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[The soilscape of Lake Tana basin, nitisols and vertisols are dominating the scene]
... As Mt. Guna is a volcano, it hosts volcanic ash soils such as Andosols and Phaeozems with stony soils of Cambisols and Leptosols (Deckers & Nyssen, 2015). ...
This study examines the spatial relationship between land cover change and its drivers at varying scale in Mt. Guna. The recent land cover map was generated from Google Earth Image (2018), and the historical land cover map generated from the 1957 and 1980 aerial photos. Multi-scale Geographically Weighted Regression (GWR) and Ordinary Least Square (OLS) were used to model the spatial relationship between land cover change and its drivers at varying scale. The change analysis revealed that Mt. Guna showed a dynamic land cover change between 1957 and 2018 dominated by conversions into cropland. Overall, 69% of the land cover change shows gains and losses, while 31% of the land cover of Mt. Guna showed persistence over 61 years. Furthermore, 77% of land cover was swapped and changed from its initial state. The result of modelling the spatial relationship between land cover change and its drivers showed that population density, slope gradient and clustered homestead density increases the likelihood of land cover change, while higher elevation, water source density and precipitation reduces the likelihood of land cover change. However, the spatial scale comparison indicated that the influence is stronger in large spatial scales than in small scales.
Field and laboratory experiments were conducted in 2002/2003 cropping season to evaluate five soil-test methods for indexing availability of phosphorus for maize grown on Alfisols of Northwestern Ethiopia. The field experiment on 20 sites was arranged in randomized complete block design with five P fertilizer rates (0, 30, 60, 90 and 150 kg P 2 O 5 ha-1) as treatments and four replications. At maturity, three central rows were harvested and grain and biomass yield data were collected. For indexing availability of phosphorus, laboratory analysis of soil samples was conducted following chemical soil analysis methods: Bray-1, Bray-2, Olsen, Mehlich-1, anion exchange resin extraction, and extraction with 0.01M CaCl 2 solution. Moreover, maize grain and stubble samples were analyzed to determine plant P uptake. Reliable methods were identified by fitting relative grain, relative dry biomass and P yields in a double log curvilinear regression model and those availability indices giving superior correlation with yield parameters were selected. Results of the experiments indicated that from the soil P analysis methods incorporated, Bray-2 and Olsen methods were found to be superior in providing reliable indices of availability of P for maize grown on Alfisols of Northwestern Ethiopia. These methods, therefore, can be used in soil-test based P fertilizer recommendation schemes of maize in the study area and other areas with similar soil type and agro-ecology.
With the prime objective of evaluating soil-test methods for indexing availability of nitrogen for maize grown on Alfisols of Northwestern Ethiopia, field and laboratory experiments were conducted in 2002/2003 cropping season. The field experiment on 20 sites was arranged in randomized complete block design with five N fertilizer rates (0, 30, 60, 90 and 200 kg N ha-1) as treatments and four replications. At maturity, three central rows were harvested and grain and biomass yield data were collected. Soil parameters determined for indexing availability of nitrogen were organic matter content, total N, NH 4 +-N, NO 3-N, inorganic N (NH 4 + +NO 3-N), inorganic N production on aerobic incubation, and ammonium-N released on autoclaving with dilute calcium chloride. Moreover, maize grain and stubble samples were analyzed to determine plant N uptake. Reliable methods were identified by fitting relative grain, relative dry biomass and N yields in a double log regression model and those availability indices giving superior correlation with yield parameters were selected. Results of the experiment revealed that organic matter, total N, and NO 3-N were the most reliable N availability indices. These methods, therefore, can be used in soil-test based N fertilizer recommendation schemes of maize in the study area and other areas with similar soil type and agro-ecology.
Field and laboratory experiments were conducted to develop equations for estimating phosphorus fertilizer requirements of maize on Alfisols of Northwestern Ethiopia. The field experiment on 20 sites was arranged in randomized complete block design with five fertilizer rates and four replications. At maturity, three central rows were harvested and yield and yield components data were collected. Laboratory analysis of soil samples was conducted following chemical soil analysis methods: Bray-1, Bray-2, Olsen, Mehlich-1, anion exchange resin and extraction with 0.01N CaCl 2. Parameters of the Quantity/Intensity relationships were also determined. Reliable methods were identified by fitting relative grain, relative dry biomass and P yields in a double log curvilinear regression model and those availability indices giving superior correlation were selected. Consequently, grain yield data and phosphorus availability indices were fitted into the Mitscherlich-Bray model to develop fertilizer recommendation equations. Results of the experiment revealed that among the methods giving quantity of available P, Bray-2 and Olsen methods gave the most reliable indices. Moreover, the intensity parameters in combination with the quantity parameters gave slightly superior correlation coefficient with yield parameters compared with their individual effects. The equations developed for estimating P fertilizer requirements of maize from soil analysis were: (a) log (100-y) = 2-0.1468b-0.007546x and (b) log (100-y) = 2-0.1167b-0.007546x for Olsen and Bray-2 methods, respectively, where y was desired relative grain yield (%); b was soil P availability index (mg kg-1); and x was P fertilizer requirement (kg ha-1). The two equations were statistically proven to provide equally reliable estimates of P fertilizer requirement of maize on Alfisols of Northwestern Ethiopia.
Field experiments were conducted in 2002/2003 cropping season to compare the effects of nitrogen and phosphorus as yield limiting nutrients for maize grown on Alfisols of Northwestern Ethiopia. The field experiments on 20 sites were arranged in randomized complete block design and four replications. Experiment 1 had four N fertilizer rates as treatments (0, 30, 60 and 90 kg N ha-1) applied as urea (46-0-0). Similarly, experiment 2 had five P fertilizer rates as treatments (0, 30, 60 and 90 kg P 2 O 5 ha-1) applied as triple superphosphate (0-46-0). Both experiments were laid out side by side in each location. During the vegetative period, plant height was measured at 35 and 60 days after emergence and at harvest. Lodging percentage, biomass yield and number of ears per plant data were measured at harvest. After harvest, grain yield, shelling percentage, 1000-grain weight and kernel per ear data were collected. Results of the experiments indicated that the increase in plant height, grain yield, dry biomass yield, 1000-grain weight and kernel number per ear were superior by increasing nitrogen rate than phosphorus rate. Ear number per plant was almost equally affected by increasing the rates of both nutrients. However, shelling percentage and lodging percentage were marginally affected by increasing the rates of both elements. From the results of the experiments it was possible to conclude that nitrogen to be more yield-limiting nutrient than phosphorus for maize grown on Alfisols of Northwestern Ethiopia. This suggests that, with out neglecting phosphorus, more attention should be given to nitrogen management including application of organic materials to sustain crop production in the study area. 2
With the prime objective of developing equations for estimating nitrogen fertilizer requirements of maize on Alfisols of Northwestern Ethiopia, field experiments were conducted at 20 sites. At each site, the treatments (five rates of N fertilizer) were arranged in a randomized complete block design with four replications. After maturity, yields and yield components data were collected. Soil parameters determined for indexing availability of nitrogen were organic matter content, total N, NH 4-N, NO 3-N, inorganic N (NH 4 +NO 3-N), inorganic N production on aerobic incubation, and ammonium-N released on autoclaving with dilute calcium chloride. Reliable methods were identified by fitting relative grain, relative dry biomass and N yields in a double log curvilinear regression model and those availability indices giving superior correlation were selected. Consequently, nitrogen availability indices that were found most reliable and grain yield data were fitted into the Mitscherlich-Bray model. Results of the experiment revealed that organic matter, total N, and NO 3-N were the most reliable N availability indices. The equations developed for estimating N fertilizer requirements of maize were: (a) log (100-y) = 2-0.1103b-0.006411x; (b) log (100-y) = 2-2.0566b-0.006481x; and (c) log (100-y) = 2-0.0220b-0.006414x for organic matter, total N and NO 3-N, respectively, where y was relative yield goal, b was N availability index expressed as % for the former two indices and mg kg-1 for the later, and x was the N fertilizer requirement. The three equations were statistically proven to give equally reliable estimates of N fertilizer requirement of maize on Alfisols of Northwestern Ethiopia. Nevertheless, in seasons where rainfall is heavy, high probability of nitrate leaching may make the later method less effective.
A study was conducted in Galessa-Jeldu areas to evaluate soil pH, organic C, total N, available P and
exchangeable bases under four indigenous and one exotic tree species, and to examine the correlation between
the different soil properties. The tree and shrub species included in the study were Senecio gigas Vatke, Hagenia
abyssinica (Bruce) J.F. Gmel., Dombeya torrida (J.F. Gmel.) P. Bamps, Buddleja polystachya Fres. and Chamaecytisus
palmensis (Christ) Bisby and K. The first four are indigenous, while the last one is an exotic N-fixing species. The
soil pH values under H. abyssinica and S. gigas were above 6.34 as compared to the soil pH values under C.
palmensis, D. torrida and B. polystachya. Total N was slightly higher under H. abyssinica although not statistically
different with the N content under other species. Organic C was higher under H. abyssinica than under B.
polystachya. The variation for exchangeable K was more at 0-15 cm soil depth than at the 15-30 and 30-50 cm soil
depths. The correlation between soil pH and total N as well as pH and organic C was positive in almost all the
horizontal positions. Hagenia abyssinica, S. gigas and C. palmensis are some of the potential species that can be
evaluated in different land-use systems of the high altitude areas to protect the loss of plant nutrients.
About the Book
The research presented in this book demonstrates how an integrated ‘systems’ approach to farming in the watershed context increases the effectiveness of a production system and improves people’s livelihoods. It takes an integrated approach, using one watershed in Ethiopia as a ‘laboratory’ or model case study to focus on the interaction and interdependence between land, water, crops, soil, water harvesting, supplemental irrigation, forestry, socio-economic aspects, livestock and farm tools.
A range of linked studies was conducted with active participation of the farming community and other relevant stakeholders, such as the local offices of agriculture and extension services. The starting point for the work was the premise that previous efforts to solve farming system constraints using a piecemeal approach or discipline-specific focus have not been successful. Thus, addressing agricultural and environmental constraints through a holistic approach enables the generation of comprehensive technologies to sustainably improve the natural resource base and livelihoods of communities. The authors discuss trade-offs and resource allocation, demonstrating how the environment can be protected while also improving productivity.
A unique feature is the methodology developed for the selection of suitable fields and farmers to implement new approaches or improved technologies, to achieve production increases while reducing degradation of sensitive agro-ecosystems. It is also shown how the watershed scale is a valuable basis for assessing the protection of fragile lands.
Eucalyptus is the tree of choice for wood production by farmers in Ethiopia. Although there are many claims about its harmful effect on ecology and water availability, little actual research exists. The main objective of this study was, therefore, to study the extent of harm of Eucalyptus on the ecosystem. This study was conducted at the Koga Watershed near Lake Tana in Ethiopia. Twenty-five farmers were interviewed and a field experiment with three replications was carried out to quantify the effect of Eucalyptus on various soil physical and chemical properties and maize crop measurements and to compare bulk density, soil moisture contents, maize crop counts and shading effects in fields bordered by Eucalyptus and Croton macrostachyus. Our results show that Eucalyptus decreased both soil nutrients and maize yields within 20 m of the trees. Although moisture content was not affected during the monsoon, it decreased faster within 30 m of the Eucalyptus trees than elsewhere. Soils become water repellent, too. Local farmers' perception agreed with our experimental findings and indicated that Eucalyptus trees are exhausting the once productive land. They also reported that Eucalyptus dries up springs. Despite this, the growers insist on planting Eucalyptus because of its cash income.
The geomorphological map of Lake Tana basin (15 077 km², Nile
basin, Ethiopia) was prepared from fieldwork data, maps and satellite
data that were processed in a GIS system. It contains four major
components: (i) hydrography, (ii) morphology and -metry, (iii) materials
and (iv) processes. The scale is 1:500 000. The geomorphological setting
of the basin consists of lavas that erupted from fissures or (shield)
volcanoes during the Tertiary and Quaternary eras, were uplifted and
ultimately sculpted by (mainly water) erosion. Lake Tana emerged by the
combination of a lava barrier blocking the Blue Nile to the south and by
epirogenetic subsidence. Since the time that the lake reached its
maximum extent, extensive floodplains were created, river valleys have
been filled with sediment and higher laying topography has been eroded.
Today, the lake plays a lesser role in landscape formation because of a
decreased lake extent (3041 km² now) as compared to the ancient
maximum (6602 km²). Dominant processes today are merely fluvial and
denudative. Recent (1886-2010) changes in lake coast are small with
exception of the delta of the major feeding river, Gilgel Abay, which
increased disproportionally the last 15 years. This indicates a large
input of sediment which is mainly due to rivers flowing through
Quaternary lavas. The recent sediment input increase is most probably
related to human induced land-use changes.
The extent and distribution of soil degradation in the highlands as a whole is outlined and shows significantly greater damage in the northern and eastern regions which were settled first. There, the poor soil quality today results in reduced crop productivity and greater vulnerability to famine. Actual rates of soil loss are estimated according to the USLE; the highest soil erosion rates occur in the western areas which clearly indicates that soils here are degrading more rapidly than soils in the north. -from Author
Growing agricultural crops under Millettia ferruginea (Hochst.) Baker, a tree that is endemic to Ethiopia, is an age-old practice in the country, but the beneficial effects of the tree on crops have not been scientifically quantified. To achieve this, four isolated and nearly identical Millettia trees growing on similar site conditions were selected and canopy coverage of each tree was divided into four radial transects. Four plots of 0.5 0.5 m were established on each radial transect at 0.5 to 1, 2.5 to 3, 4.5 to 5, and 6.5 to 7 m away from the tree bases. The control plot was established at 29.5 to 30 m. Composite soil samples from each of the four plots located at a comparable distance and at two soil depths, 0 to 10 and 20 to 30 cm, were collected and analyzed. The level of surface soil P, organic C, exchangeable base-forming cations and cation exchange capacity were all significantly higher (P < 0.000 to P < 0.015) under the trees than in the open field. Nutrient levels declined with depth and increasing distances from the tree trunk. Soil pH values did not show significant horizontal or vertical variations in all the soil samples analyzed. Maize plants grown on soils collected from underneath Millettia trees resulted in significantly better growth responses and higher dry matter yield as compared to the control (P < 0.001). Socioeconomic studies indicated that Millettia trees have good standing in the region both because of their desirable biological characteristics and because of their economic benefits.
The adverse effects of channelization on the environmental quality of streams and rivers at a global scale are well documented, but the magnitude of human-induced changes in river systems relative to the efficacy of geomorphological processes has yet to be ascertained quantitatively. Stream channelization is a common feature of the agricultural landscapes of the midwestern United States. This study shows that channelization in the Embarras River basin of east central Illinois has altered stream channel and planform geometries to an extent that exceeds background rates of change for unchannelized reaches by one to two orders of magnitude. The average rate of change in channel position resulting from stream responses to channelization also greatly exceeds the average rate of change for unchannelized reaches, yet the spatial extent of stream adjustments to channelization is limited, and most straightened or relocated channels persist in their altered state for decades following channelization. © 2003 by Association of American Geographers.
Gully formation in the Ethiopian Highlands has been identified as a major source of sediment in water bodies, and results in sever land degradation. Loss of soil from gully erosion lowers crop yields, reduces grazing land availability, and is one of the major causes of reservoir siltation in the Nile Basin. This study was conducted in the 523 ha of Debre-Mawi watershed south of Bahir Dar, Ethiopia, where gullies are actively forming in the landscape. Historic gully development in a section of the Debre-Mawi watershed was estimated with semi structured farmer interviews, remotely sensed imagery, and estimates of current gully volumes. Gully formation was assessed by instrumenting the gully and surrounding area to measure water table levels and soil physical properties. Gully formation began in the 1980's following the removal of indigenous vegetation, leading to an increase in surface and subsurface runoff from the hillsides. A comparison of the gully area, estimated from a 0.58 m resolution quick bird image, with the current gully area mapped with a GPS, indicated that the total eroded area of the gully increased from 0.65 ha in 2005 to 1.0 ha in 2007 and 1.43 ha in 2008. The gully erosion rate between 2007 and 2008 was 530 t ha-1yr-1 in the 17.4 ha area contributing to the gully, equivalent to over 4 cm soil loss over the contributing area. As a comparison, we also measured rill and inter-rill erosion rates in a nearby section of the watershed, gully erosion rates were approximately 20 times the measured rill and inter rill rates. Depths to the water table measured with piezometers showed that in the actively eroding sections of the gully the water table was above the gully bottom and, in stable gully sections the water table was below the gully bottom during the rainy season. The elevated water table facilitates the slumping of gully walls, which causes widening and up-migration on the hillside.
Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples' responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and
The spatial and seasonal distribution of microcrustacean zooplankton of Lake Tana (Ethiopia) was monthly studied for 2 years. Concurrently, various environmental parameters were measured and related to zooplankton distribution. Canonical Correspondence Analysis (CCA) was used to estimate the influence of abiotic factors and chlorophyll a content in structuring the zooplankton assemblage. Among the environmental factors, zooplankton abundance correlated most strongly with turbidity. Turbidity was negatively correlated with species abundance, especially for Daphnia spp. and to the least extent for Diaphanosoma spp. Analysis of variance (ANOVA) was used to determine spatial (littoral, sublittoral and pelagic zone) and temporal (four seasons) variation in zooplankton abundance. We observed significant temporal differences in zooplankton abundance, with highest densities during dry season (November–April). Only cladocerans showed significant differences in habitat use (highest densities in the sublittoral zone). ª
In 1998, the International Union of Soil Sciences (IUSS) officially adopted the world reference base for soil resources (WRB) as the Union's system for soil correlation. The structure, concepts, and definitions of the WRB are strongly influenced by the FAO-UNESCO legend of the soil map of the world (1-2). At the time of itsinception, the WRB proposed 30 "Soil Reference Groups" accommodating more than 200 ("second level") soil units. WRB (3-5) was endorsed by the IUSS in 1998 and provides an opportunity to create and refine a common and global language for soil classification. WRB aims to serve as a framework through which ongoing soil classification throughout the world can be harmonized. The ultimate objective is to reach international agreement on the major soil groups to be recognized at a global scale as well as on the criteria and methodology to be applied for defining and separating them. Such an agreement is needed to facilitate the exchange of information and experience, to provide a common scientific language, to strengthen the applications of soil science, and to enhance the communication with other disciplines and make the major soil names into household names
In the context of major global environmental challenges such as food security, climate change, fresh water scarcity and biodiversity loss, the protection and the sustainable management of soil resources in Africa are of paramount importance. To raise the awareness of the general public, stakeholders, policy makers and the science community to the importance of soil in Africa, the Joint Research Centre of the European Commission has produced the Soil Atlas of Africa. To that end, a new harmonised soil map at the continental scale has been produced. The steps of the construction of the new area-class map are presented, the basic information being derived from the Harmonized World Soil Database (HWSD). We show how the original data were updated and modified according to the World Reference Base for Soil Resources classification system. The corrections concerned boundary issues, areas with no information, soil patterns, river and drainage networks, and dynamic features such as sand dunes, water bodies and coastlines. In comparison to the initial map derived from HWSD, the new map represents a correction of 13% of the soil data for the continent. The map is available for downloading.
The aerial photographs (APs) acquired by the Istituto Geografico Militare (IGM) in the period of the Italian occupation of Ethiopia (1935-1941) have recently been discovered, scanned and organised. Until recently, the oldest APs of the country that were available had been taken in the period 1958-1964. The APs over Ethiopia in 1935-1941 consist of 8281 assemblages on approx. 50 cm x 20 cm hardboard tiles, each holding a label, one nadir-pointing photograph flanked by two low-oblique photographs and one high-oblique photograph. The four APs were exposed simultaneously and were taken across the flight line. The high-oblique photograph is presented alternatively at left and at right. There is approx. 60% overlap between subsequent sets of APs. One of Santoni’s glass plate multi-cameras was used, with focal length of 178 mm and with a flight height of 4000-4500 m a.s.l., which resulted in an approximate scale of 1:11,500 for the central photograph and 1:16,000 to 1:18,000 for the low-oblique APs. The surveyors oriented themselves with maps of Ethiopia at 1:400,000 scale, compiled in 1934. The flights present a dense AP coverage of Northern Ethiopia, where they were acquired in the context of upcoming battles with the Ethiopian army. Several flights preceded the later advance of the Italian army southwards to the capital Addis Ababa. Further flights took place in central Ethiopia for civilian purposes. As of 1936, the APs were used to prepare topographic maps at 1:100,000 and 1:50,000 scales. To re-process the imagery using novel techniques, procedures using digital image-based modelling have been developed. The 1935-1941 APs together with those of 1958-1964, 1994 and recent high-resolution satellite imagery are currently being used in spatio-temporal analysis, including change studies of land cover, land management and geomorphology in Ethiopia over a time span of 80 years.
Two broad kinds of swamps can be distinguished in the head waters of the White Nile of the East African Lake Plateau: seasonal (temporary) swamps and permanent. The general landscape and flora of this area have been described in Langdale-Brown et al. (1964) and Lind&Morrison (1974).
Human induced land use and land cover (LUC) changes threaten the ecosystem services of the vulnerable tropical afro-alpine vegetation. Several LUC change studies are available for the Ethiopian highlands, but relatively little is known about LUC change in the afro-alpine zones. In this study, LUC changes between 1964 and 2012 were mapped for the afro-alpine zone of Lib Amba Mountain, part of the Abune Yosef Mountains in North Ethiopia. Historical LUC was derived from georeferenced aerial photographs of 1964 and 1982, and the present LUC (2012) from Bing Map satellite imagery. Based on these successive LUC maps a time-depth map, LUC proportions, LUC transition matrices and LUC change trajectories were calculated. Two main phases of LUC change could be distinguished linked to the neo-Boserupian perspective. (i) Between 1964 and 1982, there was a large-scale deforestation and general degradation of the vegetation above 3500 m, in a period of low population pressure; (ii) Between 1982 and 2012, an intensification of land use prevailed accompanied with a slight regeneration of the vegetation and the Erica arborea L. forest, under increased population pressure. Depth interviews indicated that local and governmental land management measures are very important for the protection against vegetation depletion and soil degradation. Quick recovery of the forest on Lib Amba provides confidence that degraded afro-alpine areas would benefit in a short time from complete protection, given the vicinity of remaining patches of afro-alpine vegetation. Management interventions are thus vital to restore the important ecosystem services of the afro-alpine vegetation belt. This article is protected by copyright. All rights reserved.
Annual crop and pasture yields vary widely in some semi-arid climates. Russell (26) in South Australia reported that control yields of wheat ranged as high as 150 to 2900 kg./ha. at a single site over six years while Beekmann and Thompson (4) in Queensland found that grain sorghum yields on black earths varied from 0 to 7900 kg./ha. The best fertilizer practice in such situations is thus uncertain. This paper suggests simple Mitscherlich models which may be helpful in assessing the relative contributions of soil nutrients and nutrients applied under such conditions.
We investigated morphological characteristics and treatment potential of Cyperus papyrus, Typha domingensis, Miscanthidium violaceum, and Phragmites mauritianus receiving slaughterhouse wastewater in Kampala, Uganda, in experimental mesocosms. Unplanted mesocosms acted as controls. All planted mesocosms achieved significantly higher removals for nitrogen, phosphorus and organic matter than unplanted mesocosms. Among macrophytes, C. papyrus depicted highest pollutant uptake. The umbel of C. papyrus had the highest concentration of phosphorus (3.9 mg/g dry weight); while nitrogen concentration was highest in P. mauritianus shoot tissue (39.70 mg/g dry weight). Plants provided the necessary conditions that aided the removal of nutrients and organics through physical and biochemical processes. C. papyrus attained the highest biomass (31.0 kg dry weight/m²), compared to T. domingensis (7.5 kg dry weight/m²), P. mauritianus (7.2 kg dry weight/m²) and M. violaceum (5.0 kg dry weight/m²). C. papyrus had the largest total root surface area (200,634 cm²) in experimental mesocosms measuring 960 cm².
QuestionsWhat are the potential drivers of tree line change in the tropical African highlands? Are the temperature-sensitive tree lines in these highlands shifting as a result of climate change?SignificanceThe high-altitude forests provide important ecosystem services for the vulnerable environment of the tropical highlands. Climate change is expected to have pronounced effects on the tree line limit of these forests. Afro-alpine tropical tree lines are therefore potentially valuable as a proxy of climate change and the related response of ecosystems in the tropical highlands.LocationTropical African highlands.ResultsThe influence of climatic factors in the African tropical highlands is significantly different compared to other regions. The potentially determining factors for tree line distribution in tropical Africa are temperature, precipitation and cloudiness, carbon balance, fire and anthropo-zoogenic impacts. Despite recent temperature increase, tree lines have not risen to higher altitudes in the tropical African highlands. Instead, high human pressure has caused stabilization and even recession of the tree lines below their natural climatic limit, particularly through livestock herding. But, even neglecting human pressure, there might be a lag in response time between temperature and tree line change.Conclusions
The actual drivers of tree line change in the African tropical highlands are mainly fire and anthropogenic pressure rather than climate change. But long-term drought periods can be a trigger for fire-induced deforestation of the tree line vegetation. Additionally, in volcanic active mountains, volcanic activity is also a potentially limiting factor for the tree line distribution. Tree line dynamics can thus not be used as a proxy of climate change for the African tropical highlands.
Experimental research in the Ethiopian highlands found that saturation excess induced runoff and erosion are common in the sub-humid conditions. Since most erosion simulation models applied in the highlands are based on infiltration excess we, as an alternative, developed the Parameter Efficient Distributed (PED) model which can simulate water and sediment fluxes in landscapes with saturation excess runoff. The PED model has previously only been tested at the outlet of a watershed and not for distributed runoff and sediment concentration within the watershed. In this study, we compare the distributed storm runoff and sediment concentration of the PED model against collected data in the 95 ha Debre Mawi watershed and three of its nested sub-watersheds for the 2010 and 2011 rain seasons. In the PED model framework the hydrology of the watershed is divided between infiltrating and runoff zones, with erosion only taking place from two surface runoff zones. Daily storm runoff and sediment concentration values, ranging from 0.5 mm to over 30 mm and from 0.1 g L−1 to 35 g L−1 respectively, were well simulated. The Nash Sutcliffe efficiency values for the daily storm runoff for outlet and sub-watersheds ranged from 0.66 to 0.82 and the NSE for daily sediment concentrations were greater than 0.78. Furthermore, the model uses realistic fractional areas for surface and subsurface flow contributions, for example between saturated areas (15%), degraded areas (30%), and permeable areas (55%) at the main outlet, while close similarity was found for the remaining hydrology and erosion parameter values. One exception occurred for the distinctly greater transport limited parameter at the actively gullying lower part of the watershed. The results suggest that the model based on saturation excess provides a good representation of the observed spatially distributed runoff and sediment concentrations within a watershed by modeling the bottom lands (as opposed to the uplands) as the dominant contributor of the runoff and sediment load. This article is protected by copyright. All rights reserved.
The objective of this paper was to quantify long-term land use and land cover changes (LULCC) and to identify the spatial determinants of locations of most systematic transitions for the period 1957–2009 in the Jedeb watershed, Upper Blue Nile Basin. Black and white aerial photographs of 1957 and Landsat imageries of 1972 (MSS), 1986 (TM), 1994 (TM) and 2009 (TM) were used to derive ten land use and land cover classes by integrated use of Remote Sensing (RS) and Geographic Information System (GIS). Post-classification change detection analysis based on enhanced transition matrix was applied to detect the changes and identify systematic transitions. The results showed that 46% of the study area experienced a transition over the past 52 years, out of which 20% was due to a net change while 26% was attributable to swap change (i.e. simultaneous gain and loss of a given category during a certain period). The most systematic transitions are conversion of grassland to cultivated land (14.8%) followed by the degradation of natural woody vegetation and marshland to grassland (3.9%). Spatially explicit logistic regression modeling revealed that the location of these systematic transitions can be explained by a combination of accessibility, biophysical and demographic factors. The modeling approach allowed improved understanding of the processes of LULCC and for identifying explanatory factors for further in-depth analysis as well as for practical interventions for watershed planning and management.
The capacity to sorb P varied among some Ethiopian soils. Volcanic ash soils sorbed the maximum P while Fluvisols and Regosols
sorbed the least. Sorption of P was significantly correlated with exchangeable and extractable forms of Fe and Al as well
as pH and organic matter. But is was not related to the clay content of the soils. The role of Al was more important than
that of Fe even though more dithionite and oxalate extractable Fe than Al was found in all soils.
Comparisons were made to assess the reliability of 10 chemical methods for evaluating the availability of N in soils to Khaw Dauk Mali-105 rice and for calculating rates of N-fertilizer for rice. The methods studied were: (1) measuring soil organic matter by Walkley and Black's method, (2) measuring total soil N by Kjeldahl's method, (3) extracting soil N with acidified K2Cr2O7 solution, (4) extracting soil N with basified KMnO4 solution, (5) extracting soil N with acidified KMnO4 solution, (6) extracting soil N with solution of CaCl2 and K2SO4, (7) extracting soil nitrate according to Keeney and Nelson (1982) and then measuring the extracted nitrate by Kjeldahl distillation, (8) extracting mineral N in soils with 2 N KCl followed by distillation of NH 3 with MgO and Devarda alloy, (9) measuring NH4-N production from incubation of soils under waterlogged conditions for 7 days, and (10) measuring NH 4-N production from incubation of soils under waterlogged conditions for 14 days. The study was made with field-plot experiments at 18 sites inside and outside the Khaw Dauk Mali-105 producing areas. Only the indices from the methods (9) and (10) gave significant relationships (at 95% confidence level) with the relative paddy yields, with Method (10) showing slight superiority over the method (9). None of the chemical methods gave significant relationships among the index and the relative dry matter and amount of N in plants. The equations for calculating rates of N fertilizer required for desired paddy yields were: (a) log (100 - y) = 2 - 0.0226b - 0.0374x for method (9) and (b) log (100-y) = 2 - 0.00533b - 0.0584x for method (10); where y is the desired grain yield (as % of maximum yield), b availability index value for soil N (in ppm N), and x rate of fertilizer N required (as kg N/rai, 6.25 rais = 1 ha). Both of the two equations gave highly significant correlation between the actual paddy yields and the predicted paddy yields. However, method (10) was more recommended than method (9) for it was more reliable than method (9) in prediction of the yield.
High-resolution images available on Google Earth are increasingly being consulted in geographic studies. However, most studies limit themselves to visualizations or on-screen measurements. Google Earth allows users to create points, lines, and polygons on-screen, which can be saved as Keyhole Markup Language (KML) files. Here, the use of R statistics freeware is proposed to easily convert these files to the shapefile format [or ‘.shp file format’], which can be loaded into Geographic Information System (GIS) software (ESRI ArcGIS 9 in our example). The geospatial data integration in GIS strongly increases the analysis possibilities.
Surface horizon samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers’ fields, research station farms, and from uncultivated/ nonfertilized areas to characterize the organic and inorganic forms of phosphorus (P) in the highland plateau soils of Ethiopia using the Hedley soil P fractionation scheme. The total P values ranged from 226 mg‐kg in the Akaki Vertisol samples developed on alluvial deposits to 1570 mgkg in the Andisol samples, where the HCl fraction dominates the inorganic soil P pool. The Alfisol samples contained 400 mg‐kg of total P, with the NaOHand residual P being the dominant P fractions. The resin inorganic phosphorus (Pi) and bicarbonate Pi fractions generally accounted for less than 15% of the total P in all soils, and were positively correlated with organic C. The NaOH P fraction, which was most prominent in the surface horizon samples of the Alfisols, accounted for 4–15% of total P. The HCl P fraction, ranged from 1% in the Alfisols to 46% in the Andisols, and positively correlated with pH. All of the P fractions were negatively correlated with clay and extractable Al contents. The organic P (Po) fractions were positively related to organic carbon (C) and dithionate extractable iron (Fe). All samples collected from farmers’ fields showed a loss of P from the residual, and HCl fractions as compared to the uncultivated/nonfertilized samples. There is also a decrease in the labile P (resin Pi, bicarbonate Pi, and Po) fractions, except for the Akaki Vertisol samples. However, under research station management, the amount of labile P fractions either increased or remained at the same level as the uncultivated/nonfertilized samples, except for the Andisol. Addition of P fertilizer at the recommended rates to the Debre Zeit research station Vertisol appears to have resulted in a slight increase in the labile P and prevented loss of P from the HClP and residual P fractions.
This paper deals with the Brenta River (the Alps, Italy), a gravel-bed river strongly affected by human impact. The aims of this work are (a) to reconstruct the channel adjustments that have occurred during the last decades and (b) to analyse the present condition of the river in terms of bedload transport and sediment sources. The study reach, which is 23 km long, was investigated using historical maps, aerial photographs, 12 monumented cross-sections, laser altimetry data and field survey. Bedload transport rates were estimated by a morphological approach, which allows the construction of a sediment budget.
Dramatic channel adjustments have occurred in response to an alteration of sediment fluxes caused by different human interventions (gravel mining, dams, torrent-control works). Major channel adjustments, specifically incision (up to 8–9 m) and narrowing, took place between the 1950s and the 1980s. On the other hand, widening has become the most important process, and incision has continued only in the upper part of the study reach in more recent times (about the last 20–25 years).
The estimate of bedload transport rates for the period 1984–1997 was carried out starting from the erosion and deposition volumes of the single sub-reaches. Such an estimate has shown that (a) a high spatial variability of gravel transport rates exists (from 0 up to 73 200–85 400 m3/year) and (b) most of the bedload is supplied by local sources. Bank erosion is the main source of sediments for bedload transport and its contribution can be estimated as from 9 up to 20 times higher than the upstream contribution. Finally, from a practical point of view, results from this study should be taken into account in addressing maintenance, sediment management and restoration along a dynamic and unstable river such as the Brenta. Copyright
This paper deals with the channel changes of the Piave River in the Eastern Alps, Italy, which have occurred during this century in response to human interventions in the fluvial system. The flow regime and the sediment supply of the river have been considerably altered by hydroelectric dams, flow diversions and gravel mining. In addition, river dynamics have been affected by the construction of streambank protection structures. To document these changes, a historical analysis was performed using maps and aerial photographs. Morphological features that were examined included planform configuration, channel width, braiding index and bed elevation. The results indicate that as a consequence of decreases in the flows and sediment supply, remarkable channel changes have occurred in the river during this century, especially during recent decades. The channel has undergone a general narrowing with a decrease in average width to 35 per cent of its initial value, while the braiding index has decreased from about 3 to 1·5. In several reaches the planform pattern has changed from braided to wandering. The observed trends of channel change suggest that the river has not yet reached a new equilibrium condition and it may, therefore, be predicted that reductions in width and braiding intensity are likely to continue in the immediate future. Copyright © 1999 John Wiley & Sons, Ltd.
The ability to develop spatially distributed models of topographic change is presenting new capabilities in geomorphic research. High resolution maps of elevation change indicate locations, processes, and rates of geomorphic change, and provide a means of calibrating temporal simulation models. Methods of geomorphic change detection (GCD), based on gridded models, may be applied to a wide range of time periods by utilizing cartometric, remote sensing, or ground-based topographic survey data to measure volumetric change. Advantages and limitations of historical DEM reconstruction methods are reviewed with a focus on coupling them with subsequent DEMs to construct DEMs of difference (DoD), which can be created by subtracting one elevation model from another, to map erosion, deposition, and volumetric change. The period of DoD analysis can be extended to several decades if accurate historical DEMs can be generated by extracting topographic data from historical data and selecting areas where geomorphic change has been substantial. The challenge is to recognize and minimize uncertainties in data that are particularly elusive with early topographic data. This paper reviews potential sources of error in digitized topographic maps and DEMs. Although the paper is primarily a review of methods, three brief examples are presented at the end to demonstrate GCD using DoDs constructed from data extending over periods ranging from 70 to 90 years.
Based on farmers’ knowledge and laboratory studies, the nutrient accumulation in the topsoil (0–20cm) under Cordia africana Lam (Cordia), Millettia ferruginea Hochst (Millettia) and Eucalyptus camaldulensis Dehnhardt (Red gum) managed under two agroforestry practices on different farms at three sites was evaluated. The number
of these trees on individual farms has increased during the last two decades. The number of stems ha−1 of Red gum was higher on farms of wealthier households than on farms of poor and medium households at two of the sites, but,
at one site the number of stems ha−1 on farms of poor households was higher than on farms of wealthier households. Apart from the concentration of Na in the topsoil,
there were significant variations in the analysed soil nutrients between the tree species. At all study sites, significantly
higher concentration of P was observed under Millettia and Cordia than under Red gum. At one site, concentrations of available
P under Cordia were nearly two-fold, and four and half-fold greater than under Millettia and Red gum, respectively. At one
site, total N under Red gum was 14% and 24% lower than under Cordia and Millettia, respectively. In contrast, organic C content
under Red gum was 11.6% greater than under Millettia and 23.8% greater than under Cordia. The pH under Millettia and Cordia
were significantly higher than concentrations under Red gum at one site. Topsoil under Millettia and Cordia also had significantly higher levels of exchangeable Ca and Mg than Red gum.
The science of irrigation scheduling is well advanced, but the field application of this knowledge among irrigators is limited. Case studies are presented to show why irrigators may fail to adopt or persevere with traditional irrigation scheduling methods. This paper describes a funnel-shaped wetting front detector that is buried at an appropriate depth in the root zone. As a wetting front moves into the funnel of the detector, the water content increases due to convergence, so that the water content at the base of the funnel reaches saturation. The free water produced is detected electronically and this provides the signal to stop irrigation. Since the philosophy of drip irrigation in most cases is to supply water little and often, the "when to turn the water on" question becomes redundant and knowing when to turn the water off is more useful. Two further case studies demonstrate the benefits of scheduling micro-irrigation using wetting front detectors. The detectors retain a water sample from each irrigation event and this was used to monitor nitrate movement in and below the root zone.
In most arable soils the nitrate availability depends mainly on the quantity of nitrate present in the rooting zone at the beginning of the growing season. Easily mineralizable organic N and the release of non-exehangeable NH4 from clay minerals may in addition control the nitrogen availability during a season.
In flooded soils, ammonium is the major form of nitrogen absorbed by plants. Ammonium dynamics in these soils is similar to that of potassium. The availability of both is controlled mainly by the intensity and buffering power for ammonium or potassium, respectively.
Basically, intensity of the supply and buffering power for phosphate are the main factors determining the phosphate availability. The determination of the phosphate buffer power, especially in the root zone, however, remains to be difficult.
Soil test methods should take into consideration the major factors and processes relevant to the availability of a particular plant nutrient.
Daily runoff depths from 28 plots (5 m × 2 m) recorded during a 2-year period in the semi-arid to subhumid highlands of Tigray were analyzed to study the effect of vegetation restoration in exclosures and to identify other factors influencing runoff production. Plots are distributed over three study sites and located in different land use types and on different combinations of soil type, vegetation cover and slope gradient. Runoff was found to be significantly reduced when a degraded area is allowed to rehabilitate after closure. Runoff depth is significantly correlated with event variables such as rain depth, rainfall intensity, storm duration and soil moisture content. Total vegetation cover is the most important plot variable explaining about 80% of the variation in runoff coefficients through an exponential decay function. Also the runoff generating rainfall threshold has a positive correlation with total vegetation cover. Runoff was found to be negligible when the vegetation cover exceeds 65%. Other important variables affecting runoff production in the study sites are soil organic matter, soil bulk density, litter cover and slope gradient.
Aerial photographs are commonly used to measure planform river channel change. We investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number (6–30) and type (human versus natural landscape features) of ground-control points (GCPs) and the order of the transformation polynomial (first-, second-, and third-order) affected the spatial accuracy of a typical georectified aerial photograph. Error was assessed using the root-mean-square error (RMSE) of the GCPs as well as error in 31 independent test points. The RMSE and the mean and median values of test-point errors were relatively insensitive to the number of GCPs above eight, but the upper range of test-point errors showed marked improvement (i.e., the number of extreme errors was reduced) as more GCPs were used for georectification. Using more GCPs thus improved overall georectification accuracy, but this improvement was not indicated by the RMSE, suggesting that independent test-points located in key areas of interest should be used in addition to RSME to evaluate georectification error.
The permeability to nutrient-rich bottom water of the floating root mats of Cyperus papyrus L. and Miscanthidium violaceum (K. Schum) Robyns in Nakivubo swamp (Kampala, Uganda) was studied. The papyrus root mat was made up of an open framework of interconnecting rhizomes and adventitious roots. The Miscanthidium root mat had a spongy close-knit character created by tight interlacing of roots. Penetration of bottom water into the papyrus root mat was unimpeded while penetration into the Miscanthidium mat was limited. This implies that the floating root mat of papyrus would easily extract nutrients from the waste water underneath and provide better treatment of waste water than that of Miscanthidium.
This review analyses the environmental evolution of the Ethiopian highlands in the late Quaternary. The late Pleistocene (20,000–12,000 ¹⁴C years BP) was cold and dry, with (1) low lake levels in the Rift Valley, (2) large debris fans on the flanks of Lake Abhé basin, and (3) the Blue Nile transporting coarse bedload. Then, a period with abundant and less seasonal rains existed between 11,500 and 4800 ¹⁴C years BP, as suggested by increased arboreal pollen, high river and lake levels, low river turbidities and soil formation. Around 5000–4800 ¹⁴C years BP, there was a shift to more arid conditions and more soil erosion. Many phenomena that were previously interpreted as climate-driven might, however, well be of anthropic origin. Thick sediment deposits on pediments as well as an increase of secondary forest, scrub and ruderal species in pollen diagrams are witnesses of this human impact.
This book provides an up-to-date information on Vertisols research, and guides readers to important reference material. Four keynote papers and eight country papers and national perspectives on the management of Vertisols in Malawi, South Africa, Sudan, Tanzania, Zambia, Zimbabwe, Ghana and Ethiopia are presented. International perspectives on the management of (Vertisols in India, Australia and Texas, USA) are also discussed.
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