Semi-arid Africa Research Articles

English

  Vesicular-arbuscular mycorrhiza fungi are  associated with the majority ot the terrestrial plants. Their function ranges from stress alleviation to bioremediation in soils polluted with heavy metals. However, our knowlwdge about this symbiosis is still limited. For the semi-arid tropics, where some african countries are located, there is a great possibility of using mycorrhizas as a biological tool for sustainable agriculture. This review gives an overview on the mycorrhizal benefits and recomends some management practices for the semi-arid Africa conditions.   Key words: Arbuscular mycorrhizal fungi, endomycorrhizas, soil fungi, symbiosis, vesicular arbuscular mycorrhiza.  

African Enclosures: A Default Mode of Development

This paper draws on recent empirical studies of changing land and water use in semi-arid Africa to identify socioeconomic and political dynamics and discusses their implications for current policy which emphasizes decentralization and the strengthening of “local”––often customary––land rights. The paper presents cases where local initiative in response to market opportunities is driving investment and intensification of water use to increase production. This trend is associated with an increase in individualized control and market relationships in access to land, with increasing disadvantage to the poor. It is argued that this “default” pattern of development is occurring irrespective of the formal system of land tenure and may be promoted, rather than inhibited, by policies of decentralizing natural resource management.

Crop Technology Introduction in Semiarid West Africa: Performance and Future Strategy

SUMMARY The periodic food crises in agricultural production in semiarid sub-Saharan Africa have been the main public view of the subcontinent since the media perpetuates a Gloom and Doom perception. Actually the agricultural systems of sub-Saharan Africa have made some impressive achievements and there is potential to make more impact even in the more difficult regions where the poor are concentrated. In this paper the focus is on the successes, a strategy for introduction of new technologies in semiarid regions of West Africa, and supportive policy. More rapid technological change, with supportive policy, would have a substantial effect on rural poverty.

The use of herders' accounts to map livestock activities across agropastoral landscapes in Semi-Arid Africa

Improved understandings of the agricultural and range ecologies ofsemi-arid Africa require better information on the spatiotemporal distributionof domestic livestock across agropastoral landscapes. An empirical GIS-basedapproach was developed for estimating distributions of herded livestock acrossthree agropastoral territories (around 100 km2 each)over a two-year period. Algorithms developed from regression analyses of herdtracking data (with R2s ≥ 0.67) are used to transform a morecomprehensive but incomplete set of data generated from herders’ accounts oftheir herds’ grazing itineraries (400 herds following 6500 itineraries). Theresulting characterization registers 40 000 days of livestock activitiesacross694 land units (averaging 70 ha) over the study period. This studydemonstrates that rural producers’ knowledge of their daily extractionpracticescan be translated to fine-grained characterizations of extraction densitiesacross mixed landscapes. The spatiotemporal distribution of livestock that isrevealed by this approach diverges strongly from that predicted bycommonly-usedpoint-diffusion estimation procedures. Instead, the distribution reflects localpatterns of land use, topography, vegetation, settlements, and water points.Grazing and nongrazing times spent in land units are not spatially correlatedand the seasonality of grazing pressure is spatially variable. Therefore, theecological impacts of livestock grazing are spatially variable at fine scalesand there is a significant potential for livestock-mediated nutrient transfersacross agropastoral landscapes. The georeferenced data produced by thisapproachnot only will help evaluate the impact and sustainability of differentmanagement practices but also provides a strong empirical base for improvedspatial modeling of herded livestock.

The role of fire disturbance for global vegetation dynamics: coupling fire into a Dynamic Global Vegetation Model

AbstractDisturbances from fire, wind‐throw, insects and other herbivores are, besides climate, CO2, and soils, critical factors for composition, structure and dynamics of most vegetation. To simulate the influence of fire on the dynamic equilibrium, as well as on potential change, of vegetation at the global scale, we have developed a fire model, running inside the modular framework of the Lund–Potsdam–Jena Dynamic Global Vegetation Model (LPJ‐DGVM).Estimated litter moisture is the main driver of day‐to‐day fire probability. The length of the fire season is used to estimate the fractional area of a grid cell which is burnt in a given year. This affected area is converted into an average fire return interval which can be compared to observations.When driven by observed climate for the 20th century (at a 0.5° longitude/latitude resolution), the model yielded fire return intervals in good agreement with observations for many regions (except parts of semiarid Africa and boreal Siberia). We suggest that further improvement for these regions must involve additional process descriptions such as permafrost and fuel/fire dynamics.

Population Diallel of Elite Medium‐ and Long‐Duration Pearl Millet Composites: I. Populations and Their F1 Crosses

Pearl millet [Pennisetum glaucum (L.) R. Br.] varieties grown in semiarid Africa and Asia have low grain yields. Information on heterosis and combining ability of diverse open‐pollinated cultivars, breeding populations, and genepools is needed for efficient choice of breeding methods and parental materials to use in developing productive base populations for this crop. Data for grain and biomass yield, growth rate, time to flowering, plant height, panicle length, and productive tillers were collected from an 11‐parent variety cross diallel of diverse pearl millet populations evaluated in five field environments in peninsular India. Data were summarized using the Gardner–Eberhart Analysis II. When genotype × environment interactions were significant, ranks of parental general combining abilities (GCA) were used to identify particular environments and parents contributing most to these interactions. Parental population effects were significant for all characters, as were differences in GCA. Populations NWC C2, AfPop 88, and LHGP consistently had the poorest ranks for general combining ability for grain yield across test environments. Populations ICMV 91059, SenPop, ICMP 91751, and ICMP 92951 constitute a genetically diverse subset of the parents that consistently had the best ranks for grain yield GCA across test environments. With ICMV 155 (crosses of which performed poorly in only one of five test environments), this latter group is a good source of more broad‐based breeding populations for dual‐purpose pearl millet improvement targeting peninsular India.

Management of soil organic matter in semiarid Africa for annual cropping systems

Ensuring sustainable agriculture in semiarid Africa requires the implementation of methods to balance nutrients and to conserve soil organic matter (SOM). There is an urgent need to improve the management of all types of SOM input. In this paper; the authors review a wide range of agricultural practices and discuss their advantages, limitations and feasibility. They distinguish ‘traditional systems’ such as traditional fallow, parkland and manuring from ‘improved systems’ such as ‘improved fallow’, forest fallow, alley cropping, cover crops and application of composted manure. Biomass production (BMP) for ‘improved systems’ is mainly linked: (i) for agroforestry, to the tree species used in forest fallow, to the synchronization of nutrient supply by the soil with the cereal demand in alley cropping, and generally to the efficiency of the root system and its development with the depth; (ii) for cover crops, BMP is mainly linked to the initial soil fertility and to the ecological zone: establishment and management of cover crops are not yet fully mastered under some conditions such as an annual rainfall below 800 mm and/or on very clayey soils; (iii) for manure, BMP is mainly linked to the improvement of fallow in order to ensure sufficient forage resources. Because semiarid Africa is mainly a livestock zone, the authors emphasise manure: constraints, quality indicators and tools used to encourage its production, are analysed. Thus it was concluded that the intensification of manure production and its rational use in semiarid African regions, threatened by drought and malnutrition, is very important: this cannot be separated from the production of plant biomass, whose possibilities have been examined above.

Interpretations of environmental change and diversity: a critical approach to indications of degradation — the case of Kalakamate, Northeast Botswana

Studies of environmental change and degradation in semi-arid Africa often present contradictory results of the magnitude, severity, causes and effects of observed changes. Central questions are how findings may be generalized and extrapolated, how perceptions of the environment are recognized and analysed, and how value-judgement terms are defined and used. Emerging theories about dryland ecosystem dynamics, and ideas on interdisciplinary research, formed the background for a geographical study of the environmental history of an agropastoral communal area in North East District, Botswana. Here a comprehensive and discursive summary of the main conclusions of this study is presented. Using methods from the social and natural sciences, environmental outcomes were linked to different ‘types’ of change, such as effects of isolated events, of cyclic variation, and of trends. Since the beginning of the twentieth century, the area has been described as severely degraded, but the present results contradict previous descriptions and instead describe a temporally fluctuating, and spatially heterogeneous, environment with few signs of deterioration. Many changes were caused by isolated physical and social events, while others occurred in cycles. The few long-term ‘causative’ trends identified showed only small environmental impact. Several variables used as degradation indicators were identified, but found to constitute natural phases in the interaction of biophysical and socio-economic processes. The local understanding of environmental change corresponds quite closely with recent scientific thinking, and this study definitely supports the need for reevaluations of past ‘truths’ about environmental change in semi-arid Africa. Copyright © 2000 John Wiley & Sons, Ltd.

Interpretations of environmental change and diversity: a critical approach to indications of degradation ? the case of Kalakamate, Northeast Botswana

Studies of environmental change and degradation in semi-arid Africa often present contradictory results of the magnitude, severity, causes and effects of observed changes. Central questions are how findings may be generalized and extrapolated, how perceptions of the environment are recognized and analysed, and how value-judgement terms are defined and used. Emerging theories about dryland ecosystem dynamics, and ideas on interdisciplinary research, formed the background for a geographical study of the environmental history of an agropastoral communal area in North East District, Botswana. Here a comprehensive and discursive summary of the main conclusions of this study is presented. Using methods from the social and natural sciences, environmental outcomes were linked to different ‘types’ of change, such as effects of isolated events, of cyclic variation, and of trends. Since the beginning of the twentieth century, the area has been described as severely degraded, but the present results contradict previous descriptions and instead describe a temporally fluctuating, and spatially heterogeneous, environment with few signs of deterioration. Many changes were caused by isolated physical and social events, while others occurred in cycles. The few long-term ‘causative’ trends identified showed only small environmental impact. Several variables used as degradation indicators were identified, but found to constitute natural phases in the interaction of biophysical and socio-economic processes. The local understanding of environmental change corresponds quite closely with recent scientific thinking, and this study definitely supports the need for reevaluations of past ‘truths’ about environmental change in semi-arid Africa. Copyright © 2000 John Wiley & Sons, Ltd.

Représentativité de l'échantillonnage géochimique et hydrodynamique en nappe libre du milieu semi-aride (Reliability of geochemical and hydrodynamic sample in a semi-arid water table)

This paper evaluates the reliability of the geochemical and hydrodynamic sampling in a phreatic aquifer of semi-arid Africa. These remarks are based on a dense network and on detailed data collected for about ten years in the Continental Terminal water table near Niamey, Niger. The natural potentiometric fluctuations are seasonal (up to 6 m during the rainy season) and interannual (up to 10 m since the 1960s). Hydrodynamic measurements can be disturbed by artificial flooding into the wells (20% of the network) and by domestic drawings (up to 2 m of lowering). Geochemical characteristics can vary seasonally: isotopic modifications and salinity increase near recharge areas, with more stability further away. They can also vary artificially in wells because of their large opening towards the open air. Artifical increases of salinity of one order of magnitude and contaminations of 14C activities of up to 20 pmC occur in some wells by atmospheric dust inputs or organic matter which was has fallen into the well. In conclusion, some recommendations are given for a representative sampling in semi-arid phreatic aquifers.

Changing Land-use Systems and Socio-economic Roles of Vegetation in Semi-arid Africa: The Case of the Afar and Tigrai of Ethiopia

Changing Land-use Systems and Socio-economic Roles of Vegetation in Semi-arid Africa: The Case of the Afar and Tigrai of Ethiopia

Equilibrium and non-equilibrium models of livestock population dynamics in pastoral Africa: their relevance to Arctic grazing systems

Equilibrium grazing systems are characterised by climatic stability that results in predictable primary production. Non-equilibrium grazing systems receive low and erratic rainfall that produces unpredictable fluctuations in forage supplies. In semi-arid Africa, these two types of environment present livestock owners with very different management problems. Identifying and maintaining optimal stocking rates is useful in equilibrium systems because livestock reproduce and produce at a rate determined by the availability of feed, which is an inverse function of stock density. The only problem is to determine what stocking rate is optimal. The correct stocking rate for a grazing system will vary depending on the production strategy and the social and economic circumstances of the rangeland user - there is no single, biologically predetermined optimum density. Variable rainfall complicates the picture in non-equilibrium systems. Set stocking rates of any kind have little value if fluctuation in rainfall has a stronger effect than animal numbers on the abundance of forage. More useful in such an environment is the ability to adjust stocking rates rapidly to track sudden changes in feed availability. In semi-arid Africa, the distinction between equilibrium and non-equilibrium systems hinges on the reliability of rainfall. In northern latitudes, at least three primary variables important for plant growth and the survival of herbivores must be considered: rainfall, snow cover and temperature. It is probably not useful to consider arctic grazing systems as equilibrium systems; on the other hand, the non-equilibrium models developed in hot semi-arid environments do not capture the range of complexity which may be an inherent feature of plant-herbivore dynamics on the mountain and tundra pastures where reindeer are herded or hunted.

Reverse phenology and dry‐season water uptake byFaidherbia albida(Del.) A. Chev. in an agroforestry parkland of Sudanese west Africa

1.Faidherbia (Acacia) albidais a multipurpose tree widely distributed in semiarid Africa, notably in agroforestry parklands. It is in leaf during the dry season and defoliated during the rainy season, displaying therefore a peculiar reverse phenology. The related water‐use strategy, including leaf water potential, sapflow, hydraulic conductance and depth of uptake, were monitored on adult trees in a Sudanese west‐African parkland.2.Despite a severe drought in the superficial soil layers, the predawn leaf water potential ofF. albidadropped only toca.– 0·5 MPa during the end of the dry season, indicating only a moderate water stress.3.Radial trunk growth ceased before the end of the dry season and could have been affected by the moderate drought stress. However, leafiness remained constant during the dry season. Leaf shedding occurred after the first rains and was probably independent of drought.4.Faidherbia albidadisplayed large transpiration rates under favourable conditions but the ratio of sapflow to Penman evapotranspiration and the soil‐to‐leaf specific hydraulic conductance decreased severely towards the end of the dry season.5.Roots ofF. albidawere distributed through the weathered rock, down to a depth of 7 m, and vanished in the vicinity of a permanent water‐table. The isotopic composition of oxygen in the xylem sap (δ18O) remained very close to the values recorded in the water‐table during the course of the year. Phreatophytism thus explained the maintenance of growth and transpiration during the dry season. Nevertheless, during early rains, δ18O of sap switched towards the composition of the superficial soil layers, indicating facultative phreatophytism.6.Reverse phenology, low density and depth of water uptake ofF. albidaindicated a low competition with annual crops for water; the fraction of annual rainfall used by the trees was estimated to remain below 5%.

Household food security in semi-arid Africa—the contribution of participatory adaptive research and development to rural livelihoods in Eastern Kenya

The already precarious household food-security situation in many semi-arid areas of Africa may be rendered more so through the implementation of structural adjustment programmes that frequently prescribe austerity measures, along with a safety net to protect the vulnerable. However, longer-term development policy perspectives on the one hand, and shorter-term food-relief considerations on the other, often conflict. This paper illuminates the policy conflicts which arise when local-level research and development initiatives interface with the effects of macro-policy-initiated changes and safety-net interventions. Using a participatory agricultural research project in Eastern Kenya as a case study, the paper describes specific household food-security problem diagnosis and a range of research interventions planned within a more sustainable rural livelihoods framework. Working with local farmers, the project implemented a range of applied research and linked development interventions that showed promise in easing food security through a broadening of the livelihood base. Some of these initiatives were carried further through the local farmers' own initiative. The conclusion is that semi-arid areas, despite views that see these as low-potential and obvious safety-net candidates, often have potential for agricultural intensification and increased productivity. However, to ensure that research results are utilised and farmers have access to new technology and markets, there is a need for external or public-sector support to integrated longer-term development initiatives. This may require rethinking the scope of research and development approaches, particularly removing unhelpful boundaries between research, extension and development functions, and increasing farmer participation in the whole process—if possible as part of a less centralised and more household-oriented approach to food-security policy and strategy.

Changes in Landscape or in Interpretation? Reflections Based on the Environmental and Socio-economic History of a Village in NE Botswana

Abstract In semi-arid Africa, environmental change continues to be debated, focusing particularly on the status and significance of land degradation and on local versus scientific knowledge claims. This paper suggests an approach for using different types of data sources, and for bringing together understandings of ecosystem dynamics and of people's interaction with the environment, and thereby achieving 'closure' in a highly contested terrain. The environmental and socio-economic history of a village in north-eastern Botswana is investigated using oral histories of villagers, aerial photographs (1964 and 1988), and official records. At first, descriptions of the environment appear confusing and contradictory, and at odds with official records. Rainfall is the focal point around which most explanations of environmental change turn. Here scientists find no long-term change, while villagers perceive a decline. Overstocking has been a main concern for policymakers throughout this century, while villagers do not see this as a problem. These, and ensuing contradictory perceptions, are partly resolved by identifying the main components linking the wider society to the local and to the environment, and by seeking a shared meaning between local and official versions, as well as between different local versions, of environmental change. We found, instead of contradiction, a striking convergence between, on the one hand, recent scientific understanding of the unpredictability and complexity of semi-arid dynamics and, on the other hand, the description and explanation of change offered by villagers themselves.

Traditional goats and fat-tailed Sabi sheep in semi-arid north eastern Zimbabwe

SummaryCharacterisations are given of the little-known Sabi sheep and the local population of the Small East African goat in two areas in NE Zimbabwe. The southern area had been more affected by drought in 1991–92. For sheep (both areas combined; n = 28 in 10 flocks) the mean declared age of breeding females and the median age at first parturition were surprisingly high (6.1 years and 4 years respectively). Breeding female goats in the southern area were younger (4.9 vs. 6.4 years), and their age at first kidding was lower (3 years vs. 5 years), than in the north (n = 122 in 25 flocks total). These advanced ages could be an after-effect of the drought. Juvenile mortality and the proportions of young that were ultimately marketed were similar to what has been found elsewhere in semi-arid Africa. Breeding females were found to be smaller than their counterparts in semi-arid areas in West Africa with mean withers heights of 56.5 cm (n = 112 goats) and 60.4 cm (n = 36 sheep). Conditions in this area appear difficult for small ruminants and the populations sampled may be well adapted to marginal environments and thus worthy of conservation.

Domestic Water Use in Rural Semiarid Africa: A Case Study of Katarko Village in Northeastern Nigeria

Katarko village in the Sahel region of northeastern Nigeria relies entirely on natural sources of water such as rainfall and ground water. Thelatter is potentially the only constant source of water. This study is based on primary data collected in Katarko during a period of 8 months in 1996. Analysis indicates that per capita daily water consumption is higher (44.9 l) in the rainy season than in the dry season (26.1 l). The proportion of households who useless than 150 l per day, the minimum daily requirement recommended by the World Health Organization (Dieterich & Henderson, 1963) increases from 29% during the rainy season to 67% during the dry season. Most households prefer to use water of poor quality that is to be found closer to their homes to traveling long distances to or spending extra time at the water sources to obtain good quality water. Poor water quality, appalling sanitation, and unhygienic water-handling practices, particularly during the dry season, contribute to the high incidence of diarrhea in the village.

Crop Diversification in the Sahel through Use of Environmental Changes near Faidherbia albida (Del.) A. Chev

Pearl millet [Pennisetum glaucum (L.) R. Br.] is well adapted to the harsh environment of the West African Sahel but has relatively low genetic yield potential and market value. Crop diversification is desirable, but alternative crops generally cannot tolerate the harsh climate and soil conditions that pearl millet can. This study tested the hypothesis that alternative crops could be grown near Faidherbia albida (Del.) A. Chev. (syn. Acacia albida), a tree species of semiarid Africa, because of its ameliorating effects on the surrounding environment. Octants around trees were sown to pearl millet, maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium hirsutum L). Crop, soil, and climate measurements were made periodically during the growing season. Soil fertility and fine‐particle content decreased with distance from trees. Inside the canopy, irradiance was reduced by 0.5 to 1.0 kW m−2 and daytime soil temperature at a depth of 0.05 m was reduced by as much as 6°C. Improved conditions within the tree canopy were reflected by increased crop yield. Sorghum and maize tended to use less soil water than millet. Sorghum and maize yielded more than 120 g m−2 near the tree bole, whereas millet yielded ≈ 80 g m−2. Near the edge of the tree canopy, where pearl millet maintained yields of 40 g m−2, the other crops tended to fail. Faidherbia albida trees can be used to diversify cropping systems and increase yields in the Sahel, but adoption of this agroforestry system may be constrained by modern social factors which have disrupted traditional land husbandry practices.

Classification of multi-temporal SPOT-XS satellite data for mapping rice fields on a West African floodplain

The use of satellite imagery data to accurately map agricultural land use in semi-arid Africa has proven difficult due to the small size of cropped fields, low vegetative cover within and outside cropped areas, and high correlation between the seasonal trajectories in the signatures of cropped and uncropped surfaces. This paper evaluates the potential of computer-aided classification of multi-temporal imagery data to map traditionally-managed rice fields in Sahelian West Africa. SPOT-XS imagery data covering the southwestern corner of the Inland Niger Delta of Mali were acquired on three dates in 1988. These dates encompass the pre-flood period when ploughed surfaces contrast strongly with surrounding land surface and the first half of the flood period. Two alternative classification approaches were evaluated. Supervised and unsupervised classification of a database formed by principal component reduction proved unsuccessful as a result of the high spectral heterogeneity of ploughed and unploughed surfaces. An alternative classification approach was developed which utilizes a series of steps (unsupervised classification, stratification, and supervised classification) that progressively reduce image heterogeneity in such a way to better aid interpretation and comparison with training data. Seventy-one per cent of ploughed-field reference sites were classified correctly using this approach, while 8-20 per cent of reference sites for cover types with a potential for being confused with ploughed fields were misclassified as ploughed fields. A fuller evaluation was performed using a posterior accuracy assessment of classifications produced at five intermediate stages of the procedure. The suitability of the procedure for land-use classification in spectrally-heterogenous areas is discussed.

Variability of initial growth, water-use efficiency and carbon isotope discrimination in seedlings of Faidherbia albida (Del.) A. Chev., a multipurpose tree of semi-arid Africa. Provenance and drought effects

The panafrican provenances of #Faidherbia albida# display contrasting growth and survival rates in semi-arid zones of western Africa, when they are compared in multi-local field trials. In order to identify some potential causes for such differences, we recorded the genetic variability of ecophysiological traits (including water-use efficiency, W, and carbon isotope discrimination, A) in seven provenances from contrasting habitats of western and south-eastern Africa. Provenance and drought effects were tested on potted seedlings in a greenhouse. After 6 months, the total dry mass of the well-irrigated seedlings ranged from 31 to 86 g, and the total water-use from 8 to 18 kg. Both initial growth and water consumption were strongly correlated with leaf area. We displayed a significant inter-provenance variability, and exhibited the highest values in the south-east African provenances, which were the most vigourous, but also presented the poorest survival rates in field trials. It was negatively con-elated with the leaf-to-total dry mass ratio, LMR, and to A. The mild drought significantly reduced gas-exchange rates, leaf area, growth, water-use, specific leaf area, and A in all provenances. It also increased the intrinsic water-use efficiency, A/g, and the root-to-total dry mass ratio, but did not affect W or LMR. No provenance x drought interaction was found in any variable. The initial rate of leaf area establishment probably plays a major role in explaining the contrasting water-use strategies of the provenances. (Resume d'auteur)