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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    A comprehensive assessment of agriculture in lowlands of south Brazil: characterization and comparison of current and alternative concepts
    Theisen, Giovani - \ 2017
    Wageningen University. Promotor(en): N.P.R. Anten, co-promotor(en): L. Bastiaans. - Wageningen : Wageningen University - ISBN 9789463436380 - 234
    cropping systems - farming systems - crop management - lowland areas - wetlands - pampas - brazil - intensification - sustainability - productivity - indicators - soil management - rice - flooded rice - oryza sativa - maize - zea mays - glycine max - cover crops - livestock - rotation - mixed farming - seedbed preparation - farm machinery - teeltsystemen - bedrijfssystemen - gewasteelt - laaglandgebieden - wetlands - pampa's - brazilië - intensivering - duurzaamheid (sustainability) - productiviteit - indicatoren - bodembeheer - rijst - natte rijst - oryza sativa - maïs - zea mays - glycine max - dekgewassen - vee - rotatie - gemengde landbouw - zaaibedbereiding - landbouwwerktuigen

    Agriculture in the lowlands of south Brazil is of strategic importance at the national level, since it supplies around 80% of the rice consumed by the Brazilian population. In Rio Grande do Sul, the southernmost state in Brazil, three million hectares of lowlands are ready for grain-based agriculture. Of this area, about half is fallow, partly used for cattle grazing, and irrigated rice is the predominant crop, cultivated annually on 1.1 million ha. The remaining area is used for soybean and other crops. The predominant cropping system is a combination of irrigated rice and cattle. Over the last decades, rice yields have steadily increased, but this rise in yield level has to a large extent been obtained at the expense of a continuously higher use of external inputs. The recent introduction of soybean in rotation with rice has partially improved the system, but in most areas the situation is becoming incompatible with the modern demands for sustainability. This thesis presents a long-term study (2006-2015) of five cropping systems for lowlands. Next to monocrop rice and two rice-soybean rotations conducted in either conventional or minimum tillage, the experiment contained two novel systems based on large ridges, on which soybean and maize were combined with either cover crops or crop-livestock integration in winter. In these last systems, 8-m-wide ridges were built to avoid flooding, thus allowing for diversification of cash crops and the cultivation of cover crops or pastures in winter time, as well as the use of no-tillage. All systems were evaluated at process-level, including soil preparation, seeding, plant nutrition, pest management, irrigation, harvesting, transport and cattle management, as well as regarding their performance for the different dimensions of sustainability, particularly environment, land productivity, economics, energy-use and labour. Next to system assessment, two additional experiments were conducted for the evaluation of two specific technologies for soil management in these areas. Crop livestock integration on the ridge-based system offered the best balance between food production, environmental impact and economics. This system is well suited to be used in fields that are kept fallow, thereby enlarging the agricultural productivity of the lowlands. The additional experiments revealed that a knife-roller can successfully substitute plough-and-harrow for soil preparation after rice harvest, and that germination of weed seeds can be reduced if crop seeding is conducted at a lower speed or using a no-tillage seeder equipped with an improved cutting mechanism. Overall the results show that by using alternative cropping systems that allow for diversification and new methods of field management it is possible to simultaneously attain a larger agricultural production and improved sustainability in the lowlands.

    Agronomic and socioeconomic sustainability of farming systems : A case in Chencha, South Ethiopia
    Dersseh, Waga Mazengia - \ 2017
    Wageningen University. Promotor(en): P.C.. Struik, co-promotor(en): R.P.O. Schulte; D. Griffin. - Wageningen : Wageningen University - ISBN 9789463436830 - 157
    potatoes - solanum tuberosum - ethiopia - food security - farming systems - mixed farming - sustainability - optimization - efficiency - farm surveys - household surveys - socioeconomics - self sufficiency - profits - training - agronomic characteristics - productivity - soil fertility - rotation - animal feeding - improved varieties - inorganic fertilizers - aardappelen - solanum tuberosum - ethiopië - voedselzekerheid - bedrijfssystemen - gemengde landbouw - duurzaamheid (sustainability) - optimalisatie - efficiëntie - bedrijfsonderzoeken - huishoudonderzoeken - sociale economie - zelfvoorziening - winsten - opleiding - agronomische kenmerken - productiviteit - bodemvruchtbaarheid - rotatie - diervoedering - veredelde rassen - anorganische meststoffen

    Potato has multiple benefits and thus can play a vital role in ensuring food security in Ethiopia. However, for diverse reasons, its productivity is low. The farming systems in Ethiopia in which potato is grown, are predominantly mixed farming systems.

    Most of the research in Ethiopia is focused on crop-specific constraints and thus there is limited research in which the interrelations between crop and livestock management practices are investigated. There is also not enough research focused on combined analysis of soil nutrient and animal feed balances and agronomic and socioeconomic efficiencies at farm level.

    This study assessed production constraints and agronomic and socioeconomic sustainability of the farming systems in South Ethiopia and explored the possible synergetic options to alleviate major constraints. More specifically, the study intended to quantify the variation in input and output among farms, to identify constraints hindering expansion of potato production, to evaluate the sustainability of the farming systems at farm level, to identify constraints of sustainable intensification, and to explore synergetic solutions for the major constraints. Different research approaches were used ranging from lab analysis, household surveys, group discussions, to farm surveys.

    Results showed that constraints related to input and product use in potato production vary across households indicating a need for a pluriform advisory model recognizing (and building upon alleviation of) the diversity of constraints identified in this analysis. The sustainability of the farming system is constrained by low agricultural productivity, low soil fertility, poor labour efficiency and limited economic return associated with improper crop rotation, inappropriate soil fertility management practices, shortage of animal feed, labour- and economically inefficient farm practices and labour shortage. However, there is ample scope to overcome the major constraints and simultaneously to optimize farm management.

    The core messages of the study can be summarized as follows:

    1) the current potato production is characterized by low productivity and economic returns due to various socioeconomic, agronomic and biological factors;

    2) the soil fertility is low and there is uneven distribution of nutrients over plots with relatively high fertility levels in the homestead areas;

    3) the current labour shortage can be attributed to mainly inefficiency of agricultural management practices and labour migration to towns for economic reasons indicating that the farming system is not sustainable in terms of labour;

    4) considering the direct return from animal production, most of the farms had very low gross margin with the current management system and this reduced the overall operating profit of farms. The low return from animal rearing was offset by the relatively high profit from crop production indicating the benefit of mixed farming system in sustaining agricultural production; and

    5) each farm can have a wide range of optimized solutions mainly through introduction of improved technologies and subsequent redesigning of the farm managements.

    In general, the findings of the current study indicate that it is worthwhile to assess the sustainability of agricultural production in different farming systems and agro-ecologies of Ethiopia. In addition, the combined effect of introducing improved agricultural technologies and subsequent reconfiguring the farm management is very crucial to increase and sustain agricultural production.

    Batch and repeated-batch oil production by microalgae
    Benvenuti, G. - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Rouke Bosma; Maria Barbosa. - Wageningen : Wageningen University - ISBN 9789462576582 - 149
    algae - chlorella - arthrospira - dunaliella - nostoc - triacylglycerols - light - lipogenesis - photosynthesis - oil products - productivity - biomass conversion - economic analysis - algen - chlorella - arthrospira - dunaliella - nostoc - triacylglycerolen - licht - lipogenese - fotosynthese - olieproducten - productiviteit - biomassaconversie - economische analyse

    Microalgal triglycerides (TAGs) are promising feedstocks for the commodity markets (i.e. food, chemical and biofuel). Nevertheless, microalgal TAGs are not yet economically feasible due to the high production costs. To reduce these costs, TAG productivity needs to be maximized.

    The aim of this thesis was to increase microalgal TAG productivity by investigating the effects of biological and engineering parameters (i.e. production strain and operational strategy).

    We first screened seven marine species on their TAG productivity under nitrogen (N) starvation. Nannochloropsis sp. was identified as the most suitable species as it retained its photosynthetic activity while accumulating large amounts of TAGs ensuring the highest TAG productivity. Therefore, Nannochloropsis sp. was used in all following studies.

    Next, we aimed at optimizing TAG productivity by investigating the effect of initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area) in batch outdoor cultivations carried out in horizontal and vertically stacked tubular reactors at different initial biomass concentrations at the start of the TAG accumulation phase, over different seasons. Based on the observed trends of TAG productivity for the Dutch climate, optimal initial biomass concentrations were suggested to achieve high areal TAG productivities for each reactor configuration and season.

    Subsequently, repeated-batch processes were investigated to further increase TAG productivity compared to batch processes. For this, repeated-batch cultivations were tested and compared to batch cultivations both at lab-scale under day/night cycles and in two identical, simultaneously operated, outdoor vertically stacked tubular reactors over different seasons. Although at lab-scale, batch and repeated-batch cultivations led to similar TAG productivities, outdoor repeated-batch processes were always outcompeted by the batch. It was concluded that repeated-batch processes require further optimization.

    For this, the physiological responses of Nannochloropsis sp. to N-starvation and N-replenishment were determined under continuous light in lab-scale batch and repeated-batch cultivations and condensed into a mechanistic model describing both cultivation strategies. Scenarios for improved TAG yields on light were simulated and, based on the optimized yields, a comparison of the two processes was performed. It was concluded that under continuous light, an optimized batch process will always result in higher TAG productivities than an optimized repeated-batch process.

    Finally, a techno-economic analysis for a two-step-continuous TAG production process (i.e. growth reactors are operated in continuous mode such that multiple batch-operated stress reactors are inoculated and sequentially harvested) is performed for a hypothetical 100 ha-scale plant in southern Spain using vertically stacked tubular reactors. Photosynthetic efficiencies based on outdoor pilot data were used as model input. By optimizing both photosynthetic efficiency and process technology, the production cost could be decreased from 7.4 to 3.0 €·kg-1 of TAG-enriched biomass. We believe to be on the right track to achieve an economically feasible TAG production platform provided that photosynthetic efficiency is further improved, the whole biomass is valorized and cheaper reactors are designed.

    Uitbreiden ondanks nieuwe wetgeving?
    Berentsen, P.B.M. ; Klootwijk, C.W. ; Middelaar, C.E. van; Boer, I.J.M. de - \ 2015
    Veeteelt 32 (2015)19. - ISSN 0168-7565 - p. 12 - 14.
    fosfaat - melkveehouderij - landbouw en milieu - capaciteit - productiegroei - verkoopbaar - melkprijzen - productiviteit - phosphate - dairy farming - agriculture and environment - capacity - production growth - saleable - milk prices - productivity
    Kunnen bedrijven nog wel ontwikkelen na de komst van de Melkveewet en fosfaatrechten? Onderzoekers in Wageningen brachten via een rekenmodel de gevolgen in kaart. Zij concluderen dat het interessant blijft om beschikbare stalcapaciteit te benutten en dat fosfaatrechten niet snel de limiterende factor zijn.
    Strain improvement of oleaginous microalgae
    Jaeger, L. de - \ 2015
    Wageningen University. Promotor(en): Gerrit Eggink; Rene Wijffels, co-promotor(en): Dirk Martens. - Wageningen : Wageningen University - ISBN 9789462574847 - 200
    algen - biomassa - oliën - productiviteit - opbrengsten - transcriptomica - triacylglycerol lipase - bioreactoren - transformatie - mutanten - algenteelt - biomassa productie - algae - biomass - oils - productivity - yields - transcriptomics - triacylglycerol lipase - bioreactors - transformation - mutants - algae culture - biomass production

    The increasing world population and living standards have enlarged the demand for food, feed, and for chemicals. Traditional fossil fuel based commodities need to be replaced, not only because these resources are finite, but also to relieve the impact of carbon emission and pollution, resulting from fossil fuel derived processes. Much attention is on using plants to produce sustainable, renewable alternatives to petrochemical based processes. Palm oil is the crop with the highest lipid yield known today, but the production of palm oil causes deforestation on a large scale. Microalgae are a promising platform for the production of sustainable commodity products. A commodity product that can be produced in microalgae is triacylglycerol (TAG). The TAG molecules that are accumulated in microalgae are comparable to the TAG profiles of commonly used vegetable oils, and can directly be applied for edible oil as well as for biodiesel production. Currently, microalgae derived products have proven to be functional and a potential replacement for conventional crops. However, microalgae derived products, especially TAGs, are not economically feasible yet. In order to make microalgal derived products a reality we need to decrease the production costs by smart technological solutions, biological understanding and metabolic engineering.

    To get more insight in the lipid accumulation mechanism of microalgae, and to define targets for future strain improvement strategies, transcriptome sequencing of the oleaginous microalgae Neochloris oleoabundans was done. This oleaginous microalga can be cultivated in fresh water as well as salt water. The possibility to use salt water gives opportunities for reducing production costs and fresh water footprint for large scale cultivation.

    In chapter 2 the lipid accumulation pathway was studied to gain insight in the gene regulation 24 hours after nitrogen was depleted. Oil accumulation is increased under nitrogen depleted conditions in a comparable way in both fresh and salt water. The transcriptome sequencing revealed a number of genes, such as glycerol-3-phosphate acyltransferase and via glycerol-3-phosphate dehydrogenase, that are of special interest and can be targeted to increase TAG accumulation in microalgae. NMR spectroscopy revealed an increase in proline content in saline adapted cells, which was supported by up regulation of the genes involved in proline biosynthesis. In addition to proline, the ascorbate-glutathione cycle seems to be of importance for successful osmoregulation by removal of reactive oxygen species in N. oleoabundans, because multiple genes in this pathway were upregulated under salt conditions. The mechanism behind the biosynthesis of compatible osmolytes in N. oleoabundans can be used to improve salt resistance in other industrially relevant microalgal strains.

    Another very promising candidate for TAG production is the oleaginous green microalga Scenedesmus obliquus.

    In chapter 3, UV mutagenesis was used to create starchless mutants, since no transformation approach was available for this species, due to its rigid and robust cell wall. All five starchless mutants that were isolated from over 3500 screened mutants, showed an increased triacylglycerol productivity. All five starchless mutants showed a decreased or completely absent starch content. In parallel, an increased TAG accumulation rate was observed for the starchless mutants and no substantial decrease in biomass productivity was perceived. The most promising mutant (Slm1) showed an increase in TFA productivity of 41% at 4 days after nitrogen depletion and reached a TAG content of 49.4% (%CDW).

    In chapter 4 the Slm1 strain was compared to the wild type strain using photobioreactors. In the wild type, TAG and starch accumulated simultaneously during initial nitrogen starvation, and starch was subsequently degraded and likely converted into TAG. The Slm1 did not produce starch and the carbon and energy acquired from photosynthesis was partitioned towards TAG synthesis. This resulted in an increase of the maximum TAG content in Slm1 to 57% (%CDW) compared to 45% (%CDW) in the wild type. Furthermore, it increased the maximum yield of TAG on light by 51%, from 0.144 in the wild type to 0.217 g TAG mol-1 photon-1 in the Slm1 mutant. No differences in photosynthetic efficiency between the Slm1 mutant and the wild type were observed, indicating that the mutation specifically improved carbon partitioning towards TAG and the photosynthetic capacity was not affected.

    To identify the mutation that caused the starchless phenotype of Slm1 the transcriptome of both the wild type and the Slm1 mutant was sequenced as described in chapter 5. A single nucleotide polymorphism (SNP) was discovered in the small subunit of the starch biosynthesis rate-controlling enzyme ADP-glucose pyrophosphorylase, which resulted in the introduction of a STOP codon in the messenger RNA of the enzyme. The characterization of the mutation increases the understanding of carbon partitioning in oleaginous microalgae, leading to a promising target for future genetic engineering approaches to increase TAG accumulation in microalgae.

    To use the insight that is gained in chapters 2-5 for metabolic engineering of TAG accumulation and carbon partitioning, a metabolic engineering toolbox is required. However, the development of transformation protocols for new and less well studied industrially relevant microalgae is challenging. In chapter 6, a simple and effective tool for the optimization of transformation protocols is proposed. Optimal voltage settings were determined for five microalgae: C. reinhardtii, Chlorella vulgaris, N. oleoabundans, S. obliquus, and Nannochloropsis sp. This method can be used to speed up the screening process for species that are susceptible for transformation and to successfully develop transformation strategies for industrially relevant microalgae, which lack an efficient transformation protocol.

    In addition to the increase in productivity, improving the quality in terms of fatty acid composition of TAG molecules would be desired as well. For example, the accumulation of stearic acid rich TAG molecules is of special interest, because of the improved structural properties. The lipid accumulating starchless mutant of the model species C. reinhardtii BAFJ5 was used as model species in chapter 7, since genetic toolbox is well established for this species. In this chapter, stearoyl-ACP desaturase (SAD), is silenced by artificial microRNA. The mRNA levels for SAD were reduced after the silencing construct was induced. In one of the strains, the reduction in SAD mRNA resulted in a doubling of the stearic acid content in triacylglycerol molecules, which shows that increasing the fraction of stearic acid in TAG is possible. Furthermore, we hypothesize that in addition to direct conversion in the chloroplast, C. reinhardtii is able to redirect stearic acid from the chloroplast to the cytosol and convert it to oleic acid in the endoplasmic reticulum by stearoyl-CoA desaturase.

    In chapter 8, an outlook is given on microalgal strain improvement strategies for the future, reflecting on the results obtained in this thesis. Also a roadmap is suggested to get genetically modified microalgal derived products on the market. The results presented in this thesis, provide a significant improvement in the understanding of TAG accumulation and carbon partitioning in oleaginous microalgae. Furthermore, improved microalgal strains with increased TAG accumulation or improved TAG fatty acid composition under nitrogen depleted conditions were generated. In addition, an outlook is presented in which the major bottlenecks are presented in future industrial applications of microalgae.

    A food web model of invertebrate subtidal soft-bottom communities Part A: model derivation and effects of productivity
    Kooten, T. van; Schellekens, T. - \ 2015
    IJmuiden : IMARES (Report / IMARES Wageningen UR C130/15) - 18
    zee-invertebraten - voedselwebben - modellen - aquatische gemeenschappen - zeevisserij - productiviteit - visserijbiologie - vistuig - natura 2000 - noordzee - marine invertebrates - food webs - models - aquatic communities - marine fisheries - productivity - fishery biology - fishing gear - natura 2000 - north sea
    Om visserij in de Natura-2000 gebieden Noordzeekustzone en Vlakte van de Raan zodanig te reguleren, dat zij het behalen van de geformuleerde beleidsdoelen niet in de weg staat, is het VIBEG-akkoord gesloten. Kern van de afspraken vormt een ruimtelijke zonering waarmee wordt bepaald welke visserijtechnieken in welke gebieden wel of niet zijn toegestaan.
    Rassenproef zwarte bessen 2011-2014
    Heijerman-Peppelman, G. ; Dam, M.F.N. van - \ 2015
    Randwijk : Praktijkonderzoek Plant en Omgeving, Bloembollen, Boomkwekerij & Fruit - 19
    tuinbouw - fruitteelt - zwarte bessen - rassenproeven - classificatie van rassen - gewaskwaliteit - rassen (planten) - productiviteit - gewasbescherming - horticulture - fruit growing - black currants - variety trials - variety classification - crop quality - varieties - productivity - plant protection
    Vanaf 2011 heeft het Praktijkonderzoek Plant & Omgeving (PPO) sector Fruit te Randwijk het rassenonderzoek met zwarte bessen gedurende vier jaren voortgezet. Het doel is (nieuwe) rassen te zoeken en te toetsen onder Nederlandse (Zeeuwse) teeltomstandigheden, die een verbetering kunnen zijn van de huidige rassen voor wat betreft de productiviteit, de beskwaliteit en de gevoeligheid voor ziekten en plagen. Dit rapport is het eindverslag van het project dat eind 2014 is afgelopen.
    Hoe kan er zo'n rijk onderwaterleven verstopt zitten in onze grauwe Noordzee?
    Lindeboom, H.J. - \ 2015
    Universiteit van Nederland
    noordzee - soortenrijkdom - soortendiversiteit - productiviteit - voedingsstoffen - eutrofiëring - lesmaterialen - north sea - species richness - species diversity - productivity - nutrients - eutrophication - teaching materials
    De Noordzee is een gebied dat rijk is aan leven. Hoe kan het dat er in die troebele plas water zoveel verschillende dieren leven? Hoe zorgde die diversiteit en rijkdom voor oorlogen? En waarom is het schadelijk dat we de zee door onze welvaart vol fosfaat pompen? Die vragen en meer behandelt prof. dr. Han Lindeboom van de Wageningen UR in dit college.
    A social analysis of contested fishing practices in Lake Victoria
    Medard, M. - \ 2015
    Wageningen University. Promotor(en): Han van Dijk, co-promotor(en): Paul Hebinck; R. Mwaipopo. - Wageningen : s.n. - ISBN 9789462572478 - 278
    visserij - gemeenschappen - productiviteit - hulpbronnen - ontwikkeling - sociologie - organisatie - visserijbeheer - ondernemerschap - meren - tanzania - fisheries - communities - productivity - resources - development - sociology - organization - fishery management - entrepreneurship - lakes - tanzania

    Thesis abstract

    The thesis explored how the global market for Nile Perch fish has reconfigured the social and the natural in dramatic ways. The demand for Nile Perch and Dagaa played, willingly or unwillingly, an important role in converting its products into regionally and globally desired commodity. It has also simultaneously restructured the organisation of fisheries into a complex and aggressively managed sector. In fishing and fish trade, one needs to externalize costs and risks to the lower actors in the production and business hierarchy. From an historical point of view, power has shifted from many points of coordination and decision making into a few hands, those that own fishing camps and export processing factory. Moreover, illegal fishing and trading are continuous and corruption is rife to safe guard individual interest in turn shaping the local practices (governance) of Lake Victoria. Finally the debate about fisheries policies and fisheries regulation in L. Victoria does not address local realities and are largely irrelevant and that the real focus of power and driver of change is the international and regional markets for Nile Perch and Dagaa and global players with a lot of capital.

    The dynamics of oil accumulation in Scenedesmus obliquus
    Breuer, G. - \ 2015
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Dirk Martens; Packo Lamers. - Wageningen : Wageningen University - ISBN 9789462572348 - 268
    algen - stikstof - uithongering - triacylglycerolen - productiviteit - fotosynthese - koolstof - tussenmuren - oliën - algae - nitrogen - starvation - triacylglycerols - productivity - photosynthesis - carbon - partitions - oils

    .Abstract long

    Global demands for food and biofuels increase rapidly, together with an increase of concerns for depleting fossil resources and climate change. New sustainable sources of vegetable oil, from now on referred to as triacylglycerol (TAG), are therefore highly desired. Arable land to produce these TAGs is however limited. Microalgae have the potential to achieve much higher TAG productivities than commonly used terrestrial plants and can be cultivated on non-arable land. Microalgae are therefore often considered as a promising alternative natural-source of TAGs. Microalgae can accumulate up to 50% of their weight as TAGs, but only do so in response to nitrogen starvation. At the same time, nitrogen starvation also affects many other cellular processes, including photosynthesis. At the start of the work presented in this thesis, little was known about the quantitative aspects of photosynthesis and TAG production during nitrogen starvation. This contributed to a large uncertainty in what could be expected from microalgae. This thesis therefore provides a quantitative understanding of the microalgal response to nitrogen starvation, that can be used to understand and optimize TAG production.

    The differences between microalgae species in their response to nitrogen starvation are characterized. It was found that the difference in the response to nitrogen starvation between microalgae could be characterized in 1) how long the species could retain their photosynthetic efficiency during nitrogen starvation, 2) how much the species could in increase in biomass concentration in the absence of a nitrogen source, and 3) which fraction of the newly made biomass constitutes of TAG. The microalga species S. obliquus was chosen as the most suitable species for TAG production and used in all further studies.

    It is quantified how process conditions, such as the light intensity, pH, and temperature, influence TAG production during nitrogen starvation in S. obliquus. It was found that TAG could be produced in the ranges pH 5-9, temperature of 20-35°C, and incident light intensity of 200-1500 µmol m-2 s-1. The light intensity did not affect the maximum TAG content. The light intensity did, however, have a major effect on the photosynthetic efficiency. Suboptimal pH values and temperatures resulted in both a reduction in photosynthetic efficiency and reduction in maximum TAG content.

    It was found that during nitrogen starvation, at best approximately half of the biomass produced during nitrogen starvation is TAG. Large amounts of starch were produced simultaneously. This simultaneous starch and TAG production was therefore investigated in more detail. It was investigated how the carbon partitioning ratio (the ratio between fatty acid and starch synthesis rates), and the photosynthetic efficiency during nitrogen starvation, are influenced by the light intensity during nitrogen starvation and by the photoacclimated state at the onset of nitrogen starvation. It was found that the ratio between starch and fatty acid synthesis strongly correlated to the extent of nitrogen starvation, quantified as the biomass nitrogen content. Immediately after nitrogen depletion, mostly starch was made, but when nitrogen starvation progressed, this ratio shifted in favour of fatty acid synthesis. When nitrogen starvation progressed further, only fatty acids were made. Hereafter, the initially accumulated starch was degraded while fatty acid synthesis continued. The effects caused by the photoacclimated state persisted during nitrogen starvation. This did however not affect the photosynthetic efficiency or the carbon partitioning ratio during nitrogen starvation. The light intensity during nitrogen starvation had a major impact on the photosynthetic efficiency, but only a minor impact on the carbon partitioning ratio.

    Because large amounts of starch are produced during nitrogen starvation in wild-type S. obliquus, it is investigated how starchless mutants of S. obliquus can be used to improve TAG production. The carbon-partitioning of the wild-type and the slm1 starchless mutant of S. obliquus are therefore compared. It was found that the starchless mutant diverted all photosynthetic capacity, that was used for starch synthesis in the wild-type, towards TAG synthesis. This resulted in much higher TAG accumulation rates during initial nitrogen starvation. Furthermore, it was found that the efficiency of photosynthesis was not negatively affected in this starchless mutant. Altogether, the TAG yield on light increased by 51%.

    Using these insights, a mechanistic model was developed that describes photosynthesis and carbon partitioning during nitrogen starvation. The model was validated using experimental data from both the wild-type and starchless mutant of S. obliquus. This model was used to investigate how TAG production could be improved by advances in reactor design and strain improvement. Projections are made for productivities that seem feasible when various technologies are implemented in the microalgal cultivation process, using S. obliquus as a case-study.

    Finally, the findings of this thesis are used to evaluate the outcomes of techno-economic and life cycle analysis (LCA) studies that investigated the cost-price and net energy ratio of microalgal products, mostly biodiesel. It was found that the biomass productivity and biochemical composition associated with the cultivation of microalgae are large uncertainties in the input values for these studies. Several scenarios for microalgal cultivation are therefore presented based on the findings of this thesis. For each scenario, productivities, biochemical compositions, and nutrient requirements are provided that can be used as more realistic input values for techno-economic and LCA studies. It was concluded that the TAG productivity is commonly overestimated by 3 to 6-fold. According to these studies, approximately half of the costs and energy are used in the cultivation step. It was therefore concluded that these techno-economic and LCA studies underestimate the cost-price and energy consumption by 2 to 3.5-fold. The future improvements in productivity that might seem feasible according to the model simulations, could potentially improve the productivity such that it approaches the productivity that is commonly assumed as the base-case in current techno-economic and LCA studies. These advances in productivity can help to reduce the cost-price and specific energy consumption, but in addition, a reduction in costs and energy consumption of photobioreactors is needed before microalgal TAG production can be commercialized.

    Plants can produce much more : convert light to fresh product as efficiently as possible
    Heuvelink, E. ; Kierkels, T. - \ 2013
    In Greenhouses : the international magazine for greenhouse growers 2 (2013)1. - ISSN 2215-0633 - p. 7 - 9.
    glastuinbouw - teelt onder bescherming - plantenontwikkeling - belichting - lichtregiem - plantenfysiologie - cultuurmethoden - productiviteit - greenhouse horticulture - protected cultivation - plant development - illumination - light regime - plant physiology - cultural methods - productivity
    Imagine 200 kg of tomatoes per square metre greenhouse, 310 kg cucumbers, 120 kg peppers, 1,100 roses and 1,300 chrysanthemums. The plant is capable of producing much more than we currently achieve. However, to actually get closer to this potential production each step has to be improved.
    Mapping maize yield gaps in Africa; Can a leopard change its spots?
    Dijk, M. van; Meijerink, G.W. ; Rau, M.L. ; Shutes, K. - \ 2012
    The Hague : LEI, part of Wageningen UR (Report / LEI Wageningen UR : Research area International policy ) - ISBN 9789086155750 - 80
    maïs - voedselproductie - voedselzekerheid - markten - kunstmeststoffen - productiviteit - cartografie - afrika - maize - food production - food security - markets - fertilizers - productivity - mapping - africa
    Verbetering agribusiness in Rusland
    Valeeva, N.I. ; LEI, - \ 2012
    Kennis Online 9 (2012)april. - p. 7 - 7.
    landbouwindustrie - grote landbouwbedrijven - efficiëntie - productiviteit - rusland - opleiding - internationale samenwerking - managementonderwijs - agribusiness - large farms - efficiency - productivity - russia - training - international cooperation - management education
    Wageningen UR ondersteunt grote landbouwbedrijven in Rusland om efficiënter te produceren. En biedt een MBA aan in verschillende Russische steden voor managers van die bedrijven. De eerste cursisten studeerden onlangs af.
    Competing claims and food security in Ghana and Mali
    Berkum, S. van; Dijk, M. van; Bodegom, A.J. van; Jongschaap, R.E.E. ; Arets, E.J.M.M. ; Bindraban, P.S. - \ 2012
    The Hague : LEI, part of Wageningen UR (Report / LEI Wageningen UR : Research area International policy ) - ISBN 9789086155606 - 77
    voedselzekerheid - voedselproductie - landbouw en milieu - productiviteit - ecosystemen - bosgebieden - wetlands - savannen - landdegradatie - food security - food production - agriculture and environment - productivity - ecosystems - woodlands - wetlands - savannas - land degradation
    C/N-controlled periphyton-based freshwater prawn farming system: a sustainable approach to increase pond productivity
    Asaduzzaman, M. - \ 2012
    Wageningen University. Promotor(en): Johan Verreth; M. Abdul Wahab, co-promotor(en): Marc Verdegem. - [S.l.] : s.n. - ISBN 9789461731302 - 186
    macrobrachium rosenbergii - steurgarnalen - bedrijfssystemen - zoetwateraquacultuur - schaal- en schelpdierenteelt - vijverteelt - perifyton - voedingsstoffen - productiviteit - duurzaamheid (sustainability) - macrobrachium rosenbergii - prawns - farming systems - freshwater aquaculture - shellfish culture - pond culture - periphyton - nutrients - productivity - sustainability

    Three technologies showed to improve productivity and sustainability of pond production: (1) C/N ratio control, (2) providing substrates for periphyton development, and (3) fish driven re-suspension. The novelty of this PhD research is to combine these technologies, with the goal to raise pond productivity above levels obtained with each one of these technologies separately, and to increase the nutrient use efficiency in ponds above levels presently achieved, further enhancing sustainability. This combined technology is further referred to as C/N controlled periphyton (C/N-CP) technology. A series of experiments (Chapter 2-6) were conducted to develop such technology. The first step (Chapter 2) evaluated if increasing C/N ratio (from 10 to 20) in combination with providing vertical substrates for periphyton development in freshwater prawn monoculture ponds can enhance overall pond productivity. The results were encouraging due to the 75% increase of production; in addition it seemed that natural foods were underutilized by freshwater prawn. Therefore, the next step (Chapter 3) was further analysis of the above mentioned experiment investigating how C/N ratio control and addition of substrates influenced the natural food communities in freshwater monoculture ponds. This study suggested further investigation on the possibility of increasing stocking density of freshwater prawn and inclusion of tilapia due to its both sediment re-suspension and periphyton grazing activity. Therefore, in thethird step (Chapter 4) increasing stocking densities of prawn (from 2 to 3 m−2) and addition of different levels of tilapia (0, 0.5 and 1individual m−2) were tested. This study concludes that both stocking densities (2 and 3 juveniles m−2) of prawn with the addition of 0.5 tilapia m−2 resulted in higher fish production, good environmental condition and economic return. In the fourth step (Chapter 5), the effects of addition of periphyton substrates and tilapia driven bioturbation were tested in C/N controlled (C:N=20) system. This study showed that addition of tilapia (0.5 individual m−2) and periphytonsubstrates in C/N controlled ponds benefitedfreshwater prawn production and recommended that economicsustainability could still befurther enhanced by identifying cheaper on-farm carbohydratesources. Therefore, in the last step (Chapter 6) maize flour (Zea mays) is considered as a cheaper on-farm carbohydrate source and compared with tapioca starch. In addition, in this study considering the importance of rohu (Labeo rohita) as an indispensable species in south Asian aquaculture, both tilapia and rohu are considered to determine the suitability of either species in C/N-CP ponds. In added finfish (0.5 individual m−2),100% tilapia were found to be beneficial in C/N-controlled (C:N=20:1) prawn farming system compared to 50% tilapia+50% rohu or 100% rohu. In conclusion, a significant improvement of system environment, productivity and economic benefits was observed due to synergism among C:N ratio control, addition of periphyton substrates and tilapia driven bioturbation. Therefore, C/N-CP technology is a promising technology, improving the sustainability and productivity of present prawn farming by simple and affordable means.

    Wereldwijd 40% minder varkens nodig
    Hoste, R. - \ 2011
    Agri-monitor 2011 (2011)april. - ISSN 1383-6455 - p. 1 - 3.
    varkenshouderij - productiviteit - efficiëntie - landbouwprijzen - sectorale ontwikkeling - sectorale analyse - pig farming - productivity - efficiency - agricultural prices - sectoral development - sectoral analysis
    De wereldbevolking stijgt. Verwacht wordt dat er in 2050 ruim 9 miljard wereldburgers zullen zijn. Ook worden veel burgers welvarender. Bij een stijgend inkomen neemt de vleesconsumptie toe, hoewel niet onbegrensd. Als gevolg groeit de mondiale vraag naar vlees. De OECD verwacht over de periode 2010(2019 een toename van de vleesconsumptie van 19%. Tegelijkertijd lijken de voergrondstoffen schaarser te worden; niet alleen tijdelijk, zoals de sterk gestegen voerprijzen in de periode herfst 2006 – zomer 2008 en opnieuw vanaf midden 2010 lieten zien, maar ook structureel door een stijgende vraag naar biobrandstoffen. Kan een efficiëntieverbetering in de varkensproductie bijdragen aan een uitweg in dit dilemma? De wereldwijde productie van varkensvlees bedroeg in 2009 106 miljoen ton karkasgewicht (FAOstat, 2010). Hoeveel varkens zijn nodig om dit volume te produceren als dit zou gebeuren volgens de Nederlandse mate van productie(efficiëntie?
    Responses of the EU feed and livestock system to shocks in trade and production
    Jansen, D.M. ; Burger, C.P.J. ; Quist-Wessel, P.M.F. ; Rutgers, B. - \ 2011
    Wageningen : Platform Agriculture, Innovation & Society / Wageningen UR, PRI - 69
    agrarische economie - europese unie - economie van de veehouderij - veehouderij - voer - veevoeder - agrarische handel - voedselzekerheid - economische verandering - landbouwcrises - productiviteit - landbouwprijzen - agricultural economics - european union - livestock economics - livestock farming - feeds - fodder - agricultural trade - food security - economic change - agricultural crises - productivity - agricultural prices
    Dit rapport gaat in op de mogelijke effecten van meervoudige en/of langdurige calamiteiten die de beschikbaarheid van landbouwproducten verminderen op de Europese voedsel- en voersector in 2020.
    Improving smallholders' productivity in Bangladesh: tructural change or one-off success?
    Ruijter de Wildt, M.J.M. de - \ 2010
    Wageningen : Wageningen UR (Market, chains and sustainable development strategy & policy paper 17) - ISBN 9789461734709 - 11
    kleine landbouwbedrijven - landbouw - productiviteit - bangladesh - zuid-azië - minst ontwikkelde landen - azië - small farms - agriculture - productivity - bangladesh - south asia - least developed countries - asia
    Op weg naar optimale sturing gewasverdamping
    Stanghellini, C. ; Heuvelink, E. - \ 2008
    Groenten en Fruit. Algemeen 2008 (2008)33. - ISSN 0925-9694 - p. 20 - 21.
    kassen - groenteteelt - solanum lycopersicum - tomaten - gesloten systemen - zonnestraling - vaporisatie - besturen - temperatuur - vochtigheid - productiviteit - kastechniek - glastuinbouw - greenhouses - vegetable growing - solanum lycopersicum - tomatoes - closed systems - solar radiation - vaporization - steering - temperature - humidity - productivity - greenhouse technology - greenhouse horticulture
    In de huidige semi-gesloten kassen valt veel meer te sturen dan in een traditionele kas, waar temperatuur en vochtigheid afzonderlijk te regelen zijn, kan dit niet in traditionele kassen niet. Dit maakt het mogelijk een gewas als tomaat optimaal te sturen, waardoor een sprong in productiviteit binnen handbereik ligt
    Economic assessment of Dutch agricultural research
    Poppe, K.J. - \ 2008
    The Hague : LEI Wageningen UR (Report / LEI : Research area 1, International policy ) - ISBN 9789086152476 - 42
    landbouwkundig onderzoek - landbouwbeleid - onderzoek - productiviteit - prestatieniveau - innovatie adoptie - globalisering - agrarisch onderwijs - nederland - kennissystemen - economische verandering - landbouwvoorlichting - publiek-private samenwerking - agricultural research - agricultural policy - research - productivity - performance - innovation adoption - globalization - agricultural education - netherlands - knowledge systems - economic change - agricultural extension - public-private cooperation
    To cope with globalisation and other changes in the industry, in the last 20 years the Dutch Ministry of Agriculture has reorganised its system for education, extension and research considerably. It moved away from the concept of a linear process of innovation to that of an agro-innovation system. This paper describes the main changes. The paper argues that an evaluation of the changes is problematic. In an open economy where a large part of the public investments are targeted to reduce negative externalities of production (especially on environmental impact), a part of productivity is due to persons leaving the sector and income in farming is dependent on value added processes in its multinational cooperatives, causes and effects are hard to disentangle. The changes in the education, extension and research system cannot easily be evaluated by productivity analyses. Most research on this topic tries to develop methods for monitoring and evaluation from social learning or public administration.
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