Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Biomass transfers and nutrient budgets of the agro-pastoral systems in a village territory in south-western Burkina Faso
    Diarisso, T. ; Corbeels, M. ; Andrieu, N. ; Djamen, P. ; Tittonell, P.A. - \ 2015
    Nutrient Cycling in Agroecosystems 101 (2015)3. - ISSN 1385-1314 - p. 295 - 315.
    crop-livestock system - management strategies - northern nigeria - farming system - cover change - africa - sahel - vegetation - farmers - forage
    Privatisation of grazing resources is emerging in the agro-pastoral systems of West Africa, resulting in increased pressure on the remaining communal rangelands and greater competition between farmers for access to crop residues. Differential management strategies arise as determined by household diversity. This study quantified the flows of biomass and related nutrient budgets in relation to farm diversity in Koumbia, a representative village of south-western Burkina Faso. Four farm types were identified: subsistence-oriented and market oriented crop farmers, agro-pastoralists and pastoralists. Crop farmers collected about 30 % of their maize harvest residues for feeding during the dry hot season, while agro-pastoralists and pastoralists stocked about 50 % of their maize residues. Whilst the remaining crop residues on (agro)pastoralist farms were almost entirely grazed by their own cattle, about 90 % of the crop residues of crop farmers were consumed by cattle of (agro)pastoralists. On the other hand, available manure from cattle in the village was mainly used to fertilize the fields of the livestock owners. As a result, the cropped land of farmers with few livestock is continuously mined for nutrients. Calculated partial balances of N and K at farm level were negative for all farm types, except for N in the case of pastoralist farms. N and K balances of cropped fields were generally negative on all farm types. Partial balances of P were generally positive, which was to a large extent due to P fertilizer use. Better integration of crop and livestock production activities on farms and between farms offers a pathway to more efficient nutrient cycling with reduced nutrients losses.
    Evaluation of Satellite Rainfall Estimates for Drought and Flood Monitoring in Mozambique
    Tote, C. ; Patricio, D. ; Boogaard, H.L. ; Wijngaart, R. van der; Tarnavsky, E. ; Funk, C. - \ 2015
    Remote Sensing 7 (2015)2. - ISSN 2072-4292 - p. 1758 - 1776.
    west-africa - precipitation - validation - products - microwave - climate - dataset - gages - sahel - trmm
    Satellite derived rainfall products are useful for drought and flood early warning and overcome the problem of sparse, unevenly distributed and erratic rain gauge observations, provided their accuracy is well known. Mozambique is highly vulnerable to extreme weather events such as major droughts and floods and thus, an understanding of the strengths and weaknesses of different rainfall products is valuable. Three dekadal (10-day) gridded satellite rainfall products (TAMSAT African Rainfall Climatology And Time-series (TARCAT) v2.0, Famine Early Warning System NETwork (FEWS NET) Rainfall Estimate (RFE) v2.0, and Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS)) are compared to independent gauge data (2001–2012). This is done using pairwise comparison statistics to evaluate the performance in estimating rainfall amounts and categorical statistics to assess rain-detection capabilities. The analysis was performed for different rainfall categories, over the seasonal cycle and for regions dominated by different weather systems. Overall, satellite products overestimate low and underestimate high dekadal rainfall values. The RFE and CHIRPS products perform as good, generally outperforming TARCAT on the majority of statistical measures of skill. TARCAT detects best the relative frequency of rainfall events, while RFE underestimates and CHIRPS overestimates the rainfall events frequency. Differences in products performance disappear with higher rainfall and all products achieve better results during the wet season. During the cyclone season, CHIRPS shows the best results, while RFE outperforms the other products for lower dekadal rainfall. Products blending thermal infrared and passive microwave imagery perform better than infrared only products and particularly when meteorological patterns are more complex, such as over the coastal, central and south regions of Mozambique, where precipitation is influenced by frontal systems.
    Climate change, climate variability and adaptation options in smallholder cropping systems of the Sudano - Sahel region in West Africa
    Traore, B. - \ 2014
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Mark van Wijk; M. Corbeels. - Wageningen : Wageningen University - ISBN 9789461739612 - 163
    klimaatverandering - klimaat - klimaatadaptatie - kleine landbouwbedrijven - teeltsystemen - sahel - gewasproductie - west-afrika - climatic change - climate - climate adaptation - small farms - cropping systems - sahel - crop production - west africa

    Key words: crop production, maize, millet, sorghum, cotton, fertilizer, rainfall, temperature, APSIM, Mali,

    In the Sudano-Sahelian zone of West Africa (SSWA) agricultural production remains the main source of livelihood for rural communities, providing employment to more than 60 percent of the population and contributing to about 30% of gross domestic product. Smallholder agricultural production is dominated by rain-fed production of millet, sorghum and maize for food consumption and of cotton for the market. Farmers experience low and variable yields resulting in increasing uncertainty about the ability to produce the food needed for their families. Major factors contributing to such uncertainty and low productivity are climate variability, climate change and poor agricultural management. The objective of this thesis was to evaluate through experimentation, modelling and participatory approaches the real and perceived characteristics of climate variability and change and their effects on crop production in order to identify opportunities for enhancing the adaptive capacity of farmers in the Sudano - Sahelian zone.

    The general approach was based on, first, understanding the past trend of climate and its effect on the yield of main crops cultivated in southern Mali; second, evaluating together with farmers different adaptation options in the field; third, evaluating climate adaptation options through experimentation on station; and fourth, evaluating the consequences of different adaptation options under different long term scenarios of climate change.

    Minimum daily air temperature increased on average by 0.05oC per year during the period from 1965 to 2005 while maximum daily air temperature remained constant. Seasonal rainfall showed large inter-annual variability with no significant change over the 1965 – 2005 period. However, the total number of dry days within the growing season increased significantly indicating a change in rainfall distribution. There was a negative effect of maximum temperature, number of dry days and total seasonal rainfall on cotton yield.

    Farmers perceived an increase in annual rainfall variability, an increase in the occurrence of dry spells during the rainy season, and an increase in temperature. Drought tolerant, short maturing crop varieties and appropriate planting dates were the commonly preferred adaptation strategies to deal with climate variability. Use of chemical fertilizer enhances the yield and profitability of maize while the cost of fertilizer prohibits making profit with fertilizer use on millet. Training of farmers on important aspects of weather and its variability, and especially on the onset of the rains, is critical to enhancing adaptive capacity to climate change.

    A field experiment (from 2009 to 2011) indicated that for fertilized cereal crops, maize out yielded millet and sorghum by respectively 57% and 45% across the three seasons. Analysis of 40 years of weather data indicated that this finding holds for longer time periods than the length of this trial. Late planting resulted in significant yield decreases for maize, sorghum and cotton, but not for millet. However, a short duration variety of millet was better adapted for late planting. When the rainy season starts late, sorghum planting can be delayed from the beginning of June to early July without substantial reductions in grain yield. Cotton yield at early planting was 28% larger than yield at medium planting and late planting gave the lowest yield with all three varieties. For all four crops the largest stover yields were obtained with early planting and the longer planting was delayed, the less stover was produced.

    Analysis of predicted future climate change on cereal production indicated that the temperature will increase over time. Generally stronger increases occur in the rcp8.5 scenario compared to the rcp4.5 scenario. The total annual rainfall is unlikely to change. By mid-century predicted maize grain yield losses were 45% and 47% with farmer’s practice in the rcp4.5 and rcp8.5 scenarios respectively. The recommended fertilizer application did not offset the climate change impact but reduced the yield losses to 38% of the baseline yield with farmer’s practice. For millet median yield loss was 16% and 14% with farmer’s practice in the rcp4.5 and rcp8.5 scenario. If the recommended fertilizer rates are applied to millet, the predicted yield losses with farmer’s practice due to climate change are reversed in both climate scenarios.

    Under future climate change, food availability will be reduced for the all farm types, but that large farm will still achieve food self – sufficiency in terms of energy requirement. The medium and small farm types see a further decrease in food self-sufficiency. Addressing smallholder food self-sufficiency depends upon the capacity of each farm type to appropriately choose the planting date while taking into account the acceptable planting date window for each individual crop.

    Increasing nutrient use efficiency through improved feeding and manure manegement in urban and peri-urban livestock units of a West African city: A scenario analysis
    Diogo, V. ; Schlecht, E. ; Buerkert, A. ; Rufino, M.C. ; Wijk, M.T. van - \ 2013
    Agricultural Systems 114 (2013). - ISSN 0308-521X - p. 64 - 72.
    smallholder farming systems - cycling efficiencies - crop production - diet selection - cattle - niger - resource - sahel - kenya - agriculture
    In many African cities urban and peri-urban agriculture (UPA) plays a major role in creating jobs and contributing to food security. However, many small-scale UPA systems are characterised by excessive nutrient inputs to the livestock unit and poor handling of manure. To assess the impact of improved feeding and manure management on nutrient use efficiency within the cattle unit, simulation modelling was used to compare three typical UPA farm types in Niamey, Niger, that comprised: animal husbandry alone (AH), animal husbandry plus gardening (AH+G), and animal husbandry plus gardening plus millet cultivation (AH+G+M). Improved feeding increased annual body weight gain and milk offtake from cattle and reduced the amount of nitrogen (N) excreted in urine, thereby lowering the risk of N emissions. With improved manure management, dry matter (DM) and nutrients recycled per animal and year, and potentially available for cropping, ranged from 321–690 kg DM, 8–22 kg N, 1.2–2.5 kg phosphorus (P), and 3.0–5.6 kg potassium (K) in AH as well as AH+G+M farms compared to 221–479 kg DM, 5.0–14.0 kg N, 0.7–1.6 kg P, and 2.0–4.0 kg K in AH+G farms. These amounts were up to 2.2-, 2.5-, 1.9- and 1-fold higher than the quantities of DM, N, P and K recycled under current practices. Feeding dairy cattle according to their requirements will enhance milk and meat production; if coupled with regular manure collection and low-cost covering of manure heaps, substantial amounts of nutrients are recycled to cropland and vegetable gardens and environmental pollution is reduced.
    Linear trends in seasonal vegetation time series and the modifiable temporal unit problem
    Jong, R. de; Bruin, S. de - \ 2012
    Biogeosciences 9 (2012). - ISSN 1726-4170 - p. 71 - 77.
    proxy global assessment - land degradation - sahel - environment - america - modis - ndvi
    Time series of vegetation indices (VI) derived from satellite imagery provide a consistent monitoring system for terrestrial plant productivity. They enable detection and quantification of gradual changes within the time frame covered, which are of crucial importance in global change studies, for example. However, VI time series typically contain a strong seasonal signal which complicates change detection. Commonly, trends are quantified using linear regression methods, while the effect of serial autocorrelation is remediated by temporal aggregation over bins having a fixed width. Aggregating the data in this way produces temporal units which are modifiable. Analogous to the well-known Modifiable Area Unit Problem (MAUP), the way in which these temporal units are defined may influence the fitted model parameters and therefore the amount of change detected. This paper illustrates the effect of this Modifiable Temporal Unit Problem (MTUP) on a synthetic data set and a real VI data set. Large variation in detected changes was found for aggregation over bins that mismatched full lengths of vegetative cycles, which demonstrates that aperiodicity in the data may influence model results. Using 26 yr of VI data and aggregation over full-length periods, deviations in VI gains of less than 1% were found for annual periods (with respect to seasonally adjusted data), while deviations increased up to 24% for aggregation windows of 5 yr. This demonstrates that temporal aggregation needs to be carried out with care in order to avoid spurious model results.
    Calibration of RWEQ in a patchy landscape; a first step towards a regional scale wind erosion model
    Youssef, I.F. ; Visser, S.M. ; Karssenberg, D. ; Bruggeman, A. ; Erpul, G. - \ 2012
    Aeolian Research 3 (2012)4. - ISSN 1875-9637 - p. 467 - 476.
    land management - prediction - validation - transport - sediment - sahel - gis
    Despite the fact that wind erosion seriously affects the sustainable use of land in a large part of the world, validated wind erosion model that predicts windblown mass transport on a regional scale is lacking. The objectives of this research were to modify revised wind erosion equation (RWEQ) to estimate soil loss at a field scale in a way that it could operate at a regional scale, to calibrate the model using ground data collected from a field scale representing different land uses in Khanasser valley, Syria, and to estimate the total sediment fluxes (kg m-1) and soil losses (kg m-2) for farming fields. We implemented a modified version of RWEQ that represents wind erosion as a transient process, using time steps of 6 h. Beside this a number of adaptations including estimation of mass flux over the field boundaries, and the routing of sediment have been done. Originally, RWEQ was created and calibrated for application at the scale in USA. Due to the adaptations imparted to the original RWEQ and the different environmental condition in Syria of application areas, an intensive calibration process was required before applying the model to estimate the net soil loss from the experimental fields. The results of this test showed that the modified version of RWEQ provided acceptable predictions for the average mass flux from the measurement plot with a linear regression coefficient of R2 of 0.57 and 0.83 for the (d) test for the 20 wind events at the six tested plots
    Challenges of assessing the sustainability of (agro)-pastoral systems
    Ayatunde, A.A. ; Leeuw, J.A. de; Turner, M.D. ; Said, M. - \ 2011
    Livestock Science 139 (2011)1-2. - ISSN 1871-1413 - p. 30 - 43.
    developing-countries - southwestern niger - kajiado district - west-africa - livestock - pastoralism - commons - herders - kenya - sahel
    Pastoralism is not only a livestock-based livelihood strategy but also a way of life with socio-cultural norms and values, and indigenous knowledge revolving around livestock. Pastoral systems in Africa are facing demographic, economic, socio-political and climatic pressures which are driving many pastoralists into non-livestock based livelihood strategies. The changing contexts in which pastoralists operate raise the issue of the sustainability of pastoral systems in dryland Africa. The specific objectives of this paper are: (i) to identify the challenges of assessing the sustainability of pastoral systems with focus on East and West Africa; (ii) to propose criteria and indicators for sustainability assessment of pastoral systems; and (iii) to demonstrate the diversity of pastoral systems by elaborating on features in East and West Africa with case studies from pastoral communities in both regions, namely Samburu in Kenya and Fakara in Niger. All these objectives are to contribute to the debates on the sustainability of pastoralism. Assessing sustainability of pastoral systems is challenging and complex in view of different aspects that should be addressed over time and at different scales. The main challenges addressed in this paper include purpose and interpretation of sustainability, time dimension and scale, diversity of pastoral systems, inter-relatedness of assessment criteria, comprehensiveness and measurability of indicators. To illustrate the challenges, we proposed a number of criteria based on key systems' components of production, stability, efficiency and resilience. For each criterion, a number of indicators were proposed. The criteria we suggested are inter-related and should not be considered in isolation bearing in mind that sustainability is a composite attribute that integrates several variables. In terms of sustainability of pastoral systems in East and West Africa, the key issues are mobility, livestock diversity, livelihood diversification options, and preservation of pastoral tradition and indigenous knowledge. The degree with which these issues are constraining pastoral production and economy will largely shape the trajectory of sustainability of different pastoral systems in both regions.
    Adaptation to climate change and climate variability:The importance of understanding agriculture as performance
    Crane, T.A. ; Roncoli, C. ; Hoogenboom, G. - \ 2011
    NJAS Wageningen Journal of Life Sciences 57 (2011)3-4. - ISSN 1573-5214 - p. 179 - 185.
    southeastern usa - farm crisis - sahel - information - impacts - drought - systems - models - enso
    Most climate change studies that address potential impacts and potential adaptation strategies are largely based on modelling technologies. While models are useful for visualizing potential future outcomes and evaluating options for potential adaptation, they do not adequately represent and integrate adaptive human agency. Richards’ concept of ‘agriculture as performance’ is useful in counterbalancing the modelling approach to adaptation because it highlights how adaptive processes and technologies, whether short term or long term, are more than simple technical responses to biophysical conditions. Instead, adaptive processes are social phenomena whose significance and effects expand well beyond changing climate conditions. This examination of agriculture as performance in the context of climate adaptation draws on two different examples. The first example explores how technical aspects of climate adaptation in Mali are situated within the enactment of ethnic identities and political struggles between farmers and herders. The second example shows how farmers in southeastern United States approach climate variability and climate forecasts as risk management tools. There are substantial differences between approaching adaptation as a dynamic process that is socially embedded and approaching adaptation as a set of modelled responses to anticipated future conditions. It is unlikely that either is adequate to meet the challenges posed by the uncertainties associated with climate change. However, building a synergistic relationship between the two promises to be as difficult as it is necessary
    Host-parasite dynamics of Sorghum bicolor and Striga hermonthica - The influence of soil organic matter amendments of different C:N ratio
    Ayongwa, G.C. ; Stomph, T.J. ; Kuyper, T.W. - \ 2011
    Crop Protection 30 (2011)12. - ISSN 0261-2194 - p. 1613 - 1622.
    fertility management - western kenya - burkina-faso - infestation - fallow - maize - sahel - dissemination - decomposition - systems
    The effect of organic amendments on the interactions between Striga hermonthica and a sorghum host was studied in a field experiment during three cropping seasons, following a three-factorial design with (i) bare fallow versus continuous cropping, (ii) two Strigahermonthica infection levels and (iii) five organic matter levels, a single inorganic fertiliser treatment of 120 kg N ha-1 and a control. The effects of two different cotton by-products and their mixtures on sorghum yield were well described by their N-mineralisation pattern. The impact of organic amendments in the sorghum production system was directly related to N-mineralisation in the three cropping seasons. There was an increasing negative effect of organic matter on S. hermonthica as the quality of the applied material increased. The emerged numbers of S. hermonthica were well described by N-release after one month, while S. hermonthica biomass and sorghum biomass were well described by N-release after three months. As a stand-alone measure, addition of low-quality organic matter is disadvantageous in cropping systems with high S. hermonthica seed densities, as it does not improve sorghum performance compared to no addition of organic matter, while S. hermonthica numbers increase. Implications for integrated soil fertility and S. hermonthica management under different infection levels of S. hermonthica are discussed
    Beneficial effects of wind erosion: Concepts measurements and modeling
    Poortinga, A. ; Visser, S.M. ; Riksen, M.J.P.M. ; Stroosnijder, L. - \ 2011
    Aeolian Research 3 (2011)2. - ISSN 1875-9637 - p. 81 - 86.
    aeolian sand transport - inland drift-sand - burkina-faso - farmers perceptions - prediction system - water erosion - soil-erosion - dune - sahel - beach
    Adaptive management of irrigated rice in the changing environments of the Sahel
    Vries, M.E. de - \ 2011
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Peter Leffelaar. - [S.l.] : S.n. - ISBN 9789085859918
    oryza sativa - rijst - landbouw met irrigatie - irrigatie - klimaatverandering - simulatiemodellen - genotype-milieu interactie - senegal - sahel - oryza sativa - rice - irrigated farming - irrigation - climatic change - simulation models - genotype environment interaction - senegal - sahel

    Key words: Alternate wetting and drying, Climate change adaptation, Crop growth simulation models, Genotype × environment interaction, N use efficiency, Oryza sativa L., Phenology, Sahelian irrigation schemes, Sowing date, Spikelet sterility, Temperature increase, Water productivity, Weed control.

    In the vulnerable environment of the Sahel with its erratic rainfall pattern, irrigated rice production is of major importance. To aid Sahelian rice farmers to sustain irrigated rice production, this study explores management options. It includes field experiments performed at two typical Sahelian sites and simulation studies using crop growth simulation models. This thesis provides evidence that it is possible to use less irrigation water while maintaining rice production, thus increasing water productivity. The effects of a temperature increase on the growing cycle and spikelet sterility of new rice varieties in interaction with different sowing dates is quantified. The simulation results show that the sowing window will be restricted and that the cultivar choice may alter; together they will remain the most important determinants of rice production in the coming decades.

    In Chapter 2, field experiments involving three water saving regimes using combinations of alternate wetting and drying (AWD) and flooding and a fully flooded control show that between 480 and 1060 mm of irrigation water was used in the water saving treatments compared with 800 to 1490 mm in the flooded rice treatment. Water productivity of the water-saving treatments was higher than of the flooded control, and yields ranged between 141 and 56% of the control. When weeds were controlled, crop yields obtained with a combination of AWD and flooding were comparable with those obtained in fully flooded plots receiving the same weed management. In Ndiaye, agronomic N use efficiency was smaller in the AWD treatments compared with fully flooded conditions. An irrigation regime for rice that starts as conventional (flooded), and then changes to AWD can save water with little or no yield loss, while maintaining low weed pressure and efficient use of N. To assess genotype adaptability, in Chapter 3 the results of experiments involving five genotypes, sown on 15 consecutive dates are presented. Yield (0-12t ha–1) and crop cycle duration (117-190 days) varied with sowing date, genotype and site. Rice yield was very sensitive to sowing date and the associated temperature regimes. Spikelet sterility due to cold stress (T < 20oC) was observed when the crops were sown betweenAugust and October,and heat stress (T > 35oC) resulted in spikelet sterility for sowingin April and May. For the simulation studies of Chapter 4, experimental data were used to calibrate both the DSSAT and ORYZA2000 models. Original genetic coefficients of DSSAT did not simulate phenology well, while genetic coefficients that did, resulted in lower than observed yields. Simulations by ORYZA_S and ORYZA2000 resulted in an increase in simulation error at sowing dates in the last three months of the year. The results show that local calibration at the same sowing date is needed. In the African Sahel, a temperature increase of between 1.8 and 4.7oC is predicted by 2080. Simulations by an improved and validated version of ORYZA2000 presented in Chapter 5 show that rice crop cycle length will decrease by 10‒30 days. The results suggest that with projected temperature changes, timing of sowing and consequently of the risk for crop loss due to sterility will remain the major determinant of rice yield. There is an urgent need for heat tolerant rice varieties. Without adaptation, cropping calendars will change, in the worst case scenario only a single crop will be possible. I conclude by suggesting viable options for adaptive management of irrigated rice in the changing environments of the Sahel to sustain production in the 21stcentury.

    Local ecosystem feedbacks and critical transitions in the climate
    Rietkerk, M. ; Brovkin, V. ; Bodegom, P.M. van; Kabat, P. ; Nes, E.H. van - \ 2011
    Ecological Complexity 8 (2011)3. - ISSN 1476-945X - p. 223 - 228.
    african humid period - stable states - soil-moisture - water-balance - vegetation - sahel - scale - system - variability - cover
    Global and regional climate models, such as those used in IPCC assessments, are the best tools available for climate predictions. Such models typically account for large-scale land-atmosphere feedbacks. However, these models omit local vegetation-environment feedbacks that may be crucial for critical transitions in ecosystems at larger scales. In this viewpoint paper, we propose the hypothesis that, if the balance of feedbacks is positive at all scales, local vegetation-environment feedbacks may trigger a cascade of amplifying effects, propagating from local to large scale, possibly leading to critical transitions in the large-scale climate. We call for linking local ecosystem feedbacks with large-scale land-atmosphere feedbacks in global and regional climate models in order to improve climate predictions.
    Effects of soil moisture gradients on the path and the intensity of a West African squall line
    Wolters, D. ; Heerwaarden, C.C. van; Vilà-Guerau de Arellano, J. ; Cappelaere, B. ; Ramier, D. - \ 2010
    Quarterly Journal of the Royal Meteorological Society 136 (2010)653. - ISSN 0035-9009 - p. 2162 - 2175.
    mesoscale convective complexes - land-surface - monsoon - variability - sahel - model - precipitation - dynamics - system - field
    During the West African monsoon season, precipitation is strongly coupled to soil moisture availability. This interaction is generally understood as a positive feedback mechanism, and has been considered on very different spatial and temporal scales. Past research has mainly focused on this feedback in terms of the effects on general precipitation patterns, not on a single convective system. In this research, a single squall line is reproduced using the Weather Research and Forecasting Advanced Research (WRF-ARW) mesoscale weather model. Model results are analyzed and compared with surface and upper-air observations. A sensitivity analysis on the influence of soil moisture on the squall line is performed through five numerical experiments. In four experiments, soil moisture is increased or decreased with respect to a control experiment. This is done in two manners: by affecting soil moisture most strongly in the wetter places in the modelled domain and by affecting soil moisture most strongly in the drier places. Minor deviations occur in the path of the squall line after modifying soil moisture most strongly in the wetter places. Systematic deviations occur in its path after increasing soil moisture most strongly in the drier places. A mechanism is proposed that connects the applied soil moisture modifications to larger-scale flow patterns that determine the path of the squall line. In all five experiments, the precipitation intensity of the squall line strongly declines when the systemmoves towards western areaswith lower soil moisture values. It is concluded that a positive effect of local soil moisture on precipitation intensity in passing squall lines is likely on the considered length-scale of 100 km. Until now, this mechanism has only been shown for much smaller spatial scales.
    Striga infestation in northern Cameroon: Magnitude, dynamics and implications for managament
    Ayongwa, G.C. ; Stomph, T.J. ; Hoevers, R. ; Ngoumou, T.N. ; Kuyper, T.W. - \ 2010
    NJAS Wageningen Journal of Life Sciences 57 (2010)2. - ISSN 1573-5214 - p. 159 - 165.
    soil fertility management - sub-saharan africa - hermonthica control - savanna zone - nigeria - land - sahel - productivity - cultivation - challenges
    Surveys of Striga (S. hermonthica (Del.) Benth.) infestation in northern Cameroon over the period 1987–2005 assessed Striga dynamics and evaluated its control strategies. In that period the percentage of Striga-infested fields increased in North and Far-North Provinces. Striga incidence increased more in maize fields than in the already heavily infested sorghum fields, where it remained almost constant. During the study period increased land pressure led to a reduction in the use of fallow and a higher frequency of cereal (mono-) cropping. Yields from farmers’ fields did not correlate with Striga incidence, confirming farmers’ prioritization of soil fertility, weeds, and labour for weeding as production constraints, rather than Striga. We discuss how conceptualization of Striga as a weed in the research arena may have led to a misunderstanding of farmers’ constraints. The decline of the cotton industry reduced farmers’ access to fertilizers, while access to organic manure remained limited, increasing the soil fertility constraint. We conclude that two decades of emphasis on Striga were unsuccessful. Enhanced crop yield through soil fertility management should be the entry point to tackle low yields and further worsening of the Striga situation
    Meer profijt van inheemse fruitbomen
    Berg, J. van den - \ 2010
    Kennis Online 7 (2010)maart. - p. 11 - 11.
    voedselzekerheid - vruchtbomen - sahel - fruitproducten - levensomstandigheden - ontwikkelingslanden - food security - fruit trees - sahel - fruit products - living conditions - developing countries
    Inheemse fruitbomen zijn in de Sahel belangrijk voor de bodemvruchtbaarheid en om van te eten en producten van te verkopen. Alle sociale klassen zijn daarin betrokken. Maar er is meer mogelijk, laat onderzoek zien waar het LEI aan meewerkte
    Linking participatory and GIS-based land use planning methods; A case study from Burkina Faso
    Hessel, R. ; Berg, J. van den; Kabore, O. ; Kekem, A.J. van; Verzandvoort, S.J.E. - \ 2009
    Land Use Policy 26 (2009)4. - ISSN 0264-8377 - p. 1162 - 1172.
    soil fertility management - sub-saharan africa - desertification debate - degradation - views - sahel
    Sustainable land use planning is crucial for realizing the aim of food security and for combating land degradation in the Sahel. A participatory land use planning workshop was organised in a village in the eastern region of Burkina Faso to investigate land use problems, their causes, effects and possible solutions. Participatory research tools and GIS were combined to get insight into possible conflicts or synergies between different land use options as mapped by different ethnic groups. Pictograms were used to locate alternative land use options on the map, after which they were digitised for analysis with GIS. The workshop confirms the importance of integrating scientific and local knowledge to develop concrete options for sustainable land use that fit to local realities and aspirations. Local people are knowledgeable about the driving forces behind land degradation, they take actions to combat the effects of degradation, and they have concrete ideas about alternative land use options. The use of GIS proved its added value in the participatory process of integrated land use planning. The maps that were produced also facilitate discussions between community members, researchers and government representatives at the regional level, both regarding current land use problems and regarding alternative options as perceived by the local population.
    Modifying land management in order to improve efficiency of rainwater use in the African highlands
    Stroosnijder, L. - \ 2009
    Soil & Tillage Research 103 (2009)2. - ISSN 0167-1987 - p. 247 - 256.
    semiarid west-africa - crust formation - burkina-faso - soil-erosion - sandy soils - stone bunds - sahel - water - rainfall - ethiopia
    Water scarcity and drought in Africa are often in the news. The widespread tendency to relate farmers¿ notion of drought to changes in the occurrence of dry spells is misguided: several recent studies have yielded little evidence of an increase in the length and/or frequency of such spells. The farmers¿ concept of drought is contextual and an indirect result of land degradation. Plant production suffers because water is not available due to deteriorated physical properties of soil. Farmers¿ perception of drought refers to the Green Water Use Efficiency (GWUE), i.e. the fraction of rain that is used for plant transpiration. GWUE in Africa is remarkably low: in sub-Saharan Africa, only 15% of the terrestrial rainwater is used by plants for the production of food, fodder and fibre. Although a millet crop grown under traditional circumstances uses only 50 mm in transpiration, the crop frequently suffers from agricultural drought due to excessive losses of rainwater. A range of land management practices is available to help improve GWUE. They can be classified according to their function. Hedgerow barriers and terraces can mitigate runoff; infiltration rates below hedgerows in Kenya were found to be three to eight times higher than where the crop was grown. Mulch that triggers soil fauna can improve water availability; mulching with straw from a local perennial grass in Burkina Faso doubled the water use efficiency from 1 kg mm¿1 without fauna to 2 kg mm¿1 with fauna. Water harvesting and water¿nutrient synergy can improve water use; in case permeable barriers combined with the use of compost Sorghum yield in Burkina Faso was 2.3 times higher than in the control plots and the plots with the barriers only.
    A European daily high-resolution gridded dataset of surface temperature and precipitation for 1950-2006
    Haylock, M. ; Hofstra, N. ; Klein Tank, A. ; Klok, L. ; Jones, P. ; New, M. - \ 2008
    Journal of Geophysical Research: Atmospheres 113 (2008). - ISSN 2169-897X - 12 p.
    areal rainfall estimation - united-kingdom - satellite data - uncertainties - validation - products - series - sahel - model
    We present a European land-only daily high-resolution gridded data set for precipitation and minimum, maximum, and mean surface temperature for the period 1950–2006. This data set improves on previous products in its spatial resolution and extent, time period, number of contributing stations, and attention to finding the most appropriate method for spatial interpolation of daily climate observations. The gridded data are delivered on four spatial resolutions to match the grids used in previous products as well as many of the rotated pole Regional Climate Models (RCMs) currently in use. Each data set has been designed to provide the best estimate of grid box averages rather than point values to enable direct comparison with RCMs. We employ a three-step process of interpolation, by first interpolating the monthly precipitation totals and monthly mean temperature using three-dimensional thin-plate splines, then interpolating the daily anomalies using indicator and universal kriging for precipitation and kriging with an external drift for temperature, then combining the monthly and daily estimates. Interpolation uncertainty is quantified by the provision of daily standard errors for every grid square. The daily uncertainty averaged across the entire region is shown to be largely dependent on the season and number of contributing observations. We examine the effect that interpolation has on the magnitude of the extremes in the observations by calculating areal reduction factors for daily maximum temperature and precipitation events with return periods up to 10 years
    Microscale vegetation-soil feedback boosts hysteresis in a regional vegetation-climate system
    Janssen, R.H.H. ; Meinders, M.B.J. ; Nes, E.H. van; Scheffer, M. - \ 2008
    Global Change Biology 14 (2008)5. - ISSN 1354-1013 - p. 1104 - 1112.
    semiarid grazing systems - northern africa - spatial heterogeneity - arabian peninsula - arid ecosystems - regime shifts - biome model - midholocene - sahel - monsoon
    It has been hypothesized that a positive feedback between vegetation cover and monsoon circulation may lead to the existence of two alternative stable states in the Sahara region: a vegetated state with moderate precipitation and a desert state with low precipitation. This could explain the sudden onset of desertification in the region about 5000 years ago. However, other models suggest that the effect of vegetation on the precipitation may be insufficient to produce this behavior. Here, we show that inclusion of the microscale feedback between soil and vegetation in the model greatly amplifies the nonlinearity, causing alternative stable states and considerable hysteresis even if the effect of vegetation on precipitation is moderate. On the other hand, our analysis suggests that self-organized vegetation patterns known from models that only focus at the microscale plant¿soil feedback will be limited to a narrower range of conditions due to the regional scale climate-feedback. This implies that in monsoon areas such as the Western Sahara self-organized
    Proxy global assessment of land degradation
    Bai, Z.G. ; Dent, D.L. ; Olsson, L. ; Schaepman, M.E. - \ 2008
    Soil Use and Management 24 (2008)3. - ISSN 0266-0032 - p. 223 - 234.
    net primary production - ndvi data - vegetation - sahel - models - avhrr
    Land degradation is always with us but its causes, extent and severity are contested. We define land degradation as a long-term decline in ecosystem function and productivity, which may be assessed using long-term, remotely sensed normalized difference vegetation index (NDVI) data. Deviation from the norm may serve as a proxy assessment of land degradation and improvement - if other factors that may be responsible are taken into account. These other factors include rainfall effects which may be assessed by rain-use efficiency, calculated from NDVI and rainfall. Results from the analysis of the 23-year Global Inventory Modeling and Mapping Studies (GIMMS) NDVI data indicate declining rain-use efficiency-adjusted NDVI on ca. 24% of the global land area with degrading areas mainly in Africa south of the equator, South-East Asia and south China, north-central Australia, the Pampas and swaths of the Siberian and north American taiga; 1.5 billion people live in these areas. The results are very different from previous assessments which compounded what is happening now with historical land degradation. Economic appraisal can be undertaken when land degradation is expressed in terms of net primary productivity and the resultant data allow statistical comparison with other variables to reveal possible drivers.
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