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Apeldoorn, Netherlands

Van Os E.A.,Wageningen UR Greenhouse Horticulture
Acta Horticulturae | Year: 2010

EU legislation, laid down in the Water Framework Directive, demands to minimize emissions of nitrogen, phosphate and crop protection products to achieve an excellent chemical and ecological quality in 2015. The aim is to force growers to a better water and disease management. Supply water of excellent chemical quality will have to be recirculated as long as possible, for which adequate disinfection equipment have to be used. Several sources of water are used as supply water. Rainwater is chemically best, followed by reverse osmosis water. However, the latter is rather expensive. Tap water and surface water often have a too high salinity, while well water may vary dramatically from place to place. Rainwater and surface water are potential risk factors for importing soil-borne pathogens. Disinfection of the recirculating nutrient solution can be done adequately by heat treatment and UV radiation. Membrane filtration performs well, but is mostly too costly. Chemical treatments as sodium hypochlorite, chlorine dioxide and copper silver ionization may partly solve the pathogen problem, but introduce a potential accumulation of other elements in closed systems. Hydrogen peroxide, chlorine dioxide and sodium hypochlorite perform better to clean pipe work instead of soil-borne pathogens. Source

Gorbe E.,Wageningen UR Greenhouse Horticulture | Gorbe E.,Wageningen University | Calatayud A.,Instituto Valenciano Of Investigaciones Agrarias Ivia
Scientia Horticulturae | Year: 2012

Chlorophyll fluorescence is a rapid, non-destructive and inexpensive technique that has been used successfully in the evaluation of plant photosynthetic activity. However, this technique has been based on point measurements, and the habitual heterogeneity of photosynthetic activity over the leaf surface makes this approach highly error prone. The development of chlorophyll fluorescence imaging (CFI) overcomes this problem while including the advantages of non-imaging chlorophyll fluorescence. CFI permits the study of the spatial-temporal heterogeneities in the fluorescence emission pattern within cells, leaves or whole plants. In horticultural research, it has been mainly applied in the diagnosis of biotic or abiotic stresses in both preharvest and postharvest conditions. CFI has a useful potential to detect stresses before visual symptoms appear, which is ideal in screening of genotypes for the early identification of those with high tolerance to biotic and abiotic stress. This review provides an overview of the application of CFI in horticultural research, highlighting how CFI can be used for these purposes and in which subjects it can be applied in the future. © 2012 Elsevier B.V. Source

De Zwart H.F.,Wageningen UR Greenhouse Horticulture
Acta Horticulturae | Year: 2011

In summer, greenhouses have to deal with an excess of solar energy which is mostly discharged by ventilation. In moderate climates, on a yearly base this discharge of energy is comparable to the energy demand for heating. Thus, in times of growing awareness of the scarcity of fossil fuels, harvesting and storing of summertime heat excesses for application in winter seems to be a promising technique. Preferably the harvesting units are integrated in the greenhouse design because this enables the shared use of space and supporting constructions and the extraction of excess heat can improve the inside climate conditions, especially when one is trying to increase the inside CO 2-concentration to above outside levels. However, although the concept sounds easy, in practice a lot of difficulties have to be overcome since there are strong limits to the affordable expenses, giving the value of the energy harvested. Moreover, the harvesting of summertime excesses and the application of the (low thermal) heat results in an important electricity demand for driving ventilators and a heat pump. This means that the ratio between heat and electricity demand shifts to the latter, which is unfavourable because of the much higher value of electricity compared to heat. Nevertheless, with a carefully designed energy harvesting greenhouse, promising opportunities appear to be achievable, especially when smart choices are made around the greenhouse air temperatures and humidity control. This paper presents the reasoning of such a design called the Sunergy Greenhouse. The proposed design was built as a 550 m 2 demonstration object and has been in operation since June 2008. In this paper a number of results are presented and commented. Moreover, based on the observations, a simulation model was developed. With this model, amongst lots of other things, the impact of the prices of gas and electricity on the affordable costs of energy harvesting can be studied. The results, presented in this paper, help to understand business economical considerations. Source

Hemming S.,Wageningen UR Greenhouse Horticulture
Acta Horticulturae | Year: 2011

In intensive horticultural cultivation natural light levels often limit crop production during several periods. For an optimum plant production and product quality light intensity, spectrum and photoperiod have to be adapted to the needs of the crops at every moment. Light has to be optimised together with all other growth factors like temperature, humidity and CO 2. For a sustainable greenhouse production the use of freely available sunlight has to be preferred. New transparent greenhouse covering materials, like ETFE, glass with new anti-reflection coatings or materials with micro-surface structures, transmit a very high amount of light into the greenhouse. Other new materials are able to scatter the incoming light and make it diffuse. Diffuse light penetrates deeper into the canopy, increases light interception by the crop, influences micro-climate and increases crop production by 6.5-9.2% in The Netherlands, the potential in lower latitudes is even higher. Other materials manipulate light spectrum. Photoselective nettings have been developed in different colours influencing morphogenesis and crop production. Fluorescent plastic films combine effects on morphogenesis with high light transmission, especially important for higher latitudes. When sunlight is optimized it can still be necessary to add artificial light to ensure a year-round supply of horticultural products. There is still room for improving the crop energy efficiency under artificial lighting by changing duration and intensity of lighting, different growing systems and plant densities. Since artificial lighting requires a high amount of energy, new artificial lighting systems have been developed, such as interlighting and light emitting diodes (LED). LED give the possibility for true light spectrum control in the future. The (partial) replacement of HPS lamps by LED systems is currently under investigation in Dutch greenhouses. Integration in current growing systems has full attention. In order to reach a high sustainable and economic beneficial production the factor light has to be integrated and optimized within the total horticultural system. Source

Stanghellini C.,Wageningen UR Greenhouse Horticulture
Acta Horticulturae | Year: 2014

The central thesis of this paper is that greenhouse production of vegetables is the most water-efficient food production system and thus can contribute to meeting the challenge of feeding a better diet to an increasing world population, without increasing the need for irrigation water. The various physiological and managerial components of agricultural water use efficiency are unravelled and the potential improvements achieved by using a greenhouse are analysed. In the first place it is shown that greenhouse growers usually have better tools for water management; then it is discussed how and why a greenhouse environment leads naturally to higher productivity and transpiration efficiency than growing in the field; finally the high economic productivity of water in greenhouses is quantified. It is discussed that this would warrant the investments in infrastructure and tools that are needed to increase water use efficiency. It is also shown that, contrary to accepted wisdom, greenhouse production makes it possible to decrease the environmental impact of vegetable production. Source

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