In the Netherlands about 2000 ha of glasshouses is equipped with supplementary assimilation light (SL), which is about 19% of the total glasshouse area. Besides increased production, SL results in improved product quality, a better control of yield and quality, possibilities for earlier or year-round production and a more regular labor requirement. In this paper several recent experiments with different strategies of SL (33 up to 210 µmol m -2 s -1 ) for tomato, sweet pepper, cucumber and eggplant are presented and discussed. In general, it was concluded that SL was not economically feasible. For cucumber SL can only be attractive if the crop is grown at high plant density and according to the high-wire system. Based on 3 plantings per year, a production of 147 kg m -2 (360 cucumbers) is possible with 210 µmol m -2 s -1 SL during 3000 h/year. Application of 50% of the light within the crop (interlighting) by fluorescent tubes instead of only HPS-lamps above the crop, did not improve production but improved fruit quality in cucumber. Mobile lamps are sometimes used instead of fixed lamps. For sweet pepper and tomato, a fixed-lamp installation was economically more feasible than mobile lamps when compared at the same light intensity. A dynamic simulation model was used to predict effects of different lighting strategies at 500 and 1000 ppm CO 2 on potential production. Maximum levels of 110, 64 and 168 kg m -2 year -1 were calculated for tomato, sweet pepper and cucumber, respectively. INTRODUCTIONThe glasshouse industry in the Netherlands is the largest worldwide with 10.500 ha and a production value of 5.9 billion euro. About 40% of the glasshouse area is used for vegetable production, mainly tomato, sweet pepper and cucumber. Ornamentals, both cut flowers and pot plants are grown on the remaining 60%. Main cut flowers are roses and chrysanthemum, whereas ficus, kalanchoe and begonia are the most important pot plants considering cultivation area. Although the total glasshouse area is rather constant, the area of individual companies is growing fast. For vegetables, in 1995 442 companies (9% of the total) were larger than 2 ha, whereas in 2004 this was 686 (26% of the total). Among these are several companies larger than 20 ha. Annual production levels in the Netherlands belong to the highest in the world, e.g. for tomato (up to 70 kg m -2 ), cucumber (up to 90 kg m -2 ), large-sized cut roses under supplementary assimilation light (SL; 270 stems m -2 ) and cut chrysanthemum under SL (250 stems m -2 ). A major threat to the glasshouse industry is its high energy use. The equivalent of 4.3 × 10 9 m 3 of natural gas is used annually to heat the glasshouses, resulting in an average gas input of 41 m
Reliable and quick assessment of energy conservation measures in greenhouse cultivation supports growers in their operations. Such an overview should quantify the consequences of changes in energy flows for total energy consumption, amount and quality of production, and farm economy.Using tomato as an example crop, comprehensive energy balances were developed for a reference situation in The Netherlands. Solar radiation, primary and secondary heating circuits and CO 2 from the flue gasses of the heating system were quantified as energy sources. Energy use for air and leaf temperature increase, crop photosynthesis, crop transpiration, as well as energy losses through the roof, walls and ground surface were quantified. Subsequently, the effects of 11 energy conservation measures were computed. Consequences for gas consumption and production were simulated with a greenhouse and a crop growth model, respectively, consequences for quality were assessed on the basis of expert knowledge, and economic consequences were simulated with a cost-benefit model.For tomato, most energy was saved by increased insulation of the greenhouse cover (23% saving) and lowered temperature set point (16%), followed by increased set point for air relative humidity, screen gap control in steps, and temperature integration (all about 5%). Fresh tomato production fell in most cases, except in case of increased light transmission by the greenhouse cover. Energy use efficiency was defined as the amount of energy required to produce a certain quantity of fresh harvestable product. Energy-conservation aims to decrease the energy use efficiency. Greatest gains were reached through insulation (-20%), lowered temperature set point (-12%) and improved light transmission (-8%). Improved light transmission resulted in the strongest increase of the balance of yield and costs (€2.6, or 10%), followed by increase of RH set point, crop-based RH control, crop-based use of the energy screen, increased size of the thermal storage tank and reduction of crop transpiration (all less than €0.5).Although energy conservation reduces fuel costs, its implementation depends on the effects on production an overall economic profitability of the farm. Improved roof insulation, reduced temperature set point, screen gap control in steps, increase of the RH set point, temperature integration, and crop-based RH control are first candidates for (further) implementation. Other measures require prior technological advancements or fine-tuning. INTRODUCTIONGiven the high costs of energy and obligations imposed on national governments by the Kyoto protocol (UNFCCC, 1997), energy conservation in horticulture has become increasingly important. Reliable and quick assessment of measures to conserve energy supports growers in their operations, and policy makers in directing research funds. Energy conservation assessments require an overview of the most important energy flows and their consequences. Changes in energy flows may have consequences for the
The influence of leaf area on tomato yield was evaluated, both by simulations and experimental work. Simulated crop growth results from daily crop gross assimilation rate minus maintenance respiration rate, multiplied by a conversion efficiency factor. Dry matter partitioning is simulated based on the relative sink strengths of the plant organs. Within the plant, individual fruit trusses and vegetative units are distinguished. Leaf area increase is calculated based on temperature, unless a maximum specific leaf area is reached. In the standard situation leaves from a vegetative unit are removed one week before the truss above this unit is harvest ripe. Leaf removal could also be based on maintaining a desired leaf area index (LAI).Measurements . The model predicted a yield increase of 1.5% for the maximum LAI treatment compared to the reference, with LAI being input to the model. Simulated yield when leaf picking was based upon a desired LAI of 4, was 4% higher than for a desired LAI of 3, with hardly any effect at higher LAI. Simulations showed that removal of young leaves favored partitioning to the fruits but decreased LAI and total yield. However, if removal of old leaves was delayed such that an LAI of 3 m 2 m -2 was maintained, removal of every second young leaf improved yield by 10%. Methods of optimizing yield by controlling LAI are discussed.
ReferaatIn het Platform Duurzame Glastuinbouw heeft de glastuinbouwsector met de landelijke overheid en andere partijen afgesproken toe te werken naar een (nagenoeg) nulemissie voor nutriënten en gewasbeschermingsmiddelen (GBM) in 2027. Voor een paprikateelt (Maranello) is een emissieloze teeltstrategie gedemonstreerd voor zowel een teelt op steenwol-als op kokossubstraat. Hiervoor is gebruik gemaakt van beschikbare technieken en strategieën, zoals ozonisatie voor ontsmetting van recirculatiewater en OpnameAnalyse voor sturing bemesting, en een nieuw ontwikkelde einde-teeltstrategie voor minimalisatie van afvoer van water, meststoffen en gewasbeschermingsmiddelen. Op steenwol (28,1 kg/m 2 ) werd een iets hogere productie gehaald dan op kokos (26,5 kg/m 2 ), doordat vanaf de start de teelt op kokos niet generatief genoeg gestuurd is. De kwaliteit van de vruchten was op orde. Door een storing aan de apparatuur is tijdens de teelt water verloren gegaan (3,8% bij steenwol, 0,7% bij kokos), maar dit heeft niet significant bijgedragen aan het verlagen van de concentratie natrium in het recirculatiewater (belangrijkste reden in de praktijk om te lozen).Er zijn geen overige parameters in het water waargenomen die een negatieve invloed hebben gehad op de productiviteit. AbstractThe Dutch greenhouse horticultural sector has committed itself to reach a (practically) zero emission for nutrients and plant protection products at latest in 2027. A zero emission production strategy is demonstrated for the production of sweet pepper (Maranello) on either Rockwool and coco peat. Readily available technologies and strategies, like ozonation for disinfection of recirculation water and Uptake Analysis for control of nutrients, were combined to reach this goal, together with a newly developed strategy to minimise discharge of water, nutrients and plant protection products at the end-of-season crop change. Productivity on Rockwool substrate (28.1 kg/m 2 ) was slightly higher than on coco peat (26.5 kg/m 2 ), due to less generative steering on the coco peat substrate from the start of the cropping season. Quality of the fruits was good on both substrates. Technical failure of equipment caused overflow of drain tanks (3.8% on Rockwool, 0.7% on coco peat), but this did not significantly reduce the amount of sodium in the water (main reason for discharge). No other water quality parameters were observed that could have negatively influenced productivity.
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