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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    Climate Change in Southern Africa: Farmers’ Perceptions and Responses
    Kuivanen, K. ; Alvarez, S. ; Langeveld, C.A. - \ 2015
    Wageningen UR - 46
    climatic change - farmers - attitudes - knowledge systems - adaptation - rural communities - southern africa - klimaatverandering - boeren - attitudes - kennissystemen - adaptatie - plattelandsgemeenschappen - zuidelijk afrika
    Southern Africa is characterized by natural climate variability onto which human-induced climate change is being superimposed. Rural communities that depend heavily on rain-fed agriculture for their livelihood are particularly vulnerable to the effects of climate-related change. This report takes stock of existing perceptions of- and responses to climate change among smallholder farmers in the region, in the hope of contributing to a better understanding of the complexities of local knowledge- and adaptation systems.
    Structural, physiognomic and above-ground biomass variation in savanna–forest transition zones on three continents– how
    Veenendaal, E.M. ; Torello-Raventos, M. ; Feldpausch, T.R. ; Domingues, T.F. ; Gerard, F. ; Schrodt, F. ; Saiz, G. ; Quesada, C.A. ; Djagbletey, G. ; Sykora, K.V. - \ 2015
    Biogeosciences 12 (2015). - ISSN 1726-4170 - p. 2927 - 2951.
    alternative stable states - tropical forest - cerrado vegetation - brazilian cerrado - woody vegetation - national-park - tree height - amazonian forest - functional types - southern africa
    Through interpretations of remote-sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands located mostly within zones of transition (where both vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant leaf area index variation was related to tree canopy cover in a similar way for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey grasses and herbs progressively replaced by shrubs as the canopy closes over was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna–forest-species discontinuum is observed compared to that inferred when trees of a basal diameter > 0.1 m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater amount of above-ground biomass than in South America. Up to three times as much above-ground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna–forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three continents coexistence was found to be confined to a well-defined edaphic–climate envelope with soil and climate the key determinants of the relative location of forest and savanna stands. Moreover, when considered in conjunction with the appropriate water availability metrics, it emerges that soil exchangeable cations exert considerable control on woody canopy-cover extent as measured in our pan-continental (forest + savanna) data set. Taken together these observations do not lend support to the notion of alternate stable states mediated through fire feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical lands.
    Conservation tillage of rainfed maize in semi-arid Zimbabwe: A review
    Nyakudya, I.W. ; Stroosnijder, L. - \ 2015
    Soil & Tillage Research 145 (2015). - ISSN 0167-1987 - p. 184 - 197.
    zea-mays l. - sandy soils - sustainable agriculture - water conservation - rural livelihoods - smallholder farms - southern africa - use efficiency - rainwater use - long-term
    Food security in Sub-Saharan Africa, particularly in semi-arid tropics (41% of the region; 6 months of dry season) is threatened by droughts, dry spells and infertile soils. In Zimbabwe, 74% of smallholder farming areas are located in semi-arid areas mostly in areas with soils of low fertility and water holding capacity. The dominant crop in these areas, maize (Zea mays L.), is susceptible to drought. Under smallholder farming in Zimbabwe, conventional tillage entails cutting and turning the soil with a mouldboard plough thereby burying weeds and crop residues. Seed is planted by hand into a furrow made by the plough, ensuring that crops germinate in relatively weed free seedbeds. Inter-row weed control is performed using the plough or ox-drawn cultivators and hand hoes. Conventional tillage has been criticised for failure to alleviate negative effects of long dry spells on crops and to combat soil loss caused by water erosion estimated at 50 to 80 t ha-1 yr-1. Therefore, conservation tillage has been explored for improving soil and water conservation and crop yields. Our objective was to determine the maize yield advantage of the introduced technology (conservation tillage) over conventional tillage (farmers’ practice) based on a review of experiments in semi-arid Zimbabwe. We use a broad definition of conservation tillage instead of the common definition of =30% cover after planting. Eight tillage experiments conducted between 1984 and 2008 were evaluated. Conventional tillage included ploughing using the mouldboard plough and digging using a hand hoe. Conservation tillage included tied ridging (furrow diking), mulch ripping, clean ripping and planting pits. Field-edge methods included bench terraces (fanya juus) and infiltration pits. Results showed small yield advantages of conservation tillage methods below 500 mm rainfall. For grain yields =2.5 t ha-1 and rainfall =500 mm, 1.0 m tied ridging produced 144 kg ha-1 and mulch ripping 344 kg ha-1 more than conventional tillage. Above 2.5 t ha-1 and for rainfall >500 mm, conventional tillage had =640 kg ha-1 yield advantage. Planting pits had similar performance to ripping and conventional tillage but faced digging labour constraints. Experiments and modelling are required to test conservation tillage seasonal rainfall thresholds. Constraints to adoption of conservation tillage by smallholder farmers necessitate best agronomic practices under conventional tillage while work on adoption of alternative tillage methods continues.
    Reconciling interests concerning wildlife and livestock near conservation areas: A model for analysing alternative land uses
    Chaminuka, P. ; Groeneveld, R.A. ; Ierland, E.C. van - \ 2014
    Ecological Economics 98 (2014). - ISSN 0921-8009 - p. 29 - 38.
    reserve network - southern africa - biodiversity - selection - policy - costs
    Land use decisions are central to both biodiversity conservation and rural development goals at local, national and international levels. Transfrontier Conservation Areas (TFCAs), now common in Southern Africa, present an opportunity to address these goals simultaneously. This paper proposes a theoretical spatial land allocation model that enables analysis of alternative scenarios for realising rural development and biodiversity conservation within TFCAs. The model includes socioeconomic and ecological factors such as income, fencing, connectivity, predation and disease costs and allows for clarification of opportunities and tradeoffs in land use. The model demonstrates alternative spatial options for diversification in land use, whilst accommodating the connectivity requirements and endogenous effects of wildlife on other land uses. The model is illustrated using several scenarios which include changes in key parameters, and limitations on total land allocated per land use. Illustrated scenarios show that land allocated to different land uses varies with output prices and costs such as fencing and wildlife damages, resulting in different spatial land use allocations. In addition, total revenue also changes when limitations are placed on land allocated to wildlife and tourism uses. The model can be used to reconcile interests where conservation and agricultural development activities compete for land.
    Fertilizer use should not be a fourth principle to define conservation. Response to the opinion paper of Vanlauwe et al. (2014)
    Sommer, R. ; Thierfelder, C. ; Tittonell, P.A. ; Hove, L. ; Mureithi, J. ; Mkomwa, S. - \ 2014
    Field Crops Research 169 (2014). - ISSN 0378-4290 - p. 145 - 148.
    zea-mays l. - soil quality - residue management - southern africa - ecological intensification - water relations - systems - maize - tillage - yield
    Application of remote sensing to understanding fire regimes and biomass burning emissions of the tropical Andes
    Oliveras Menor, I. ; Anderson, L.O. ; Malhi, Y. - \ 2014
    Global Biogeochemical Cycles 28 (2014)4. - ISSN 0886-6236 - p. 480 - 496.
    burned-area - amazonian forest - southern africa - carbon - modis - tree - variability - mortality - deforestation - biodiversity
    In the tropical Andes, there have been very few systematic studies aimed at understanding the biomass burning dynamics in the area. This paper seeks to advance on our understanding of burning regimes in this region, with the first detailed and comprehensive assessment of fire occurrence and the derived gross biomass burning emissions of an area of the Peruvian tropical Andes. We selected an area of 2.8 million hectares at altitudes over 2000¿m. We analyzed fire occurrence over a 12 year period with three types of satellite data. Fire dynamics showed a large intra-annual and interannual variability, with most fires occurring May–October (the period coinciding with the dry season). Total area burned decreased with increasing rainfall until a given rainfall threshold beyond which no relationship was found. The estimated fire return interval (FRI) for the area is 37¿years for grasslands, which is within the range reported for grasslands, and 65¿years for forests, which is remarkably shorter than other reported FRI in tropical moist forests. The greatest contribution (60–70%, depending on the data source) to biomass burning emissions came from burned montane cloud forests (4.5 million Mg CO2 over the study period), despite accounting for only 7.4–10% of the total burned area. Gross aboveground biomass emissions (7.55¿±¿2.14 Tg CO2; 0.43¿±¿0.04 Tg CO; 24,012¿±¿2685¿Mg CH4 for the study area) were larger than previously reported for the tropical Andes.
    Comparative assessment of maize, finger millet and sorghum for household food security in the face of increasing climatic risk
    Rurinda, J. ; Mapfumo, P. ; Wijk, M.T. van; Mtambanengwe, F. ; Rufino, M.C. ; Chikowo, R. ; Giller, K.E. - \ 2014
    European Journal of Agronomy 55 (2014). - ISSN 1161-0301 - p. 29 - 41.
    southern africa - soil fertility - pearl-millet - sandy soil - zimbabwe - variability - management - adaptation - productivity - agriculture
    Questions as to which crop to grow, where, when and with what management, will be increasingly challenging for farmers in the face of a changing climate. The objective of this study was to evaluate emergence, yield and financial benefits of maize, finger millet and sorghum, planted at different dates and managed with variable soil nutrient inputs in order to develop adaptation options for stabilizing food production and income for smallholder households in the face of climate change and variability. Field experiments with maize, finger millet and sorghum were conducted in farmers’ fields in Makoni and Hwedza districts in eastern Zimbabwe for three seasons: 2009/10, 2010/11 and 2011/12. Three fertilization rates: high (90 kg N ha-1, 26 kg P ha-1, 7 t ha-1 manure), low (35 kg N ha-1, 14 kg P ha-1, 3 t ha-1 manure) and a control (zero fertilization); and three planting dates: early, normal and late, were compared. Crop emergence for the unfertilized finger millet and sorghum was 70% for the fertilized treatments. In contrast, the emergence for maize (a medium-maturity hybrid cultivar, SC635), was >80% regardless of the amount of fertilizer applied. Maize yield was greater than that of finger millet and sorghum, also in the season (2010/11) which had poor rainfall distribution. Maize yielded 5.4 t ha-1 compared with 3.1 t ha-1 for finger millet and 3.3 t ha-1 for sorghum for the early plantings in the 2009/10 rainfall season in Makoni, a site with relatively fertile soils. In the poorer 2010/11 season, early planted maize yielded 2.4 t ha-1, against 1.6 t ha-1 for finger millet and 0.4 t ha-1 for sorghum in Makoni. Similar yield trends were observed on the nutrient-depleted soils in Hwedza, although yields were less than those observed in Makoni. All crops yielded significantly more with increasing rates of fertilization when planting was done early or in what farmers considered the ‘normal window’. Crops planted early or during the normal planting window gave comparable yields that were greater than yields of late-planted crops. Water productivity for each crop planted early or during the normal window increased with increase in the amount of fertilizer applied, but differed between crop type. Maize had the highest water productivity (8.0 kg dry matter mm-1 ha-1) followed by sorghum (4.9 kg mm-1 ha-1) and then finger millet (4.6 kg mm-1 ha-1) when a high fertilizer rate was applied to the early-planted crop. Marginal rates of return for maize production were greater for the high fertilization rate (>50%) than for the low rate (100%) than for the high rate (
    The evaluation and adoption of annual legumes by smallholder maize farmers for soil fertility maintenance and food diversity in central Malawi
    Kamanga, B.C.G. ; Kanyama-Phiri, G.Y. ; Waddington, S.R. ; Almekinders, C.J.M. ; Giller, K.E. - \ 2014
    Food Security 6 (2014)1. - ISSN 1876-4517 - p. 45 - 59.
    analytic hierarchy process - southern africa - technologies - mucuna - agriculture - management - systems - model - crop
    We studied the process of assessment and adoption of 10 grain- and green-manure legumes by smallholder maize farmers differing in resource endowment in Chisepo, central Malawi. The legumes had been promoted with the farmers from 1998 to 2004, primarily as a way to diversify food production and maintain the fertility of their soils. Farmers (n¿=¿136) were surveyed in 2004 at the end of the period of promotion to assess the degree of awareness and uptake of the legumes and the reasons for adoption. A follow-up survey was conducted in 2007 among a broader sample of Chisepo farmers (n¿=¿84) to measure the persistence of adoption. An Analytic Hierarchy Process (AHP) was used in 2004 to create scales of priority and as a tool to compare predicted with actual legume uptake. Actual adoption of food grain legumes reflected predictions by the AHP but it over-predicted uptake of the non-food legumes. The AHP helped us understand how farmer perceptions and needs influence adoption, as well as limitations with the legumes. Suitability for food was the most important criterion that farmers identified for adoption, followed by contribution to soil fertility and suppression of weeds. Over 75 % of the farmers surveyed in 2004 were aware of most of the legumes. Frequent use of the grain legumes was reported in 2004 (79 % for CG7 groundnut, 77 % for soyabean and 47 % for pigeonpea) by both the better-resourced (wealthier) and less-well-resourced (poorer) farm households. Awareness rose to over 90 % of farmers surveyed in 2007 but adoption fell somewhat to 67 % for soyabean, 57 % for CG7 groundnut and 43 % with pigeonpea among the wealthier farmers, while Bambara groundnut rose to 38 %. Fifty-two percent of poorer farmers reported adoption of CG7, 46 % soyabean, 35 % Bambara groundnut and 27 % pigeonpea in 2007. There was greater uptake by the wealthier farmers than those with fewer resources. Overall, although the legumes were promoted for maintenance of soil fertility, farmers were largely interested in and mainly adopted those legumes they considered most useful for food diversity and security, and with potential for market sale. Only a few wealthier farmers used mucuna and tephrosia among the green manure legumes. Improving the food value of vigorous and productive multi-purpose legumes, particularly mucuna, may help raise the farmers’ interest, with secondary benefits for soil fertility.
    Three interwoven dimensions of natural resource use: Quantity, quality and access in the Great Limpopo transfrontier conservation area
    Milgroom, J.M. ; Giller, K.E. ; Leeuwis, C. - \ 2014
    Human Ecology 42 (2014)2. - ISSN 0300-7839 - p. 199 - 215.
    southern africa - property - institutions - environment - management - community - politics - land
    Quality and quantity of natural resources are often studied in isolation from access. We question the usefulness of this separation for resolving conflicts over natural resources and present an approach that facilitates a deeper understanding of natural resource use through a joint analysis of quantity of, quality of and access to resources. The approach was developed as part of an in-depth case study of resettlement in southern Mozambique in which newly resettled residents struggled to reestablish their livelihoods. We estimated the quality and quantity of, and investigated rules and norms of access to four key natural resources: water, agricultural fields, grazing, and forest resources in both pre- and post-resettlement. We then contrast this with the actual access that resettled residents gained to these resources in practice, what we call ‘accessing.’ Our analysis suggests that locally-specific, dynamic relationships among quality, quantity and access are critically important for understanding human-environment interactions and natural resource-based livelihoods.
    Managing soil fertility to adapt to rainful variability in smallholder cropping systems in Zimbabwe
    Rurinda, J. ; Mapfumo, P. ; Wijk, M.T. van; Mtambanengwe, F. ; Rufino, M.C. ; Chikowo, R. ; Giller, K.E. - \ 2013
    Field Crops Research 154 (2013). - ISSN 0378-4290 - p. 211 - 225.
    climate-change - southern africa - sandy soil - corn production - use efficiency - food security - management - maize - farmers - yield
    Adaptation options that address short-term climate variability are likely to lead to short-term benefits and will help to deal with future changes in climate in smallholder cropping systems in Sub-Saharan Africa (SSA). In this study we combined field experimentation and long-term rainfall analyses in Makoni and Hwedza districts in eastern Zimbabwe to evaluate cropping adaptation options to climate variability. Analyses of long-term rainfall data closely supports farmers’ perceptions that the mean annual total rainfall has not changed, but the pattern of rainfall within-season has changed: the number of rainfall days has decreased, and the frequency of dry spells has increased at the critical flowering stage of maize. On-farm experiments were conducted over two cropping seasons, 2009/10 and 2010/11 to assess the effects of planting date, fertilization and cultivar on maize production. Three maize cultivars were sown in each of the early, normal and late planting windows defined by farmers. Each of the nine cultivar-planting date combinations received N, P, K and manure combinations at either zero, low or high fertilization rates. Overall, there were no significant differences in maize development or grain yield among cultivars. Maize grain yield was increased by increasing the amount of nutrients applied. Average yield was 2.5 t ha-1 for the low rate and 5.0 t ha-1 for the high rate on early planted cultivars on relatively fertile soils in Makoni in 2009/10 season. Yields on poorer soils in Hwedza were small, averaging 1.5 t ha-1 for the low rate and 2.5 t ha-1 for the high rate. Maize grain yields for the early and normal planted cultivars were similar for each fertilization rate, suggesting there is a wide planting window for successful establishment of crops in response to increased rainfall variability. Yield reduction of >50% was observed when planting was delayed by 4 weeks (late planting) regardless of the amount of fertilizer applied. Soil nutrient management had an overriding effect on crop production, suggesting that although the quality of within-season rainfall is decreasing, nutrient management is the priority option for adaptation in rain-fed smallholder cropping systems.
    Dynamic biomass burning emission factors and their impact on atmospheric CO mixing ratios.
    Leeuwen, T.T. van; Peters, W. ; Krol, M.C. ; Werf, G.R. van der - \ 2013
    Journal of Geophysical Research: Atmospheres 118 (2013)12. - ISSN 2169-897X - p. 6797 - 6815.
    transform infrared-spectroscopy - trace gas emissions - zoom model tm5 - carbon-monoxide - southern africa - fire emissions - burned-area - interannual variability - laboratory measurements - smoldering combustion
    [1] Biomass burning is a major source of trace gases and aerosols, influencing atmospheric chemistry and climate. To quantitatively assess its impact, an accurate representation of fire emissions is crucial for the atmospheric modeling community. So far, most studies rely on static emission factors (EF) which convert estimates of dry matter burned to trace gas and aerosol emissions. These EFs are often based on the arithmetic mean of field measurements stratified by biome, neglecting the variability in time and space. Here we present global carbon monoxide (CO) emission estimates from fires based on six EF scenarios with different spatial and temporal variability, using dry matter emission estimates from the Global Fire Emissions Database (GFED). We used the TM5 model to transport these different bottom-up estimates in the atmosphere and found that including spatial and temporal variability in EFs impacted CO mixing ratios substantially. Most scenarios estimated higher CO mixing ratios (up to 40% more CO from fires during the burning season) over boreal regions compared to the GFED standard run, while a decrease (~15%) was estimated over the continent of Africa. A comparison to atmospheric CO observations showed differences of 10–20¿ppb between the scenarios and systematic deviations from local observations. Although temporal correlations of specific EF scenarios improved for certain regions, an overall “best” set of EFs could not be selected. Our results provide a new set of emission estimates that can be used for sensitivity analyses and highlight the importance of better understanding spatial and temporal variability in EFs for atmospheric studies in general and specifically when using CO or aerosols concentration measurements to top-down constrain fire carbon emissions.
    What could have caused pre-industrial biomass burning emissions to exceed current rates?
    Werf, G.R. van der; Peters, W. ; Leeuwen, T.T. van; Giglio, L. - \ 2013
    Climate of the Past 9 (2013)1. - ISSN 1814-9324 - p. 289 - 306.
    rain-forest fires - past 2 millennia - amazonian forests - southern africa - trace gases - model tm5 - land-use - carbon - 20th-century - climate
    Recent studies based on trace gas mixing ratios in ice cores and charcoal data indicate that biomass burning emissions over the past millennium exceeded contemporary emissions by up to a factor of 4 for certain time periods. This is surprising because various sources of biomass burning are linked with population density, which has increased over the past centuries. We have analysed how emissions from several landscape biomass burning sources could have fluctuated to yield emissions that are in correspondence with recent results based on ice core mixing ratios of carbon monoxide (CO) and its isotopic signature measured at South Pole station (SPO). Based on estimates of contemporary landscape fire emissions and the TM5 chemical transport model driven by present-day atmospheric transport and OH concentrations, we found that CO mixing ratios at SPO are more sensitive to emissions from South America and Australia than from Africa, and are relatively insensitive to emissions from the Northern Hemisphere. We then explored how various landscape biomass burning sources may have varied over the past centuries and what the resulting emissions and corresponding CO mixing ratio at SPO would be, using population density variations to reconstruct sources driven by humans (e.g., fuelwood burning) and a new model to relate savanna emissions to changes in fire return times. We found that to match the observed ice core CO data, all savannas in the Southern Hemisphere had to burn annually, or bi-annually in combination with deforestation and slash and burn agriculture exceeding current levels, despite much lower population densities and lack of machinery to aid the deforestation process. While possible, these scenarios are unlikely and in conflict with current literature. However, we do show the large potential for increased emissions from savannas in a pre-industrial world. This is mainly because in the past, fuel beds were probably less fragmented compared to the current situation; satellite data indicates that the majority of savannas have not burned in the past 10 yr, even in Africa, which is considered "the burning continent". Although we have not considered increased charcoal burning or changes in OH concentrations as potential causes for the elevated CO concentrations found at SPO, it is unlikely they can explain the large increase found in the CO concentrations in ice core data. Confirmation of the CO ice core data would therefore call for radical new thinking about causes of variable global fire rates over recent centuries
    Transfrontier Conservation Areas: people living on the edge
    Andersson, J.A. ; Garine-Wichatitsky, M. de; Cumming, D.H.M. ; Dzingirai, V. ; Giller, K.E. - \ 2013
    Oxon, UK : Routledge - ISBN 9781849712088 - 216
    beschermingsgebieden - grensgebieden - natuurlijke hulpbronnen - duurzaamheid (sustainability) - samenleving - sociologie - toerisme - wild - wildbescherming - mensen - zuidelijk afrika - conservation areas - frontier areas - natural resources - sustainability - society - sociology - tourism - wildlife - wildlife conservation - people - southern africa
    This book focuses on the forgotten people displaced by, or living on the edge of, protected wildlife areas. It moves beyond the grand 'enchanting promise' of conservation and development across frontiers, and unfounded notions of TFCAs as integrated social-ecological systems. Peoples' dependency on natural resources – the specific combination of crop cultivation, livestock keeping and natural resource harvesting activities – varies enormously along the conservation frontier, as does their reliance on resources on the other side of the conservation boundary. Hence, the studies in this book move from the dream of eco-tourism-fuelled development supporting nature conservation and people towards the local realities facing marginalized people, living adjacent to protected areas in environments often poorly suited to agriculture.
    Top-down and bottom-up control of large herbivore populations: a review of natural and human-induced influences
    Gandiwa, E. - \ 2013
    Tropical conservation science 6 (2013)4. - ISSN 1940-0829 - p. 493 - 505.
    gonarezhou national-park - community structure - african savannas - food-web - wildlife conservation - aboriginal overkill - trophic cascades - southern africa - body-size - ecosystems
    The question whether animal populations are top-down and/or bottom-up controlled has motivated a thriving body of research over the past five decades. In this review I address two questions: 1) how do top-down and bottom-up controls influence large herbivore populations? 2) How do human activities and control systems influence the top-down and bottom-up processes that affect large herbivore population dynamics? Previous studies suggest that the relative influence of top-down vs. bottom-up control varies among ecosystems at the global level, with abrupt shifts in control possible in arid and semi-arid regions during years with large differences in rainfall. Humans as super-predators exert top-down control on large wild herbivore abundances through hunting. However, through fires and livestock grazing, humans also exert bottom-up controls on large wild herbivore abundances through altering resource availability, which influences secondary productivity. This review suggests a need for further research, especially on the human-induced top-down and bottom-up control of animal populations in different terrestrial ecosystems.
    Pushing the envelope? Maize production intensification and the role of cattle manure in recovery of degraded soils in smallholder farming areas of Zimbabwe
    Rusinamhodzi, L. ; Corbeels, M. ; Zingore, S. ; Nyamangara, J. ; Giller, K.E. - \ 2013
    Field Crops Research 147 (2013). - ISSN 0378-4290 - p. 40 - 53.
    repellent sandy soil - organic-matter - ecological intensification - conservation agriculture - fertility gradients - southern africa - management - systems - carbon - resource
    Soil fertility decline is a major constraint to crop productivity on smallholder farms in Africa. The objective of this study was to evaluate the long-term (up to nine years) impacts of nutrient management strategies and their local feasibility on crop productivity, soil fertility status and rainfall infiltration on two contrasting soil types and different prior management regimes in Murehwa, Zimbabwe. The nutrient management strategies employed in the study were: a control with no fertiliser, amendments of 100 kg N ha-1, 100 kg N + lime, three rates of manure application (5, 15 and 25 t ha-1) in combination with 100 kg N ha-1, and three rates of P fertiliser (10, 30 and 50 kg P ha-1) in combination with 100 kg N, 20 kg Ca, 5 kg Zn and 10 kg Mn ha-1. Maize grain yields in sandy soils did not respond to the sole application of 100 kg N ha-1; manure application had immediate and incremental benefits on crop yields on the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 in the clay outfield, 7.6 t ha-1 in the homefield and 3.4 t ha-1 in the eighth season. Yields of the largest manure application on the sandy outfields were comparable to yields with 100 kg N in combination with 30 kg P, 20 kg Ca, 5 kg Zn and 10 kg Mn ha-1 in the homefields suggesting the need to target nutrients differently to different fields. Manure application improved rainfall infiltration in the clay soils from 21 to 31 mm h-1 but on the sandy soils the manure effect on infiltration was not significant. Despite the large manure applications, crop productivity and SOC build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. The major cause of poor crop productivity on the degraded sandy soils despite the large additions of manure could not be ascertained. The current practice of allocating manure and fertiliser to fields closest to homesteads exacerbates land degradation in the sandy outfields and increases soil fertility gradients but results in the most harvest for the farm. On clay soils, manure may be targeted to outfields and mineral fertiliser to homefields to increase total crop productivity. Farmers who owned cattle in the study site can achieve high manure application rates on small plots, and manure application can be rotated according to crop sequences. Consistent application of manure in combination with mineral fertilisers can be an effective option to improve crop yield, SOC and moisture conservation under smallholder farming conditions. Combined manure and mineral fertiliser application can be adapted locally as a feasible entry point for ecological intensification in mixed crop–livestock systems.
    Nuances and nuisances : Crop production intensification options for smallholder farming systems of southern Africa
    Rusinamhodzi, L. - \ 2013
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): M. Corbeels. - Wageningen : Wageningen University - ISBN 9789461735737 - 222
    bedrijfssystemen - intensivering - kleine landbouwbedrijven - boeren - gewasproductie - zuidelijk afrika - farming systems - intensification - small farms - farmers - crop production - southern africa

    Key words: crop production, intensification, extensification, farming systems, tradeoff analysis, maize, legume, manure, fertiliser, southern Africa

    Soil fertility decline and erratic rainfall are major constraints to crop productivity on smallholder farms in southern Africa. Crop production intensification along with efficient use of chemical fertiliser is required to produce more food per unit area of land, while rebuilding soil fertility. The objective of this thesis was to identify appropriate crop production intensification options that are suitable to the socio-economic and biophysical conditions of selected smallholder maize-based farming systems in southern Africa. Three sites that formed a gradient of intensity of crop and livestock production were selected for the study. Murehwa in Zimbabwe is characterised by the largest intensity followed by Ruaca and lastly Vunduzi both in central Mozambique. In all three sites, maize is a key staple and cash crop.A literature review, field methods based on participatory research, and modelling tools were combined in analysing potential crop production options across an agricultural intensification gradient. A meta-analysis on maize grain yieldunder rain-fed conditions revealed thatconservation agriculture required legume rotations and high nitrogen input use especially in the early years.Reduced tillage without mulch cover leads to lower yields than with conventional agriculture in low rainfall environments. Mulch cover in high rainfall areas leads to smaller yields than conventional tillage due to waterlogging, and improved yields under CA are likely on well drained soils. Crop productivity underconservation agriculture depends on the ability of farmers to achieve correct fertiliser application, timely weeding, and the availability of crop residues for mulching and systematic crop rotations which are currently lacking in southern Africa. Anadditive design of within-row intercropping was compared to a substitutive design with distinct alternating rows of maize and legume (local practice) under no-tillin the Ruaca and Vunduzi communities of central Mozambique. Intercropping increased productivity compared to the corresponding sole crops with land equivalent ratios (LER) of between 1.0 and 2.4. Maize yield loss was only 6-8% in within-row intercropping but 25-50% in the distinct-row option. Relay planting of maize and cowpea intercropping ensured cowpea yield when maize failed thus reduced the negative effects of dry spells. The residual benefits of maize-pigeonpea intercropping were large (5.6 t ha-1) whereas continuous maize (0.7 t ha-1) was severely infested by striga(Striga asiatica). The accumulation of biomass which provided mulch combined with no tillageincreased rainfall infiltration. Intensification through legume intercropping is a feasible option to increase crop productivity and farm income while reducing the risk of crop failureespecially where land limitation. Cattle manure in combination with chemical fertiliser that included N, P, Ca, Zn, Mn were evaluated for their potential to recover degraded soils and to support sustainable high crop productivity in Murehwa, Zimbabwe over nine years. The experiment was established on sandy and clay soils in two field types. Homefields were close to the homestead and relatively more fertile than the outfields due to previous preferential allocation of nutrients. Maize grain yields in sandy soils did not respond to the sole application of fertiliser N (remained less than 1 t ha-1); manure application had immediate and incremental benefits on crop yields in the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 on clay outfield, 7.6 t ha-1 on sandy homefield and 3.4 t ha-1 in the eighth season. Despite the large manure applications of up to 25 t ha-1, crop productivity and soil organic carbon build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. Manure can be used more efficiently if targeted to fields closest to homesteads but this exacerbates land degradation in the outfields and increases soil fertility gradients. The NUANCES-FARMSIM model for simulating crop and animal productivity in mixed crop-livestock farming systems was used to perform trade-off analysis with respect to crop residue management, animal and crop productivity in Murehwa, Zimbabwe. Retaining all maize residues in the field led to severe losses in animal productivity but significant gains in crop productivity in the long-term. Yield increased 4 to 5.6 t farm-1 for RG1, and from 2.8 to 3.5 t farm-1 for RG2. Body weight loss was on average 67 kg per animal per year for RG1 and 93 kg per animal per year for RG2. Retention of all crop residues reduced farm income by US37 and US38 per year for RG1 and RG2 respectively.Farmers who own cattle have no scope of retaining crop residues in the field as it results in significant loss of animal productivity. Non-livestock farmers (60% of the farmers) do not face trade-offs in crop residue allocation but have poor productivity compared to livestock owners and have a greater scope of retaining their crop residues if they invest in more labour to keep their residues during the dry season. This study has revealed that crop production intensification options developed without considering the biophysical conditions as well as socio-economic circumstances of farmers are nuisances. External ideas should be used to stimulate local innovations to push the envelope of crop production without creating new constraints on resource use.

    Impact of farm dams on river flows; A case study in the Limpopo River basin, Southern Africa
    Meijer, E. ; Querner, E.P. ; Boesveld, H. - \ 2013
    Wageningen : Alterra (Alterra-rapport 2394) - 62
    dammen - landbouw - rivieren - regenwateropvang - irrigatiebehoeften - zuidelijk afrika - dams - agriculture - rivers - water harvesting - irrigation requirements - southern africa
    The study analysed the impact of a farm dam on the river flow in the Limpopo River basin. Two methods are used to calculate the water inflow: one uses the runoff component from the catchment water balance; the other uses the drainage output of the SIMFLOW model. The impact on the flow in a sub-catchment with and without the presence of a farm dam, has been analysed. Different farm dam storage capacities and infiltration rates of the soil were considered. In general, the change in natural flow is decreasing when the farm dam capacity becomes higher. On the other hand, the Remaining Natural Flow is increasing when the catchment area becomes larger. The Crop Water Availability was expressed as the relative difference between the crop water requirements and the amount of water supplied by precipitation and irrigation from the farm dam. For a given storage capacity of the farm dam the change in natural flow is calculated when the farm dam covers 90% of the potential evapotranspiration of maize.
    Exploring the potential of intersectoral partnerships to improve the position of farmers in global agrifood chains: findings from the coffee sector in Peru
    Bitzer, V.C. ; Glasbergen, P. ; Arts, B.J.M. - \ 2013
    Agriculture and Human Values 30 (2013)1. - ISSN 0889-048X - p. 5 - 20.
    public-private partnerships - fair-trade - northern nicaragua - rural livelihoods - southern africa - impact - sustainability - certification - initiatives - standards
    Despite their recent proliferation in global agricultural commodity chains, little is known about the potential of intersectoral partnerships to improve theposition of smallholder farmers and their organizations.This article explores the potential of partnerships bydeveloping a conceptual approach based on the sustainablelivelihoods and linking farmers to market perspectivewhich is applied in an exploratory study to six partnerships in the coffee sector in Peru. It is concluded that partnerships stimulate the application of standards to receivemarket access and therefore emphasize human capitaldevelopment of farmers to facilitate certification. Bytransferring knowledge to farmers, partnerships present a new source of technological change, which, in combination with certification,holds potential for improved environmentalmanagement and price premiums for producers. However, the emphasis on certification results in a comparativelynarrow target group of farmers and is associatedwith high financial burdens for producer organizations. Atthe same time, other assets of producer organizations areoften not strengthened sufficiently for them to operatsuccessfully without further external support. This suggeststhat preparing producers for certification is prioritized over empowering organizations toward self-dependence
    A proposed framework for short-, medium- and long-term responses by range and consumer States to curb poaching for African rhino horn
    Ferreira, S.M. ; Ouma, B.O. - \ 2012
    Pachyderm 51 (2012). - ISSN 1026-2881 - p. 52 - 59.
    kruger-national-park - southern africa - elephants - conservation - population - management - science - impact
    African rhinos are suffering a new poaching onslaught for their high-priced horns. Despite intensified anti- poaching activities, the number of rhinos poached per day has continued to increase since 2008. Between 2010 and 2011 more than 1.5% of the African rhino population was poached each year: a higher percentage is projected for 2012. This trend in increased poaching will reverse overall positive rhino population growth in the long term. In response, a rhino emergency summit comprising representatives of rhino range States, the private sector, government officials and non-governmental organizations met in Nairobi during April 2012. Following this meeting, we propose an integrated framework directed at reducing the demand-and-supply ratio associated with the use of rhino horn. The framework is envisaged to guide short- as well as medium- to long-term responses by range States directed at reducing the incentives for poaching and ensuring the persistence of rhinos.
    Holocene dynamics of the salt-fresh groundwater interface under a sand island, Inhaca, Mozambique
    Vaeret, L. ; Leijnse, A. ; Cuamba, F. ; Haldorsen, S. - \ 2012
    Quaternary International 257 (2012). - ISSN 1040-6182 - p. 74 - 82.
    last glacial maximum - sea-level change - southern africa - aquifers - climate
    The configuration of coastal groundwater systems in southeast Africa was strongly controlled by the Holocene sea-level changes, with an Early Holocene transgression ~15 m (10,000–5000 cal BP), and two assumed high-stand events in the Middle and Late Holocene with levels higher than the present. The fluctuation of the salt–fresh groundwater interface under Inhaca Island in Mozambique during the Holocene has been studied using an adapted version of the numerical code SUTRA (Saturated-Unsaturated Transport). In this study, small-scale variations such as tidal effects have not been considered. A number of transient simulations were run with constant boundary conditions until the steady state condition was reached in order to study the sensitivity of response time, salt–fresh interface position, and thickness of the transition zone to different parameters such as hydraulic conductivity, porosity, recharge, and dispersivity. A 50% increase in horizontal hydraulic conductivity yields a rise in the location of the interface of >15 m, while an increase in recharge from 8% to 20% of mean annual precipitation (MAP) causes a downward shift in the interface position of >40 m. A full transient simulation of the Holocene dynamics of the salt–fresh groundwater interface showed a response time of several hundred years, with a duration sensitive to porosity, hydraulic conductivity and recharge and a position determined by the recharge rate and the hydraulic conductivity. Dispersivity controls the thickness of the transition zone in this non-tidal model. Physical processes, such as changes in recharge and/or the sea level, may cause rapid shifts in the interface position and affect the thickness of the transition zone
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