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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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    Evaluating rainwater harvesting systems in arid and semi-arid regions
    Ammar, Adham Ali - \ 2017
    Wageningen University. Promotor(en): C.J. Ritsema, co-promotor(en): M.J.P.M. Riksen; M. Quessar. - Wageningen : Wageningen University - ISBN 9789463431460 - 207
    water harvesting - rain - water - arid zones - semiarid zones - geographical information systems - water management - climatic change - tunisia - iraq - regenwateropvang - regen - water - aride klimaatzones - semi-aride klimaatzones - geografische informatiesystemen - waterbeheer - klimaatverandering - tunesië - irak

    Rainwater harvesting (RWH) is an ancient traditional technology practised in many parts of the world, especially in arid and semi-arid regions (ASARs). ASARs represent 40% of the earth’s land surface and are characterised by low average annual rainfall and uneven temporal and spatial distributions of that rainfall. In these regions an efficient use of the limited amount of rainfall available is important, e.g. by collecting and using surface runoff (water harvesting). Lately, access to water for agriculture and domestic use has become worse because of increasing population, higher levels of human activity and the impacts of climate change. The inhabitants of ASARs have developed several RWH techniques to increase the water availability, thus coping with water shortages. RWH is an important mitigation strategy to the impact of climate change on water availability in ASARs.

    Four main methodologies of site selection were categorised, ranging from those based only on biophysical criteria to more integrated approaches that include socioeconomic criteria. Our analysis suggests that the integration of multi-criteria analysis (MCA) with a geographic information system (GIS) is the most advanced approach. It offers high potential in data-poor regions; GIS-based hydrological modelling is always recommended for data-rich regions.

    The potential for RWH in wadi Horan (western desert of Iraq) was identified using a GIS-based suitability model. The method for selecting suitable sites for RWH was then further developed into an evaluation and decision support tool for assessing the overall performance of existing RWH systems by integrating engineering, biophysical and socioeconomic criteria using MCA supported by GIS. It was tested in the wadi Oum Zessar in southeastern Tunisia.

    A simple but generally applicable water harvesting model (WHCatch) was developed to investigate and optimise the performance of the RWH systems under various scenarios of design and management, It was tested in wadi Oum Zessar. The advantages of simulating long-term water balances at the sub-catchment level for improving our understanding of hydrological processes in an RWH system are emphasised. Several solutions for optimising RWH performance in various scenarios are provided.

    Finally, the impact of climate change on existing RWH systems in the Oum Zessar watershed under current and future scenarios of climate was investigated. The downscaled maximum and minimum temperatures clearly indicated an increasing trend in the mean monthly temperature and the generated precipitation tended to decrease in the future. It was shown that the combination of changing the flow direction and the spillway height had a large impact on the performance of the RWH systems under current and future conditions. Water management and structural design at the sub-catchment level plays a more important role than climate change in the performance of RWH.

    Effect of water harvesting techniques on hydrological processes and sediment yield in Northern Ethiopia
    Woldegiorgis, Berhane Grum - \ 2017
    Wageningen University. Promotor(en): V. Geissen; C.J. Ritsema, co-promotor(en): R. Hessel; C.A. Kessler. - Wageningen : Wageningen University - ISBN 9789463431682 - 156
    hydrology - water harvesting - arid zones - semiarid zones - water availability - ethiopia - hydrologie - regenwateropvang - aride klimaatzones - semi-aride klimaatzones - waterbeschikbaarheid - ethiopië

    The study was conducted in the semi-arid northern Ethiopia aimed at selecting appropriate water harvesting techniques (WHTs) for implementation. A plot-scale experiment was set up, in the Gule catchment, on a farmland to monitor the effect of in-situ WHTs such as tied ridges and straw mulch mainly on event-based runoff, soil-moisture, and soil and nutrient losses. The off-site effect of WHTs such as check dams and percolation ponds on catchment-scale event-based runoff and sediment yield was also monitored in the Gule catchment (~12 km2) and Misbar sub-catchment (~2.4 km2), northern Ethiopia. First, a decision support approach was developed to aid the selection of WHTs in arid and semi-arid areas. The decision support approach was validated with a case study for WHTs in the upper Geba watershed in northern Ethiopia. Using the decision support methodology, eight potential WHTs were pre-selected for implementation in the watershed. Next, using suitability indicators for WHTs and a GIS-based multi-criteria analysis, suitable areas were identified for three of these WHTs, namely check dams, percolation ponds and bench terraces and suitability maps were generated. The multi-criteria analysis was validated by comparing the predicted suitable areas with the already existing locations of WHTs in the watershed. The result was that 90% of the existing check dams and 93% of the percolation ponds in the upper Geba watershed were correctly identified by the approach. The field study showed runoff reduction by WHTs from farmland between 40 to 88% and soil loss between 60 to 90%. Nutrient loss reduction from farmland by WHTs also ranged between 52 and 86%. Soil-moisture also improved due to the use of the in-situ WHTs. Model-based simulation at the Gule and Misbar outlets using LISEM showed that the current WHTs applied in the catchment are able to decrease event-based runoff by 41 and 45%, respectively. Similarly, sediment yield was reduced at both the Gule outlet and Misbar sub-outlet, by 67 and 55%, respectively. This study has verified that in semi-arid areas, such as the northern Ethiopian highlands, in-situ and catchment-scale WHTs can be used to improve the efficiency of rainwater harvesting and water availability for agricultural uses. Furthermore, these WHTs help to mitigate land degradation by decreasing soil and nutrient losses from farmland and sediment yield from catchments.

    How small is beautiful? : food self-sufficiency and land gap analysis of smallholders in humid and semi-arid sub Saharan Africa
    Hengsdijk, H. ; Franke, A.C. ; Wijk, M.T. van; Giller, K.E. - \ 2014
    Wageningen : Plant Research International, Business Unit Agrosystems Research (Report / Plant Research 562) - 46
    zelfvoorziening - kleine landbouwbedrijven - voedsel - landbouwhuishoudens - huishoudens - gewasproductie - humide klimaatzones - semi-aride klimaatzones - afrika ten zuiden van de sahara - self sufficiency - small farms - food - agricultural households - households - crop production - humid zones - semiarid zones - africa south of sahara
    Water management for rainfed maize in semi-arid Zimbabwe
    Nyakudya, I.W. - \ 2014
    Wageningen University. Promotor(en): Leo Stroosnijder. - Wageningen : Wageningen University - ISBN 9789461738981 - 148
    waterbeheer - zea mays - regenafhankelijke landbouw - akkerbouw - semi-aride klimaatzones - zimbabwe - grondbewerking gericht op bodemconservering - water management - zea mays - rainfed agriculture - arable farming - semiarid zones - zimbabwe - conservation tillage
    Recovery of rangelands : the functioning of soil seed banks in a semi-arid African savanna
    Tessema, Z.K. - \ 2011
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Fred de Boer; R.M.T. Baars. - [S.l.] : S.n. - ISBN 9789085859987 - 198
    zaadbanken - zaden - bodem - savannen - vegetatie - begrazing - kieming - graszaden - semi-aride klimaat - semi-aride klimaatzones - plantenecologie - ecologie - afrika - seed banks - seeds - soil - savannas - vegetation - grazing - germination - grass seeds - semiarid climate - semiarid zones - plant ecology - ecology - africa

    Rangelands in Africa provide important forage resources for herbivores; particularly perennial grasses provide grazing for domestic and wild herbivores. However, semi-arid African rangelands experience severe vegetation and soil degradation due to heavy grazing, causing negative impacts on the ecosystems, livestock production and livelihoods of the people. Semi-arid African rangelands can be described by a state-and-transition models, often with three stable states, the first one being a state with ample herbaceous cover, perennial grasses and scattered trees, the second one as a state with a poor cover of annual grasses, absence of perennial grasses, and the third state with a high proportion of bare soil and/or often bush encroached. This thesis aims to fill important information gaps concerning soil seed banks that play in the recovery and possible restoration of degraded semi-arid African rangelands with particular emphasis on Ethiopia. This was done through investigating the mechanisms of how heavy grazing affects the soil seeds bank dynamics so as to understand stable states and transition processes of aboveground vegetation. In this thesis, aboveground vegetation and soil seed bank dynamics were studied under heavy and light grazing pressures in a field and experimental conditions. Results show that heavy grazing resulted in the disappearance of perennial grasses, a reduction in herbaceous species diversity and their plant abundance, standing biomass and basal cover, as well as a decrease in the soil nutrient conditions. The soil seed banks was correlated to differences in grazing pressure, with a greater seedling density under light grazing compared with heavy grazing. Immediately after seed dispersal, the seedling density increased over the first first three months until the eight months of soil sampling, and decreased thereafter. Under light grazing, perennial grass species dominated, whereas annual species were abundant at the heavily grazed sites, indicating that perennial grasses, with good fodder value, are replaced by annual species in the soil seed banks due to heavy grazing. With increasing soil depth, the seedling density and its species richness declined. Moreover, the seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. The similarity in species composition between the soil seed banks and aboveground vegetation was low under heavy grazing. Results also show that annual grasses had a lower germination and mortality, and higher viability, leading to a longevity of 62% over the 120 days burial in the soil, which was high compared to the 28% for perennials. Moreover, most perennial grasses germinate rapidly after initial seed dispersal at the first rains early in the year, whereas annual grasses show a linear germination pattern over time, indicating that perennial grasses have different survival strategy in semi-arid Africa. As a result, annual species are expected to dominate the soil seed banks, whereas most perennial grass species do not form persistent soil seed banks.The mean mortality from the seedling stage to adult plants in grass species was 65%, and the seed–to–seedling stage was found the most critical transitional stage for grass survival on these rangelands, suggesting that exclusion from grazing and trampling in the early germination stage is important to facilitate the transition from seedling to established plants. Depletion of perennial grass seeds in the soil due to heavy grazing coupled with high seedling mortality leads to a strong decrease in perennial grasses both in the soil seed banks, as well as in the aboveground vegetation. I found that the positive relationship between plant cover and differences in soil seed bank dynamics, i.e., seed density, seed germination rate and longevity, trigger the transition from perennial grasses to annuals and from annual plant cover to bare soil under heavy grazing. I hypothesize that the restoration of perennial grasses from the soil seed banks in heavily grazed areas in semi-arid African rangelands cannot be successful without an extraneous source of perennial grass seeds and without protecting the young plant’s regrowth from trampling and grazing. Therefore, the persistence of species and maintenance of biodiversity in semi-arid rangelands depends mainly on the recruitment of seedlings from annual species, and on vegetative reproduction of perennial grasses and woody species. These findings have important implications for the management, conservation and restoration of semi-arid African rangelands.

    Keywords:Africa; Aboveground vegetation; Ethiopia; Pastoral system; Rangeland; Restoration; Soil seed bank; Savanna; Semi-arid ecosystem; Vegetation and soil degradation

    Agricultural intensification : saving space for wildlife?
    Baudron, F. - \ 2011
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): M. Corbeels; Jens Andersson; Pablo Tittonell. - [S.l.] : S.n. - ISBN 9789085859642 - 244
    semi-aride klimaatzones - beschermingsgebieden - intensivering - kleine landbouwbedrijven - boeren - wild - hulpbronnenbeheer - katoen - natuurbescherming - zimbabwe - semiarid zones - conservation areas - intensification - small farms - farmers - wildlife - resource management - cotton - nature conservation - zimbabwe

    Key words: agricultural frontier; smallholder; intensification; semi-arid area; wildlife; conservation agriculture; cotton; Zimbabwe.

    Increasing agricultural production and preventing further losses in biodiversity are both legitimate objectives, but they compete strongly in the developing world. In this study, current tensions between agricultural production and environmental conservation were described and analysed in Mbire District, an agricultural frontier shared with wildlife that lies in the Mid-Zambezi Valley, in the northern fringe of Zimbabwe. The potential of conservation agriculture (CA) to intensify agricultural production with minimum negative environmental effects was then explored. The population of Mbire District almost doubled between 1992 and 2002, while the livestock densities increased at rates above 15% in the early 1990s and the late 2000s. From 1980 to 2007, the expansion of farmland over the years was described by an exponential relationship. It was suggested that these changes affected elephant and buffalo numbers negatively. Increase in human population, increase in cattle population, and expansion of cotton farming were all drivers on the observed land use change. However, cotton farming was demonstrated to be paramount, enabling cattle accumulation and expansion of plough-based agriculture. The ‘environmental footprint’ per farm was increasing significantly with the area under cotton and with the number of draught animals owned. A kilogram of seed cotton required 50% more land, removed twice as much N, 50% more K and 20% more P than a kilogram of cereal. However, except for pesticide, one man-day invested in cotton production had a smaller environmental footprint than a man-day invested in cereal production. As farming in Mbire District is limited by labour more than by land, specialising in cereal production would increase the total area occupied by crops and fallows, whilst specializing in cotton production would reduce this area. Therefore, maintaining or increasing the relative profitability of cotton vs. cereal may ‘spare land’ for nature. Compared with current farmers’ cropping practices (CP), CA had no effect on cotton productivity during years that received average or above average rainfall. During a drier year, however, CA was found to have a slightly negative effect (110 kg ha-1 less in on-farm trials and 220 kg ha-1 less in farmers’ cotton fields). Most soils in the study area are coarse-textured soils, on which runoff were significantly greater with CA than with CP. For these reasons, farmers perceived ploughing as necessary during drier years to maximize water infiltration, but saw CA as beneficial during wetter years as a means to ‘shed water’ and avoid waterlogging. In Zimbabwe, the approach used in the extension of CA appears to differ little from an earlier attempt to intensify smallholder agricultural production almost a century earlier: the Alvord model. In particular, the rationale of African smallholder farming has been persistently ignored. The analysis of smallholder farming practices in Mbire District showed how the socio-economic constraints they faced predisposed them towards extensification. In particular, labour availability for weeding was found to be a major limiting factor in the area. The increased weed pressure in CA is therefore a major reason preventing smallholders from embracing it. As a conclusion, mitigating conflicts between agricultural production and biodiversity conservation will require major innovations, far beyond CA. CA should be seen as part of a larger basket of technologies aiming at ‘ecological intensification’. In parallel to the development of technical innovations, local institutions should be empowered and strong regulations put in place.

    Assessment of soil salinisation risks under irrigation with brackish water in the semi-arid Tunisia
    Fethi, B. ; Akissa, B. ; Ronny, B. ; Rozema, J. ; Zee, S.E.A.T.M. van der - \ 2010
    landbouwgrond - bodemchemie - verzilting - irrigatie - semi-aride klimaatzones - tunesië - agricultural land - soil chemistry - salinization - irrigation - semiarid zones - tunisia
    In semiarid Tunisia, based on the findings related to the soil and groundwater properties, soil salinisation factors were identified and soil salinisation risk map were elaborated. This map is appreciated by both land planners and farmers to make appropriate decisions related to crop production, and soil and water management.
    Nutrients in an African Savanna: the consequences of supply heterogeneity for plants and animals
    Waal, C. van der - \ 2010
    Wageningen University. Promotor(en): Herbert Prins; H. de Kroon, co-promotor(en): Ignas Heitkonig. - [S.l. : S.n. - ISBN 9789085856740 - 151
    voedingsstoffen - bodemvruchtbaarheid - heterogeniteit - savannen - bomen - grassen - biologische mededinging - herbivoren - begrazing - afgrazen - foerageren - vegetatie - semi-aride klimaatzones - schaalverandering - voedingsstoffenbeschikbaarheid - zuid-afrika - nutrients - soil fertility - heterogeneity - savannas - trees - grasses - biological competition - herbivores - grazing - browsing - foraging - vegetation - semiarid zones - scaling - nutrient availability - south africa
    In savannas, trees and grasses co-exist and share resources such as water and
    nutrients. The ratio between the tree and grass components (i.e., vegetation structure)
    importantly controls productivity, animal assemblages and earth-atmosphere
    feedbacks. As the structure of savanna vegetation is inherently unstable and easily
    disturbed, finding out how the vegetation structure is controlled is of great importance
    for rangeland management and conservation. Currently four factors are believed to
    control the vegetation structure in savannas; namely, water, nutrients, herbivory and
    fire. While the water and fire factors have been intensely studied, the roles of nutrients
    and herbivores as factors are less well known. Improving our understanding of the
    role of nutrients in savannas is relevant, because it is increasingly realised that global
    change also alter the availability of nutrients, e.g., increased nitrogen deposition. How
    savanna systems respond to nutrient perturbations is uncertain. Changes in soil
    nutrient availability are also likely to feed back to changes in forage quality, which
    may influence large herbivore use and vegetation impact patterns, thus indirectly
    influencing vegetation structure. Moreover, it is increasingly realised that not only
    changes in the availability of nutrients influence plants and subsequently herbivores,
    but also how nutrients become spatially available. In fact, new ideas suggest that
    differences in the scale of spatial resource heterogeneity may control how resources
    are partitioned between co-existing species differing in size, e.g., large trees coexisting
    with small grasses in savanna systems. To test how changes in nutrient
    availability and spatial configurations influence savanna systems, several field
    experiments were conducted in a semi-arid savanna in South Africa.
    In the study area we found that nutrient (N, P and K) availability negatively
    affected tree (Colophospermum mopane) seedling establishment in fertilization
    experiments. Also, trees failed to re-colonize nutrient-rich kraal sites that were
    abandoned almost half a century ago. In dry savannas, it is currently believed that the
    success of tree seedling establishment exercises large control over the relative
    dominance of trees, thus an increase in nutrient availability may feed back to a
    structurally more open vegetation state. Different explanations may account for
    constrained tree seedling establishment under fertile soil conditions. We tested the
    hypothesis that the intensification of grass competition reduces tree seedling
    recruitment in fertile environments. In controlled competition experiments it was
    shown that negative nutrient effects on tree seedlings only occur when seedlings were
    competing with grasses in mixtures. Furthermore, we found that adding both water
    and nutrients to tree seedling-grass plant mixtures cancelled the negative effects of
    added nutrients on tree seedlings. Thus the suppressing effect of increased nutrient
    availability on seedlings appears to operate indirectly through the pre-empting of soil
    water resources by vigorous herbaceous growth under fertile conditions. Since woody
    seedlings are vulnerable to water stress, increased nutrient-induced water stress
    translates into higher mortality rates and suppressed growth of tree seedlings in fertile
    areas. In support, transplanted tree seedling mortality increased during a mid-season
    drought as local fertilizer concentration increased. In conclusion, intensified
    herbaceous competition under fertile soil conditions appears to be a viable
    mechanism explaining poor tree seedling recruitment under fertile soil conditions.
    Savannas and nutrients
    While establishing tree seedlings suffer under fertile conditions, our data
    suggest that established (mature) tree growth benefitted from an increase in nutrient
    availability, especially following an increase in N availability. With regards to
    increased atmospheric N deposition, we predict that tree cover may initially expand
    following nutrient enrichment in dry savannas, although tree cover responses may be
    insensitive to current levels of N deposition. However, in the long-term tree cover is
    expected to decline, because of constrained tree recruitment that appears to be more
    sensitive to small increases in N availability.
    The relative availability of nutrients such as N and P may also influence how
    resources are partitioned between co-existing trees and grasses. In a field experiment
    we found evidence that trees were relatively more limited by N than P availability. An
    East African study has shown that grasses underneath trees are more P than N limited
    and we found evidence that the competiveness of sub-canopy grasses in our study
    increased when only P was supplied. The relative availability of N vs. P may therefore
    offer an additional axis governing resource partitioning between trees (non N-fixing)
    and grasses in savanna systems. This supports the idea that organisms with a high
    growth potential, apparently grasses in savannas, have relatively high P requirements
    to sustain rapid protein synthesis, while slower growing organisms such as trees are
    more limited by the availability of N.
    The availability of soil nutrients strongly mediated where large herbivores
    concentrated their impact in the landscape. Both grazers and browsers responded
    positively to fertilization, apparently via the control that soil nutrient availability has
    on forage quality. Tree and grass leaf N and P concentrations increased and
    condensed tannin concentrations in trees decreased following fertilization. Under high
    local soil nutrient concentrations the vegetation biomass was in some instances
    reduced below control biomass by herbivores, indicating that top-down herbivore
    effects potentially override bottom-up nutrient effects under fertile conditions.
    In ecology, it is increasingly realized that it is not only the availability of
    nutrients, but also how nutrients become spatially available that matters. Data from a
    large field experiment where a gradient in the scale of nutrient patchiness (i.e., patch
    grains sizes 2 x 2 m, 10 x 10 m or 50 x 50 m) was created, suggested that the scale of
    nutrient patchiness controlled the partitioning of resources between co-existing trees
    and grasses. For the same local fertilizer concentration, tree leaf quality was
    unresponsive to fertilization in small patches, but responded in the larger patches.
    Grass leaf quality increased with local fertilizer concentration regardless of patch size.
    The differential responses of trees and grasses to scale differences subsequently
    modulated the responses of the browser and grazer guilds. For the same high local
    fertilizer concentration, grazers responded to both fine and coarse scales of nutrient
    patchiness, while browsers responded only to the coarse scale of nutrient patchiness.
    In turn, the selective grazing in the fine scale of nutrient patchiness treatment,
    apparently stimulated tree growth. In the coarser scale of patchiness treatment both
    browsers and grazer impact intensified locally. Thus the scale of nutrient patchiness
    controlled nutrient partitioning between trees and grasses, which was apparently
    closely tracked by the large herbivore assemblage, resulting in differential local
    impacts on the tree and grass layers. Apart from local effects, the scale of nutrient
    patchiness may also regulate the use and quality of forage resources at larger (e.g.,
    landscape) scales. In the large field fertilizer experiment, calculations suggest that the
    total herbaceous off-take by grazers peaked where the same fertilizer amount (15 kg N
    plot-1) was spread over the whole plot surface area rather than concentrated in 10 x 10
    m patches. Thus, how nutrients are distributed in an area controls secondary
    productivity and where herbivores concentrate their impact.
    The scale related patterns observed in the large fertilizer experiment may have
    been reinforced by plastic responses (e.g., fine root proliferation in nutrient-rich soil)
    to heterogeneous nutrient supplies of trees in the coarse scale treatments and grasses
    in the fine scale treatments, respectively. To test this, the same nutrient amount was
    supplied at two different scales of patchiness to focal trees with their associated
    grasses. Two years after fertilization, large-scale fertilized trees showed increased
    shoot growth and increased leaf N concentrations compared to small-scale fertilized
    trees receiving the same N amount. Conversely, trees in a small-scale configuration
    fertilized with P showed negative responses compared to large-scale counterparts.
    These results suggest that differences in the local scale of nutrient patchiness also
    influence how nutrients are partitioned between co-existing trees and grasses.
    Herbivores not only respond to nutrient heterogeneity, but may also create
    spatial heterogeneity in nutrient availability, which, in turn, may influence the
    vegetation structure of savannas. We studied the current soil nutrient status, tree and
    grass biomass patterns and large herbivore use of nine former livestock holding pen
    areas (kraals) in a semi-arid, nutrient poor savanna. These were contrasted with
    nearby control sites located in the surrounding landscape. The kraals, formerly
    enriched by livestock dung and urine, were abandoned around 1970 and since then
    wildlife replaced livestock in these parts. We found that around 40 years later, kraal
    soil had elevated concentrations of inorganic N, extractable P, K, Ca and Mg
    compared to control sites, which resulted in high quality forage in kraal sites. Trees
    also failed to invade these sites, thus kraals remained as structurally open patches in
    the otherwise dense savanna. Evidently, wild large herbivores maintain the high
    nutrient status of kraal sites, probably by importing nutrients into these sites and by
    accelerating local nutrient cycling. In turn, the increased local nutrient availability
    prevents tree seedlings from establishing under these fertile conditions.
    Finally, this study provided evidence that changes in the availability of
    nutrients influenced the success of woody seedling establishment, which may feed
    back to changes in the relative proportions of trees and grasses in dry savannas.
    Furthermore, this study supports the new idea that the scale of resource heterogeneity
    influences how resources are partitioned between co-existing trees and grasses, which,
    in turn, modulated browser vs. grazer use and impact patterns on the vegetation.
    In conclusion, this study provides new information on nutrient-plant-herbivore
    interactions in a dry savanna with potentially important implications for the
    management of dry savannas in general.
    Understanding cropping systems in the semi-arid environments of Zimbabwe: options for soil fertility management
    Ncube, B. - \ 2007
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): S.J. Twomlow; Mark van Wijk. - [S.l.] : S.n. - ISBN 9789085046356 - 155
    teeltsystemen - semi-aride klimaatzones - bodemvruchtbaarheid - bodembeheer - landbouwbedrijven - kleine landbouwbedrijven - boeren - fabaceae - dierlijke meststoffen - kunstmeststoffen - zimbabwe - cropping systems - semiarid zones - soil fertility - soil management - farms - small farms - farmers - fabaceae - animal manures - fertilizers - zimbabwe
    African smallholder farmers face perennial food shortages due to low crop yields. The major cause of poor crop yields is soil fertility decline. The diversity of sites and soils between African farming systems isgreat,therefore strategies to solve soil fertility problems should suit the opportunities and problems encountered in the different climatic regions. This thesis characterizes the semi-arid regions of south-western Zimbabwe and explores some of the strategies that can be used to provide farmers with more options for soil fertility improvement.

    Resource flow maps were used to study the characteristics of the semi-arid farming system of Tsholotsho (Mkhubazi)in south-westernZimbabwe. The results revealed that farmers in the region face perennial cereal grain shortages, but the poorly-resourced farmers are the most affected. Nutrient management is limited to the use of limited amounts of manure by the better-resourced and medium-resourced farmers. Poorly-resourced farmers did not apply any nutrients to their crops.

    The use of low rates of manure and fertilizer is one option that farmers in the semi-arid regions can adopt. Farmers who had access to small amounts of manure and fertilizer were able to increase cereal yields through farmer participatory research experiments. Previously the farmers did not apply manure to crops. In 2003-2004, with good rainfall maize yields due to manure applications at 3 and 6 t ha −1 were 1.96 and 3.44 t ha −1 compared to 1.2 and 2.7 t ha −1 from plots without. Top dressing with 8.5 kg N ha −1 increased yields to 2.5 t ha −1 with 3 t ha −1 of manure, and to 4.28 t ha −1 with 6 t ha −1 of manure. In dry years manure in combination with N fertilizer increased grain yield by about 0.14 and 0.18 t ha −1 .

    The research results also showed that it is possible to successfully grow grain legumes under the semi-arid conditions and derive substantial residual yield benefits to sorghum grown after the legumes. New varieties of grain legumes seemed to be well adapted to dry environments.Sorghum grain yields after legumes reached1.62 t ha -1in 2003/04, more than double the yields in the sorghum after sorghum rotation, and the yields were also higher in 2004/05.

    The Agricultural Production SIMulator (APSIM) was used to model the legume-sorghum rotation to test it's capability in simulating cropping systems in the semi-arid southernAfrica.The model output of N and water stress factors on plant growth assisted in better understanding the water, N and plant growth interactions within a cropping season, as well as the residual benefits of legumes interacting with variable seasonal conditions. The model showed that the residual benefits of the legumes were driven by nitrogen availability more than water even under the semi-arid conditions.

    Further research will focus on the simulation of long-term effects of the manure/fertilizer experiments and the legume-cereal rotations. The use of farming systems models is required in order to get a better understanding of the functioning of smallholder farming systems in semi-arid regions and identify possible development pathways of the systems.
    Coping with drought : options for soil and water management in semi-arid Kenya
    Biamah, E.K. - \ 2005
    Wageningen University. Promotor(en): Leo Stroosnijder. - Wageningen : Wageningen University and Research Centre - ISBN 9789085041788 - 119
    droogte - waterbeheer - grondbeheer - bodembeheer - semi-aride klimaatzones - kenya - drought - water management - land management - soil management - semiarid zones - kenya
    In semi-arid Kenya, episodes of agricultural droughts of varying severity and duration occur. The occurrence of these agricultural droughts is associated with seasonal rainfall variability and can be reflected by seasonal soil moisture deficits that significantly affect crop productivity. The aim of this study was to analyse agricultural drought, and to evaluate soil and water management options and strategies for sustainable crop production in drought-prone semi-arid Kenya. Research was conducted at an experimental site in Katumani and in Iiuni watershed, both in Machakos district. First the occurrence of dry and wet spells in Iiuni was modelled using a Markov model. The study revealed that the short rains (October-December) are more reliable for crop production than the long rains (March-May). A literature review on tillage methods for soil and water conservation in eastern Africa showed the importance of appropriate tillage practices and the benefits of residue management for improved soil moisture conditions. Especially conservation tillage techniques were found to be promising for the improvement of crop productivity under semi-arid climatic conditions. Moreover, farm yard manure application in combination with tillage appeared effective in reducing surface runoff from a crusting and compacting soil, especially during the early stages of the rainy season. At the watershed scale, the AGNPS model was applied to evaluate the effect of land use changes on watershed runoff volume. Changes in land use covering a period of nearly 20 years were significant, with an dramatic increase in the area for crop cultivation, but this did not have a significant effect on the hydrology. The reason is the widespread adoption of soil and water conservation measures (mainly bench terracing) that occurred during the same period. The last part of the thesis deals with suitable options for watershed conservation in semi-arid Kenya. Apart from technical solutions, the enabling conditions to farmers at various hierarchical policy levels are discussed. A few of these enabling conditions that are elaborated upon include agricultural policy, focus on smallholder agriculture and public-community partnerships
    Soil quality improvement for crop production in semi-arid West Africa
    Ouédraogo, E. - \ 2004
    Wageningen : Wageningen University and Research Centre (Tropical resource management papers 51) - ISBN 9789067547321 - 193
    bodemvruchtbaarheid - bodemdegradatie - bodembescherming - grondbewerking - gewasproductie - semi-aride gronden - semi-aride klimaatzones - west-afrika - bodemkwaliteit - soil fertility - soil degradation - soil conservation - tillage - crop production - semiarid soils - semiarid zones - west africa - soil quality
    Soil quality improvement for crop production in semi-arid West Africa
    Ouédraogo, E. - \ 2004
    Wageningen University. Promotor(en): Leo Stroosnijder, co-promotor(en): Lijbert Brussaard. - Wageningen : Wageningen Universiteit - ISBN 9789058089922 - 193
    bodemvruchtbaarheid - bodemdegradatie - bodembescherming - grondbewerking - gewasproductie - semi-aride gronden - semi-aride klimaatzones - west-afrika - bodemkwaliteit - soil fertility - soil degradation - soil conservation - tillage - crop production - semiarid soils - semiarid zones - west africa - soil quality
    Soil quality maintenance and crop production improvement in semi-arid West Africa require appropriate cropping technologies, which are ecologically sound and economically viable. Thus, on-farm and on-station experiments have been carried out on the central plateau and in the south of Burkina Faso The results show that adoption of improved soil fertility technologies such as composting by farmers is determined by soil fertility status, access to the market and social reasons. Organic amendments increase crop production but its effects on soil carbon depend on its quality. Soil tillage improves crop performance as a result of enhanced crop nutrient uptake and water use efficiency but decrease soil carbon with fertilisation. Combination of crop residues and urea may reverse this negative effect. Soil fauna accounted for 50 % of crop production. Termites mediated the disappearance of low-quality organic amendments. Soil carbon build-up in the presence of soil fauna requires the use of easily decomposable organic material or combined low quality organic material with nitrogen fertiliser. Phosphate rock-derived phosphorus availability is 4 times higher in earthworm casts than in surrounding soil. Single use of nitrogen fertiliser leads to low use efficiency by crop and induces low to negative economic benefit. Combination of organic resource and fertiliser significantly increases crop performance and economic benefit of N fertilisers. Without both organic and mineral external inputs, soil quality maintenance and crop production improvement cannot be achieved at the same time in semi-arid West-Africa. Improving soil quality and crop performance in semi-arid West-Africa is best achieved with an integrated soil fertility management including external inputs (organic and mineral), the contribution of soil fauna and soil and water conservation measures and in some cases with tillage
    Integrated water and nutrient management for sorghum production in semi-arid Burkina Faso
    Zougmoré, R. - \ 2003
    Wageningen University. Promotor(en): Leo Stroosnijder. - [S.l.] : S.n. - ISBN 9789058089069 - 150
    gewasproductie - sorghum - voedingsstoffenbeschikbaarheid - semi-aride klimaatzones - burkina faso - integraal waterbeheer - crop production - sorghum - nutrient availability - semiarid zones - burkina faso - integrated water management
    Loss of water and nutrients through runoff are major agriculture problems for inherent poor fertile soils in semiarid West Africa. The intensification of crop production requires an integration of soil, water and nutrient management that is locally acceptable and beneficial for smallholder farmers. To that end, two semi-permeable soil and water conservation measures (stone rows, grass strips) and two nitrogen inputs (compost, urea) applied alone or in combination were studied on the Central Plateau of Burkina Faso. Stone rows greatly reduce runoff, soil erosion and improve soil moisture. Under unfertilised continuous sorghum cropping, stone rows induced limited effect on soil fertility improvement. During erratic rainfall years in the Sahelian zone, stone rows alone doubled sorghum yield compared to plots without stone rows and therefore, can reduce risks of crop failure. During well-distributed rainfall years, stone rows alone did not induce significant yield increase. Grass strips of Andropogon gayanus was also an efficient anti-erosion measure and could be an interesting alternative to stone rows, especially in stone-limiting areas. However, Andropogon grass must be managed properly to alleviate shading and other effects of competition on crops near to the strips. The sole applications of compost or urea improved nutrient uptake and crop biomass production that subsequently demands more available water for transpiration. Combining stone rows or grass strips with compost in intensified crop production systems resulted into substantial crop yields and economic benefits. This integrated water and nutrient management may help to alleviate poverty and may empower smallholder farmers to invest in soil management for better crop production in West Africa.
    Off-farm income, risk, and agricultural production: a case study of smallholders in India's semi-arid tropics
    Berg, M.M. van den - \ 2001
    Wageningen University. Promotor(en): A. Kuyvenhoven; J.W. Gunning; R. Ruben. - S.l. : S.n. - ISBN 9789058084859 - 167
    landbouw bedrijven - kleine landbouwbedrijven - werkgelegenheid buiten het landbouwbedrijf - inkomsten van buiten het landbouwbedrijf - landbouwproductie - gewasproductie - risico - semi-aride klimaatzones - tropen - india - farming - small farms - off-farm employment - non-farm income - agricultural production - crop production - risk - semiarid zones - tropics - india

    The purpose of the current study was to determine to what extent development of the nonfarm sector stimulates crop production and agricultural employment in India's semi-arid tropics (SAT). Two characteristics of India's SAT agriculture formed the basis for the study: i) that the major agricultural producers, smallholders, earn a significant part of their income outside their own farm, especially in the daily labour market; and ii) that crop production risk is high. As the farmers are risk averse and they have limited options to smooth consumption through changes in assets and liabilities, they try to stabilise income. This could result in the choice of crop production technologies that render relatively stable, but low yields. On the other hand, off-farm income may provide an alternative for stabilising income and ensure minimum consumption in all years. Hence, because they can earn off-farm income, farm households may be willing and able to increase crop incomes, even if this involves higher crop income variability from year to year.

    The study shows that the labour market is extremely important in preventing farm households in India's SAT from experiencing very low incomes. Households actively adapt family labour supply to production risk. Much more important for income stability, however, is the flow of labour income that households earn independent of their risk preferences. As expected, production risk affects not only farm-household labour supply, but also the use of the major inputs in crop production: male and female labour and fertiliser use. Depending on the specific input and the production environment, risk appears to increase or decrease the use of a specific input.

    The above suggests that the household labour endowment will affect crop input use and income from crop production. The first is true, given that there is sufficient year-round off-farm employment and not just employment during the agricultural growing season. In this case, households with a larger labour endowment feel less need to adapt the use of crop labour and fertilisers to production risk. However, these small changes in input use hardly seem to affect the magnitude and stability of crop income: the estimated input elasticities of the mean and variability of crop yields are low. Surprisingly, the household labour endowment thus has little effect on crop income.

    Actual labour income may, however, still have a significant impact on net crop income: some farmers work longer hours than others do. Moreover, income from minor sources of off-farm employment, like nonfarm self-employment, may also affect net crop income. Empirical estimates show that the size and nature of the effect of off-farm income on net crop income depends on the characteristics of the income flow. Activities that require labour simultaneous to crop production and that have low returns on labour decrease net crop income. If the returns on the off-farm activity are certain and high relative to the casual farm wage, households will, however, simply substitute hired labour or capital for family labour. Moreover, they will use part of the off-farm income to intensify crop production. Finally, if the nonfarm activity becomes the main source of interest of the farm household, income from this activity will no longer affect crop production.

    Gestion de la fertilité des sols par classe d'exploitation au Mali-Sud
    Kanté, S. - \ 2001
    Wageningen University. Promotor(en): H. van Keulen; E.M.A. Smaling. - S.l. : S.n. - ISBN 9789058085696 - 236
    bodemvruchtbaarheid - mest - oogstresten - voedingsstoffen - boekhouding - agrarische bedrijfsvoering - kosten-batenanalyse - semi-aride klimaatzones - mali - soil fertility - manures - crop residues - nutrients - accounting - farm management - cost benefit analysis - semiarid zones - mali
    In Southern Mali, it becomes increasingly difficult to take poor and overused arable land and pastures temporarily out of production, at a time when growing human and animal populations require increasing amounts for food and feed. In fact, the tendency is towards continuous cultivation, and as organic and mineral fertilizers appear not to compensate for nutrient losses, farmers, herdsmen and development workers are all worried about the sustainability of the current arable and agro-pastoral systems. This study carried out in two villages and for three 'manure and residue management' categories of farms, intends to: (1) identify manure production and residue management strategies that reflect differences in pressure on the land; (2) measure, monitor and calculate nutrient inputs and outputs per farm category; (3) perform a cost-benefit analysis on the management of crop residues; (4) develop a decision support tool for residue and manure management. The study shows that the higher the pressure on the land, the more efforts farmers have to make to feed their animals and to keep their soils fertile. During the 3 years of monitoring, partial nutrient balances (nutrient inputs in mineral and organic fertilizers minus nutrients withdrawn in crops and residues) were positive. Also, it is shown that the use of manure, including its residual effect during a second year, generates a surplus of 0.2-2 West African Francs (CFA) for every franc invested. Production of manure can be increased by 1 to 4 tons per farm holding, depending on the farm category. These all have their own strategy based on the socio-economic realities. Finally, some research avenues for soil fertility improvement are depicted, based on effective participation of all individuals that have a stake in rural development in Southern Mali.

    ILRI workshop: water and food security in (semi-)arid areas : proceedings of the [second] Wageningen water workshop 1998, [2-4 November]
    Schrevel, A. - \ 1999
    Wageningen : ILRI (Special report / ILRI ) - 182
    water management - irrigation - food supply - arid zones - semiarid zones - waterbeheer - irrigatie - voedselvoorziening - aride klimaatzones - semi-aride klimaatzones
    Monitoring for groundwater management in (semi)-arid regions
    Lanen, H.A.J. van - \ 1998
    Paris : Unesco - ISBN 9789231035791 - 224
    grondwater - waterbeheer - monitoring - semi-aride klimaatzones - hydrogeologie - groundwater - water management - monitoring - semiarid zones - hydrogeology
    Woody plants in agro-ecosystems of semi-arid regions
    Breman, H. ; Kessler, J.J. - \ 1995
    Springer Verlag (Advanced Series in Agricultural Sciences ) - ISBN 9783642792090
    bosbouw - agroforestry - ecologie - gewassen - landbouw - fenologie - acclimatisatie - gemengde teelt - tussenteelt - meervoudige teelt - tussenplanting - bedrijfssystemen - relaties - steppen - pampa's - semi-aride klimaatzones - agro-ecosystemen - forestry - ecology - crops - agriculture - phenology - acclimatization - mixed cropping - intercropping - multiple cropping - interplanting - farming systems - relationships - steppes - pampas - semiarid zones - agroecosystems
    A quantitative analysis of the role of woody plants in semi-arid regions, focusing on the Sahel and Sudan zones in West-Africa, is given for the assessment of their benefits in agro-sylvopastoral land-use systems with productive and sustainability objectives.
    Improving land care in West Africa.
    Stroosnijder, L. - \ 1994
    LEISA : ILEIA newsletter for low-external-input and sustainable agriculture 10 (1994)2. - ISSN 1569-8424 - p. 12 - 13.
    inheemse kennis - pampa's - plattelandsontwikkeling - plattelandsplanning - sahel - semi-aride klimaatzones - sociale economie - steppen - duurzaamheid (sustainability) - economische planning - indigenous knowledge - pampas - rural development - rural planning - semiarid zones - socioeconomics - steppes - sustainability - economic planning
    Rainfed agriculture in the West African Sahel is in transition between shifting cultivation based on renewable resources and more permanent farming with addition of external inputs. Some important issues concerning this agricultural development including the aspect of land degradation, are shortly described
    Groundwater monitoring in (semi-) arid regions. A general outline.
    Lanen, H.A.J. van - \ 1994
    In: International workshop on groundwater monitoring and recharge in semi - arid areas, Hyderabad, India, January 18-20, 1994 - p. SI1 - SI13.
    woestijnen - grondwater - hydrologie - instrumenten (meters) - meting - monitoring - pampa's - semi-aride klimaatzones - steppen - waterbeheer - waterkwaliteit - aride klimaatzones - netwerken - deserts - groundwater - hydrology - instruments - measurement - pampas - semiarid zones - steppes - water management - water quality - arid zones - networks
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