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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    Impact of microbial variability on food safety and quality
    Aryani, D.C. - \ 2016
    Wageningen University. Promotor(en): Marcel Zwietering, co-promotor(en): Heidy den Besten. - Wageningen : Wageningen University - ISBN 9789462577381 - 190
    listeria monocytogenes - lactobacillus plantarum - growth analysis - kinetics - growth models - inactivation - heat stress - strain differences - food safety - milk - ham - microbial diversity - food quality - listeria monocytogenes - lactobacillus plantarum - groeianalyse - kinetica - groeimodellen - inactivatie - warmtestress - stamverschillen - voedselveiligheid - melk - ham - microbiële diversiteit - voedselkwaliteit
    AlgaeEconomics: bio-economic production models of micro-algae and downstream processing to produce bio energy carriers
    Spruijt, J. ; Schipperus, R. ; Kootstra, A.M.J. ; Visser, C.L.M. de - \ 2015
    EnAlgae Swansea University - 67
    algenteelt - teeltsystemen - productiekosten - biomassa productie - economische modellen - groeimodellen - biobrandstoffen - biobased economy - bioraffinage - algae culture - cropping systems - production costs - biomass production - economic models - growth models - biofuels - biobased economy - biorefinery
    This report describes results of work carried out within the EnAlgae project to describe production costs and identify the variables that have most effect in determining future cost prices so that R&D can be focussed on these issues. This has been done by making use of pilots within the EnAlgae consortium and by describing the process in Excel models that have been spread among and discussed with stakeholders active in the field of commercial algae production. The expectation is that this transparency and interaction will lead to an increase of the learning curve to make algae production cheaper and thus supplying more markets.
    Investering in kennis en diepgang, hulpmiddel voor teeltoptimalisatie : Groeimodel gerbera klaar voor gebruik
    Arkesteijn, M. ; Visser, P.H.B. de - \ 2014
    Onder Glas 11 (2014)9. - p. 7 - 9.
    glastuinbouw - snijbloemen - gerbera - groeimodellen - registratie - bedrijfsapplicaties - computer software - kastechniek - greenhouse horticulture - cut flowers - gerbera - growth models - registration - business software - computer software - greenhouse technology
    Sinds deze zomer is het groeimodel gerbera klaar voor gebruik door Nederlandse telers. Zij kunnen dan zelf met dit hulpmiddel aan de slag om bijvoorbeeld te zien wat hun oogst is op de korte termijn, maar ook teeltbeslissingen of investeringen toetsen.
    Gewasfactoren voor beregeningssignaal
    Evert, F.K. van - \ 2014
    Wageningen : PPO AGV - 8
    akkerbouw - aardappelen - beregening - groeimodellen - gewassen, groeifasen - precisielandbouw - arable farming - potatoes - overhead irrigation - growth models - crop growth stage - precision agriculture
    Voor de Beregeningswijzer is het nodig over gewasfactoren te beschikken voor aardappel. Het doel van dit werk is deze gewasfactoren te berekenen aan de hand van een gewasgroeimodel voor aardappelen.
    Groeimodel Gerbera : eindrapport van teeltproef en ontwikkeling van een groeimodel voor de Gerbera
    Visser, P.H.B. de; Helm, F.P.M. van der; Buwalda, F. ; Lagas, P. - \ 2014
    Wageningen : Wageningen UR Glastuinbouw (Rapport / Wageningen UR Glastuinbouw 1311) - 66
    gerbera - snijbloemen - groeimodellen - proeven - gewaskwaliteit - cultuurmethoden - teeltsystemen - belichting - temperatuur - gerbera - cut flowers - growth models - trials - crop quality - cultural methods - cropping systems - illumination - temperature
    Deze rapportage bevat een verslag van een daglengteproef uitgevoerd bij WUR Glastuinbouw te Bleiswijk en de beschrijving van opbouw en resultaten van het groeimodel gerbera. Het onderzoek, gefinancierd door het Productschap Tuinbouw op verzoek van de landelijke commissie gerbera, had tot doel inzicht te verkrijgen hoe de bloemproductie te maximaliseren zonder in te leveren op bloemkwaliteit.
    Improvement of energy and nitrogen utilisation in pork production : genetics and growth models
    Shirali, M. - \ 2014
    Wageningen University. Promotor(en): R. Roehe; Johan van Arendonk, co-promotor(en): Egbert Kanis. - Wageningen : Wageningen University - ISBN 9789461738479 - 186
    dierveredeling - varkens - dierlijke productie - groeimodellen - genetica - stikstof - excretie - voederconversievermogen - animal breeding - pigs - animal production - growth models - genetics - nitrogen - excretion - feed conversion efficiency

    Expansion ofdemand for porkis expected to meet the nutritional requirements of an increasing world population. However, higher levels of pig production are using limited feed resources and are often associated with higher levels of environmental pollution, which provide substantial challenges for pork producers. Therefore, strategies that simultaneously improve feed efficiency and increase production with reduction of environmental pollution of pork production (e.g. per kg product) is necessary. The general aim of the current project was to investigate opportunities for improvement of energy usage and nitrogen excretion at different stages of growth in pigs, and to determine their phenotypic and genetic background in association with other performance traits as well as to provide the basis for developing strategies for improvement of these traits using biological growth models.Feed efficiency was characterised by residual energy intake (REI) as the surplus of energy intake which is not used for protein and lipid deposition along with maintenance throughout growth to 140 kg BW whereas nitrogen excretion was estimated as the difference between nitrogen intake and retention. The results of phenotypic analyses indicate that nitrogen excretion increases substantially during growth of pigs and can be reduced most effectively by improving feed efficiency and to a lesser extent through the improvement of weight gain and/or body composition. Results of genetic analyses indicate that REI as a measure of feed efficiency is highly heritable (h2= 0.44), suggesting great potential for genetic improvement. REI has different genetic background at different stages of growth, suggesting that genetic improvement of REI should consider the stage of growth. In addition, REI explains a large portion of variance in nitrogen excretion, suggesting that selection for lower REI is expected to reduce nitrogen excretion of pork production as well as improve feed efficiency. Genomic analysis showed that different genes are responsible for efficiency of feed utilisation at different stages of growth.The results further suggest that only a small proportion of the variance in REI was explained by variation in feed intake, whereas underlying factors of feed utilisation, such as metabolism and protein turnover, are likely to have great influence on REI. A biological growth model was used to characterize a crossbred population regarding feed energy and nitrogen efficiency in comparison to two purebred population selected for different performances. The results of the biological growth model can be used to developed optimal genetic, nutritional and production strategies, e.g. the impact of reduction in slaughter weight on marginal energy efficiency and nitrogen excretion was estimated. Furthermore, based on the results of the biological growth model, the influence of changes of production traits during growth on energy and nitrogen efficiency can be estimated to optimise genetic strategies. Furthermore, opportunities for further improvement of energy and nitrogen utilisation have been outlined.

    Assessing climate change and associated socio-economic scenarios for arable farming in the Netherlands: An application of benchmarking and bio-economic farm modelling
    Kanellopoulos, A. ; Reidsma, P. ; Wolf, J. ; Ittersum, M.K. van - \ 2014
    European Journal of Agronomy 52 (2014)Part A. - ISSN 1161-0301 - p. 69 - 80.
    akkerbouw - klimaatverandering - opbrengsten - groeimodellen - scenario-analyse - alternatieve landbouw - arable farming - climatic change - yields - growth models - scenario analysis - alternative farming - agricultural land-use - integrated assessment - european-community - future - crop - efficiency - impacts - systems
    Future farming systems are challenged to adapt to the changing socio-economic and bio-physical environment in order to remain competitive and to meet the increasing requirements for food and fibres. The scientific challenge is to evaluate the consequences of predefined scenarios, identify current “best” practices and explore future adaptation strategies at farm level. The objective of this article is to assess the impact of different climate change and socio-economic scenarios on arable farming systems in Flevoland (the Netherlands) and to explore possible adaptation strategies. Data Envelopment Analysis was used to identify these current “best” practices while bio-economic modelling was used to calculate a number of important economic and environmental indicators in scenarios for 2050. Relative differences between yields with and without climate change and technological change were simulated with a crop bio-physical model and used as a correction factors for the observed crop yields of current “best” practices. We demonstrated the capacity of the proposed methodology to explore multiple scenarios by analysing the importance of drivers of change, while accounting for variation between individual farms. It was found that farmers in Flevoland are in general technically efficient and a substantial share of the arable land is currently under profit maximization. We found that climate change increased productivity in all tested scenarios. However, the effects of different socio-economic scenarios (globalized and regionalized economies) on the economic and environmental performance of the farms were variable. Scenarios of a globalized economy where the prices of outputs were simulated to increase substantially might result in increased average gross margin and lower average (per ha) applications of crop protection and fertilizers. However, the effects might differ between different farm types. It was found that, the abolishment of sugar beet quota and changes of future prices of agricultural inputs and outputs in such socio-economic scenario (i.e. globalized economy) caused a decrease in gross margins of smaller (in terms of economic size) farms, while gross margin of larger farms increased. In scenarios where more regionalized economies and a moderate climate change are assumed, the future price ratios between inputs and outputs are shown to be the key factors for the viability of arable farms in our simulations
    Groeimodel aardappel in QMS akkerbouw (97)
    Evert, F.K. van; Kempenaar, C. - \ 2013
    Wageningen : Plant Research International - 11
    akkerbouw - aardappelen - groeimodellen - precisielandbouw - teeltsystemen - arable farming - potatoes - growth models - precision agriculture - cropping systems
    Het teeltbegeleidingssysteem QMS Akkerbouw kan gebruikt worden om gemakkelijk en overzichtelijk de groei van gewassen van percelen te vergelijken. Hiertoe dienen de percelen ingetekend te zijn op en dienen kerngegevens in Mijnakker te zijn ingevuld (opkomstdatum, ras, grondsoort, e.d.). Daarnaast dienen telers of adviseurs zelf ook aanvullende gegevens over het perceel toe te voegen (zoals mestgift e.d.) om gericht percelen met elkaar te kunnen vergelijken.
    Virtuele roos: experimenteel en modelmatig onderzoek naar gewasopbouw roos
    Marcelis, L.F.M. ; Heuvelink, E. ; Wubs-Timmermans, A.M. ; Buck-Sorlin, G.H. ; Heijden, G.W.A.M. van der; Eveleens, B.A. ; Vos, J. - \ 2013
    Wageningen : Wageningen UR Glastuinbouw (Rapporten GTB 1234) - 66
    bloementeelt - rozen - rassen (planten) - cultuurmethoden - plantenontwikkeling - gewaskwaliteit - groeimodellen - methodologie - floriculture - roses - varieties - cultural methods - plant development - crop quality - growth models - methodology
    De gewasopbouw of gewasstructuur is een belangrijke bepalende factor voor productie en kwaliteit bij roos. Met name het uitlopen van een okselknop en en de daarop volgende uitgroei tot bloemscheut hangen nauw samen met de gewasstructuur. De ideale gewasopbouw is niet gelijk voor alle rassen, terwijl nieuwe rassen elkaar in snel tempo opvolgen. Ook de ontwikkelingen op het gebied van robotisering en mobiele teeltsystemen gaan nieuwe eisen stellen aan de gewasopbouw. De gewasopbouw zal zodanig moeten zijn dat het enerzijds voldoet aan de eisen van de techniek en dat anderzijds een optimale productie en kwaliteit geleverd worden. Dit vraagt om keuzen te maken in teeltstrategieën. Gewasopbouw is een complex proces dat niet los gezien kan worden van plantverband, raseigenschappen, snoeistrategie en klimaat. Om hier meer grip op te kunnen krijgen is een aantal proeven uitgevoerd naar verschillen in plantopbouw. Tevens is een gewasgroeimodel ontwikkeld dat de gewasontwikkeling en gewasopbouw (in 3 dimensies) kan berekenen.
    Participatory design of farm level adaptation to climate risks in an arable region in The Netherlands
    Schaap, B.F. ; Reidsma, P. ; Verhagen, A. ; Wolf, J. ; Ittersum, M.K. van - \ 2013
    European Journal of Agronomy 48 (2013)7. - ISSN 1161-0301 - p. 30 - 42.
    akkerbouw - opbrengsten - groeimodellen - klimaatverandering - flevoland - arable farming - yields - growth models - climatic change - flevoland - crop production - change impacts - agriculture - variability - events - europe - model
    In the arable farming region Flevoland in The Netherlands climate change, including extreme events and pests and diseases, will likely pose risks to a variety of crops including high value crops such as seed potato, ware potato and seed onion. A well designed adaptation strategy at the farm level can reduce risks for farmers in Flevoland. Currently, most of the impact assessments rely heavily on (modelling) techniques that cannot take into account extreme events and pests and diseases and cannot address all crops, and are thus not suited as input for a comprehensive adaptation strategy at the farm level. To identify major climate risks and impacts and develop an adaptation measure portfolio for the most relevant risks we complemented crop growth modelling with a semi-quantitative and participatory approach, the Agro Climatic Calendar (ACC), A cost-benefit analysis and stakeholder workshops were used to identify robust adaptation measures and design an adaptation strategy for contrasting scenarios in 2050. For Flevoland, potential yields of main crops were projected to increase, but five main climate risks were identified, and these are likely to offset the positive impacts. Optimized adaptation strategies differ per scenario (frequency of occurrence of climate risks) and per farm (difference in economic loss). When impacts are high (in the +2 °C and A1 SRES scenario) drip irrigation was identified as the best adaptation measure against the main climate risk heat wave that causes second-growth in seed and ware potato. When impacts are smaller (the +1 °C and B2 SRES scenario), other options including no adaptation are more cost-effective. Our study shows that with relatively simple techniques such as the ACC combined with a stakeholder process, adaptation strategies can be designed for whole farming systems. Important benefits of this approach compared to modelling techniques are that all crops can be included, all climate factors can be addressed, and a large range of adaptation measures can be explored. This enhances that the identified adaptation strategies are recognizable and relevant for stakeholders.
    A regional implementation of WOFOST for calculating yield gaps of winter wheat across the European Union
    Boogaard, H. ; Wolf, J. ; Supit, I. ; Niemeyer, S. ; Ittersum, M.K. van - \ 2013
    Field Crops Research 143 (2013). - ISSN 0378-4290 - p. 130 - 142.
    tarwe - gewasproductie - akkerbouw - groeimodellen - klimaatverandering - wheat - crop production - arable farming - growth models - climatic change - crop growth simulation - fertilizer application - global radiation - models - land - opportunities - agriculture - tropics - system
    Wheat is Europe’s dominant crop in terms of land use in the European Union (EU25). Most of this wheat area is sown in autumn, i.e., winter wheat in all EU25 countries, apart from southern Italy, southern Spain and most of Portugal, where spring wheat varieties are sown in late autumn. We evaluated the strengths and limitations of a regional implementation of the crop growth model WOFOST implemented in the Crop Growth Monitoring System (CGMS) for calculating yield gaps of autumn-sown wheat across the EU25. Normally, CGMS is used to assess growing conditions and to calculate timely and quantitative yield forecasts for the main crops in Europe. Plausibility of growth simulations by CGMS in terms of leaf area, total biomass and harvest index were evaluated and simulated yields were compared with those from other global studies. This study shows that water-limited autumn-sown wheat yields, being the most relevant benchmark for the largely rain fed wheat cultivation in Europe, are plausible for most parts of the EU25 and can be used to calculate yield gaps with some precision. In parts of southern Europe unrealistic simulated harvest index, maximum leaf area index and biomass values were found which are mainly caused by wrong values of phenology related crop parameters. Furthermore CGMS slightly underestimates potential and water-limited yields, which calls for a calibration using new field experiments with recent cultivars. Estimated yield gap is between 2 and 4 t ha-1 in main parts of the EU25, is smaller north-western Europe and highest in Portugal.
    Participatory design of farm level adaptation to climate risks in an arable region in The Netherlands
    Schaap, B.F. ; Reidsma, P. ; Verhagen, A. ; Wolf, J. ; Ittersum, M.K. van - \ 2012
    akkerbouw - opbrengsten - groeimodellen - klimaatverandering - modellen - arable farming - yields - growth models - climatic change - models
    Currently, most of the impact assessments for farming systems rely heavily on (modelling) techniques that cannot take into account extreme events and pests and diseases and cannot address all crops and are thus not suited as input for a comprehensive adaptation strategy at the farm level. In this study, crop growth modelling with WOFOST is complemented with the Agro Climate Calendar (ACC), a semi-quantitative and participatory approach.
    Botrytisvoorspeller in gerbera: Praktijkervaringen met het gebruik van de Botrytisvoorspeller van Wageningen UR Glastuinbouw via
    Helm, F.P.M. van der; Visser, P.H.B. de - \ 2012
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1208) - 54
    botrytis - plantenziekteverwekkende schimmels - groeimodellen - gerbera - sierteelt - gewasbescherming - gebruikswaarde - computertechnieken - botrytis - plant pathogenic fungi - growth models - gerbera - ornamental horticulture - plant protection - use value - computer techniques
    In het project parapluplan Gerbera is een Botrytisvoorspeller ontwikkeld. Dit model kan op de PC van de kweker draaien, maar dit vereist een installatieprocedure die een grote belemmering blijkt voor toepassen van de voorspeller. Kwekers hebben in een Pilotperiode van een half jaar gestest of de weergave van het model in een eenvoudiger alternatief is. gebruikt de informatie uit de klimaatcomputer dan automatisch voor het draaien van het model. Gedurende de pilotperiode is weinig Botrytis voorgekomen in de kas. Als dit wel het geval was, dan is dit ook berekend/voorspeld. De voorspelling vooraf bleek lastig te interpreteren. Na uitleg over de grafieken in de tussentijdse bijeenkomst realiseerde de kwekers zich de betekenis van de lijnen beter. Kwekers blijken al snel een veilige strategie te voeren, met hoger energieverbruik dan strict noodzakelijk tot gevolg. Aanbevelingen voor verbetering zijn de voorspelling en de realisatie te combineren zodat van het verleden geleerd kan worden voor de toekomst. Beter begrip van het model en de gevolgen van klimaatinstellingen voor de voorspelling, kan leiden tot een klimaat regeling met lager energieverbruik. Voor de kwekers is het wenselijk dat een bandbreedte van gevoeligheid van het model is in te stellen, zodat zij dit aan hun eigen situatie kunnen tunen. Ten slotte zou een SMS bij hoog infectierisico voor de telers gewenst zijn, omdat zij niet elke dag (kunnen) kijken. De waarde van de Botrytisvoorspeller was voor de deelnemers van de pilotgroep groot genoeg om na de pilotfase verder te gaan tegen betaling. Abstract A predcition model for Botrytis in Gerbera is developped by Wageningen UR greenhouse horticulture. The installation of the software and separate interface from regular climate control evaluation have appeared to be tresholds for adapting the model in everyday practice. A pilotgroup of 10 growers have used the digital platform of for data exchange and consulting the model in combination with regular climate control evaluation. Little incidence of Botrytis has occurred during the pilotperiod, although climate was favourable for Botrytis at certain periods during the pilot. One case of Botrytis occurred and was predicted by the model. The interpretation of the data and figures appeared to be more complex than expected. Only after presentation of interpretation of the graphs growers realised how to translate the information to their situation and climate control. Growers tend to use the model to be on the safe side, however it could results in higher use of energy than needed. Growers would like to be able to adjust the sensitivity of the model to tune the model to their specific situation. Also an SMS service when risks are high would is expected to be helpful. Growers still did not use the model on a daily basis, although tresholds were lower. The value was high enough for growers of the pilot to continue using the model and pay for it after the pilotperiod was over.
    Assessing climate change effects on European crop yields using the Crop Growth
    Supit, I. ; Diepen, C.A. van; Wit, A.J.W. de; Wolf, J. ; Kabat, P. ; Baruth, B. ; Ludwig, F. - \ 2012
    Agricultural and Forest Meteorology 164 (2012). - ISSN 0168-1923 - p. 96 - 111.
    gewasproductie - akkerbouw - groeimodellen - kooldioxide - bedrijfssystemen - klimaatverandering - crop production - arable farming - growth models - carbon dioxide - farming systems - climatic change - atmospheric co2 concentration - daily precipitation models - solanum-tuberosum l. - wind-speed analysis - change scenarios - daily rainfall - carbon-dioxide - brassica-napus - part ii - simulation
    Climate change impacts on potential and rainfed crop yields on the European continent were studied using output of three General Circulation Models and the Crop Growth Monitoring System in combination with a weather generator. Climate change impacts differ per crop type and per CO2 emission scenario. Crops planted in autumn and winter (winter wheat) may benefit from the increasing CO2 concentration. Rainfall is sufficient and if the CO2 concentration increase is high, yields may increase up to 2090. If the CO2 increase is less, increasing temperatures result in declining or stagnating yields after 2050. Crops planted in spring (potato, sugar beet) initially benefit from the CO2 increase, however as time progresses the increasing temperatures reduce these positive effects. By the end of the century yields decline in southern Europe and production may only be possible if enough irrigation water is available. In northern Europe depending on the temperature and CO2 concentration increase, yields either stagnate or decline. However in some of the cooler regions yield increase is still possible. Crops planted in late spring and summer (maize) may suffer from droughts and high temperature in summer. By the end of the century, depending on the temperature rise, crop yields decline almost everywhere. If the temperature increase is less only in north western Europe yields remain stable.
    Botrytisvoorspeller in Letsgrow
    Visser, P.B. - \ 2012
    botrytis - plant pathogenic fungi - growth models - gerbera - ornamental horticulture - greenhouse horticulture - plant protection
    Handleiding Paprika model “Cultivista” - Project Topmodel4all / 2010-2011
    Driever, S.M. ; Kromdijk, J. - \ 2011
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1145) - 29
    glastuinbouw - cultuurmethoden - groeimodellen - plantenontwikkeling - capsicum - beslissingsondersteunende systemen - computer software - kwekers - greenhouse horticulture - cultural methods - growth models - plant development - capsicum - decision support systems - computer software - growers
    Abstract NL Deze handleiding is bedoeld voor telers die aan de slag willen met het paprika model “Cultivista”. Er wordt uitgelegd hoe met het interactieve paprika model “Cultivista” kan worden gewerkt. De installatie van het model en de verschillende in te voeren gegevens (inputs) van het model worden besproken. Vervolgens worden de werking van het model en de onderdelen van de interface besproken. Tevens worden de voorwaarden voor mogelijke automatisering van de inputs en het oplossen van de meest voorkomende problemen besproken. Abstract UK This manual is meant for growers who would like to work with the sweet pepper growth model “Cultivista”. This manual explains how the model works, how to install the model and which inputs are used. Furthermore, the different parts of the interface are explained. Finally, the conditions for automation of the inputs and troubleshooting of the most common problems are discussed.
    Freesia groeimodel: Ontwikkeling van een groeimodel voor gebruik door telers
    Labrie, C.W. ; Visser, P.H.B. de; Buwalda, F. ; Helm, F.P.M. van der - \ 2011
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1075) - 35
    freesia - groeimodellen - grensvlak - droge stof - groei - kwekers - klimaatfactoren - teelt onder bescherming - nederland - freesia - growth models - interface - dry matter - growth - growers - climatic factors - protected cultivation - netherlands
    Abstract Wageningen UR Greenhouse Horticulture conducted in close cooperation with the Dutch freesia sector research on the effects of climate on dry matter production of Freesia plants. The relationships were established on the basis of photosynthesis, growth and climate data measured in greenhouses of Freesia growers. The relationships were incorporated in a dynamic growth model that correctly simulated the dry matter growth in a series of trials. A user-friendly interface was satisfactorily developed interactively with a number of Freesia growers. The model can be used by growers to find the most optimal combination of climate factors for Freesia growth at given plant age and greenhouse settings.
    Computermodel helpt haakgroei freesia te verbeteren (interview met Pieter de Visser en Fokke Buwalda)
    Petter, M. ; Visser, P.H.B. de; Buwalda, F. - \ 2011
    Vakblad voor de Bloemisterij 66 (2011)16. - ISSN 0042-2223 - p. 44 - 45.
    snijbloemen - freesia - computertechnieken - groeimodellen - bloemstelen - optimalisatiemethoden - cut flowers - freesia - computer techniques - growth models - pedicels - optimization methods
    Met een gratis groeimodel voor freesia kunnen kwekers zelf en op een gebruiksvriendelijke manier hun teeltstrategie controleren. Voor het sturen en plannen van de teelt is echter een verdere ontwikkeling van het model nodig.
    Koppeling groeimodellen en logistieke modellen voor optimale sturing, Thema: Innovatieve tuinbouw BO-12.03-006-005
    Marcelis, L.F.M. ; Noort, F.R. van - \ 2011
    glastuinbouw - teelt onder bescherming - plantenkwekerijen - logistiek - planning - monitoring - groeimodellen - computertechnieken - agrarische bedrijfsplanning - greenhouse horticulture - protected cultivation - nurseries - logistics - planning - monitoring - growth models - computer techniques - farm planning
    Onderzoek naar het ontwikkelen en koppelen van groeimodellen met logistieke modellen bij potplantenkwekerijen om teelt en logistiek beter op elkaar te kunnen afstemmen.
    Champignons op Compost of Vloeibare Voeding?, Thema: Innovatieve tuinbouw BO-12.03-006-001.01
    Sonnenberg, A.S.M. ; Baars, J.J.P. ; Hendrickx, P.M. - \ 2011
    substraten - compost - cultuurmethoden - innovaties - groeimodellen - voedingsonderzoek - alternatieve methoden - substrates - composts - cultural methods - innovations - growth models - nutrition research - alternative methods
    Onderzoek naar het huidige teeltsysteem bij champignons, maar ook naar alternatieve systemen. Concrete activiteiten zijn het meten en analyseren van alle relevante parameters in het huidige systeem (Input-Output Project), het analyseren van deze data om het systeem te begrijpen en te verbeteren en het ontwikkelen van teeltmodellen voor voedingsonderzoek.
    40 kg Paprika
    Eveleens-Clark, B.A. ; Lagas, P. ; Driever, S.M. ; Zwinkels, J. ; Vaate, J. Bij de; Kaarsemaker, R.C. - \ 2010
    Bleiswijk/Wageningen/Delfgauw : Wageningen UR Glastuinbouw/DLV Plant/Groen Agro Control - 87
    capsicum - gewasproductie - productiegroei - glasgroenten - tuinbouw - assimilatie - groeimodellen - teeltsystemen - brix - diffuus glas - snoeien - teelt in rijen - capsicum - crop production - production growth - greenhouse vegetables - horticulture - assimilation - growth models - cropping systems - brix - diffused glass - pruning - alley cropping
    Rapport beBestaand uit de volgende onderdelen: 1. Een kasproef, waarin het doel was de productie te verhogen door een combinatie van maatregelen; diffuus glas, verneveling en gewashandelingen 2. Praktijktoepassing en ontwikkeling van een plantmodel dat zetting voorspelt 3. Toetsing van een nieuwe methode om beschikbaarheid van assimilaten voor zetting te meten
    Workshop Freesia Groeimodel: Inzicht in fotosynthese en groei van freesia
    Visser, Pieter de - \ 2010
    horticulture - floriculture - freesia - growth models - growth - developmental stages - growth analysis - climatic factors - photosynthesis - optimization methods - greenhouse horticulture
    Grassland simulation with the LPJmL model : version 3.4.018
    Boons-Prins, E.R. - \ 2010
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 172) - 174
    graslanden - graslandbeheer - gewassen - groeimodellen - landgebruik - simulatiemodellen - gewasgroeimodellen - grasslands - grassland management - crops - growth models - land use - simulation models - crop growth models
    One third of the land surface is covered with natural and cultivated grasslands. Most of these grasslands are intensively or extensively exploited by humans to feed animals. With growing wealth, causing an increase of meat consumption, there is a need to better understand the processes that influence the grass production of these ecosystems. The project aims to improve the knowledge basis regarding grassland productivity and the relationship between management of grasslands and productivity. The research will led to modification of the Dynamic global vegetation model with natural and managed land (LPJmL, version 3.4.018, 2010) for the simulation of grassland and grassland management. Crop growth models such as LPJmL can help to clarify and understand grass production processes. A checked and calibrated model gives useful insights in the carrying capacity of grasslands and enables us to estimate the risk for environmental damage with increase of grass and/or meat production.
    Automatiseerder en onderzoekers inspireren elkaar
    Verkerke, W. - \ 2010
    Syscope Magazine 2010 (2010)26. - p. 7 - 8.
    kassen - teelt onder bescherming - plantenontwikkeling - groeimodellen - computertechnieken - automatisering - planning - teeltsystemen - glastuinbouw - logistiek - greenhouses - protected cultivation - plant development - growth models - computer techniques - automation - planning - cropping systems - greenhouse horticulture - logistics
    De glastuinbouw gebruikte tot voor kort alleen plantengroeimodellen om de gewasgroei te beschrijven. Ze waren niet goed te koppelen aan de logistieke processen op moderne bedrijven. Hier komt verandering in door het project Plant-iT. Voor het eerst werken logistieke ICT-ers en plantenfysiologen samen aan een nieuwe generatie bedrijfsoplossingen, waarin groene kennis en logistiek echt geïntegreerd worden.
    Detection, occurence, growth and inactivation of Cronobacter spp. (Enterobacter sakazakii)
    Kandhai, M.C. - \ 2010
    Wageningen University. Promotor(en): Leon Gorris; Marcel Zwietering, co-promotor(en): Martine Reij. - [S.l. : S.n. - ISBN 9789085855569 - 240
    enterobacter sakazakii - flesvoedingsamenstelling - detectie - groeianalyse - groeimodellen - inactivatie - risicoschatting - voedselveiligheid - microbiële besmetting - blootstellingsbepaling - enterobacter sakazakii - infant formulae - detection - growth analysis - growth models - inactivation - risk assessment - food safety - microbial contamination - exposure assessment
    The genus Cronobacter consists of Gram-negative, motile, non-spore forming, facultative anaerobic bacteria, and was originally defined as one species “Enterobacter sakazakii” within the genus Enterobacter in 1980. Cronobacter spp. have been documented as a rare cause of outbreaks and sporadic cases of neonatal meningitis, necrotizing enterocolitis, and sepsis in infants with a high mortality. Among these infants, those at greatest risk are infants less than 2 months of age, particularly pre-term infants, low birth weight (LBW) infants (< 2500 g), and immuno-compromised infants.
    At the onset of the work for this thesis, Cronobacter spp. had been isolated from milk-based powdered formulae which have a direct link to the sub-population at greatest risk. However, there was a need to more closely investigate whether and where Cronobacter spp. occurs in environments in which these powdered are manufactured and packed but also to investigate other sources which could lead to exposure of vulnerable sub-populations. The main objective of this study was to develop isolation and detection methods that would allow quick and reliable investigation into the occurrence of the micro-organism in potential sources. Furthermore, more insight into the growth behavior of Cronobacter spp. in reconstituted infant formula was necessary in order to provide data to be used in Microbiological Risk Assessment (MRA) dedicated to this particular food product.
    A selective enrichment method was developed for the rapid and reliable enrichment and detection of Cronobacter spp. in environmental samples. The detection method which was developed is based on two features of Cronobacter spp. combined: their yellow pigmented colonies when grown on tryptone soy agar and their constitutive -glucosidase, which can be detected in a 4-h colorimetric assay. The initially developed method and refinements thereof were applied for routine screening for the presence of Cronobacter spp. in environmental samples and a variety of food products manufactured or marketed in The Netherlands. The detection method described in this thesis has been the basis for a series of media for Cronobacter spp. that have recently been commercialized.
    Quantitative data on product contamination at manufacture, during preparation, and also growth after reconstitution are required in order to assess the risk associated with Cronobacter spp. exposure. Next to that, tools are needed to asses the micro-organisms growth potential as well as its inactivation (thus, its survival) due to specific control measures applied. In this thesis, predictive growth models were developed that capture key growth parameters. Minimum– and maximum temperatures estimated with the Secondary Rosso equation were 3.6 ºC and 47.6 ºC, respectively. The estimated lag time of the micro-organisms was found to vary from 83.3 ± 18.7 h at 10 ºC to 1.73 ± 0.43 h at 37 ºC and could be described with the hyperbolic model and reciprocal square root relation. The models for growth rates and lag times as a function of temperatures obtained during this study allow estimating the potential growth of Cronobacter spp. in reconstituted infant formula stored at any temperature below 47 C.
    As growth rates of Cronobacter at refrigeration temperatures are relatively small, caregivers are advised to store reconstituted infant at low temperature as a control measure to prevent microbial growth. It is evident that storage of reconstituted formula in a refrigerator may require a significant amount of the time before the formula reach the targeted refrigeration temperature. Therefore, a mathematical model was built to predict the temperature profile and the resulting growth of Cronobacter spp. during cooling, i.e. under dynamic temperature conditions. Predictions showed that proliferation of Cronobacter spp. during cooling strongly depends on the size of the container used for storage and that it may be prevented by limiting the volume to be cooled to portion-size only or by reconstituting at temperatures of 25 °C or lower.
    The survival of two Cronobacter strains in dry powdered infant formula (PIF) was tested and compared to the survival of six other bacterial strains after inoculation and storage at several temperatures between 7 and 42 ºC. The effect of temperature on survival in PIF, was described using both the Weibull distribution model and the log-linear model. Differences were found in the rate of survival that can be due to difference in the resistance to inactivation in dry environments between Cronobacter species, which could be relevant to consider when establishing quantitative risk assessments on consumer risks related to PIF.
    The research described in this thesis contributes to the existing knowledge on the natural habitat of Cronobacter spp. and its occurrence and behavior in PIF. The models developed for quantifying the growth of Cronobacter spp. in reconstituted formulae under various conditions can be applied in risk assessments set-up to estimate the probability of vulnerable sub-populations becoming ill after consuming infant formulae. International and national governmental bodies may use these predictive models in risk assessments and to establish guidelines for health care professionals to provide effective hygiene training to parents and professional caregivers to ensure that PIF is prepared handled and stored appropriately.

    Sunergiekas toont prima teeltresultaat en netto energieproductie (Onderzoekspagina Wageningen UR Glastuinbouw)
    Wageningen UR Glastuinbouw, - \ 2009
    Onder Glas 6 (2009)12. - p. 63 - 63.
    kassen - tomaten - teeltsystemen - smaakpanels - leerlingen - klimaatregeling - groeimodellen - plantenontwikkeling - gewasbescherming - botrytis - glastuinbouw - semi-gesloten kassen - duurzame energie - groenten - greenhouses - tomatoes - cropping systems - taste panels - pupils - air conditioning - growth models - plant development - plant protection - botrytis - greenhouse horticulture - semi-closed greenhouses - sustainable energy - vegetables
    Onderzoek bij WUR Glastuinbouw : sunergiekas toont positieve resultaten in de tomatenteelt, de ontwikkeling van een kispanel als smaakteam in Bleijswijk en een groeimodel voor freesia om de effecten van de verschillende klimaatfactoren op groei en ontwikkeling te structureren en botrytisvoorspeller gerbera nu beschikbaar als rekenmodel
    Crop models: main developments, their use in CGMS and integrated modeling
    Wolf, J. ; Ittersum, M.K. van - \ 2009
    Agro Informatica 22 (2009)2. - ISSN 0925-4455 - p. 15 - 18.
    gewassen - groeimodellen - oogstvoorspelling - gewasopbrengst - monitoring - wiskundige modellen - gewasgroeimodellen - crops - growth models - yield forecasting - crop yield - monitoring - mathematical models - crop growth models
    Het artikel beschrijft de voornaamste ontwikkelingen in gewasgroeimodellen (WOFOST), hun gebruik in CGMS en geïntegreerde modellering
    Rekenmodel voor Botrytis en groei
    Visser, Pieter de - \ 2009
    gerbera - growth models - crop quality - plant development - energy consumption - air conditioning - simulation models
    Beheersing intrinsieke kwaliteit potplanten met als pilot Ficus en Anthurium : Deelproject 1b, Bepaling intrinsieke kwaliteit van uitgangsmateriaal Ficus
    Snel, J.F.H. ; Jalink, H. ; Schoor, R. van der; Carvalho, S.M.P. ; Heuvelink, E. ; Dijkhuis, P. ; Verberkt, H. ; Geest, J. van - \ 2008
    Wageningen : Wageningen UR Glastuinbouw (Nota / Wageningen UR Glastuinbouw 556) - 12
    gewaskwaliteit - methodologie - groei - ficus - groeimodellen - glastuinbouw - potplanten - crop quality - methodology - growth - ficus - growth models - greenhouse horticulture - pot plants
    Verslag van onderzoek naar bepaling van intrinsieke productkwaliteit om de groeikracht van Ficus stekken te kunnen voorspellen.
    Sensoren: meten en weten wat de plant wil
    Marcelis, L.F.M. ; Dieleman, J.A. ; Meinen, E. ; Tuijl, B.A.J. van; Gieling, T.H. ; Janssen, H.J.J. ; Voogt, W. - \ 2007
    teelt onder bescherming - groeimodellen - sensors - meetapparatuur - fotosynthese - glastuinbouw - protected cultivation - growth models - sensors - indicating instruments - photosynthesis - greenhouse horticulture
    Wageningen UR Glastuinbouw heeft een breed scala aan sensoren, meetmethodieken en groeimodellen. Daarmee kan de vertaalslag van meting naar bruikbare informatie worden gemaakt
    Groeimodellen: rekenen aan planten
    Marcelis, L.F.M. ; Elings, A. ; Buwalda, F. ; Visser, P.H.B. de; Heuvelink, E. ; Nieboer, S. - \ 2007
    groeimodellen - groei - gewasteelt - teelt onder bescherming - gewasgroeimodellen - glastuinbouw - growth models - growth - crop management - protected cultivation - crop growth models - greenhouse horticulture
    Wat zijn de toepassingen van groeimodellen?
    Virtuele planten: groeimodellen in 3D
    Visser, P.H.B. de; Marcelis, L.F.M. ; Heijden, G.W.A.M. van der; Vos, J.W. ; Heuvelink, E. - \ 2007
    groei - modellen - groeimodellen - planten - plantenontwikkeling - simulatie - growth - models - growth models - plants - plant development - simulation
    Informatie over 3D modellen van planten ('virtuele planten'). Hoe werkt dit en wat is de toepassing van deze 3D modellen?
    Aanvullende COCO-berekeningen in het kader van nazorg van het DynAqua-project (kokkelkweek deel)
    Vries, P. de; Veenstra, F.A. - \ 2007
    Den Helder : IMARES (Rapport / Wageningen IMARES nr. C096/07) - 23
    schaaldieren - kokkels - groei - groeitempo - groeimodellen - watertemperatuur - chlorofyl - zwevende deeltjes - organische stof - mariene ecologie - shellfish - clams - growth - growth rate - growth models - water temperature - chlorophyll - suspended solids - organic matter - marine ecology
    COCO (COmputer COckle model) is ontwikkeld door het voormalig Nederlands Instituut voor Visserij Onderzoek (RIVO), tegenwoordig bekend als Wageningen IMARES. COCO berekent ondermeer de groei van een individuele kokkel, maar kan ook informatie met betrekking tot de productie van pseudo-feces opleveren. Het model bevat feedback loops bij de opname en het metabolisme van voedsel en het verdelen van koolstof naar de verschillende interne toestandsvariabelen: somatisch weefsel, opslag (glycogeen), organische schelpmatrix en gameten. In de eerste plaats is het de bedoeling met deze rapportage een sterkere link van de COCO-modelberekeningen (uitgevoerd in het kader van het DynAqua-project) met de praktijk te leggen. Hieraan wordt vorm gegeven met aanvullende berekeningen, die in dit rapport beschreven worden.
    Hoge kilogramopbrengst gaat niet altijd samen met hoge kwaliteit
    Heuvelink, E. ; Kierkels, T. - \ 2007
    Onder Glas 4 (2007)5. - p. 54 - 55.
    groeimodellen - plantenontwikkeling - plantenfysiologie - gewaskwaliteit - stressfactoren - stress - maximum opbrengst - relatie tussen groei en oogst - milieubeheersing - kwaliteitszorg - secundaire metabolieten - glastuinbouw - growth models - plant development - plant physiology - crop quality - stress factors - stress - maximum yield - growth yield relationship - environmental control - quality management - secondary metabolites - greenhouse horticulture
    Samengaan van hoge productie en een goede kwaliteit vergt drie stappen. Ten eerste moet de fotosynthese optimaal zijn. Ten tweede is een goede verdeling van de assimilaten naar nuttige delen van de plant belangrijk. De derde stap is per gewas anders. Soms is het nodig af te zien van de hoogste productie om een goede kwaliteit te krijgen. Bij tomaat geeft een hogere EC een betere smaal maar minder productie. Bij roos zou continue groeilicht veel meer opbrengst geven, maar bij de consument verwelkt de bloem dan zeer snel. Bij veel gewassen is enige stress niet verkeerd. Bloemisterijgewassen zijn dan sterker; groenten smaken soms beter. In Wageningen wordt getracht nieuwe groeimodellen te maken die tuinder en veredelaar bijstaan in het streven naar meer interne kwaliteit
    Verfijnd rekenmodel voor belichting in rozen blijft toekomst muziek : beslissingsondersteunend model geeft 10-15% besparing
    Staalduinen, Jan van; Raaphorst, M.G.M. - \ 2007
    Onder Glas 4 (2007)5. - p. 78 - 79.
    groeimodellen - groei - rozen - belichting - lichtsterkte - efficiëntie - optimalisatie - groeianalyse - plantenfysiologie - netto-assimilatiesnelheid - beslissingsondersteunende systemen - energiebesparing - glastuinbouw - snijbloemen - growth models - growth - roses - illumination - light intensity - efficiency - optimization - growth analysis - plant physiology - net assimilation rate - decision support systems - energy saving - greenhouse horticulture - cut flowers
    In opdracht van het ministerie van LNV en PT onderzocht Wageningen UR Glastuinbouw de behoefte van rozentelers aan een beslissingsondersteunend model om energie-efficiëntie van belichten te optimaliseren. Onderzoeker Raaphorst ervoer dat sommige telers enthousiast zijn. Ondanks een verwacht besparingspotentieel van 10 tot 15% heeft maar een beperkte groep rozentelers interesse in een beslissingsondersteunend rekenmodel voor het optimaliseren van de belichtingsinstellingen. Eisen aan het rekenmodel zijn eenvoudige bediening, bewezen praktijkwaarde, rasafhankelijke instellingen, input vanuit de bedrijfsadministratie en professionele ondersteuning. Voor vervolgonderzoek is dat een te smalle basis. Onderzoekers en telers verwachten wel dat het draagvlak over enkele jaren breder is
    Macroscopic modelling of solid-state fermentation
    Hoogschagen, M.J. - \ 2007
    Wageningen University. Promotor(en): Hans Tramper, co-promotor(en): Arjen Rinzema. - [S.l.] : S.n. - ISBN 9789085045786 - 120
    fysische modellen - groeimodellen - computersimulatie - aspergillus - tarwe - vast-substraatfermentatie - physical models - growth models - computer simulation - aspergillus - wheat - solid-state fermentation

    Solid-state fermentation is different from the more well known process of liquid fermentation because no free flowing water is present. The technique is primarily used in Asia. Well-known products are the foods tempe, soy sauce and saké. In industrial solid-state fermentation, the substrate usually consists of loose substrate particles, although in research situations agar like substrates are also common. Solid-state fermentations cannot be mixed as easily as liquid fermentations. Because of this, it is difficult to maintain the temperature in the fermentation at an acceptable level and to prevent differences in substrate availability throughout the solid material. An advantage of solid-state fermentation is that the process is cheap, and that products are in some cases easier to separate from the substrate than in liquid. Because of this, the technique is economically interesting. The process has not been studied as extensively as liquid fermentation. This thesis extends the available knowledge by providing several mathematical models for both biological and physical processes that occur in aerated packed beds.

    In aerated packed beds, the metabolic heat that is released in the microbial process is removed by blowing air through the packed material. The effectiveness of the aeration is the result of both the heat uptake capacity of the air itself and of the evaporation of moisture to the air. In fact, the evaporation contributes more to the heat removal than the air itself. A side effect of the evaporation is that the decreasing moisture level in the substrate can become limiting for the microbial process.

    In this thesis, the growth of Aspergillus oryzae and Aspergillus sojae, two related species of fungi, in an aerated packed bed of moist wheat kernels is studied. The study deals with both the microbial and physical aspects of the system.

    Many different types of substrate have been used in studies on solid-state fermentation. Prior to starting the work on the mathematical models, we checked if the fermentation results of A. oryzae on several types of wheat matched, The check was done by matching respiration profiles for several types of wheat and two pretreatment methods. It turned out that considerable differences between the pretreatment methods can exist, which indicated the importance of using the exact same type of substrate and pretreatment in experiments that are to be compared.

    No accurate model description of the microbial aspects of SSF is available yet. Because the focus of the major part of the thesis is on deriving model descriptions for the physical aspects of cooling and drying-out in aerated packed beds, it was decided that using a temperature-response model for the description of heat development would incorporate too many uncertainties in the overall packed-bed model. The heat development in the further studies presented was therefore based on fitted oxygen consumption profiles instead of on modelled microbial growth.

    For the validation of the physical models in this thesis, experiments were carried out in a packed bed of approximately 50 cm height. This packed bed was insulated thermally, and offered the possibility of taking online temperature measurements and sampling the moisture content. The models that were derived to describe the changes in growth conditions in the packed bed in time and space were based on well-known physical relations. All physical models are composed of heat- and mass balances. As described above, the temperature dependence of the fungus was neglected, and the metabolic heat development was incorporated in the balances by means of fitted respiration profiles. This way, inaccuracies in the heat production in the physical model were prevented, allowing the focus on the correct description of heat and mass transfer.

    The first model presented was based on an existing model, which overestimated the drying out of the solid material. This overestimation was due to the assumption of constant saturation of the gas phase with water vapour. The overestimation of the drying out meant that the assumption of vapour saturation needed to be adjusted. Heat and mass transfer coefficients were determined for the substrate involved, and besides this water activity was introduced as a factor that limited the evaporation of water from the substrate. The addition of water activity was of great influence on the model results.

    The insight in the effect of local water activity on the fermentation was the onset for a study on the response of fungi to changing water activity. A system was designed that allowed the dynamic response of the fungus on decreasing water activity to be measured. The experimental set-up was based on isothermal experiments that were slowly dried out by blowing dry air through them, with simultaneous experiments carried out at aw ~ 1 for comparison with the response to the drying out. Considering the fact that all studies on water activity that preceded this approach were based on static and artificial conditions, this set-up is more similar to the actual conditions in a packed-bed fermentation.

    Contrary to the expectations, the system that was dried out showed a decreased fungal growth rate when the water activity in the substrate was still the same as it was in the reference experiment. We checked two possible causes for this phenomenon. Moisture gradients in the particle were ruled out, because these were too small to be able to cause the difference in growth rate. We found that there is most likely a region of very cold substrate material due to wet-bulb cooling. Wet-bulb cooling is a phenomenon in which the evaporation of water from a system to a passing airflow allows the system to cool to temperatures below the temperature of the air. Because we used dry air in our experiment, the effect was too large to be compensated through conduction. An estimated 5% of the bed could not be fermented because of the low temperature. For a successful series of experiments, we need to obtain drying with a 100% constant bed temperature. For such a series, a good comparison of the effect of drying on fungal behaviour will be possible.

    During the experiments in the packed-bed involving Aspergillus oryzae strong shrinkage of the packed-bed occurred because the fungus tied the substrate particles together. Because of the shrinkage, the aeration lost effectivity and the fermentation results were suboptimal. A model was designed to describe the amount of shrinkage, based on the decrease in water content in the bed. The validation of this model could not be performed with A. oryzae, because it was impossible to carry out controlled fermentations with this fungus. Therefore, A. sojae was used, which has the same growth characteristics as A. oryzae, except for the formation of substrate ties. The model on shrinkage offers a good prediction of the shrinkage that is expected with the combined effect of fungal growth and dehydration. 1f in industrial fermentations a different shrinkage pattern is observed, this is an indication that there is channel formation somewhere in the bed. This observation can be than followed by for instance a mixing event, improving the overall performance of the fermentation.

    In the final chapter of this thesis, an overview of the work that could possibly offer further improvements to the present models is given. It was concluded that the modelling of the microbial aspects offer the biggest chances for success in this respect, since this aspect has of yet been modelled less accurately than the physical part.

    Jongschaap: 'Met juiste strategie energie en geld besparen' : 16% energie besparen en toch 2,00 euro per m2 verdienen
    Arkesteijn, Marleen ; Jongschaap, R.E.E. ; Dieleman, J.A. - \ 2006
    Onder Glas 4 (2006)5. - p. 56 - 57.
    plantenontwikkeling - kassen - groeimodellen - belichting - kunstmatige verlichting - rozen - energiekosten - lichtsterkte - optimalisatie - cultuurmethoden - milieubeheersing - toegepast onderzoek - energiebesparing - warmtekrachtkoppeling - glastuinbouw - snijbloemen - plant development - greenhouses - growth models - illumination - artificial lighting - roses - energy expenditure - light intensity - optimization - cultural methods - environmental control - applied research - energy saving - cogeneration - greenhouse horticulture - cut flowers
    Modelbouwer Raymond Jongschaap heeft 200 verschillende belichtingsscenario’s bij roos in een model doorgerekent. Daaruit blijkt dat een belichtingsduur van 16 uur voldoende is behalve in de donkere maanden, want dan is 20 uur nodig. De belichtingsintensiteit mag ‘s zomers lager zijn dan ’s winters. Ook mag de belichting ’s zomers eerder uit dan in de rest van het jaar. Wie per periode van vier weken de meest energie-efficiënte strategie volgt, kan 16% energie besparen en € 2,00 per m2 verdienen
    Proceedings of the Third International Symposium on Models for Plant Growth, Environmental Control and Farm Management in Protected Cultivation (HORTIMODEL)
    Marcelis, L.F.M. ; Straten, G. van; Stanghellini, C. ; Heuvelink, E. - \ 2006
    Leuven : ISHS (Acta horticulturae 718) - ISBN 9789066056091 - 688
    teelt onder bescherming - tuinbouwgewassen - tuinbouw - kassen - modellen - simulatiemodellen - gewasopbrengst - groei - groeimodellen - glastuinbouw - protected cultivation - horticultural crops - horticulture - greenhouses - models - simulation models - crop yield - growth - growth models - greenhouse horticulture
    Vruchtzetting paprika spel van vraag en aanbod
    Marcelis, L.F.M. ; Heuvelink, E. - \ 2005
    Groenten en Fruit. Algemeen (2005)33. - ISSN 0925-9694 - p. 20 - 21.
    capsicum - teelt - cultuurmethoden - vruchtzetting - hormonen - zaadzetting - assimilatie - plantenfysiologie - groeimodellen - gewasopbrengst - relatie tussen groei en oogst - capsicum - cultivation - cultural methods - fructification - hormones - seed set - assimilation - plant physiology - growth models - crop yield - growth yield relationship
    Voor een goede productie bij paprika is niet het aantal bloemen, maar het aantal gezette vruchten de beperkende factor. De zetting wordt vooral bepaald door de beschikbaarheid van assimilaten. Die beschikbaarheid wordt bepaald door de aanmaak van deze suikers en de vraag ernaar van al gezette vruchten. De effecten van vraag en aanbod van assimilaten werden door Plant Research International en Wageningen Universiteit opgenomen in een groeimodel, dat op basis van klimaatgegevens en enkele teeltgegevens de groei en productie berekent. Met behulp van dit groeimodel bleek de zetting van te voren redelijk te voorspellen
    Better insight into the control of Kalanchoe
    Carvalho, S.M.P. ; Heuvelink, E. - \ 2005
    FlowerTECH 8 (2005)5. - ISSN 1388-8439 - p. 24 - 25.
    potplanten - sierplanten - kalanchoe - teelt - cultuurmethoden - groeimodellen - belichting - temperatuur - oogsttijdstip - pot plants - ornamental plants - cultivation - cultural methods - growth models - illumination - temperature - harvesting date
    Productie van planten van hoge kwaliteit volgens een vooropgezet schema is niet eenvoudig, zelfs niet voor een ervaren kalanchoe teler. Wageningen UR ontwikkelde een groeimodel voor dit gewas, dat een beter inzicht in de mogelijkheden tot teeltcontrole geeft. De gevolgde systematische aanpak kan een voorbeeld zijn voor de ontwikkeling van groeimodellen voor andere bloeiende potplanten
    Rustig telen: zwaardere planten met meer bloemschermen
    Carvalho, S.M.P. ; Heuvelink, E. ; Kierkels, T. - \ 2005
    Onder Glas 2 (2005)6/7. - p. 20 - 21.
    potplanten - kalanchoe - teeltsystemen - kassen - licht - groeimodellen - temperatuur - regulatie - landbouwkundig onderzoek - glastuinbouw - pot plants - kalanchoe - cropping systems - greenhouses - light - growth models - temperature - regulation - agricultural research - greenhouse horticulture
    Uit onderzoek van Wageningen UR blijkt dat bij kalanchoë niet alleen de temperatuur de teeltduur bepaalt, maar dat licht ook een belangrijke rol speelt. Meer licht maakt de teeltduur korter. Een teler heeft dus twee keuzes als hij het goede levertijdstip niet dreigt te halen. Spelen met de temperatuur of spelen met het licht. Als het sneller moet, is meer licht beter dan een hoge temperatuur. Als het langzamer moet dan moet de temperatuur omlaag, want dat vertraagt de groei terwijl het niet ten koste gaat van de kwaliteit
    Grenswaarden voor temperatuurfluctuaties van verschillende duur bij siergewassen : beschrijving van het gewasmodel
    Buwalda, F. - \ 2004
    Naaldwijk : Praktijkonderzoek Plant & Omgeving B.V. Glastuinbouw - 29
    sierteelt - kalanchoe - kasproeven - klimaatregeling - teeltsystemen - groeimodellen - gewassen, groeifasen - ornamental horticulture - kalanchoe - greenhouse experiments - air conditioning - cropping systems - growth models - crop growth stage
    Een voorlopig model voor groei en ontwikkeling van Kalanchoe werd ontwikkeld. Het model berekent versgewicht en ontwikkelingsstadium van individuele phytomeren aan de hoofdscheut van de plant, van de zijscheuten en van de generatieve delen in relatie tot licht en temperatuur. De snelheid van verandering van deze toestandsvariabelen wordt bepaald door de processen groei, ontwikkeling en verdeling van biomassa op basis van de relatieve sinksterkte van individuele organen. Activering van okselknoppen, waaruit de zijscheuten ontstaan, werd beschreven op basis van source/sink en ontwikkelingsstadium. De potentiële groei van onderdelen werd beschreven als een Richardsfunctie van het ontwikkelingsstadium. In het geval van de generatieve delen werd de potentiële groei nog vermenigvuldigd met het gemiddelde gewicht per phytomeer in de betreffende scheut. Het model kon zo worden gekalibreerd dat het verloop van een eerdere proef met effecten van licht en temperatuur bij Kalanchoe (Horst, voorjaar 2003) behoorlijk goed simuleerde
    Grenswaarden voor temperatuurfluctuaties van verschillende duur bij siergewassen : verslag van een teeltproef met modelgestuurd temperatuursverloop : Deelverslag 3: Toetsing van een dynamisch gewasmodel voor groei, ontwikkeling en sierwaarde van Kalanchoe
    Buwalda, F. - \ 2004
    Naaldwijk : Praktijkonderzoek Plant & Omgeving B.V. Glastuinbouw - 29
    sierplanten - potplanten - kalanchoe - groeimodellen - gewassen, groeifasen - klimaatregeling - teeltsystemen - kasproeven - ornamental plants - pot plants - kalanchoe - growth models - crop growth stage - air conditioning - cropping systems - greenhouse experiments
    Het gewasmodel zoals beschreven in rapport 3 van dit project (zie ook Buwalda et al., 2004) is ontwikkeld en gekalibreerd op basis van de resultaten van een teeltproef uitgevoerd in het najaar van 2003. Met het oog op een algemene toepasbaarheid van het model is het van belang dat het ook in andere perioden van het jaar accurate simulatieresultaten op kan leveren. De algemene theorie met betrekking tot het totstandkomen van uitwendige kwaliteit (sierwaarde) zoals uiteengezet in rapport 1 (Buwalda, 2003) is gebaseerd op het idee dat de laterale groei (uitgroeien van zijscheuten) en allocatie van biomassa naar generatieve delen de belangrijkste kwaliteitsbepalende processen zijn. Verondersteld wordt dat de verhouding tussen groeisnelheid en ontwikkelingstempo de bepalende factor is voor beide processen.
    Grenswaarden voor temperatuurfluctuaties van verschillende duur bij siergewassen : samenvatting
    Noort, Filip van; Buwalda, F. ; Gelder, Arie de - \ 2004
    Naaldwijk : Praktijkonderzoek Plant & Omgeving B.V. Glastuinbouw - 21
    sierteelt - potplanten - kasproeven - teeltsystemen - klimaatregeling - gewassen, groeifasen - groeimodellen - energiebehoeften - ornamental horticulture - pot plants - greenhouse experiments - cropping systems - air conditioning - crop growth stage - growth models - energy requirements
    De modelgestuurde klimaatregeling had effecten op het energieverbruik, de gemiddelde ruimtetemperatuur en de teeltduur. Hoe hoger de temperatuur, des te meer energie werd gebruikt. Daar stond tegenover dat de teeltduur bij hogere temperaturen korter was. Omgekeerd leidde een lager temperatuurniveau tot een geringer energieverbruik per dag, maar ook een langere teeltduur. Het bleek dat de doeldefinitie in het stuurmodel die streefde naar een lichte plantbalans leidde tot een vermindering van de energie)efficiëntie van de teelt met 5% per m2 en met 10% per plant. In het geval van de middelste en zware plantbalans werd juist een grotere energie)efficiënte bereikt, nl. in beide gevallen 11% op oppervlaktebasis en 9 resp. 8% per afzonderlijke plant.
    Modelling responses of broiler chickens to dietary balanced protein
    Eits, R.M. - \ 2004
    Wageningen University. Promotor(en): Martin Verstegen; Leonard den Hartog, co-promotor(en): Rene Kwakkel. - [S.I.] : S.n. - ISBN 9789085040705 - 163
    vleeskuikens - pluimvee - voedingseiwit - voedingsstoffen - eiwitbalans - groeitempo - voederconversie - karkasopbrengst - vleesopbrengst - vleeskuikenresultaten - groeimodellen - diervoeding - pluimveevoeding - voedingsfysiologie - broilers - poultry - dietary protein - nutrients - protein balance - growth rate - feed conversion - carcass yield - meat yield - broiler performance - growth models - animal nutrition - poultry feeding - nutrition physiology
    Protein is an important nutrient for growing broiler chickens, as it affects broiler performance, feed cost as well as nitrogen excretion. The objective of this dissertation was to develop a growth model for broiler chickens that could be easily used by practical nutritionists. The model should facilitate the selection of feeding strategies (in terms of dietary protein and energy)that resultsin the desired body composition of broilers while minimizing costs.

    Two important theories that are generally used in animal growth models were validated for broiler chickens. It was confirmed that, where protein is limiting, protein deposition rate will not increase with additional energy intake. The second theory, stating that the fat-free body composition is independent from nutrition, is not a valid assumption for broiler growth models.

    It was demonstrated that broiler responses to dietary balanced protein level (DBP) depend on previous protein nutrition. These results suggest that DBP levels in grower and finisher diets should not be optimised independently, but simultaneously.

    A model was developed that predicts broiler responses (growth rate, feed conversion ratio, carcass yield and breast meat yield) to DBP level. The model makes it possible to construct tailor-made dose-response curves without actual experimentation.

    Based on the predictions by this new model and data on feed and meat prices, the economic aspects of DBP level in broiler diets were evaluated. It was shown that formulating diets for maximum profit instead of maximum broiler performance may strongly increase profitability of a broiler production enterprise. Model simulations revealed as well that DBP level for maximum profitability depend on how the broilers are marketed; as whole birds, carcass or cut up.

    Dietary influences on nutrient partitioning and anatomical body composition of growing pigs; modelling and experimental approaches
    Halas, V. - \ 2004
    Wageningen University. Promotor(en): Martin Verstegen; L. Babinszky, co-promotor(en): Jan Dijkstra; Walter Gerrits. - [S.I.] : S.n. - ISBN 9789085040262 - 217
    varkens - voedingsstoffenopname (mens en dier) - lichaamssamenstelling - groeimodellen - groei - mestresultaten - voedingsstoffen - voer - varkensvoeding - diervoeding - pigs - nutrient intake - body composition - growth models - growth - fattening performance - nutrients - feeds - pig feeding - animal nutrition
    Prediction of pig performance from data on nutrient intake and animal properties makes it easier to obtain a better productivity. It provides tools to arrive at desired outputs, or to calculate required inputs. Thus it enables production to be flexible, safe and less erratic. It is to be expected that the results will give a more profitable pig production. In practice, different types of models are used, mostly by feed producers, but also in farm management programmes. Each of these existing models was designed to meet a certain objective. The classification of different types of models, and the benefits of using them, are presented in the literature overview of the thesis. After a general overview of modelling, a critical evaluation was provided on existing models. It was concluded from the literature, that a comprehensive model, which predicts the chemical composition in different parts of the body, like in lean or in the meat, does not exist. It was also concluded that mechanistic approach should be used to modelling growth. The conceptual basis of a mechanistic model was developed in accordance with basic properties of protein and lipid metabolism. Since nutrients are almost exclusively absorbed in the hydrolyzed form, simulation of use of nutrients for growth should, at least to some extent, make use of biochemical pathways. Therefore, a biological approach to simulation of anatomical body composition is pretended as it follows nutrients from ingestion through intermediary metabolism to deposition as body fat and protein, preferably in distinct tissues or tissue groups. Prediction of anatomical body composition therefore has to be based on deposition of the chemical entities.

    Therefore the scope of the present thesis was 1) to develop a mechanistic-dynamic model for growing and fattening pigs which predicts anatomical and chemical body composition at slaughter; 2) to determine which model parameters are sensitive to changes in the model; 3) to determine the model accuracy by quantitative and qualitative prediction of the model tested with independent data; 4) to complete an experiment to define fat production potential of different energy sources at low and high feeding levels, and 5) to study the effect of different energy sources at two feeding levels on the distribution of fat deposition during the fattening period.

    The thesis presents both the description and the evaluation of the growth model. It was concluded that the developed model predicts growth rate as well as chemical and anatomical body compositions of gilts in the 20-105 kg live weight range, from nutrient intake. The model represents partitioning of nutrients from feed intake through intermediary metabolism to synthesis of body protein and body fat. State variables of the model are lysine, acetyl-CoA equivalents, glucose, VFA, and fatty acids as metabolite pools, as well as protein in muscle, hide, bone and viscera and body fat as body constituent pools. It is assumed that fluxes of metabolites follow saturation kinetics depending on metabolite concentrations. Anatomical body composition is predicted from chemical body composition and accretion. Partitioning of protein, fat, water and ash into muscle, organs, hide and bone fractions are described by allometric equations, driven by rates of muscle protein and body fat deposition. Two experiments were used in the model calibration process, one with 95 growing pigs (20-45 kg) fed different ileal digestible lysine intakes at two feeding levels, and another with 100 growing and fattening pigs (20-105 kg), which received different energy intakes. Differential equations were solved numerically for a given set of initial conditions and parameter values. The integration interval used was 0.01 day, with the fourth-order fixed-step-length Runge-Kutta algorithm. The muscle protein and body fat deposition rates were considered in different weight ranges and for the whole fattening period. Results presented were not sensitive to small changes in initial conditions, or to smaller integration step sizes.

    In the model evaluation the predicted response of the pigs to changes in model parameters, and to changes in nutrient intakes, are shown. As a result of the sensitivity analysis, the model was responsive to changes in a number of the model parameters examined. Changes in maintenance energy requirements, and the fractional degradation rate of muscle protein, have the largest impact on tissue deposition rates. The model is highly sensitive to changes in the maximal velocity and steepness parameter of lysine utilisation for muscle protein synthesis. Those parameters which directly affect the size of the lysine pool generally have a considerable influence on model predictions. Furthermore, it should be noted that results of this sensitivity analysis depend on nutrient intakes of the reference simulation. The model was relatively insensitive to changes of parameters regarding energy metabolism. It was concluded that the probable reason was that protein and/or lysine was more limiting within the simulated conditions. The model was further tested by independent published data. In general, the model satisfactorily predicted qualitative pig responses to a wide range of variations in nutrient supply. The predicted chemical and anatomical body composition, and also the distribution of protein and fat, were satisfactory in model testing. In most cases, errors in the predicted parameters attributed to the deviation of the regression slope were minor. It was assumed that the major factors contributing to the relatively large bias, observed for most predicted growth characteristics, was variation in pig performance among genotypes, or differences in environmental conditions. Based on the comparison of model simulations with independent data sets, it was recommended to improve the model regarding prediction of protein and fat deposition rates from nutrient intake of different energy sources.

    It was found that literature data on the effect of different energy sources on fat deposition was limited. In non-protein energy fraction of the diet, dietary lipids, starch and rapidly fermentable non-starch polysaccharides (NSP) are major energy sources. Lipids are absorbed as long-chain fatty acids and starch as glucose. Dietary NSP is fermented and the short-chain fatty acids produced enter intermediary metabolism as an energy source. Equal intakes of energy from glucose, long-chain fatty acids and short-chains fatty acids might result in different fat deposition rates, and quite likely, result in different distributions of body fat over the tissues. There is, however, little quantitative data available on effects of energy source on partitioning of body lipids. Therefore a fattening trial was completed to: 1) study the effect of extra energy intake from fermentable NSP, digestible starch and digestible fat used for fat deposition under protein limiting conditions; 2) determine the location of the fat deposition resulting from extra intake fermentable NSP, digestible starch and digestible fat; 3) determine if the extra fat deposition from different energy sources depends on the level of feed intake, and 4) quantify potential interactions between feed intake level and energy source on the location of extra body fat deposition.

    A total of 58 hybrid individually housed pigs were used in the trial with an initial body weight of 48±4 kg. The experimental treatments were arranged in a 3x2 factorial design, with three energy sources (i.e. fermentable NSP, digestible starch and digestible fat, all added to a control diet) at each of two energy levels. Within each energy level, daily nutrient intakes were the same with regard to digestible protein, ileal digestible lysine and other amino acids, vitamins and minerals. Treatments had an isocaloric proportion of daily nutrient intake derived from each energy source (0.2 MJ DE/kg 0.75 ), in addition to the nutrients from control diet. It was equal with 11 g/kg 0.75 highly fermentable NSP, 11 g/kg 0.75 starch or 5 g/kg 0.75 digestible fat daily. The DE intakes were 2.0 and 3.0 maintenance requirement in control groups. The additional energy from different sources increased DE intake up to 2.4 and 3.4 times maintenance requirement at low and high feeding levels, respectively. To obtain initial values, ten pigs were slaughtered at 48±4 kg and the treatment pigs at 106±3 kg body weight. Each body was dissected into four fractions being: 1) lean, 2) organs, 3) hide and subcutaneous fat, and 4) offal. Chemical body composition was determined in each body fraction. The differences between fat deposition of body parts in the control group, and the other treatments, resulted in the additional energy derived from each energy source. As a conclusion from the study, under protein limiting conditions, extra energy intake from fermentable NSP, digestible starch and digestible fat resulted in similar fat deposition. Preferential deposition of extra energy intake in various fat depots did not depend on the energy source. The extra fat deposition from fermentable NSP, digestible starch and digestible fat deposited as body fat was similar at both the low and high levels of feed intake.

    In the General Discussion, some consequences of the mechanistic approach were discussed and then substantial attention was devoted to the practical aspects of the model. The later part of the General Discussion focuses on representation of different energy sources as an aspect of the model. The energetic efficiency of the different dietary energy sources is discussed, based on data from Chapter 6. The growth model is further evaluated by results of the fattening study. Moreover, data from the fattening study are analysed regarding the distribution of fat deposition. Consequences of the fattening study on the model is discussed regarding the effect of energy sources on energetic efficiency, and on location of fat deposition in the pig. Finally, a new application of the present model is introduced in addition to development of feeding strategies and identifying research priorities.
    Clostridium perfringens: spores & cells, media & modeling
    Jong, A.E.I. de - \ 2003
    Wageningen University. Promotor(en): Frans Rombouts, co-promotor(en): Rijkelt Beumer. - [S.l.] : S.n. - ISBN 9789058089311 - 128
    clostridium perfringens - pathogenen - sporulatie - koelen - erwten - soepen - groeimodellen - voedselhygiëne - clostridium perfringens - pathogens - sporulation - cooling - peas - soups - growth models - food hygiene
    Clostridium perfringensis one of the five major food borne pathogens in the western world (expressed as cases per year). Symptoms of C. perfringens food poisoning are caused by an enterotoxin, which is released when ingested cells sporulate in the intestines. To increase knowledge on this bacterium, it was tried to optimize sporulation of a variety of strains, but only strain dependent effects were noted. Since many media are available to isolate C. perfringens from foods, a selection of these media was compared and it was shown that these media performed equally well. Cooling and storage of food are often the cause of gastro enteritis. Therefore, the behavior of this microorganism was studied at low temperatures and a model was designed to predict the effect of various cooling procedures applied to food on growth of C. perfringens . The model can be used to set up Good Manufacturing Procedures (GMP).
    Regional analysis of maize-based land use systems for early warning applications
    Rugege, D. - \ 2002
    Wageningen University. Promotor(en): J. Bouma; A.K. Skidmore; P.M. Driessen. - S.l. : S.n. - ISBN 9789058085849 - 121
    landgebruik - landevaluatie - regionale planning - regionale verkenningen - gewasproductie - gewasopbrengst - remote sensing - oogstvoorspelling - simulatiemodellen - groeianalyse - groeimodellen - verliezen - voedselproductie - maïs - zimbabwe - land use - land evaluation - regional planning - regional surveys - crop production - crop yield - remote sensing - yield forecasting - simulation models - growth analysis - growth models - losses - food production - maize - zimbabwe

    Conventional analytical crop growth models cannot handle actual Land Use Systems because of massive data needs, algorithm complexity and prohibitive error propagation. It is possible however to describe rigidly simplified 'Production Situations' representing Land Use Systems with annual row crops and minimal environmental constraints. The simplest Production Situation imaginable is a Land Use System in which all constraints that can be eliminated by a farmer are indeed (assumed to be) eliminated. Crop growth and yield are then entirely conditioned by crop physiology and weather conditions, notably by the temperature and radiation during the crop cycle. The calculated production level is not the actual production but the production potential.

    In many countries, water availability to the crop is the main constraint to crop production. The biophysical production potential model has therefore been extended with a water budget routine that matches actual water use with the crop's requirement in order to calculate the "water-limited production potential". In this configuration, crop physiology, temperature, radiation and water availability condition the calculated level of crop (potential) production. This thesis discusses the use of satellite-derived rainfall data for regional analysis of water-limited yield potentials.

    Monitoring and crop yield forecasting for early warning applications require insight in farmers' reality. Often, a score of environmental and socio-economic constraints reduce on-farm production to a level that lags far behind the theoretical production potential. This thesis explores farmers' insights, in an attempt to identify the causes and structure of the "yield gap" between potential (reference) production levels and production levels realized on-farm.

    So far, actual production could only be established through field measurements. This thesis presents a methodology for estimating regional levels of actual crop production. The difference between remotely sensed canopy temperature and ambient temperature is used to estimate the degree of stomata closure of the crop. Introducing this Remote Sensing based degree of stomata closure in calculations of assimilatory activity permits to calculate the actual rate of crop growth over regions.

    Repeated measurements during the crop cycle allow monitoring of the sufficiency of actual management practices. Introducing estimated or forecast weather data in crop growth calculations for the remainder of the crop cycle permits to make repeated estimates of anticipated crop production and to timely signal a need for remedial action.

    Quantification of fungal growth: models, experiment, and observations
    Lamour, A. - \ 2002
    Wageningen University. Promotor(en): M.J. Jeger; F. van den Bosch; A.J. Termorshuizen. - S.l. : S.n. - ISBN 9789058086235 - 132
    bodemschimmels - plantenziekteverwekkende schimmels - kwantitatieve analyse - groei - hyfen - mycelium - groeimodellen - armillaria - thanatephorus cucumeris - soil fungi - plant pathogenic fungi - quantitative analysis - growth - hyphae - mycelium - growth models - armillaria - thanatephorus cucumeris

    This thesis is concerned with the growth of microscopic mycelial fungi (Section I), and that of macroscopic fungi, which form specialised hyphal structures such as rhizomorphs (Section II). A growth model is developed in Section I in relation to soil organic matter decomposition, dealing with detailed dynamics of carbon and nitrogen. Substrate with a certain carbon:nitrogen ratio is supplied at a constant rate, broken down and then taken up by fungal mycelium. The nutrients are first stored internally in metabolic pools and then incorporated into structural fungal biomass. Analysis of the overall-steady states of the variables (implicitly from a cubic equation) showed that the conditions for existence had a clear biological interpretation. The 'energy' (in terms of carbon) invested in breakdown of substrate should be less than the 'energy' resulting from breakdown of substrate, leading to a positive carbon balance. For growth the 'energy' necessary for production of structural fungal biomass and for maintenance should be less than this positive carbon balance in the situation where all substrate is colonised. Under the assumption that nutrient dynamics are much faster than the dynamics of fungal biomass and substrate, a quasi-steady analysis was performed. From the resulting simplified model an explicit fungal invasion criterion was derived, which was not possible in the analysis of the original fungal growth model. The fungal invasion criterion takes two forms: one for systems where carbon is limiting, another for systems where nitrogen is limiting. For cases where only carbon is limiting, nitrogen dynamics were excluded from the model, and this further simplification resulted in a model that was fitted to data on growth of the soil-borne plant pathogen Rhizoctonia solani . Fungal growth and colonisation of discrete nutrient sites in Petri plates were assessed microscopically for two carbon concentrations of the substrate. Colonisation was faster at the higher carbon concentration. The model predicted a lower asymptote for non-colonised substrate and this value was estimated from the data by non-linear regression for each carbon concentration. A key composite parameter, the positive carbon balance per carbon unit of colonised substrate, was lower for the higher carbon concentration. The carbon decomposition rate was estimated by least squares minimisation, after correction for a lag phase expected after robust handling of the inoculated fungus. The delay in subsequent fungal growth after inoculation was extended when there was less carbon available for physical recovery and physiological adaptation to the new environment. The simplified mean-field model with parameters estimated as described above produced a good fit to the data.

    In Section II quantitative studies on the epidemiology of Armillaria root rot are reviewed. This fungus is a serious disease in many forests and horticultural tree crops world-wide, and consequently there is much interest in options for avoiding or restricting the spread of disease through growth of the specialised rhizomorphs in soil. Two rhizomorph networks of A. lutea growing through a natural soil were observed over areas of 25 m 2in Pinus nigra and Picea abies tree plantations. Both rhizomorph systems had numerous branches and anastomoses resulting in cyclic paths, i.e. regions of the system that start and end at the same point. Each rhizomorph network exhibited both exploitative and explorative characteristics within its overall network structure. One of the observed rhizomorph networks of A. lutea was restricted to the cyclic paths only, and the resulting graph was drawn in the plane. The plane graph consisted of 169 rhizomorphs, termed edges, and 107 rhizomorph nodes, termed vertices. The connectivity of the rhizomorph network was explored by focusing on each bridge, i.e. an edge whose removal disconnects the graph into two components. In only two instances was a nutrient source connected to the cycles, and disruption of these two connecting edges would remove the whole network from the sources. A shortest path from a given vertex to a nutrient source was defined in terms of number of edges, and also in terms of length (m). The length of the edges enclosing the faces, i.e. two-dimensional regions defined by the edges in the plane drawing, showed that the fungus exhibited both exploitative and explorative growth, and we speculate about the underlying reasons for these foraging strategies. The introduction of graph-theoretic concepts to fungal growth might lead to an improved ecological understanding of fungal networks in general, provided that relevant biological interpretations can be made.

    Meteorologische gegevens ten behoeve van modellering : variabiliteit in het centrale zetmeelaardappelteeltgebied van de AVEBE-regio, gedurende de jaren 1960-1998
    Steenhuizen, J.W. ; Haren, R.J.F. van - \ 2001
    Wageningen : Plant Research International (Nota / Plant Research International 111) - 24
    solanum tuberosum - zetmeelgewassen - groeimodellen - agrometeorologie - meteorologische waarnemingen - nederland - fabrieksaardappelen - solanum tuberosum - starch crops - growth models - agricultural meteorology - meteorological observations - netherlands - starch potatoes
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