Energiezuinigheid door innovatieve vlijt

Inaugurele rede van Prof.dr.ir. L.F.M. Marcelis, waarin de achtergrond belicht wordt van het economisch belang van de tuinbouwsector en het belang van energiebesparing bij energiezuinige teelt. Tevens aandacht voor de continue innovatie in de sector en de plaats van het onderzoek van zijn leerstoel daarbi

Calculating light & lighting

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

Crop management in greenhouses: adapting the growth conditions to the plant needs or adapting the plant to the growth conditions?

Strategies for improving greenhouse crop production should target both developing advanced technological systems and designing improved plants. Based on greenhouse experiments, crop models and biotechnological tools, this paper will discuss the physiology of plant-greenhouse interactions. It is discussed how these interactions can be applied to control the production process at Northern and Mediterranean climatic conditions. Absorption of light by the leaves is important for maximum crop photosynthesis. For this, it is important to have plants that develop as fast as possible a sufficient leaf area index. The question is: what leaf area index is needed for optimal crop performance? Most of the light is absorbed by the upper part of the canopy. Can we improve the light distribution in the canopy and, moreover, does this increases yield or quality? Virtual plant models may help to address this question. In some cases removal of older leaves can improve yield, while in other cases removal of young leaves may accomplish the same objective. In summer time the light transmission of the greenhouse is often reduced by growers to avoid plant stress. However, in several cases this stress is only an indirect effect of light, because other growth factors (e.g. temperature, humidity) tend to be suboptimal. In Northern countries CO2 supply is commonly used. The introduction of semi-closed greenhouses allows to maintain high CO2 concentrations all year round. In Mediterranean countries, a large yield increase is still feasible by CO2 supply. Optimum growth conditions means that there is a good balance among different climate conditions. The source/sink ratio of a crop (ratio between production and demand of assimilates) often reflects whether these conditions are balanced. Variation in the source/sink balance affects formation and abortion of organs, product quality and production fluctuations. Some examples are shown on temperature control based on the source/sink balance of a crop. Drought and salinity may limit production especially in the Mediterranean. Morphological and metabolic traits, with known genetic bases, can be functionally altered to test current hypotheses on plant-environment interactions and eventually design a greenhouse plant. Reasonably, such a plant should have specific shoot vs. root developmental patterns, efficient water and nutrient uptake systems as well as other specific features that have not been sufficiently explored. Elucidation of the complex plant-greenhouse interactions would establish a physiological basis to improve both product quality and resource use efficiency in greenhous

PPS - Publiek private samenwerkingen van Wageningen UR: Glastuinbouw op weg naar klimaatneutraal

De glastuinbouwsector kan steeds meer produceren met minder energie. Ook de CO2-uitstoot van de glastuinbouw blijft dalen. De doelstellingen in het programma Kas als Energiebron, voor een duurzame, concurrentiekrachtige sector voor 2020, komen in zicht

Climate and Yield in a closed greenhouse

The so-called closed greenhouse (closed ventilation windows) is a recent innovation in Dutch greenhouse industry. The technical concept consists of a heat pump, underground (aquifer) seasonal energy storage as well as daytime storage, air treatment units with heat exchangers, and air distribution ducts. Savings of up to 30% in fossil fuel and production increases by up to 20%, mainly because of the continuously high CO2 concentration, have been reported. Economic feasibility of this innovative greenhouse highly depends on the yield increase that can be obtained. In this simulation study the effects of greenhouse climate on tomato yield in a closed greenhouse are presented. The explanatory model INTKAM was used, which has several submodels e.g. for light interception, leaf photosynthesis and biomass partitioning. The closed greenhouse offers possibilities for combinations of light, temperature, air humidity and CO2 concentration that are impossible in a conventional greenhouse. At high CO2 concentration and high light intensity, leaf photosynthesis shows a more narrow optimum for temperature than at high CO2 and moderate light intensity. However, the response of crop photosynthesis to temperature has a much broader optimum than that of leaf photosynthesis. Besides photosynthesis, temperature also influences aspects like partitioning, leaf area development and fruit development. Yield potential reduces at temperatures above 26°C, with fruit set being one of the first processes that is negatively influenced by supra-optimal temperatures. Based on actual climatic conditions in a conventional and a closed greenhouse (same crop management) measured during two years, INTKAM predicts an increase in yield by about 17%. Hence, in a closed greenhouse a higher stem density can be maintained for obtaining the same average fruit weight (size) as in a conventional greenhouse. In 2005 actual yield increase was similar to the simulated one (16%), but in 2004 only a 9% higher yield was realized, at least partly because of botrytis infection in the closed greenhouse

Stochastic dynamic simulation of fruit abortion: a case study of sweet pepper

Abortion of reproductive organs diminishes yields in many crops. In indeterminate greenhouse crops, alternating periods of fruit abortion and fruit set exist, resulting in fluctuations in fruit yield. Factors affecting the level of abortion are e.g., the supply and demand for assimilates (source and sink strength, respectively), temperature and cultivar. However, simulation of fruit abortion is still a weak part of crop simulation models. Variation in fruit abortion exists between plants, which results in differences in the timing and the number of set fruits. Therefore, simulating fruit abortion with variation could give more realistic simulation results. The probability of a fruit to abort should be related to factors like source strength and sink strength. The more favourable the circumstances are for fruit abortion, e.g., low source strength or high sink strength, the more likely it is that the fruit aborts. Survival analysis estimates parameters quantifying the influence of explanatory variables on the abortion rate. Time-varying explanatory variables can be used in the analysis. In a case study, we used survival analysis to analyse a data set with observations on flowering, fruit abortion and fruit harvest for sweet pepper. Source and sink strength were used as explanatory variables. The resulting equation determining the probability of abortion per day was implemented in a simple simulation model to simulate fruit set. The model output, as an average of 100 plants, showed similar timing in the fluctuations in fruit set as the observations, although the amplitude of the fluctuations was in some cases underestimated. The percentage fruit set was simulated correctl

Effects of anti-transpirants on transpiration and energy use in greenhouse cultivation

Greenhouse production in North-West Europe consumes a lot of energy. The energy is needed for heating the greenhouse and controlling air humidity. Transpiration of a crop increases the energy use. The aim of this study was to explore the possibilities for the application of anti-transpirants to save energy by reducing crop transpiration without reducing crop yield. Literature and model calculations were used to explore the effects of increased leaf resistances on transpiration, energy use and production in tomato, cucumber and sweet pepper. In literature a large number of compounds are described that act as anti-transpirant. A two to five fold increase in stomatal resistance can be expected from treatment with anti-transpirants. Model calculations for tomato showed that increasing the stomatal resistance (from 2 to 5 times) throughout the whole year leads to substantial yield reduction: crop growth was reduced by 6-19%, while transpiration by 15-42% and consequently energy use by 9-16%. However, in the winter period (beginning of October/end of March) the growth reduction was only 0.3-1.3%, as in this period light levels are low and CO2 concentrations in the greenhouse are relatively high. Raising the (maximum) set-point for CO2 concentration from 1000 ppm to 3000 ppm, increased the actual concentration during day-time from 892 to 1567 ppm (flue gases were the only source of CO2). When the application of anti-transpirants was combined with raising the set-point for CO2 concentration, the model showed no growth reduction due to the application of anti-transpirants, while the annual energy use was reduced by 5.5-10.4% in tomato. Similar results were obtained for sweet pepper (5-9% energy saving) and cucumber (2-5% energy saving). These model calculations show that increasing stomatal resistance by anti-transpirants during the winter period may potentially save a substantial amount of energy (2-10%), without affecting yield of vegetables such as tomato, cucumber and sweet pepper. It is concluded that increasing the stomatal resistance by anti-transpirants in wintertime may lead to substantial energy saving due to the reduced transpiration and need for humidity management, without yield reduction. Such model calculations are useful to analyse beforehand the chances of a good combination of energy saving and yield loss of a possible application. Experiments will be needed to verify the result

Morfogenese en stofverdeling van kasgewassen in relatie tot het kasklimaat : een verkennende bijdrage voor toekomstig onderzoek

Dit rapport omvat een literatuurstudie naar de groei van afzonderlijke planteorganen en de verdeling van drogestof over deze organe