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Biological pest control with mass-produced arthropod natural enemies is well developed in greenhouse crops and has often resulted in the evolution of complex ecosystems with persistent populations of multiple arthropod natural enemy species. However, there are cases where arthropod natural enemies are either not effective enough, not available, or their use is rather costly. For these reasons, biological control based on microorganisms, also referred to as ‘microbials’, represents a complementary strategy for further development. Although commercially available microbials have been around for quite some time, research on and the applied use of combinations of arthropod natural enemies and microbials have remained relatively under explored. Here, we review current uses of entomopathogenic fungi, bacteria and viruses, and their possible direct and indirect effects on arthropod natural enemies in European greenhouses. We discuss how microbials might be combined with arthropod natural enemies in the light of new methodologies and technologies such as conservation biological control, greenhouse climate management, and formulation and delivery. Furthermore, we explore the possibilities of using other microorganisms for biological control, such as endophytes, and the need to understand the effect of insect-associated microorganisms, or symbionts, on the success of biological control. Finally, we suggest future research directions to optimize the combined use of microbials and arthropod natural enemies in greenhouse production. peerReviewed

Cell division, endoreduplication and cell expansion are key processes for plant growth and development. Light is the main source of energy for plants and as such has a strong effect on plant growth and development. Insight into the role of light in cellular processes is important for our understanding of plant responses to light. Recent advances in artificial plant lighting, cell imaging techniques and molecular biology have provided opportunities to study light responses of plants at the cell and gene level. Regulatory networks for cellular processes have also been unravelled and many transcription factors identified. In this review, we highlight key transcription factors and photoreceptors involved in the regulation of cell division, endoreduplication and cell expansion by light. We suggest that light responses result from either degradation of transcription factors or inhibitory competition between transcription factors for promoter regions of target genes. We also suggest that light stimulates cell division irrespective of the organ under consideration, while endoreduplication and cell expansion responses to light vary from organ to organ.

Roses in Kenya are mostly grown in soil with an open drip irrigation system which is inefficient as water and nutrients are lost through drainage. A study was carried out from January to December 2013 at a commercial rose farm in Naivasha, Kenya, to evaluate the potential of a cocopeat-based system, which additionally enables re-use of the drain water in a soil-based system. Vegetative growth in both systems was assessed in terms of leaf expansion, number of leaves, stem length, chlorophyll content (represented by the measured SPAD value) and flower head expansion. The water used throughout the year was also measured. Leaf expansion was characterized by an initial slow expansion rate followed by a fast expansion rate before levelling off. Maximum leaf length reached was 63 mm in the cocopeat system, while it was 60 mm in soil system; however, the difference was not significant. The number of leaves did not differ between the soil and cocopeat system. The maximum number of leaves per stem was 20 for both systems. There was no significant difference in stem length of plants in cocopeat system (650 mm) and in soil system (630 mm). Measured SPAD value on plants grown in the cocopeat system were significantly higher than for plants grown in soil (P0.01). Net water use for the cocopeat system was lower than for the soil system, with a difference of 1197 L m-2 or 58%, due to the re-use of water in a soil system. There was a significant substrate effect on the number of stems m-2 and measured SPAD value, which are associated with differences in leaf chlorophyll and nitrogen content. It is likely that the optimized fertigation regime in cocopeat system led to higher growth rates and enabled a higher stem production. Other parameters were not significantly affected by the substrate type under the same greenhouse climatic conditions.

In this study, we present a new light absorption enhancement method for p-i-n thin film silicon solar cells using pyramidal surface structures, larger than the wavelength of visible light. Calculations show a maximum possible current enhancement of 45% compared with cells on a flat substrate. We deposited amorphous silicon (a-Si) thin film solar cells directly onto periodically pyramidal-structured polycarbonate (PC) substrates, which show a significant increase (30%) in short-circuit current over reference cells deposited on flat glass substrates. The current of the cells on our pyramidal structures on PC is only slightly lower than that of cells on Asahi U-type TCO glass (Asahi Glass Co., Tokyo, Japan), but suffer from a somewhat lower open circuit voltage and fill factor. Because the used substrates have a locally flat surface area due to the fabrication process, we believe that the current enhancement in the cells on structured PC can be increased using larger or more closely spaced pyramids, which can have a smaller flat surface area.

Species of the genus Vaccinium are commercially cultivated in Europe for their berries, which are highly valued for dietary and pharmaceutical properties. Cultivation is severely limited due to a range of fungal diseases, especially those caused by species of Diaporthe. A number of Diaporthe isolates have been collected from Vaccinium growing regions in Europe, and initially identified as D. vaccinii based on host association. Using DNA sequence inference of the combined ß-tubulin, calmodulin, translation elongation factor 1-alpha and the internal transcribed spacer region of the nuclear rDNA, along with morphological characteristics, six species were characterised. Diaporthe eres, D. vaccinii and D. viticola are known species and three novel taxa are described here as D. asheicola, D. baccae and D. sterilis. This study is the first confirmed report of D. vaccinii in Latvia and the Netherlands.

This work was conducted to investigate the efficacy of chlorophyll fluorescence (CF) sorting to improve seed germination, seedling emergence, and vigor of seeds produced from different maturity fruits of four different cultivars. Four harvest dates from each cultivar were evaluated by harvesting orange (immature), bright red (half-mature), dark red (mature), and dark red and soft (overmature) fruits. Seeds were either sorted or nonsorted after harvesting and standard laboratory germination, seedling emergence, and controlled deterioration tests were conducted. CF sorting significantly increased laboratory germination, seedling emergence, and seed vigor. Maximum improvements were obtained from seeds harvested from half-mature and mature stages. Mean germination improvement among cultivars between CF-sorted and nonsorted seeds were 14% in the immature seeds, 11% in half-mature seeds, 6% in mature seeds, and 9% in overmature seeds. Improvements in seedling emergence were 21%, 17%, 9%, and 10% and 4%, 11%, 10%, 14% for seed vigor (CD germination) in the all maturity stages of seed lots, respectively. CF has the potential to upgrade seed quality in pepper lots as a non-destructive sorting technology.

Public pressure to use peat alternatives in horticultural rooting media offers room for the re-use of local organic waste materials. The re-use of organic wastes requires value added processing such as composting, co-composting, digestion, fractioning/sieving, pressing, binding, stabilising by torrefaction and charification, washing and nutrient exchange. Three cases are presented. In case 1, the new growing media project showed a successful reduction of peat in potting soil mixes at nurseries of 15 plant species. Peat use decreased from 78 to 27%-v/v. The 51%-v/v extra peat alternatives used were, averaged over all mixes used, 24%-v/v coir products, 13%-v/v wood fibre, 6%-v/v bark products and 2%-v/v for each of compost, rice husks, perlite or rockwool granulate. When compared to the standard control mixes yield decreased for two species, increased for two species and was equal for the remaining species. Important, sometimes limiting, properties were stability, nitrogen fixation, EC level, sodium level, rewetting rate and water holding capacity. In case 2 torrefaction at 250°C was used to turn a fast degrading nitrate fixing reed (Phragmites australis) into a non-toxic potting soil constituent which could be added to potting soil mixes up to 80%-v/v. In case 3 the cation exchange complex of coir was measured and saturated with calcium ions. The amount and concentration of a solution necessary to exchange sodium and potassium was 600 meq kg -1 and was dosed as 10 L of 30 mmol L -1 calcium nitrate. In all 3 cases product quality measurements and adapted processing or cultivation practises were discussed. A set of the most important measurements is presented, including: pH, EC, EC level, sodium level, potassium level, stability, nitrogen fixation, easily available water and rewetting rate. In conclusion additional or adapted processing of organic waste guided by proper measurements can increase the value of such organic waste for use in horticulture.

To fulfill the market demand for year-round high-quality production, the use of assimilation light has increased over the last decades by 10% per year and continues to expand. The electrical consumption involved largely contributes to the high CO2 emission of greenhouse horticulture. Following the Kyoto protocol, the emission of greenhouse gases should be reduced. Light-emitting diodes (LEDs) can contribute to the reduction in carbon footprint by their high efficiency in converting electricity into light. Due to their low heat emission, LEDs can be positioned within the canopy, which allows the design of new, low-carbon production systems. Inter-canopy LED lighting is already commercially used on a small scale. This paper describes the steps taken to further optimize LED-based production systems. Since it is impossible to test all possible strategies of using LED lighting, a 3D functional-structural plant model was used to do scenario calculations to determine the light interception of the canopy and crop photosynthesis at different positions and orientations of the LEDs. Orienting inter-lighting LEDs 30° downwards positively affected the light interception by the crop, provided that there was sufficient leaf area below the LEDs to prevent light loss to the floor. Replacing the conventional high-pressure sodium (HPS) lamps by LED lamps (efficiency 2.3 μmol J-1) reduced the carbon footprint of a tomato crop by approximately 15%, due to a combination of the higher efficiency of LEDs and an increased use of thermal energy to maintain plant temperatures. These calculations were validated in a greenhouse trial, where the production and energy consumption of a HPS+LED hybrid system was compared to those of a LED top-lighting and LED inter-lighting combination. Plant development and production levels were comparable, whereas the electrical consumption in the LED+LED system was 37% lower than under HPS+LED lighting. Approximately half of the reduction in electricity was used for additional heat input to maintain plant development rate, which agreed well with the carbon footprint calculations. Work in the near future will focus on plant architecture and LEDs with altered light emission patterns, aiming to design new LEDbased production systems, which combine a high production level with a low-carbon footprint.

Semi-closed greenhouse management may increase greenhouse productivity. However, it relies on the application of mechanical cooling. Cooling can be applied from above or below the canopy. The positioning of the cooling affects the vertical climate profile in the canopy. In order to determine how this affects the vertical profile of transpiration and crop temperature, in this work we used the energy balance of different crop layers to develop a modified “big leaf” model for its temperature and transpiration. The model was validated with data from a large greenhouse experiment (tomato) where the position of cooling elements and climate set-points ensured different vertical profiles of air properties. In particular, we had the combination of two positions of cooling elements (above and below the crop) and two temperature set-points; and a control (not cooled and naturally ventilated) compartment. For the validation we used measurements of crop temperature at different heights in the canopy and of transpiration of the whole crop. Finally we used the model to determine and discuss the effect of the various types of air conditioning on the vertical profile of transpiration within the crop. The compartment with natural ventilation had the highest simulated transpiration (which agreed with the measurements) and the largest uniformity of distribution of transpiration among layers. The least homogeneous distribution was with the cooling elements below, which had also the smallest total transpiration, which was 95% of the transpiration of the crop cooled from above.

Wageningen University & Research centre heeft samen met het Universitair Medisch Centrum Utrecht en Universitair Medisch Centrum Groningen een hypoallergene appel geïdentificeerd, de Santana, die sinds 2006 als zodanig verkrijgbaar is in de supermarkt. In 2011 is hier het ras Elise met een ander smaakprofiel en andere bewaareigenschappen als nieuwe hypoallergene appel bijgekomen. Hiermee is het aanbod verbreed. Daarnaast zijn appels genetisch gemodificeerd (GM) om te onderzoeken of de techniek van ‘gene silencing’ geschikt is om het meest voorkomende allergeen in appel, Mal d 1, uit te schakelen. Deze GM-appels zijn niet bestemd voor consumptie. Ten slotte is met een combinatie van DNA-onderzoek en veredelingsonderzoek een mogelijk laagallergene eiwitvariant van Mal d 1 geïdentificeerd die slechts één aminozuur verschilt van een hoogallergene variant. De kennis uit dit onderzoek wordt benut om de ontwikkeling van hypoallergene appelrassen en andere hypoallergene plantaardige producten te versnellen en daarmee de kwaliteit van leven van de allergische consument te verbeteren.

An ideal agropark is envisaged as a planned agribusiness system in which all activities are geared towards sustainable development based on the principles of industrial ecology. The agropark concept offers in theory a variety of economic advantages as well as environmental benefits. The implementation of the concept, however, has encountered many challenges. This paper introduced an analytical framework for evaluating the synergy and risk of agroparks. The analysis brought into prominence the impact of institutional arrangements on the success or failure of agropark formation. An overview of the risks related to the agropark concept was provided. It was concluded that the key to successful formation and operation of the an agropark is the choice of proper institutional arrangements that create high incentives to cooperate and incur low institution cost

Greenhouse operators strive to be as economic as possible with energy. However, investing in fancy energy-saving equipment is often not cost-effective for smaller operations and in climate zones with mild winters. It is possible, though, for many growers to save energy without buying special equipment. The trick is choosing optimal settings for heating and venting, and checking the graphs.

Performance results are given of a new type of greenhouse, which combines reflection of near infrared radiation (NIR) with electrical power generation using hybrid photovoltaic cell/thermal collector modules. Besides the generation of electrical and thermal energy, the reflection of the NIR will result in improved climate conditions in the greenhouse. In a previous paper (Sonneveld, P. J., Swinkels, G. L. A. M., Bot, G. P. A., & Flamand, G. (2010). Feasibility study for combining cooling and high grade energy production in a solar greenhouse. Biosystems Engineering, 105, 51–58) a design and feasibility study of this electricity-producing greenhouse was presented. After the description of the construction of this greenhouse, the peak power for Dutch climate circumstances is determined based on the amount of electrical and thermal energy (hot water) produced. The typical yearly yield of this greenhouse system is determined as a total electrical energy of 20 kW h m−2 and a thermal energy of 160 kW h m−2. Improvements are possible in the spectral range of the NIR film and in the focusing unit of the system. In future the improved electricity-producing greenhouse system could generate 31 kW h m−2 of electrical energy and 270 kW h m−2 of thermal energy, so it could operate independent of fossil fuels.

BACKGROUND: Iodine is an essential trace element for humans. Two billion individuals have insufficient iodine intake. Biofortification of vegetables with iodine offers an excellent opportunity to increase iodine intake by humans. The main aim was to study the effect of iodine form and concentration in the nutrient solution on growth, development and iodine uptake of lettuce, grown in water culture. RESULTS: In both a winter and summer trial, dose rates of 0, 13, 39, 65, and 90 or 129 µg iodine L-1, applied as iodate (IO3-) or iodide (I-), did not affect plant biomass, produce quality or water uptake. Increases in iodine concentration significantly enhanced iodine content in the plant. Iodine contents in plant tissue were up to five times higher with I- than with IO3-. Iodine was mainly distributed to the outer leaves. The highest iodide dose rates in both trials resulted in 653 and 764 µg iodine kg-1 total leaf fresh weight. CONCLUSION: Biofortification of lettuce with iodine is easily applicable in a hydroponic growing system, both with I- and IO3-. I- was more effective than IO3-. Fifty grams of iodine-biofortified lettuce would provide, respectively, 22% and 25% of the recommended daily allowance of iodine for adolescents and adults

This paper briefly describes the foundations and characteristics of biological control in protected cropping and what drivers are behind adoption of this management system within this industry. Examining a brief history of biological control in greenhouses and what makes it a successful management strategy within the industry, the authors describe the rapid growth of biological control in parts of Europe and what this may mean for the industry in other parts of the world. The reaction of the greenhouse industry to several consumer led campaigns aimed at reducing the incidence of pesticides in the marketplace may be replicated in many other parts of the world. The size and robustness of the biological control industry in greenhouses, which is a reflection of the inherent characteristics of this industry that lends itself to biological control, is strong and growing with indications that this trend will be followed in many areas of the world.

Schade aan kasgewassen door Botrytisaantasting (smet) is één van de belangrijkste knelpunten in de kasteelt. Te hoge luchtvochtigheid en lokale koude plekken met condensvorming zijn de belangrijkste oorzaken van smet. Het instellen van een droog kasklimaat kost veel energie, maar door het gebruik van een waarschuwings- of sturingsmodel is het mogelijk om naast het vermijden van besmetting straks ook energiewinst te behalen ten opzichte van telen zonder model. Met verklarende computermodellen kunnen plantengroei, -kwaliteit en schimmelinfectie berekend worden. De modellen kunnen Botrytis helpen voorkomen door de juiste klimaatinstellingen en de inrichting van de kas.

Massive amounts of water are required for the production of our food, varying from several cubic metres per kilogram of beef to as low as 4 litres per kilogram for tomatoes grown in high-tech glasshouses. This article presents data on Product Water Use (PWU) of some foods and discusses how the water requirement for fresh tomatoes can be brought down from 300 to 4 litres/kg.

In this manuscript we provide evidence for the seed transmission of Pepino mosaic virus (PepMV) in tomato. Fruit was harvested from a tomato crop artificially infected with both European and CH2 genotypes of PepMV and more than 100,000 seeds were extracted and cleaned using an enzymatic treatment without disinfection. Infection assays using indicator plants confirmed the presence of viable virus on the seeds. Seeds were distributed to ten different laboratories in three separate batches, where they were germinated and the young plants tested by ELISA. In total over 87,000 plants were tested and 23 positives detected, indicating an overall transmission rate of 0.026%. However, the observed seed transmission rates varied from 0.005% to 0.057%, depending on the seed batch used. Results clearly showed that PepMV can be transmitted from seeds contaminated with virus to seedlings, highlighting the risk of using seeds from PepMV-infected plants and the potential for seed transmission to contribute to the further spread of PepMV.

Tomato plants under attack from boyritis fungus give off an aromatic substance that can be measured in greenhouses. This observation is the result of research by Dr. Roel Jansen during his doctoral studies at Wageningen University in the Netherlands. Working with a team of scientists from Wageningen and Germany, Jansen has opened the door to a new way of preventing and managing disease problems in greenhouse horticulture

Pepino mosaic virus (PepMV) has recently emerged as a highly infectious viral pathogen in tomato crops. Greenhouse trials were conducted under conditions similar to commercial tomato production. These trials examined whether tomato plants can be protected against PepMV by a preceding infection with an attenuated isolate of this virus. Two potential attenuated isolates that displayed mild leaf symptoms were selected from field isolates. Two PepMV isolates that displayed severe leaf symptoms were also selected from field isolates to challenge the attenuated isolates. The isolates with aggressive symptoms were found to reduce bulk yields by 8 and 24% in single infections, respectively. Yield losses were reduced to a 0–3% loss in plants that were treated with either one of the attenuated isolates, while no effects were observed on the quality of the fruits. After the challenge infection, virus accumulation levels and symptom severity of the isolates with aggressive symptoms were also reduced by cross-protection. Infection with the attenuated isolates alone did neither affect bulk yield, nor quality of the harvested tomato fruits.

Het Polderproject Woudse Droogmakerij moet leiden tot een meetbare verbetering van de waterkwaliteit met teeltmaatregelen die het rendement van de bedrijven garanderen of verbeteren. De kennis die ontstaat wordt landelijk ingezet om de emissie van gewasbeschermingsmiddelen en nutriënten vanuit de glastuinbouw te verminderen.

De afgelopen jaren is er gezocht naar duurzame oplossingen voor gewasschade veroorzaakt door het wortelknobbelaaltje (Meloidogyne spp.) in de biologische teelt van bloemen en groenten onder glas. Op dit moment wordt grondstomen nog steeds gezien als het belangrijkste wapen tegen wortelknobbelaatjes. Grondstomen is effectief maar kost veel energie en doodt ook nuttig bodemleven en past daarom eigenlijk niet goed in een biologische teelt. Het onderzoek was daarom gericht op het ontwikkelen van alternatieve beheerssystemen voor wortelknobbelaaltjes waardoor stomen overbodig wordt. Er is gezocht naar zowel middelen als systemen, variërend van onderstammen, biologische middelen en grondontsmetting tot teeltsysteem- oplossingen. Het onderzoek werd gefinancierd door het ministerie van Landbouw, Natuur en Voedselkwalteit (LNV) en het eindrapport is verkrijgbaar in het Nederlands en Engels (Wurff et al 2010).

This paper describes a model to calculate the concentrations of (Z)-3-hexenol, a-pinene, a-terpinene, ß-caryophyllene, and methyl salicylate in a greenhouse on the basis of their source and sink behaviour. The model was used to determine whether these volatile organic compounds (VOCs) can be used to indicate Botrytis cinerea infection in a large-scale tomato production greenhouse with a volume of 5 × 104 m3 containing 2.2 × 104 plants. Seven experiments were done to parameterise the model for these VOCs. Based on model predictions, the B. cinerea-induced increase in concentration of methyl salicylate is detectable in a large-scale tomato production greenhouse when: (a) windows are fully opened, and (b) the increase continues for at least 1 h, and (c) 5% of the plants are infected. The B. cinerea-induced increase in concentration of methyl salicylate is also detectable when: (a) windows are closed, and (b) the increase continues for at least 6 h, and (c) 5% of the plants are infected. The B. cinerea-induced increase in concentration of (Z)-3-hexenol is detectable under all conditions studied. However, it is expected that besides infected plants, many additional sources of (Z)-3-hexenol exist including plant debris and nearby field crops especially upon harvest or stress. The B. cinerea-induced increases in concentration of a-pinene, a-terpinene and ß-caryophyllene are probably undetectable in a large-scale tomato production greenhouse. Therefore, it is recommended to focus on the detection of methyl salicylate to indicate B. cinerea infections in large-scale tomato production greenhouses.

Door op twaalf bedrijven in drie meetronden van zes weken wekelijks te oogsten en de gerealiseerde klimaatdata te analyseren bleek dat het microklimaat rond de plant van grote invloed was op het ontstaan van pokken in de naoogstfase. Hoe vochtiger het is, hoe groter de snelheid van Botrytisontwikkeling. Overdag moeten de omstandigheden rond de bloem zodanig zijn dat sporen òf doodgaan (lage vochtigheid, hoge temperatuur), òf niet kunnen hechten (lage vochtigheid) of verspreid worden. ‘s Nachts moet de vochtigheid tussen de bladeren niet te hoog oplopen om groei en ontwikkeling van de schimmel te remmen.

Drastic improvements in growing technology in the Netherlands have achieved a large reduction in energy use and a striking increase in production.

Wat veroorzaakt nu meer CO2-emissie : tomaten uit Spanje of tomaten die hier zijn geteeld, weliswaar in verwarmde kassen maar met gebruik van wkk's? Het blijkt er maar net aan te liggen wat er wordt meegenomen in de berekening en welke aannames worden gemaakt

De toepassing van chemische grondontsmettingsmiddelen is in Nederland aan banden gelegd. Hierdoor groeit de noodzaak om niet-chemische middelen te ontwikkelen. Voor buitenteelten zijn er voor de praktijk momenteel twee mogelijkheden, die allebei hun beperkingen kennen: inundatie en biologische grondontsmetting. Voor het ontsmetten van de grond in kassen is momenteel stomen de enige optie. Tot nu toe is in onderzoek voornamelijk gekeken naar het bestrijdende effect van BGO tegen bodemorganismen maar kon dat niet of nauwelijks worden gekoppeld aan de processen die zich in de grond afspelen tijdens deze ontsmetting. Door het ontbreken van die kennis over het werkingsmechanisme kon en kan niet worden verklaard waarom de resultaten meestal heel goed zijn maar soms tegenvallen. Mede daardoor stagneert de doorontwikkeling van BGO in de praktijk. PPO-AGV, als onderdeel van Wageningen UR, voert in opdracht van het ministerie van LNV een driejarig onderzoek (2009-2011) uit naar het werkingsmechanisme van BGO.

Lighting in a greenhouse is surrounded by questions. How much light to supply and when?. What intensity and light sum to aim for? Is it radiation, light growlight, PAR, photons or quanta? How much is joule, watt, lux?. What does wavelength, nanometer, spectrum, UV, IR and NIR mean?

Light Emitting Diodes (LED's) are a promising technology for greenhouse lighting with their efficiency to activate plant photosynthesis potentially higher in red LEDs than in HPS lamps. Due to their particular light colour, LEDs can initiate special effects in plants or steer plant processes and plant balance

For the pilot crop tomato, business concepts of low emission greenhouses for the midterm (10 year) have been designed. The study is carried out in cooperation with innovators in the horticultural sector, suppliers and extension services. The business concepts are evaluated for different indicators in the field of planet and compared to the current situation. The focus is on the reduction of energy consumption and CO2 emission for the cultivation with and without supplementary lighting. The energy concepts differ in the way the heat and power are produced or supplied on business level. The results show that the energy concepts without supplementary lighting have a lower environmental impact and have a better energy efficiency than the energy concepts with lighting. The energy concepts without supplementary lighting show that simultaneous production of heat and power on business level and the delivery of electricity to the public grid is most favorable looking at the energy use and CO2 emission on a national level. Second best is the conditioned greenhouse. In this energy concept solar energy is collected in summertime, stored and re-used in wintertime. Conditioned greenhouses also have good perspectives in reducing the use and emission of pesticides.

Crop models are powerful tools to test hypotheses, synthesize and convey knowledge, describe and understand complex systems and compare different scenarios. Models may be used for prediction and planning of production, in decision support systems and control of the greenhouse climate, water supply and nutrient supply. The mechanistic simulation of tomato crop growth and development is described in this paper. The main processes determining yield, growth, development and water and nutrient uptake of a tomato crop are discussed in relation to growth conditions and crop management. Organ initiation is simulated as a function of temperature. Simulation of leaf area expansion is also based on temperature, unless a maximum specific leaf area is reached. Leaf area is an important determinant for the light interception of the canopy. Radiation shows exponential extinction with depth in the canopy. For leaf photosynthesis several models are available. Transpiration is calculated according to the Penman-Monteith approach. Net assimilate production is calculated as the difference between canopy gross photosynthesis and maintenance respiration. The net assimilate production is used for growth of the different plant organs and growth respiration. Partitioning of assimilates among plant organs is simulated based on the relative sink strengths of the organs. The simulation of plant-nutrient relationships starts with the calculation of the demanded concentrations of different macronutrients for each plant organ with the demand depending on the ontogenetic stage of the organ. Subsequently, the demanded nutrient uptake is calculated from these demanded concentrations and dry weight of the organs. When there is no limitation in the availability at the root surface, the actual uptake will equal the demanded uptake. When the root system cannot fulfil the demand, uptake is less, plant nutrient concentration drops and crop production might be reduced. It is concluded that mechanistic crop models accurately simulate yield, growth, development and water and nutrient relations of greenhouse grown tomato in different climate zones

The properties of vermicompost, green compost, and their mixes as substitutes for peat were evaluated regarding their recommendation for potting media. The mixes with a maximum of 50% of vermicompost or green compost had acceptable air filled porosity (AFP) and easily available water (EAW). In the vermicompost the level of organic matter (OM), dry bulk density (DBD) and shrinkage were acceptable; however, the AFP and EAW together were not at the recommended level in the different batches; as a consequence, vermicompost should not be used alone for potting media. In the green compost, the level of OM was low which increased the DBD and consequently the AFP was diminished. The particle size distribution (PSD) was different among peat, vermicompost and green compost. The coarse peat had the lower proportion of particles from 0.25 to 2.00 mm (41%) whereas the green compost had the lower coarseness index (CI: percentage by weight of particles larger than 0.5 mm in diameter), 48.4%. The direct effect of the PSD, OM and DBD in the water and air availability was confirmed. Moreover, there were high correlations between the OM, DBD, shrinkage, pore volume and PSD with the water release curve. Those properties should be considered in order to increase the level of substitution of vermicompost in peat-based potting media.

Soil-dwelling predatory mites can be very effective as biological control agents against larvae of the lepidopteral pest Duponchelia fovealis. Some growing media were reported to have natural high level and stable populations of predatory mite. The objective of this experiment was to define conditions to establish stable predatory mite populations in the rooting medium and to assess the direct effect of the rooting media on pest development. Eight rooting media were prepared, including a range of degradabilities as measured with the Oxygen Uptake Rate method (OUR). The OUR range was created by mixing peat products, coir dust, bark, perlite, compost and wood fiber. Each treatment was split: half with and half without a commercially used mulch to create a drier top layer. Kalanchoës were grown on these rooting media. After one week soil-dwelling predatory mites (Hypoaspis miles) were added. Adults of the pest Duponchelia fovealis were released during a number of weeks. Both populations were counted. Results show that the OUR range was successfully achieved. The commercial mulch, a cork based fine granulate, reduced the numbers of Duponchelia by 32%. The number of predatory mites was related to the oxygen uptake of the rooting media (R2=0.87). The predatory mite reduced the numbers of Duponchelia larvae on average by 58%. Thus, biological control by soil-dwelling predatory mites can be improved by offering rooting media with an increased degradability as measured by the oxygen uptake rate. The combined effects of using predatory mite and mulch layers are discussed.

Only about half of the energy that enters a greenhouse as sun radiation is in the wavelength range that is useful for photosynthesis (PAR, Photosynthetically Active Radiation). Nearly all the remaining energy fraction is in the Near InfraRed range (NIR) and only warms the greenhouse and crop and does contribute to transpiration, none of which is necessarily always desirable. Materials or additives for greenhouse covers that reflect a fraction of the NIR radiation have recently become commercially available. Besides lowering greenhouse temperature, a NIR-excluding cover has quite a few side-effects that may become quite relevant in the passive or semi-passive greenhouses typical of mild climates. For instance, the ratio of assimilation to transpiration (the water use efficiency) should increase. On the other hand, by lowering the ventilation requirement, such a cover may hinder in-flow of carbon dioxide, thereby limiting the photosynthesis rate. In addition, there are obviously conditions where the warming up caused by NIR may be desirable rather than a nuisance. NIR-reflecting materials are becoming available in forms that are suitable for various types of applications, such as permanent, seasonal or mobile. By means of a simulation study, we discuss in this paper the best form of application in relation to the external climate and climate management options available

The system, developed under the FLOW-AID (an FP6 project), is a farm level water management system of special value in situations where the water availability and quality is limited. This market-ready precision irrigation management system features new models, hardware and software. The hardware platform delivers a maintenance-free low cost dielectric tensiometer and several low-end irrigation or fertigation controllers for serving different situations. The software includes a complete, web based, Decision Support System (DSS) that consists of an expert planner for farm zoning (MOPECO) and a universal irrigation scheduler, based on crop-water stress models (UNIPI) and water and nutrient uptake calculations. The system, designed also to service greenhouse fertigation and hydroponics, is scalable from one to many zones. It consists of 1) a data gathering tool which uploads agronomic data, from monitored crops around the world, to a central web Data Base (DB), and 2) a web based Decision Support System (DSS). The DSS processes intelligently the data of the crop using Crop Response Models, Nutrient Uptake Models and Water Uptake Models. The central system returns over Internet to the low-end controller a command file containing water scheduling and nutrient supply guidelines

The plant's water status is the balance of water uptake and water loss. Transpiration (water loss) in influenced by sun, wind humidity, leaf area, and opening of stomatal pores in the leaves.

Pathogen attack and herbivore infestation have a major impact on plant health. In a model study, these two plant health issues were simulated to study whether plant health can be monitored at greenhouse scale through the analysis of volatile organic compounds (VOCs) in greenhouse atmosphere. To simulate pathogen attack and herbivore infestation, we repeatedly stroked the stems of tomato plants (Lycopersicon esculentum) and repeatedly removed their side shoots. In addition, we studied the effect of fruit picking on the concentration of plant-emitted VOCs in greenhouse atmosphere. Analysis of air samples obtained before these treatments revealed up to 17 VOCs that are known to be released from tomato plants, of which the most dominant one was the monoterpene ß-phellandrene. When plants were 7 weeks old, the concentration of this VOC was approximately 0.06 ppbv before treatment. When plants were 12 weeks old, this concentration was raised to approximately 0.14 ppbv. Stroking of the stems, removing the side shoots and fruit picking resulted in an increase in the concentrations of all mono- and most sesquiterpenes up to 60-fold, which was expected because these VOCs are well-known constituents of trichomes. The treatments did not result in substantially increased concentrations of the stress-related compounds ¿-copaene, methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast to stroking and fruit picking, shoot removal resulted in the emission of the lipoxygenase-derived product (Z)-3-hexenol in greenhouse atmosphere expressing cell membrane degradation. The findings presented in this paper focus on the feasibility of monitoring plant health through the analysis of VOCs in greenhouse air, but findings might also be relevant for atmospheric chemistry.

n a greenhouse without carbon fertilization, the CO2 absorbed in the process of photosynthesis must ultimately come from the external ambient through the ventilation openings. The ventilation of the greenhouse implies a trade-off between ensuring inflow of carbon dioxide and maintaining an adequate temperature within the house, particularly during sunny but chilly days. Crop production is known to increase both with carbon dioxide concentration and with [average] temperature. Therefore, the management of ventilation in such conditions is looking for ¿the lesser of two evils¿. After recalling the conclusion of a previous paper that carbon fertilization up to at least external concentration is the surest and cheapest way to increase productivity in such conditions, we deal with the question of optimal fertilisation in presence of natural ventilation. Allowing for a higher than external concentration obviously reduces the efficiency of the supply, but it does not necessarily reduce profit. By applying some economics to a simple assimilation model, we show that in many conditions¿particularly with relatively high radiation¿ maintaining higher than external concentrations does make economic sense, certainly up to ventilation rates of 10 per hour. We conclude that the optimal management of carbon fertilisation should aim at concentrations well above 1000 vpm in the absence of ventilation, and gradually decrease to maintaining the external value at ventilation rates well in excess of 10 per hour. Market conditions (value of produce v price of CO2) should determine the trend between these two extremes, that is, how fast or gradually should a grower limit fertilisation to only maintaining the external concentration.

Substrate grown roses appear to be susceptible to chlorosis, which indicates problems with Fe or Mn uptake and hence yield reduction. In common practice this problem is often treated by the addition of extra Fe-chelate, or the use of Fe-EDDHA instead of Fe-DTPA. In previous tests, it was shown that the pH in the root environment is a major factor in the prevention of chlorosis. Moreover, the application of Fe-EDDHA does not always show satisfying improvements in practice. The interaction between Fe-chelate types (EDDHA and DTPA) and pH was studied with roses cv. ‘Kiss’ and ‘Escimo’ on glasswool substrate, reusing drainage water. pH levels compared were about 7, 5.8 and 4.5. The treatments resulted in significant chlorosis and consequently yield reduction at high pH with both cultivars and both chelate types. Highest yields were obtained at low pH, especially with ‘Escimo’. The Fe uptake was clearly affected by the pH with both chelate types. At high pH the Fe-uptake was significantly higher with Fe-EDDHA; however the Mn contents in the plant were significantly lower with these treatments. The uptake of Zn and Cu was also affected by specific combinations of pH and the type of chelate. It was concluded that an optimal pH control was the best method of preventing chlorosis. The choice of the chelate type was less effective and could enhance Mn deficiency.

Detailed measurements of crop photosynthesis at supra-optimal temperatures and high CO2 levels, to validate models for use in model-based greenhouse climate control, are still lacking. We performed CO2 gas exchange measurements to estimate gross crop photosynthesis (Pgc) from measured net crop gas exchange in the daytime, and at night, with temperature and CO2 conditions higher than the normal temperature range, and with two crops of different architecture: tomato, and cut chrysanthemum. From these measurements, Pgc was predicted at photosynthetic photon flux densities (IPPFD) of 300, 600, 900 and 1,200 ¿mol m-2 s-1 for different temperatures (from 20°C to 33°C) and CO2 concentrations (400, 700, and 1,000 ¿mol mol-1). From these predictions, the optimum temperature that maximised Pgc was determined. CO2 concentration had a strong and similar effect on Pgc in both crops, and this effect decreased with increasing CO2 level. For example, at 32°C, there was a 55% or 49% increase in Pgc between 400 and 1,000 ¿mol mol-1 CO2 in chrysanthemum and tomato, respectively. A clear shift to higher optimum temperatures at elevated CO2 levels was observed, and was different for the two crops. Chrysanthemum had a lower temperature optimum than tomato for a maximum Pgc (e.g., at 1,000 ¿mol mol-1 CO2 and 600 ¿mol m-2 s-1 IPPFD, the difference was 3.1°C). Compared to leaf photosynthesis, crop photosynthesis had a lower temperature optimum (the difference could be several °C), and the shift in optimum temperature from a low to a high CO2 level was lower for a canopy compared to a leaf. Therefore, optimising the leaf photosynthetic rate in model-based greenhouse climate control would not result in optimum crop photosynthesis

In 1974 the 1:1½ volume extract was published (Sonneveld et al., 1974) as a water extraction method for the determination of available nutrient elements and of the salinity status of peaty substrates. The analytical data of this extract were related to the data of the “substrate” solution extracted from the substrates with a moisture condition of -3.2 kPa. The method has been widely used and offers a suitable basis for fertilization of peaty substrates. In the years after publication, the composition and application of substrates has undergone much change and the irrigation methods have also been thoroughly adjusted. The latter was responsible for increased water contents in the substrate during crop growth. Therefore, another study was carried out in which the analytical data of the 1:1½ volume extract was compared with the analytical data of the “substrate” solution, where the “substrate” solution was defined at the moisture condition of -1.0 kPa. There was a good agreement between the results of both studies. However, the regression coefficients for the relationships between the data of the extracts differ, as expected, because of the higher moisture contents on which the substrate solution was defined. In addition to the data of major elements published, in the second study, micro nutrients were determined in the extracts, but not published. Therefore in this paper the relationships between the concentrations of micro nutrient as determined in the 1:1½ extract and in the “substrate” solution are given. The relationships presented support the interpretation of analytical data of micro nutrients by means of water extraction.

Levels of abortion of reproductive organs (i.e., buds, flowers, and young fruits) in sweet pepper plants (Capsicum annuum L.) are high, and cyclical fluctuations occur in fruit set. Stages susceptible to abortion are very young buds (

Based on differences in dynamic response times in the crop production process, a hierarchical decomposition of greenhouse climate management is proposed. To a large extent the proposed decomposition builds on the time-scale decomposition of singularly perturbed systems commonly found in the literature. Main difference with these existing theoretical concepts is that the proposed decomposition is able to deal with rapidly fluctuating deterministic external inputs or disturbances acting on the fast sub-processes. For an example of economic optimal greenhouse climate management during one lettuce production cycle, the decomposition was successfully evaluated in simulations. Using these favourable results, a hierarchical concept for economic optimal greenhouse climate management is derived and discussed in view of application in horticultural practice.