The SD was significantly higher(p 0.05) in the poor vegetation cover density than in the other two and lowest in the dense cover; root colonization showed the reverse trend. Management practices significantly(p 0.05) influenced AMF SD and RC, with the fenced plots being more favoured. Seasons significantly(p 0.05) affected RC and SD. More RC and SD were observed in the wet period than the dry period. Correlating AMF SD and RC with soil physical and chemical properties showed no significant difference(p 0.05) except for total nitrogen. Disturbance, vegetation cover density, season and total nitrogen are significant factors that control the dynamics and management interventions to maintain the forest health of dry Afromontane forests.     

Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

Purpose  

The Ethiopian highlands are a fragile environment characterized by steep slopes, intense rainfall, a sparse vegetation cover, and the occurrence of flash floods. Although important efforts have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100–10,000 km²) are not fully understood. Therefore, this study aims to provide a better understanding of sediment export processes and the importance of flash flood events in semi-arid tropical catchments.     

Characterization of <Emphasis Type="Italic">Faidherbia albida</Emphasis> (Del.) A. Chev. population in agroforestry parklands in the highlands of Northern Ethiopia: impact of conservation,environmental factors and human disturbances

Concerns about sustainable management and conservation of multipurpose trees in their habitat have led to increased number of studies on the ecological characterization of their population. Such knowledge on Faidherbia albida, the most used tree in agroforestry parklands in Ethiopia, is limited. F. albida population was characterized in and compared between two agroforests having different conservation status in Northern Ethiopia. Population structural parameters along with environmental factors and human activities were assessed in 42 randomly installed plots using a transect method. Size class distribution was used to describe and analyze the species long-term population dynamics. Adult density was almost three times higher in Zongi agroforest (19.9 ± 2.9 trees ha^?1) where the species has been conserved and managed for longer time compared to Abraha-atsbeha agroforest (7.9 ± 2.5 trees ha^?1). The same trend was observed for tree morphological parameters which were significantly higher at Zongi than Abraha-atsbeha. However, size class distributions coefficient of skewness and the median diameter indicated a declining and vulnerable population at Zongi and an increasing population at Abraha-atsbeha. Species population characteristics were influenced by environmental factors such as altitude, stone cover, erosion severity, slope, and human-related disturbances including land use, fodder harvesting, distance away from the center of the village and proximity of household to the plots. The study confirms the impact of conservation, environmental factors and human disturbances on shaping F. albida population and recommends the consideration of the trade-offs between them to design effective conservation and management strategies to sustain F. albida agroforests.     

Effect of replacing concentrate feed with leaves of Oldman saltbush (<Emphasis Type="Italic">Atriplex nummularia</Emphasis>) on feed intake,weight gain,and carcass parameters of highland sheep fed on wheat straw in northern Ethiopia

Atriplex nummularia (oldman saltbush) is widely planted on salt-affected land to provide a vegetative cover, which can be used as an alternative feed resource. The study was conducted to evaluate the replacement of commercial concentrate with oldman saltbush (SB) leaf on the feed intake, live weight gain, and carcass parameters of local sheep. Twenty-five sheep with an age of 6 months and weighting 14.60?±?2.47 kg were used in randomized complete block design and distributed into five equal groups, with five animals each. The selected sheep were fed with the dietary treatments for 2 weeks for adaptation and continued until the end of the study, which lasted for 90 days. In the control treatment (SB-0), sheep were fed 100% concentrate mix, while in SB-5, SB-10, SB-15, and SB-20, 5, 10, 15, and 20% of the concentrate mix was replaced by SB, respectively. Wheat straw and water were given at ad libitum throughout the experiment period. Data on feed intake and live weight gain were recorded daily and weekly, respectively, for 90 days. Three animals from each treatment were slaughtered for carcass analysis. Atriplex nummularia leaf (Oldman saltbush) contained 92.02% dry matter (DM), 21.99% crude protein (CP), 24.77% ash, 58.27% neutral detergent fiber (NDF), and 26.56% acid detergent fiber (ADF). Dry matter intake, live weight gain, and carcass parameter were not statistically different among the treatments. Result indicated that concentrate feed can be replaced with Atriplex nummularia leaf up to 20% in sheep diet without negative effect on growth performance and carcass characteristics.     

Biological nitrogen fixation in faba bean (Vicia faba L.) in the Ethiopian highlands as affected by P fertilization and inoculation

 N₂ fixation by leguminous crops is a relatively low-cost alternative to N fertilizer for small-holder farmers in developing countries. N₂ fixation in faba bean (Vicia faba L.) as affected by P fertilization (0 and 20 kg P ha^–1) and inoculation (uninoculated and inoculated) with Rhizobium leguminosarium biovar viciae (strain S-18) was studied using the ¹⁵N isotope dilution method in the southeastern Ethiopian highlands at three sites differing in soil conditions and length of growing period. Nodulation at the late flowering stage was significantly influenced by P and inoculation only at the location exhibiting the lowest soil P and pH levels. The percentage of N derived from the atmosphere ranged from 66 to 74%, 58 to 74% and 62 to 73% with a corresponding total amount of N₂ fixed ranging from 169 to 210 kg N ha^–1, 139 to 184 kg N ha^–1 and 147 to 174 kg N ha^–1 at Bekoji, Kulumsa and Asasa, respectively. The total N₂ fixed was not significantly affected by P fertilizer or inoculation across all locations, and there was no interaction between the factors. However, at all three locations, N₂ fixation was highly positively correlated with the dry matter production and total N yield of faba bean. Soil N balances after faba bean were positive (12–58 kg N ha^–1) relative to the highly negative N balances (–9–44 kg N ha^–1) following wheat (Triticum aestivum L.), highlighting the importance of rotation with faba bean in the cereal-based cropping systems of Ethiopia. Received: 13 January 2000     

Biserrula pelecinus L. is a promising forage legume for the central Ethiopian highlands

The availability of effective inoculant rhizobia is often critical to the successful development of productive forage legumes. Biserrula pelecinus L. is a legume with potential as forage in Ethiopia to improve livestock feed quality and soil fertility. B. pelecinus can form N₂‐fixing symbiosis with rhizobia in the genus Mesorhizobium. This study investigated the N₂ fixation effectiveness of 15 B. pelecinus‐nodulating Mesorhizobium strains on two subspecies of B. pelecinus (B. pelecinus ssp. leiocarpa, native to Ethiopia, and the introduced B. pelecinus ssp. pelecinus). The most effective strain (WSM3873) on both subspecies was assessed at two sites; one with pre‐existing populations of B. pelecinus‐nodulating rhizobia (Modjo), and one without (Holeta). No inoculation response was observed at Modjo when B. pelecinus ssp. pelecinus was inoculated with WSM3873 alone, however, biomass yield was greatest (11.5 tonne DM/ha) following inoculation along with co‐application of phosphorus and nitrogen. At Holeta, a strong inoculation response was achieved with WSM3873 alone on B. pelecinus ssp. pelecinus. In contrast, B. pelecinus ssp. leiocarpa did not show any response at Modjo and failed to emerge after sowing at Holeta. While the native legume B. pelecinus ssp. leiocarpa appears poorly suited to development as a forage, B. pelecinus ssp. pelecinus and WSM3873 represents a promising legume‐rhizobia symbiosis that could benefit farming systems of the central Ethiopian highlands.     

Sediment in Alluvial and Lacustrine Debris Fans as an Indicator for Land Degradation Around Lake Ashenge (Ethiopia)

Sediments deposited by (paleo) flash floods can hold valuable information on processes of environmental change, land degradation or desertification. In order to assess the suitability of flash flood deposits as proxies for land degradation, we monitored a representative gully segment in North Ethiopia (Ashenge catchment), investigated a sequence of alluvial debris fans downstream of this segment and dated a neighbouring subaquatic debris fan using short‐lived ²¹⁰Pb isotope counting. During one rainy season (July–September 2014), we measured daily rainfall, peak discharge, bedload transport, suspended sediment load and sediment deposition rates. The data show that sediment deposition in the debris fans is significantly dependent on micro‐topography (net incision in micro‐channels) (p < 0·1) and position within the sequence (net incision farther away from the lake) (p < 0·05). As sediment transfer to the lake significantly depends on the balance between available water and sediment (ratio rainfall depth/bedload transport) (p < 0·05), we could reconstruct the hydro‐sedimentary evolution of the gully over the past half century and validate it with aerial photographs and semi‐structured interviews. The findings are consistent with the short‐lived isotope count results, indicating increased sediment supply from the 1970s onwards, when little amounts of clay were deposited in the lake (<5%), and a subrecent clear water effect that resulted in increased deposition rates of clay in the lacustrine debris fan. Overall, our analysis indicates that debris fan sediments can be used to estimate past environmental degradation rates, if the contemporary water and sediment behaviour is well understood. Copyright © 2015 John Wiley & Sons, Ltd.