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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Redressing the balance: Quantifying net intercatchment groundwater flows
Bouaziz, Laurène ; Weerts, Albrecht ; Schellekens, Jaap ; Sprokkereef, Eric ; Stam, Jasper ; Savenije, Hubert ; Hrachowitz, Markus - \ 2018
Hydrology and Earth System Sciences 22 (2018)12. - ISSN 1027-5606 - p. 6415 - 6434.

Intercatchment groundwater flows (IGFs), defined as groundwater flows across topographic divides, can occur as regional groundwater flows that bypass headwater streams and only drain into the channel further downstream or directly to the sea. However, groundwater flows can also be diverted to adjacent river basins due to geological features (e.g., faults, dipping beds and highly permeable conduits). Even though intercatchment groundwater flows can be a significant part of the water balance, they are often not considered in hydrological studies. Yet, assuming this process to be negligible may introduce misrepresentation of the natural system in hydrological models, for example in regions with complex geological features. The presence of limestone formations in France and Belgium potentially further exacerbates the importance of intercatchment groundwater flows, and thus brings into question the validity of neglecting intercatchment groundwater flows in the Meuse basin. To isolate and quantify the potential relevance of net intercatchment groundwater flows in this study, we propose a three-step approach that relies on the comparison and analysis of (1) observed water balance data within the Budyko framework, (2) results from a suite of different conceptual hydrological models and (3) remote-sensing-based estimates of actual evaporation. The data of 58 catchments in the Meuse basin provide evidence of the likely presence of significant net intercatchment groundwater flows occurring mainly in small headwater catchments underlain by fractured aquifers. The data suggest that the relative importance of net intercatchment groundwater flows is reduced at the scale of the Meuse basin, as regional groundwater flows are mostly expected to be self-contained in large basins. The analysis further suggests that net intercatchment groundwater flow processes vary over the year and that at the scale of the headwaters, net intercatchment groundwater flows can make up a relatively large proportion of the water balance (on average 10 % of mean annual precipitation) and should be accounted for to prevent overestimating actual evaporation rates.

HESS Opinions: Science in today's media landscape - Challenges and lessons from hydrologists and journalists
Lutz, Stefanie R. ; Popp, Andrea ; Emmerik, Tim Van; Gleeson, Tom ; Kalaugher, Liz ; Möbius, Karsten ; Mudde, Tonie ; Walton, Brett ; Hut, Rolf ; Savenije, Hubert ; Slater, Louise J. ; Solcerova, Anna ; Stoof, Cathelijne R. ; Zink, Matthias - \ 2018
Hydrology and Earth System Sciences 22 (2018)7. - ISSN 1027-5606 - p. 3589 - 3599.

Media such as television, newspapers and social media play a key role in the communication between scientists and the general public. Communicating your science via the media can be positive and rewarding by providing the inherent joy of sharing your knowledge with a broader audience, promoting science as a fundamental part of culture and society, impacting decision- and policy-makers, and giving you a greater recognition by institutions, colleagues and funders. However, the interaction between scientists and journalists is not always straightforward. For instance, scientists may not always be able to translate their work into a compelling story, and journalists may sometimes misinterpret scientific output. In this paper, we present insights from hydrologists and journalists discussing the advantages and benefits as well as the potential pitfalls and aftermath of science-media interaction. As we perceive interacting with the media as a rewarding and essential part of our work, we aim to encourage scientists to participate in the diverse and evolving media landscape. With this paper, we call on the scientific community to support scientists who actively contribute to a fruitful science-media relationship..

1.2 Deforestation-free claims:scams or substance?
Noordwijk, M. van; Dewi, Sonya ; Minang, Peter ; Simons, T. - \ 2017
In: Zero deforestation: A commitment to change / Pasiecznik, Nick, Savenije, Herman, Wageningen : Tropenbos International (ETFRN News 58) - ISBN 9789051131345 - p. 11 - 16.
Looking beyond general metrics for model comparison – Lessons from an international model intercomparison study
Boer-Euser, Tanja de; Bouaziz, Laurène ; Niel, Jan De; Brauer, Claudia ; Dewals, Benjamin ; Drogue, Gilles ; Fenicia, Fabrizio ; Grelier, Benjamin ; Nossent, Jiri ; Pereira, Fernando ; Savenije, Hubert ; Thirel, Guillaume ; Willems, Patrick - \ 2017
Hydrology and Earth System Sciences 21 (2017)1. - ISSN 1027-5606 - p. 423 - 440.

International collaboration between research institutes and universities is a promising way to reach consensus on hydrological model development. Although model comparison studies are very valuable for international cooperation, they do often not lead to very clear new insights regarding the relevance of the modelled processes. We hypothesise that this is partly caused by model complexity and the comparison methods used, which focus too much on a good overall performance instead of focusing on a variety of specific events. In this study, we use an approach that focuses on the evaluation of specific events and characteristics. Eight international research groups calibrated their hourly model on the Ourthe catchment in Belgium and carried out a validation in time for the Ourthe catchment and a validation in space for nested and neighbouring catchments. The same protocol was followed for each model and an ensemble of best-performing parameter sets was selected. Although the models showed similar performances based on general metrics (i.e. the Nash–Sutcliffe efficiency), clear differences could be observed for specific events. We analysed the hydrographs of these specific events and conducted three types of statistical analyses on the entire time series: cumulative discharges, empirical extreme value distribution of the peak flows and flow duration curves for low flows. The results illustrate the relevance of including a very quick flow reservoir preceding the root zone storage to model peaks during low flows and including a slow reservoir in parallel with the fast reservoir to model the recession for the studied catchments. This intercomparison enhanced the understanding of the hydrological functioning of the catchment, in particular for low flows, and enabled to identify present knowledge gaps for other parts of the hydrograph. Above all, it helped to evaluate each model against a set of alternative models.

Should we use a simple or complex model for moisture recycling and atmospheric moisture tracking?
Ent, R.J. van der; Tuinenburg, O.A. ; Knoche, H.R. ; Kunstmann, H. ; Savenije, H.H.G. - \ 2013
Hydrology and Earth System Sciences 17 (2013)12. - ISSN 1027-5606 - p. 4869 - 4884.
water-vapor - deuterium excess - hydrologic-cycle - climate model - part ii - precipitation - rainfall - regions - deforestation - dispersion
This paper compares state-of-the-art atmospheric moisture tracking models. Such models are typically used to study the water component of coupled land and atmosphere models, in particular quantifying moisture recycling and the source-sink relations between evaporation and precipitation. There are several atmospheric moisture tracking methods in use. However, depending on the level of aggregation, the assumptions made and the level of detail, the performance of these methods may differ substantially. In this paper, we compare three methods. The RCM-tag method uses highly accurate 3-D water tracking (including phase transitions) directly within a regional climate model (online), while the other two methods (WAM and 3D-T) use a posteriori (offline) water vapour tracking. The original version of WAM is a single-layer model, while 3D-T is a multi-layer model, but both make use the "well-mixed" assumption for evaporation and precipitation. The a posteriori models are faster and more flexible, but less accurate than online moisture tracking with RCM-tag. In order to evaluate the accuracy of the a posteriori models, we tagged evaporated water from Lake Volta in West Africa and traced it to where it precipitates. It is found that the strong wind shear in West Africa is the main cause of errors in the a posteriori models. The number of vertical layers and the initial release height of tagged water in the model are found to have the most significant influences on the results. With this knowledge small improvements have been made to the a posteriori models. It appeared that expanding WAM to a 2-layer model, or a lower release height in 3D-T, led to significantly better results. Finally, we introduced a simple metric to assess wind shear globally and give recommendations about when to use which model. The "best" method, however, very much depends on the research question, the spatial extent under investigation, as well as the available computational power.
A data acquisition framework for runoff prediction in ungauged basins
McGlynn, B.L. ; Blöschl, M. ; Borga, H. ; Bormann, H. ; Hurkmans, R. ; Komma, J. ; Nandagiri, L. ; Uijlenhoet, R. ; Wagener, T. - \ 2013
In: Runoff Prediction in Ungauged Basins: Synthesis Across Processes, Places and Scales / Blöschl, G., Sivapalan, T., Wagener, T., Viglione, A., Savenije, H., Cambridge University Press - ISBN 9781107028180 - p. 29 - 52.
Prediction of low flows in ungauged basins
Laaha, G. ; Hisdal, H. ; Kroll, C.N. ; Lanen, H.A.J. van; Nester, T. ; Rogger, M. ; Sauquet, E. ; Tallaksen, L.M. ; Woods, R.A. ; Young, A. - \ 2013
In: Run-off Prediction in Ungauged Basins, Synthesis across Processes, Places and Scales / Bloschl, G., Wagener, S., Viglione, Th.M., Savenije, H., Cambridge University Press - ISBN 9781107028180 - p. 163 - 188.
Forest Landscape Restoration in the Netherlands: Policy Aspects and Knowledge Management
Hendriks, R.J.J. ; Boot, R.G.A. ; Haas, W. de; Savenije, H.J.F. ; Madsen, P. ; Lamb, D. - \ 2012
In: A Goal-Oriented Approach to Forest Landscape Restoration / Stanturf, J., Madsen, P., Lamb, D., Dordrecht : Springer (World Forests 16) - ISBN 9789400753389 - p. 21 - 40.
Governance of nontimberforest products in the Congo Basin
Ingram, V. - \ 2012
In: Moving Forward with Forest Governance / Broekhoven, G, Savenije, H, von Scheliha, S, Wageningen : Tropenbos International (ETFRN news 53) - ISBN 9789051131079 - p. 36 - 45.
Non-timber forest product value chains The processes involved as non-timber forest products (NTFPs)1 are harvested, processed, sold and used create what is known as a value chain. A chain perspective allows the impacts of governance arrangements to be assessed. High levels of forest cover in the Congo Basin give rise to at least 951 species used as NTFPs in the Democratic Republic of Congo (DRC) and 706 in Cameroon. Approximately one-third of these are traded; around 50 plant-based and 70 animal-based NTFPs are exported (Ingram 2012). The vast majority of NTFPs are sourced from the wild: only 5% of plants are cultivated and less than 1% of animals are wild-sourced (Ingram 2012). The value chains operate in a context of increasing urbanization, significant poverty, a difficult business environment and significant corruption (de Wasseige et al. 2009)
Strengthening Effective Forest Governance Monitoring Practice : An approach for integrating forest governance into national forest-related monitoring systems
Bodegom, A.J. van; Wigboldus, S.A. ; Blundell, A. ; Harwell, E. ; Savenije, H. - \ 2012
Rome : FAO (Forestry Policy and Institutions working paper 29) - 62
This publication is a collaborative effort of FAO, the Wageningen UR Centre for Development Innovation, NCA and Tropenbos International, with inputs of a range of experts. The present working paper documents experiences of work to date. It has been prepared by the two teams of international consultants and reflects the experiences and insights based on the pilots in Zambia and Vietnam.
Strengthening forest governance monitoring : Zambia and Vietnam
Bodegom, A.J. van; Savenije, H. ; Blundell, A. ; Sekeleti, M. ; Khac Coi, L. Le; Rametsteiner, E. - \ 2012
In: Moving Forward with Forest Governance Wageningen : Tropenbos International (ETFRN news 53) - ISBN 9789051131079 - p. 73 - 79.
Assessment of strip tillage systems for maize production in semi-arid Ethiopia: effects on grain yield, water balance and water productivity
Temesgen, M. ; Savenije, H.H.G. ; Rockström, J. ; Hoogmoed, W.B. - \ 2012
Physics and Chemistry of the Earth 47-48 (2012). - ISSN 1474-7065 - p. 156 - 165.
hydraulic-properties - soil - evapotranspiration - generation - drought - area
The Maresha, the traditional Ethiopian plow, requires repeated cross-plowing which causes increased surface runoff, less infiltration and hence lower water availability to crops. The main reasons for increased surface runoff and reduced infiltration are plowing along the slope and the formation of a plow pan at shallow depths. Conservation tillage is seen as a way to alleviate these problems. The widely advocated zero-tillage, however, is not feasible for smallholder farmers in semi-arid regions of Ethiopia because of difficulties in maintaining adequate soil cover, the practice of communal grazing, and high costs of herbicides. Strip tillage systems, on the other hand, may offer a solution. This study was initiated to test strip tillage systems and to evaluate the impacts of new tillage systems on the water balance and grain yields of maize. Experiments have been conducted in a semi-arid area called Melkawoba in the central Rift Valley of Ethiopia during 2003-2005. Strip tillage systems involved cultivation along planting lines at a spacing of 0.75 m using the Maresha plow followed by subsoiling along the same lines (STS) or without subsoiling (ST). Results have been compared with traditional tillage involving 3 to 4 overpasses with the Maresha plow (CONV). Soil moisture has been monitored to a depth of 1.8 m using a Time Domain Reflectometer (TDR) while surface runoff has been measured using a specially designed rectangular trough installed at the bottom of each plot. STS resulted in the least surface runoff (Qs=18 mm-season-1) and the highest grain yields (Y=2130 kg-ha-1) followed by ST (Qs=26 mm-season-1, Y=1840 kg-ha-1) and CONV (Qs=43 mm-season-1, Y=1720 kg-ha-1) provided sowing was carried out within a week after subsoiling. Thus, STS resulted in the highest water productivity, WP=0.60 kg-m-3, followed by ST (WP=0.52 kg-m-3) and CONV (WP=0.48 kg-m-3). The main conclusion of the paper is that even in dry areas reasonable yields can be obtained provided moisture conservation in the root zone is guaranteed. In this regard subsoiling is essential. Moreover, it is concluded that the time between subsoiling and planting is a key factor and should not exceed one week
Ecosysteemdiensten erkennen, identificeren en waarderen
Leemans, R. ; Savenije, H. - \ 2010
Kien : Nieuwsbrief Kennis en Innovatie 2010 (2010)7. - ISSN 2210-2590 - p. 4 - 5.
ecosystemen - biodiversiteit - natuurlijke hulpbronnen - landgebruik - duurzaamheid (sustainability) - maatschappelijke betrokkenheid - ecosysteemdiensten - natuurbeheer - ecosystems - biodiversity - natural resources - land use - sustainability - community involvement - ecosystem services - nature management
De mens is voor zijn bestaan afhankelijk van ecosysteemdiensten: diensten die de natuur ons levert. Schapen produceren de wol voor onze kleding. Duinen zuiveren ons water. En van de natuur om ons heen genieten we. Veel ecosysteemdiensten beschouwden we altijd als vanzelfsprekend. Nu deze steeds meer onder druk komen te staan, groeit het besef en de urgentie dat zonder maatschappelijke omslag in de waardering en het gebruik van biodiversiteit, ons bestaan in gevaar komt.
The water footprint of bioenergy from Jatropha curcas L
Jongschaap, R.E.E. ; Blesgraaf, R.A.R. ; Bogaard, T.A. ; Loo, E.N. van; Savenije, H.H.G. - \ 2009
Proceedings of the National Academy of Sciences of the United States of America 106 (2009)35. - ISSN 0027-8424 - 1 p.
Forests and climate change: adaptation and mitigation
Bodegom, A.J. van; Savenije, H. ; Wit, M. de - \ 2009
Wageningen : Tropenbos International (ETFRN news issue no. 50) - ISBN 9789051131000 - 160
bosbouw - bossen - klimaatverandering - opwarming van de aarde - broeikasgassen - bosbedrijfsvoering - adaptatie - herstel - bosexploitatie - mitigatie - forestry - forests - climatic change - global warming - greenhouse gases - forest management - adaptation - rehabilitation - forest exploitation - mitigation
ETFRN news No. 50: Forests and Climate Change: adaptation and mitigation. This newsletter contains interesting materials for those who think about the question how to proceed with forests and climate change after Copenhagen, with or without an agreement. Here below are presented some observations from this newsletter: • Adaptation and mitigation are separate issues in the climate discussions, but in forest practice they are two sides of the same coin. • We need forest management directed at the realization of different objectives at the same time, we do not need pure ‘carbon forests’. Not addressing ‘people’ and ‘planet’ considerations is increasingly seen – by both the public and private sector – as a business risk. • Not all countries will be able to comply with REDD rules in the short term. The voluntary carbon market will remain important. • REDD is an opportunity and a risk for local communities. Risks should be made transparent, and open and equal participation by communities in design and decision-making should be promoted • REDD and other forest-based climate change mitigation measures are likely to be low-cost and effective in the short to medium term. Some stakeholders fear that forests may become a too-cheap mitigation option and corrupt the overall climate agreement. In most calculations, however, the costs of developing, operating and managing the institutional system required to produce credible and sustainable forest carbon credits are not internalized in forest carbon prices. If they were, forest carbon prices would become much higher and more realistic. • The role of forests must be clarified and articulated in National Adaptation Programs of Action (NAPAs). At present most political attention and financing is focused on REDD, and, in general, on climate mitigation. Only recently has the concern for the role of forests in adaptation gained ground; this emanates from the growing recognition that climate change will happen anyway. Moreover, climate change will affect the most vulnerable ecosystems and poorer regions. • There is a clear need for harmonization and coherence in the certification market (SFM, and carbon, fair trade etc.). Certification is not necessarily the only credible basis for payment. As illustrated in this issue, mutual trust can be an alternative, particularly for small-scale initiatives that cannot afford the high transaction costs of certification.
Photoconductance of Bulk Heterojunctions with Tunable Nanomorphology Consisting of P3HT and Naphtalene Diimide Siloxane Oligomers
Grzegorczyk, W.J. ; Ganesan, P. ; Savenije, T.J. ; Bavel, S. van; Loos, J. ; Sudhölter, E.J.R. ; Siebbeles, L.D.A. ; Zuilhof, H. - \ 2009
The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces 113 (2009)18. - ISSN 1932-7447 - p. 7863 - 7869.
organic solar-cells - charge separation efficiency - polymer photovoltaic cells - carrier generation - thin-films - morphology - polythiophene - network - tio2 - semiconductors
The relation between the morphology, optical, and photoconductive properties of thin-film bulk heterojunctions of poly(3-hexylthiophene) (P3HT) with a series of electron-accepting siloxanes with a different number (x = 2, 4, 5) of pendant naphthalene diimide (NDIS) moieties is reported. All NDIS siloxanes show good electron-accepting properties, when blended with P3HT. Interestingly, the film (nano)morphology can be controlled by relatively small changes in the molecular structure of the NDIS siloxanes. Spin-coating from ortho-dichlorobenzene (ODCB) yields complex film (nano)morphologies, being correlated with the weight ratios of P3HT and NDIS siloxanes, and the molecular structure of the latter. On the other hand, all blends spin-coated from chloroform (CHCl3) show good mixing of the components at the molecular level. It is inferred that the nanomorphology of the blends can greatly influence their photoconductive properties: samples spin-coated from ODCB invariably display a higher photoconductance than corresponding samples spin-coated from CHCl3. This is explained in terms of a higher mobility of holes in samples spin-coated from ODCB, as measured by time-resolved microwave conductivity measurements. These data are useful to delineate the conditions for the research in strives for efficient organic photovoltaics
Conservation tillage implements and systems for smallholder farmers in semi-arid Ethiopia
Temesgen, M. ; Hoogmoed, W.B. ; Rockstrom, J. ; Savenije, H.H.G. - \ 2009
Soil & Tillage Research 104 (2009)1. - ISSN 0167-1987 - p. 185 - 191.
Smallholder farmers in Ethiopia practice traditional tillage systems using an ard plow called Maresha. Traditional tillage systems that involve repeated cultivations with the Maresha plow have caused land degradation (a.o. formation of a plow pan) and poor utilization of rainwater that led to low crop productivity. Experience in other countries has shown that conservation tillage systems could improve utilization of rain water through increased infiltration. However, the implements used for conservation tillage in other countries were found to be too heavy and too expensive for smallholder farmers in Ethiopia. On the other hand, lighter and low cost implements have been developed in Ethiopia as modifications to the Maresha plow. These implements are the Subsoiler, the Tie-ridger, and the Sweep. Field tests were carried out to evaluate the modified implements and a rip plant type of conservation tillage systems using the modified implements. The results showed that the Subsoiler reached a depth of approx. 24 and 27 cm after 1 resp. 2 passes through the furrow made by the Maresha, and thus was capable of disrupting the plow pan. Compared to the Maresha plow and the inverted broad bed maker (BBM), the Tie-ridger required less draft power (79 kg vs. 96 for the Maresha and 103 for the BBM) and lower lifting force (¿43%) while forming furrows with larger (+36 resp. +15%) cross-sectional areas. The Sweep enabled deeper root growth of tef (Eragrostis tef (Zucc.)) apart from accomplishing sowing operations faster (+50%). It is concluded that the newly developed implements are suitable to undertake conservation tillage under smallholder farming systems in the semi-arid regions of Ethiopia. The rip-plant type of conservation tillage systems, however, was not found to be viable for maize (Zea mays) production under the study conditions in which loss of soil moisture through evaporation is high. Both grain and biomass yields were highest in the conventional systems, although differences were statistically not significant. On the other hand, a reduced tillage system tested on tef resulted in higher grain yields as compared to conventional tillage.
Open Access in Nederland: de volgende stap
Savenije, B. ; Daalmans, P. ; Heijden, E. van der; Krekels, H.G.M. ; Woutersen-Windhouwer, S. ; Franken, S. - \ 2008
[S.l.] : UKB - 51
bibliotheken - informatiecentra - informatieverspreiding - netwerken (activiteit) - technische vooruitgang - informatieontsluiting - wetenschappelijke bibliotheken - informatiemanagement - libraries - information centres - diffusion of information - networking - technical progress - information retrieval - scientific libraries - information management
Ten gevolge van de invloed van ICT-ontwikkelingen op onderzoek en wetenschappelijke communicatie zien we een fundamentele verandering ten opzichte van het ‘papieren tijdperk’. Toegang tot wetenschappelijke kennis, informatie en data, essentieel voor hoger onderwijs en onderzoek, kan door deze technische ontwikkeling drastisch verbeterd worden. Het is binnen de instellingen de basis voor de kennisoverdracht (onderwijs) en kennisontwikkeling (onderzoek). Maar ook in de relatie met de samenleving (kennisvalorisatie) is toegang tot kennis en informatie van groot belang. Uitgangspunt is dat resultaten van met publieke middelen gefinancierd onderzoek ook publiekelijk toegankelijk dienen te zijn. De afgelopen jaren heeft Open Access een relatief hoge vlucht genomen. Vele instellingen wereldwijd (waaronder alle Nederlandse universiteiten) hebben de zgn. Berlin Declaration ondertekend, daarmee aangevend dat men Open Access van wetenschappelijke informatie actief wil bevorderen. Er is sprake van Open Access wanneer: 1. een publicatie online wordt gepubliceerd en in minimaal een online repository (een vrij toegankelijk digitaal archief) wordt opgenomen; 2. de publicatie voor iedereen met een internetverbinding kosteloos toegankelijk is en blijft; 3. de auteur de gebruiker toestemming geeft om de content te mogen (her)gebruiken voor onderzoek en onderwijs; 4. die toestemming voor (her)gebruik twee voorwaarden heeft: een correcte bronvermelding en geen plagiaat; 5. de auteur deze toestemming vooraf geeft voor het vrije, wereldwijde en onherroepelijke gebruik. Er zijn twee scenario’s m.b.t. Open Access: 1. The Green Road / Repositories: vrijwel alle universiteiten in Europa en de VS en hebben een begin gemaakt met een “institutional repository” waarin publicaties van de instelling voor iedereen toegankelijk kunnen worden ontsloten. Via harvesting kunnen vervolgens disciplinegewijs aanvullende diensten worden geleverd met het in repositories aanwezige materiaal. De universiteit van Nottingham houdt een lijst bij van alle repositories (OpenDoar). Nederland, waar alle universiteiten, dank zij het DARE project inmiddels een redelijk gevuld repository hebben, is koploper. 2. The Golden Road / Open Access Tijdschriften: dit zijn tijdschriften waar niet de lezer betaalt (in de vorm van een abonnementsprijs) maar de kosten op een andere wijze worden gedekt. Een veel voorkomende variant is dat dit geschiedt in de vorm van article processing charges (publicatiekosten, ook wel publication fees genoemd), wat betekent dat de financier/opdrachtgever voor het onderzoek betaalt.
Determinants of tillage frequency among smallholder farmers in two semi-arid areas in Ethiopia
Temesgen, M. ; Rockstrom, J. ; Savenije, H.H.G. ; Hoogmoed, W.B. ; Alemu, D. - \ 2008
Physics and Chemistry of the Earth 33 (2008)1-2. - ISSN 1474-7065 - p. 183 - 191.
soil-water storage
Traditional tillage systems practiced by farmers in semi-arid regions of Ethiopia are characterized by repeated and cross plowing with an indigenous plow called Maresha. Repeated and cross plowing have led to land degradation. Conservation tillage systems that advocate minimum soil disturbance can alleviate land degradation problems. However, before introducing reduced tillage systems, it was found necessary to study why farmers undertake repeated plowing. The study was undertaken in two semi-arid areas called Melkawoba and Wulinchity located in the central rift valley of Ethiopia and on two major crops; Tef (Eragrostis Tef (Zucc.)) and maize (Zea mays XX). Fifty farmers from each area were randomly selected and interviewed using a structured questionnaire. The results showed that farmers in the study area plow repeatedly in order to completely disturb unplowed strips of land left between adjacent furrows. Unplowed strips are the results of the V-shaped furrows created by the Maresha plow. Farmers generally do not plow before the soil is wetted by rainfall. Wetting and drying cycles due to dry spells occurring between rainfall events force farmers to plow frequently to avoid moisture losses through surface runoff, evaporation and weed transpiration. Tef fields are plowed 4¿5 times while maize fields are plowed 3¿4 times. Tillage frequency increased with the education level and experience of farmers; with their perception about the purpose of tillage such as moisture conservation, weed control and soil warming; and with resource availability such as area of land and family labor. Tillage frequency was higher for Tef than for maize and in heavy soils than in light soils.
Tetrahedral n-type materials: Efficient quenching of the excitation of p-type polymers in amorphous films
Ganesan, P. ; Yang, X.N. ; Loos, J. ; Savenije, T.J. ; Abellon, R.D. ; Zuilhof, H. ; Sudhölter, E.J.R. - \ 2005
Journal of the American Chemical Society 127 (2005)42. - ISSN 0002-7863 - p. 14530 - 14531.
plastic solar-cells - morphology - diimides - bilayers
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