S. Hemming

Wageningen University, Wageningen, Gelderland, Netherlands

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Publications (104)11.64 Total impact

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    ABSTRACT: Worldwide competitive challenges urge growers to further improve operational performance. In this paper, the objective ‘model-based analysis and improvement of the operation of horticultural production systems’ was narrowed to ranking simulated labour management scenarios in a multi-operations and multi-worker static cut-rose cultivation system. Eight scenarios with worker skill as a central theme were simulated including a practical labour management scenario applied by a Dutch cut-rose grower. The GWorkS-model was prepared for simulation of disbudding and bending in addition to harvest, three crop operations representing over 90% of crop-bound labour time, as well as for full scale simulation of the greenhouse using all workers and equipment. The sub-models on disbudding and bending were verified using data acquired in practice. Both processes were reproduced accurately. The model study on work scenarios showed that labour organisation choices might yield up to 5 s per harvested rose difference in total labour time for harvest, bending and disbudding between the best and worst scenario, which is equivalent to 7.1 € m−2 labour costs difference per year. Scenarios pointed out that working with low skilled, low paid workers is not effective. Specialised workers were most time effective, −17.5% compared to the reference, but overall a permanent team of skilled generalists ranked best in a multi-factorial assessment. Reduced crop operation diversity per day improved labour organisational outputs but ranked almost the same as the reference. The reference scenario was outranked by 5 scenarios. Overall, the GWorkS-model provided clear answers to research questions using the full complexity of crop operations.
    Biosystems Engineering 07/2015; 135. DOI:10.1016/j.biosystemseng.2015.04.014 · 1.62 Impact Factor
  • A. Elings · S. Hemming · Os, E.A., van · J.B. Campen · J.C. Bakker ·

  • G.L.A.M. Swinkels · F.L.K. Kempkes · S. Hemming ·
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    ABSTRACT: Dit project richt zich op mogelijk om vooral in de wintermaanden meer licht in de kas te kunnen krijgen. Middels metingen en modelberekeningen wordt onderzocht in hoeverre er mogelijkheden v.w.b. kasdek, coatings en condensatiegedrag.
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    ABSTRACT: Combination of production of algae and tomato increases efficient use of available resources of greenhouse enterprises, such as controlled environment, water and nutrients, carbon dioxide, greenhouse space and infrastructure and knowledge. No information is available, however, about the potential productivity and related costs of a combined tomato and algae production in Dutch greenhouses. The objective was to determine the algae productivity in tubular photobioreactors (PBRs) and the economic feasibility of combined production of tomato and algae in Dutch greenhouses. A model was developed to predict greenhouse climate from outside climate, to predict tomato and algae biomass production and to analyse scenarios of different locations and dimensions of tubular PBR in the greenhouse with regard to algae productivity and cost price of algae production. The results show that algal productivity is low if PBRs are installed under a tomato crop due to limited light levels. Areal algal productivity was calculated to be 5–6.5 kg DM m−2 if PBRs are installed in a separate greenhouse compartment next to tomato. In this case the minimum cost prices of algae production was calculated to be €11 kg−1 DM algae, which give perspectives for the future. The proposed model is important because it gives insight into the feasibility of algae and tomato production in Dutch greenhouses. This novel model approach and the scenario results provide better knowledge about the potential productivity and related costs and returns of algae production in greenhouses.
    Biosystems Engineering 06/2014; 122:149–162. DOI:10.1016/j.biosystemseng.2014.04.008 · 1.62 Impact Factor

  • Acta horticulturae 05/2014; DOI:10.17660/ActaHortic.2014.1037.1
  • S. Hemming · V. Mohammadkhani · J. van Ruijven ·

    Acta horticulturae 05/2014; DOI:10.17660/ActaHortic.2014.1037.118
  • F.L.K. Kempkes · J. Janse · S. Hemming ·

    Acta horticulturae 05/2014; DOI:10.17660/ActaHortic.2014.1037.6
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    ABSTRACT: Labour is the most dominant cost factor in Dutch cut-rose production. To improve crop production systems and labour management, a generic process modelling approach was developed enabling the impact of different scenarios on labour productivity to be assessed. The crop production system with crop handling processes is defined as a stochastic discrete event system. This paper demonstrates the model flexibility and transferability by adapting an existing model developed for a mobile rose production system to a model for a static growing system for cut roses. The paper describes the adaptation process. The adapted model was validated for the harvest process at a 3.6 ha production site in the Netherlands. Work scenarios were simulated to examine effects of skill, equipment, and harvest management. The model reproduces the harvest process accurately. A seven workday validation for an average skilled harvester showed a relative root mean squared error (RRMSE) under 5% for both labour time and harvest rate. A validation over 96 days for various harvesters showed a higher RRMSE, 15.2% and 13.6% for labour time and harvest rate respectively, mainly caused by the absence of model parameters for individual harvesters. The model was successfully used in scenario studies and indicated that worker skill was an important cost factor, differences associated with harvest trolley type are small, and that an extra harvest cycle per day is only feasible when compensated by product price. Overall, the generic model concept performs well for a static growing system when extended with system specific properties and process elements.
    Biosystems Engineering 04/2014; 120:34–46. DOI:10.1016/j.biosystemseng.2013.04.005 · 1.62 Impact Factor
  • T. Kierkels · S. Hemming · T.A. Dueck ·
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    ABSTRACT: Diffuus glas is over vijftien jaar de standaard. Wie nu nieuw bouwt, heeft veel goede redenen om voor diffuus te kiezen en vrijwel geen om het te laten, zeggen Silke Hemming en Tom Dueck van Wageningen UR Glastuinbouw. De inzichten in het nut van diffuus licht én de technische ontwikkelingen schrijden nog elk jaar voort. Een update.
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    ABSTRACT: Een consortium van tuinbouw toeleveranciers bestaande uit Boal systems, VDH Foliekassen, AGC Chemicals Europe (AGCCE) en Van der Valk Systemen heeft een kasconcept ontwikkeld dat een hoge isolatiegraad van het kasdek met beperkte investeringen bereikbaar moet maken. In deze haalbaarheidsstudie zijn de energetische, gewas technische en economische haalbaarheid van dit Glas-Film-Kasconcept, beter bekend als het 2saveEnergy concept bestudeerd.
  • S. Hemming · W. Voogt · A. Sapounas ·
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    ABSTRACT: De productie van hoogwaardige stoffen zoals kleurstoffen of voedingssupplementen uit algen biedt perspectief voor Nederlandse tuinbouwondernemers. Tuinbouwondernemers hebben veel ervaring om de teeltcondities van hun huidige gewassen door klimaatregeling, CO2 dosering, water- en nutriënten voorziening optimaal te sturen voor een hoogwaardig eindproduct. Ze hebben ervaring met de productie van voedingsmiddelen en om aan de daaraan gestelde kwaliteitseisen te voldoen en logistiek en afzet te organiseren. Het ligt voor de hand om deze ervaring te benutten voor de teelt van algen en hiermee nieuwe duurzame producten te leveren en bij te dragen aan de biobased economy. In dit project is experimenteel onderzoek uitgevoerd naar de invloed van verschillende teeltfactoren op de algenproductie in een nieuwe proeffaciliteit met buisvormige algenreactoren in kassen in Bleiswijk. Daarnaast zijn in dit project economische getallen van investerings- en exploitatiekosten verzameld en is er een economisch rekenmodel ontwikkeld om een realistisch perspectief van algenteelt in kassen in schetsen. Hiermee wordt nieuw strategisch inzicht verkregen wat een geschikt teeltsysteem voor de teelt van hoogwaardige algen in combinatie met tuinbouwproductie op grote schaal in de toekomst is.
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    ABSTRACT: Greenhouse crop system design for maximum efficiency and quality of labour is an optimisation problem that benefits from model-based design evaluation. This study focussed on the harvest process of roses in a static system as a step in this direction. The objective was to identify parameters with strong influence on labour performance as well as the effect of uncertainty in input parameters on key performance indicators. Differential sensitivity was analysed and results were tested for model linearity and superposability and verified using the robust Monte Carlo analysis method since in the literature, performance and applicability of differential sensitivity analysis has been questioned for models with internal stochastic behaviour. Greenhouse section length and width, single rose cut time, and yield influence labour performance most, but greenhouse section dimensions and yield also affect the number of harvested stems directly. Throughput, i.e. harvested stems per second, being the preferred metric for labour performance, is most affected by single rose cut time, yield, number of harvest cycles per day, greenhouse length and operator transport velocity. The model is insensitive for σ of lognormal distributed stochastic variables describing the duration of low frequent operations in the harvest process, like loading and unloading rose nets. In uncertainty analysis, the coefficient of variation for the most important outputs, labour time and throughput, is around 5%. Total sensitivity as determined using differential sensitivity analysis and Monte Carlo analysis essentially agreed. The combination of both methods gives full insight into both individual and total sensitivity of key performance indicators.
    Biosystems Engineering 12/2013; 116(4):457–469. DOI:10.1016/j.biosystemseng.2013.10.009 · 1.62 Impact Factor
  • L.F.M. Marcelis · S. Hemming ·

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    ABSTRACT: The light transmission is an important property for horticultural screens. For energy screens in particular, an accurate measurement of the light transmission is important because these screens are often used during the day, in the winter period when radiation is limited. For shading screens the shading factor is an important factor. To enable a fair comparison between horticultural screens Wageningen UR in collaboration with screen producers Ludvig Svensson, Novavert and Bonar, developed a new protocol for measuring the transmission of horticultural screens. The protocol is based on the earlier developed protocol for measuring the light transmission of greenhouse covering materials, which was developed by TNO and Wageningen UR. The protocol covers the measurement of the transmission of horticultural screens for photosynthetically active radiation (PAR) in terms of hemispherical transmission. The scope of the protocol is limited to transparent screens with hemisferical transmittance greater than 10% and does not include the measurement of blackout screens. The protocol is regarded as the standard by the parties involved. The transmission measured can serve as a basis for comparing horticultural screens and can be used in calculating the performance of greenhouses.

  • J. Bezemer · T.A. Dueck · S. Hemming ·
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    ABSTRACT: Het gebruik van diffuus glas heeft een positief effect op de teeltresultaten. Maar de teler die voor de investering wil kiezen, ziet verschillende vragen op zich afkomen. Want het ene diffuse glas is het andere niet. De teler moet de verschillen kennen en de effecten van diffuus glas op zijn gewas begrijpen. Daarna kan hij op zoek naar het glas van zijn keuze.
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    ABSTRACT: The Dutch horticultural sector shows interest in production of microalgae. When microalgae and a tomato crop are produced in the same greenhouse, both shared advantage of and competition for resources will occur. In this study a model was developed to predict algae biomass production in tubular photobioreactors (PBR) and to assess the economic feasibility of combined production of tomatoes and algae. The effects of the location of the PBR in the greenhouse, the diameter of the PBR tubes, the algae biomass concentration, the light intensity and the PBR temperature were considered. The economic feasibility of combined production was calculated, taking into account both investment and running costs. Three possible locations for the PBRs were considered. The most sensitive growth factor influencing economics of the systems was light. Economic feasibility of algae production underneath the tomato crop was poor; a minimum unit biomass production cost of 70 € kg-1 dry matter (DM) was calculated. Increasing the light intensity by decrease of the tomato LAI through extra leaf picking increases economic feasibility of algae production underneath the crop. Economic feasibility of algae production in a separated compartment was computed to be good with a minimum unit biomass production cost of 11 € kg-1 DM. The developed model can function as a basis for further research on combined production of a crop and microalgae in Dutch greenhouses.
    Acta horticulturae 10/2012; DOI:10.17660/ActaHortic.2012.956.68
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    Journal of Agricultural Engineering 06/2012; 41(2). DOI:10.4081/jae.2010.2.1
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    ABSTRACT: For a better understanding of growth and development of tomato plants in three dimensional space, tomato plants were monitored using a computer vision system. It is commonly known that leaves of tomato plants do not have a fixed position and orientation during the day; they move in response to changing environmental conditions such as the position of the sun. For better understanding, it was desired to quantify this motion. Using a stereovision concept, two cameras were mounted in an experimental greenhouse a short distance apart from each other to enable depth measurement. Markers were placed on strategic spots on the tomato plant branches and leaves in the field of view of both cameras. Images were taken every ten minutes during daytime on several consecutive days. In the greenhouse, a virtual 3D coordinate system was defined and camera and tomato plant position and orientation were defined in this coordinate system. Image processing techniques were used to trace the markers and the 3D position coordinate of each marker in each image was calculated to obtain the course of a marker during several days. Stems, branches, and leaf nerves were considered as kinematic mechanical, robot like, links and corresponding theory was used to model and calculate the motion of stems and leaves of a tomato plant. Analysis of the images showed both small (1-2 degrees) and large rotations (10 degrees or more) of the branches and the different leaves on a branch during the course of a day. Leaves on one side of a branch showed a parallel motion in the same direction; the leaves on the opposite side of the branch showed a mirrored motion. However, deviating patterns occurred too. The developed method proved to be able to precisely quantify the motion of stems, branches and leaves of tomato plants during several days.
    Acta horticulturae 06/2012; 952(952). DOI:10.17660/ActaHortic.2012.952.116
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    ABSTRACT: Mobile rose systems are designed to increase labour efficiency. However, many questions remain on best design and settings of operational parameters for best performance. The ultimate goal of this research is an assessment of re-designed horticultural crop production systems and work scenarios on labour and machine performance before implementation. To attain this goal, a queueing network model, GWorkS(1)-rose, is presented for simulation of labour processes in a greenhouse with a mobile rose cultivation system. The objective for modelling is to quantify effects of production system changes by means of a flexible and generic model approach. A state-of-the-art mobile rose production system was used to validate and test the GWorkS-rose model. Data from the labour registration system and from video recordings were used for validation. System performance was simulated and compared to the performance measured in the real situation. Results of a single day validation show that the model estimates harvest labour time with an accuracy of 94%. For a one month validation an accuracy of 92% and RRMSE of 18% resulted. The value of RRMSE was caused by missing data on the number of workers at the loop and on the actual gutter speed level. The model can determine best system settings as is illustrated for operator and mobile gutter speed settings at given rose yield levels. It is concluded that the model can be used for studies on design and management of this kind of production systems. (c) 2012 IAgrE. Published by Elsevier Ltd. All rights reserved.
    Biosystems Engineering 06/2012; 112(2):108–120. DOI:10.1016/j.biosystemseng.2012.03.004 · 1.62 Impact Factor

Publication Stats

237 Citations
11.64 Total Impact Points


  • 2005-2014
    • Wageningen University
      • • Department of Farm Technology
      • • Plant Research International
      • • Department of Food Sciences and Agrotechnology
      Wageningen, Gelderland, Netherlands
  • 2005-2006
    • Wageningen UR
      Wageningen, Gelderland, Netherlands