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The propagation sector demands a very high quality of irrigation water to avoid negative growth effects and diseases. Discharge of nutrient solution is sometimes used to avoid risks for the crop. The project “Good Irrigation Water” aims to develop sustainable water management and technology for nurseries in greenhouse horti¬culture. The underlying aim is to reduce the emission of nutrients and crop protection agents and to meet the EU Water Framework Directive demands. Within the project quality standards of the irrigation water were drawn up and critical values of these standards were described. Wherever knowledge was lacking, critical limits were established by measuring sets of four levels in bioassays under laboratory conditions. Concerning potentially harmful substances, the tested materials were a disinfectant (sodium hypochlorite), two organic compounds (POW-humic and fulvo acids and coir chips), a growth control agent (Alar) and a surfactant as used in rockwool substrate. Sodium hypochlorite inhibited growth in the bioassays from 45 mg/L on and Alar (daminozide) reduced growth of seedlings from 45 mg/L on. The organic substances with TOC-levels from 0 to 540 mg/L and surfactant with levels from 0 to 100% gave no growth inhibition. A subsequent series of tests showed that advanced oxidation (AOX; the combination of UV light and an oxidizer) is not suitable to destruct sodium hypochlorite or POW humus or the exudate of coir chips when applied in practical UVc/oxidizer doses (up to 250 mJ/cm2 and 1 mmol/L oxidizer). Surfactant with a high dose peroxide (30 mg/L) and 240 mJ/cm2 UVc is broken down for up to 45%. AOX did not readily destruct growth control agents. The concentrations of the oxidant were too low for the entire oxidation of the carbon compounds. With a higher concentration of oxidizer it seems there is still room for an improved breakdown of these retardants.

In a Plant-Microbial Fuel Cell anode-conditions must be created that are favorable for plant growth and electricity production. One of the major aspects in this is the composition of the plant-growth medium. Hoagland medium has been used until now, with added phosphate buffer to reduce potential losses over the membrane because of differences in pH between anode and cathode. We developed a new, improved plant-growth medium that improves current production, while the plant keeps growing. This medium is a nitrate-less, ammonium-rich medium that contains all macro- and micro-nutrients necessary for plant growth, with a balanced amount of bicarbonate buffer. Sulphate presence in the plant-growth medium helps to keep a low anode-potential. With the new plant-growth medium the maximum current production of the Plant-Microbial Fuel Cell increased from 186 mA/m(2) to 469 mA/m(2).

Within the framework of the international KIWA quality label for rooting media representatives of plant propagators and the rockwool industry agreed to develop a method to characterize the influence of the rooting medium materials on the pH in cultivation. A method for the characterization of building materials was studied and the instrumental set up was replicated in a laboratory. In a series of experiments various parameters were optimized to characterize the pH buffer capacity of rockwool and perlite. In the final method a solution of pH 5 was recirculated at a set pace over a sample of rockwool. Dissolution of the material resulted in a gradual pH raise which was corrected by the addition of hydrochloric acid every hour for five minutes. After nine more cycles of pH rise and correction, the final consumption of acid per unit weight of sample was calculated. A norm proposal aims at characterizing the maximum pH level to be reached and the capacity of the material to influence the pH. Typical values were a maximum pH of well below 7.0 and a pH buffering capacity of 5-10 mmol hydrogen ions per kilogram of dry rockwool and 10-20 mmol of hydrogen ions per kilogram of perlite.

This paper describes attempts to find practical methods for mulching in Freesia to prevent evaporation from the soil. If mulching could insulate soil not only for temperature, but also for evaporation, more energy might be saved. Two experi-ments at commercial greenhouses were done to test soil insulation. The first experi-ment aimed to test materials and strategies. This experiment showed that a mulch of styromul bound together with synthetic glue or paper cellulose did not inhibit or harm the crop. In the second experiment soil was insulated using: Biofoam® (5 mm layer), Styromul (5 mm layer), Biofoam® glued together with synthetic glue (20 mm layer, Biofoam® glued together with organic glue (20 mm layer), styromul glued together with synthetic glue (20 mm layer) and an untreated control. Slightly increased evaporation using any mulch layer was measured. However, soil temperature was also higher because of soil heating resulting in higher evaporation of the soil. Net evaporation is calculated to have been decreased by 12% using 20 mm instead of 5 mm mulch, which is expected to result in energy saving of 11.1 MJ.m-2.yr-1 on humidity control, which is too low to make up for the cost. Soil insulation decreased temperature fluctuations. Increasing the thickness of the mulch increased temperature insulation, however the effect appeared to decrease rapidly with increasing layer thickness

This paper reviews robotics for protected cultivation systems. Based on a short description of the greenhouse crop production process, the current state in greenhouse mechanization and the challenges for robotics in protected cultivation are identified. Examples of current greenhouse robotics research are presented. Since the complex working environment constitutes a considerable challenge to robotics, opportunities will be identified to deal with this complexity. Solutions can be found in developing more advanced technology, including multiple sensor approaches, sensor fusion and artificial intelligence concepts and in human-robot collaboration. Alternatively, solutions can be found in modifying the working environment. The paper also pleas for the development of more generic solutions to deal with the small and very scattered markets of robots in protected cultivation.

In many developing plant tissues and organs, differentiating cells switch from the classical cell cycle to an alternative partial cycle. This partial cycle bypasses mitosis and allows for multiple rounds of genome duplication without cell division, giving rise to cells with high ploidy numbers. This partial cycle is referred to as endoreduplication. Cell division and endoreduplication are important processes for biomass allocation and yield in tomato. Quantitative trait loci for tomato fruit size or weight are frequently associated with variations in the pericarp cell number, and due to the tight connection between endoreduplication and cell expansion and the prevalence of polyploidy in storage tissues, a functional correlation between nuclear ploidy number and cell growth has also been implicated (karyoplasmic ratio theory). In this paper, we assess the applicability of putative mechanisms for the onset of endoreduplication in tomato pericarp cells via development of a mathematical model for the cell cycle gene regulatory network. We focus on targets for regulation of the transition to endoreduplication by the phytohormone auxin, which is known to play a vital role in the onset of cell expansion and differentiation in developing tomato fruit. We show that several putative mechanisms are capable of inducing the onset of endoreduplication. This redundancy in explanatory mechanisms is explained by analysing system behaviour as a function of their combined action. Namely, when all these routes to endoreduplication are used in a combined fashion, robustness of the regulation of the transition to endoreduplication is greatly improved.

Plant growth and development are highly responsive to plant temperature. In greenhouses, plant temperatures are often not monitored and air temperature (Tair) is used as their approximation. However, even under controlled conditions the temperature of a plant may not always equal Tair. Leaf initiation in the shoot apical meristem is a critical process for plant development and growth. Tair is considered as the dominant environmental factor influencing the rate at which new leaves are initiated (LIR). Recent studies suggested that considering Tair as the only factor influencing LIR may not always be correct. The temperature of the shoot apical meristem (Tmeristem) in cucumber and tomato plants was found to deviate from Tair by several degrees Celsius even under moderate conditions. This deviation was a function of other environmental factors, such as radiation, air humidity, wind speed, and plant traits that influence the heat budget of the shoot apical meristem. In addition, it was demonstrated that LIR is reduced by low light intensities at constant Tmeristem in cucumber and tomato plants. This paper reviews these findings suggesting that LIR is determined by more than Tair and discusses considerations and their potential implications in greenhouse climate control and crop modeling.

The aims of this paper was to modify the photosynthesis model of Farquhar, von Caemmerer and Berry (FvCB) to be able to predict light dependency of the carboxylation capacity ( V c ) and to improve the prediction of temperature dependency of the maximum carboxylation capacity ( V cmax ) and the maximum electron transport rate ( J max ). The FvCB model was modified by adding a sub-model for Ribulose-1,5-bisphosphate carboxylase (Rubisco) activation and validating the parameters for temperature dependency of V cmax and J max . Values of parameters for temperature dependency of V cmax and J max were validated and adjusted based on data of the photosynthesis response to temperature. Parameter estimation was based on measurements under a wide range of environmental conditions, providing parameters with broad validity. The simultaneous estimation method and the nonlinear mixed effects model were applied to ensure the accuracy of the parameter estimation. The FvCB parameters, V cmax , J max , α (the efficiency of light energy conversion), θ (the curvature of light response of electron transport), and R d (the non-photorespiratory CO 2 release) were estimated and validated on a dataset from two other years. Observations and predictions matched well ( R 2 = 0.94). We conclude that incorporating a sub-model of Rubisco activation improved the FvCB model through predicting light dependency of carboxylation rate; and that estimating V cmax , J max , α , θ , and R d requires data sets of both CO 2 and light response curves.

The closed greenhouse is a recent innovation in the horticulture industry. Cooling by ventilation is replaced partly (in semi-closed greenhouses) or completely (in closed greenhouses) by mechanical cooling. Excess solar energy is collected and stored to be reused to heat the greenhouse. In temperate climates, this concept combines improved crop production with energy savings. This paper presents an overview of climate, crop growth and development, and crop yield in closed and semi-closed greenhouses. The technical principles of a closed greenhouse are described and the macroclimate and microclimate arising from this are studied. The consequences of the typical growth conditions found in closed greenhouses for crop physiology and crop yield are examined. Finally, the experiences of commercial growers are presented. In temperate climates, closed greenhouses can reduce the use of fossil fuel-derived energy by 25 – 35%, compared with open greenhouses. With high global radiation, the climate in closed greenhouses is characterised by high CO2 concentrations, high air humidity, improved temperature control, and a vertical temperature gradient. An annual increase in production of 10 – 20% is realistic, with reduced amounts of supplied CO2. The yield increase is primarily obtained through increased rates of photosynthesis due to the higher CO2 concentrations in closed greenhouses. To introduce this innovation into practice, knowledge transfer was a key factor for its implementation and the realisation of increased production levels. Future trends will require minimising the use of fossil fuels and increasing the level of control of the production process. Closed and semi-closed greenhouses fit seamlessly into this trend as they allow for a more controlled climate and higher levels of production, combined with savings in fossil fuel use.

Background and Aims - At present most process-based models and the majority of three-dimensional models include simplifications of plant architecture that can compromise the accuracy of light interception simulations and, accordingly, canopy photosynthesis. The aim of this paper is to analyse canopy heterogeneity of an explicitly described tomato canopy in relation to temporal dynamics of horizontal and vertical light distribution and photosynthesis under direct- and diffuse-light conditions. Methods - Detailed measurements of canopy architecture, light interception and leaf photosynthesis were carried out on a tomato crop. These data were used for the development and calibration of a functional–structural tomato model. The model consisted of an architectural static virtual plant coupled with a nested radiosity model for light calculations and a leaf photosynthesis module. Different scenarios of horizontal and vertical distribution of light interception, incident light and photosynthesis were investigated under diffuse and direct light conditions. Key Results - Simulated light interception showed a good correspondence to the measured values. Explicitly described leaf angles resulted in higher light interception in the middle of the plant canopy compared with fixed and ellipsoidal leaf-angle distribution models, although the total light interception remained the same. The fraction of light intercepted at a north–south orientation of rows differed from east–west orientation by 10 % on winter and 23 % on summer days. The horizontal distribution of photosynthesis differed significantly between the top, middle and lower canopy layer. Taking into account the vertical variation of leaf photosynthetic parameters in the canopy, led to approx. 8 % increase on simulated canopy photosynthesis. Conclusions - Leaf angles of heterogeneous canopies should be explicitly described as they have a big impact both on light distribution and photosynthesis. Especially, the vertical variation of photosynthesis in canopy is such that the experimental approach of photosynthesis measurements for model parameterization should be revised.

The ability to concentrate CO2 around Rubisco allows C-4 crops to suppress photorespiration. However, as phosphoenolpyruvate regeneration requires ATP, the energetic efficiency of the C-4 pathway at low photosynthetic flux densities (PFD) becomes a balancing act between primary fixation and concentration of CO2 in mesophyll (M) cells, and CO2 reduction in bundle sheath (BS) cells. At low PFD, retro-diffusion of CO2 from BS cells, relative to the rate of bicarbonate fixation in M cells (termed leakiness phi), is known to increase. This paper investigates whether this increase in phi could be explained by incomplete inhibition of photorespiration. The PFD response of phi was measured at various O-2 partial pressures in young Zea mays plants grown at 250 (LL) and 750 mu mol m-2 s-1 PFD (HL). phi increased at low PFD and was positively correlated with O-2 partial pressure. Low PFD during growth caused BS conductance and interveinal distance to be lower in the LL plants, compared to the HL plants, which correlated with lower phi. Model analysis showed that incomplete inhibition of photorespiration, especially in the HL plants, and an increase in the relative contribution of mitochondrial respiration at low PFD could explain the observed increases in phi.

Experience is the main guide for cut rose growers to make decisions on crop management and climate control. Because of continuous change in cultivar characteristics and technology there is a need for a general theory, capturing how the number of flower shoots produced and their quality depend on the main determinants: plant structure (as a product of the interaction of natural growth and development with manipulation by the grower), cultivar characteristics and greenhouse environment. ‘Virtual Rose’ is an interdisciplinary project working on the development of a 3D model that simulates and visualizes shoot production over time. 3D modelling, or rather functional-structural plant modelling, differs fundamentally from previously published rose crop models, the most striking aspect being the 3D simulation and visualization of plant structure. This paper introduces the basic modelling approach, i.e., the use of Relational Growth Grammars (RGG) and the modelling language eXtended L-Systems (XL). The final model needs to be able to use greenhouse climate data from practice as input, most importantly the light regime, consisting of light from the sun and additional assimilation lamps (SON-T). Furthermore, the model needs to be equipped with provisions that allow the model user to execute ‘virtual’ bending, harvesting, and pruning. In this paper, we will focus on new modelling techniques for simulating complex interventions in plant growth

Background and aims A fast and reliable phenotyping system forms a major bottleneck in root exudation research. Our goal was to develop such a system to quantify genetic and environmental effects on root exudation. Another aim was characterizing non-sterile phenotyping. Methods We developed a system in which plants can be grown with non-sterile shoot environments and sterile rhizospheres. These sterile systems were compared with non-sterile controls. Results In non-sterile rhizospheres exogenous carbon disappeared quickly with a half-life of 2 to 3 h and root exudate concentrations remained below detection limit. In sterile rhizospheres exogenous carbon levels were relatively stable or depleted slower than in non-sterile rhizospheres and organic acid build-up occurred. Tomato (Solanum lycopersicum) could be grown with sterile roots for several months. Conclusions The differences in carbon depletion in sterile and non-sterile rhizospheres was most likely due to the absence of microbial catabolism in sterile rhizospheres. These results prove that using a sterile phenotyping system is essential to study the quantity and composition of root exudates. The sterile system described in this paper eliminates the obscuring effect caused by microbes on exudation levels. It offers a stable, reliable and easy phenotyping method and can be used to investigate genetic and environmental effects on exudation.

Recycling of the nutrient solution during cultivation of greenhouse crops reduces the total input of water and fertilizers and decreases emission of nutrients to the environment. However growers fear accumulation of harmful substances in the drain water. For this reason drain water in practice is regularly discharged into the environment. In this study drain water from a commercial rose grower in The Nether¬lands was tested with a phytotoxicity test (Phytotoxkit) during a period of one year. The Phytotoxkit was used to assess growth response of drain water without disinfec¬tion; drain water disinfected with UV; drain water disinfected with UV and peroxide. In this phytotoxicity test, garden cress (Lepidium sativum) and mustard (Sinapis alba) are grown in a Phytotoxkit container on a filter paper moistened with the drain water under analysis. After incubation for three days in a climate-controlled cabinet, root length is measured. The Phytotoxkit showed growth decrease caused by untreated drain water disappeared when using a UV disinfection of 100 MJ.cm-2 or UV disinfection of 100 MJ.cm-2 combined with 10-25 ppm peroxide. Untreated drain water caused growth responses of -20% root length in only 3 out of 10 sample moments. Control of drain water with the Phytotoxkit provides the grower information about the presence of phytotoxic substances in the drain water and the effectiveness of treatments. The Phytotoxkit thus can prevent unnecessary discharge of drain water to the environment.

In our post-genomic world, where we are deluged with genetic information, the bottleneck to scientific progress is often phenotyping, i.e. measuring the observable characteristics of living organisms, such as counting the number of fruits on a plant. Image analysis is one route to automation. In this paper we present a method for recognising and counting fruits from images in cluttered greenhouses. The plants are 3-m high peppers with fruits of complex shapes and varying colours similar to the plant canopy. Our calibration and validation datasets each consist of over 28,000 colour images of over 1000 experimental plants. We describe a new two-step method to locate and count pepper fruits: the first step is to find fruits in a single image using a bag-of-words model, and the second is to aggregate estimates from multiple images using a novel statistical approach to cluster repeated, incomplete observations. We demonstrate that image analysis can potentially yield a good correlation with manual measurement (94.6%) and our proposed method achieves a correlation of 74.2% without any linear adjustment for a large dataset.

International audience; Mapping studies using populations with introgressed marker-defined genomic regions are continuously increasing knowledge about quantitative trait loci (QTL) that correlate with variation in important crop traits. This knowledge is useful for plant breeding, although combining desired traits in one genotype might be complicated by the mode of inheritance and co-localization of QTL with antagonistic effects, and by physiological trade-offs, and feed-back or feed-forward mechanisms. Therefore, integrating advances at the genetic level with insight into influences of environment and crop management on crop performance remains difficult. Whereas mapping studies can pinpoint correlations between QTL and phenotypic traits for specific conditions, ignoring or overlooking the importance of environment or crop management can jeopardize the relevance of such assessments. Here, we focus on fruit load (a measure determining competition among fruits on one plant) and its strong modulation of QTL effects on fruit size and composition. Following an integral approach, we show which fruit traits are affected by fruit load, to which underlying processes these traits can be linked, and which processes at lower and higher integration levels are affected by fruit load (and subsequently influence fruit traits). This opinion paper (i) argues that a mechanistic framework to interpret interactions between fruit load and QTL effects is needed, (ii) pleads for consideration of the context of agronomic management when detecting QTL, (iii) makes a case for incorporating interacting factors in the experimental set-up of QTL mapping studies, and (iv) provides recommendations to improve efficiency in QTL detection and use, with particular focus on model-based marker-assisted breeding

Since the expansion of soil-less culture in the Netherlands in the mid-eighties of the previous century, emission of nutrients and plant protection products (PPP’s) used in the root environment was considered as a huge problem. Eventually, the government and growers organisations reached an agreement which aimed at reducing the N, P and PPP emissions. For soil-less culture, reuse of drain water or closed growing systems became obligatory. Recently, the regulation changed by shifting the focus on reaching emission targets for N rather reaching 100 % closure of the systems. Yet, recirculation is still the key issue for reaching the goal of zero emission by 2027. These closed systems will potentially lead to substantial reduction of mineral leaching to the environment, however, they require adequate water quality and nutrient management. Moreover, satisfactory disinfection to control root diseases and removal of organic components is needed. In practice, substantial loss of water and minerals still occurs occasionally, when growers decide to flush the system and drainage water is partially discharged to the surface water or sewage system, causing emission of nutrients and PPP’s. There are several reasons for growers to discharge e.g. accumulation of Na, mismanagement in EC or pH or nutrient supply, and serious problems with soil borne diseases or growth inhibition. This paper will give an overview of the state of the art of systems for nutrient solution recycling, and the requirements for water treatment, water quality and nutrient supply and strategies to obtain the highest efficiencies for nutrient and water use.

In the first part of this paper, we review the extent to which various types of plant growth models incorporate ecophysiological mechanisms. Many growth models have a central role for the process of photosynthesis; and often implicitly assume C-gain to be the rate-limiting step for biomass accumulation. We subsequently explore the extent to which this assumption actually holds and under what condition constraints on growth due to a limited sink strength are likely to occur. By using generalized dose–response curves for growth with respect to light and CO2, models can be tested against a benchmark for their overall performance. In the final part, a call for a systems approach at the supra-cellular level is made. This will enable a better understanding of feedbacks and trade-offs acting on plant growth and its component processes. Mechanistic growth models form an indispensable element of such an approach and will, in the end, provide the link with the (sub-)cellular approaches that are yet developing. Improved insight will be gained if model output for the various physiological processes and morphological variables (‘virtual profiling’) is compared with measured correlation networks among these processes and variables. Two examples of these correlation networks are presented

Since the expansion of soil-less culture in the Netherlands in the mid-eighties of the previous century, emission of nutrients and plant protection products (PPP’s) used in the root environment was considered as a huge problem. Eventually, the government and growers organisations reached an agreement which aimed at reducing the N, P and PPP emissions. For soil-less culture, reuse of drain water or closed growing systems became obligatory. Recently, the regulation changed by shifting the focus on reaching emission targets for N rather reaching 100 % closure of the systems. Yet, recirculation is still the key issue for reaching the goal of zero emission by 2027. These closed systems will potentially lead to substantial reduction of mineral leaching to the environment, however, they require adequate water quality and nutrient management. Moreover, satisfactory disinfection to control root diseases and removal of organic components is needed. In practice, substantial loss of water and minerals still occurs occasionally, when growers decide to flush the system and drainage water is partially discharged to the surface water or sewage system, causing emission of nutrients and PPP’s. There are several reasons for growers to discharge e.g. accumulation of Na, mismanagement in EC or pH or nutrient supply, and serious problems with soil borne diseases or growth inhibition. This paper will give an overview of the state of the art of systems for nutrient solution recycling, and the requirements for water treatment, water quality and nutrient supply and strategies to obtain the highest efficiencies for nutrient and water use.

Protected cultivation systems are used throughout the world as a powerful instrument to produce crops. They protect the crops from unfavorable outdoor climate conditions and pests and offer the opportunity to modify the indoor climate to create an environment that is optimal for crop growth and production, both in terms of quality and quantity. A quick scan of protected cultivation systems presently in use reveals that quite a variety of protected cultivation systems can be found throughout the world. They range from fully passive “solar greenhouses” with thick energy storage walls as found in China to the high-tech “closed greenhouses” in Western Europe. This variety is due to local conditions, including the local climate, the availability of resources like water, energy, capital, labor and materials, local legislation and social aspects, to mention a few. This paper presents a methodology of a model based method for designing protected cultivation systems. First results will be reported as well as directions for future research.

The closed greenhouse is a recent innovation in the horticulture industry. Cooling by ventilation is replaced partly (in semi-closed greenhouses) or completely (in closed greenhouses) by mechanical cooling. Excess solar energy is collected and stored to be reused to heat the greenhouse. In temperate climates, this concept combines improved crop production with energy savings. This paper presents an overview of climate, crop growth and development, and crop yield in closed and semi-closed greenhouses. The technical principles of a closed greenhouse are described and the macroclimate and microclimate arising from this are studied. The consequences of the typical growth conditions found in closed greenhouses for crop physiology and crop yield are examined. Finally, the experiences of commercial growers are presented. In temperate climates, closed greenhouses can reduce the use of fossil fuel-derived energy by 25 – 35%, compared with open greenhouses. With high global radiation, the climate in closed greenhouses is characterised by high CO2 concentrations, high air humidity, improved temperature control, and a vertical temperature gradient. An annual increase in production of 10 – 20% is realistic, with reduced amounts of supplied CO2. The yield increase is primarily obtained through increased rates of photosynthesis due to the higher CO2 concentrations in closed greenhouses. To introduce this innovation into practice, knowledge transfer was a key factor for its implementation and the realisation of increased production levels. Future trends will require minimising the use of fossil fuels and increasing the level of control of the production process. Closed and semi-closed greenhouses fit seamlessly into this trend as they allow for a more controlled climate and higher levels of production, combined with savings in fossil fuel use.

High energy use in rose cultivation at higher latitudes is caused by the need for artificial light to supplement scarce sun radiation. On the other hand, too high radiation levels are known to reduce flower quality. Therefore shading is widely applied during spring and summer, either through movable screens or seasonal whitewash. In both cases damage to the crop is avoided at the cost of reducing potential assimilation. Recent research on cucumber (Hemming et al., 2008a) has shown that diffusing cover materials improve the uniformity of vertical light distribution in a crop, therefore decreasing the energy load on the uppermost crop layer to the advantage of the underlying leaves avoiding light saturation in the upper leaves. These properties lead to an increase in production up to 10%. The application of such a cover on roses could decrease the need for shading so that a desired radiation sum could be achieved with less need for artificial light. Moreover, if the light distribution improvement on the crop leads to an increase in production, the same production could be achieved with less supplemental light, increasing the potential energy saving. Diffusion, however, usually implies a loss of overall transmission. This drawback can be avoided by antireflection coatings so that most recently diffusive glass covers have become available with the same transmission as standard glass. A rose crop (‘Red Naomi!’) was cultivated from August 2010 till September 2011 at the research station of Wageningen UR Greenhouse Horticulture in Bleiswijk in two compartments, one of them covered with diffuse, anti-reflection coated glass. This paper describes the effect of the diffusing cover on the photosynthetic properties of the crop, and the resulting production and quality.

International audience; BACKGROUND AND AIMS: Manipulation of plant structure can strongly affect light distribution in the canopy and photosynthesis. The aim of this paper is to find a plant ideotype for optimization of light absorption and canopy photosynthesis. Using a static functional structural plant model (FSPM), a range of different plant architectural characteristics was tested for two different seasons in order to find the optimal architecture with respect to light absorption and photosynthesis.METHODS: Simulations were performed with an FSPM of a greenhouse-grown tomato crop. Sensitivity analyses were carried out for leaf elevation angle, leaf phyllotaxis, leaflet angle, leaf shape, leaflet arrangement and internode length. From the results of this analysis two possible ideotypes were proposed. Four different vertical light distributions were also tested, while light absorption cumulated over the whole canopy was kept the same.KEY RESULTS: Photosynthesis was augmented by 6 % in winter and reduced by 7 % in summer, when light absorption in the top part of the canopy was increased by 25 %, while not changing light absorption of the canopy as a whole. The measured plant structure was already optimal with respect to leaf elevation angle, leaflet angle and leaflet arrangement for both light absorption and photosynthesis while phyllotaxis had no effect. Increasing the length : width ratio of leaves by 1·5 or increasing internode length from 7 cm to 12 cm led to an increase of 6-10 % for light absorption and photosynthesis.CONCLUSIONS: At high light intensities (summer) deeper penetration of light in the canopy improves crop photosynthesis, but not at low light intensities (winter). In particular, internode length and leaf shape affect the vertical distribution of light in the canopy. A new plant ideotype with more spacious canopy architecture due to long internodes and long and narrow leaves led to an increase in crop photosynthesis of up to 10 %.

Organic greenhouse production within the European context is limited both by its own principles, among them restrictions concerning soil and fertilizers, and by legislative restrictions on manure, compost and fertilizer applications. Results of a monitoring project on organic greenhouses were evaluated concerning the various legal constraints. Important bottle necks are related to the limitations in the N and P input, the unbalanced input of nutrients and the restrictions on irrigation with consequently increased salinity problems. The development of an organic fertilizer database and a decision support model for fertilizer and organic matter application is evaluated. Balanced mineral supply is possible within the prevailing legal mineral targets, but risk of salinity is a concrete concern. Challenges in the very near future will be the upcoming targets on N and P emission and new regulations on organic manure. INTRODUCTION Organic vegetable production as expressed by the IFOAM Basic Standards (IFOAM, 2007) discerns itself in many aspects from conventional production. One of the key issues is the approach to soil and soil fertility, as is manifest in the regulations on permitted fertilizers and soil amendments in the EU regulation for organic food production (Anonymous, 2002). This entails restrictions for crop production, for the goal in organic production is equilibrium between the production capacity of the soil and other production factors, rather than maximizing yields. Organic greenhouse production operates under the same principles; however, greenhouse crops are characterized by high production levels and consequently require high inputs of nutrients. High yields are considered necessary to recoup investment costs. This aspect, however, conflicts with basic organic principles and guidelines. In addition to the guidelines and standards of the organic label itself, European and national regulations on fertilizer inputs, as derived from the Nitrate Directive (ND) (Anonymous, 1991) or the WaterFramework Directive (WFD) (Anonymous, 2007), will restrict organic greenhouse production even more. This may sound strange, since organic production is often thought to be synonymous with sustainability and an environmentally friendly way of agricultural production. However, the generic way the regulations are described, by which there is no differentiation between greenhouse and field crops, and the strong dependence on organic fertilizers and composts, makes fertilization in organic greenhouse production quite complicated. In this paper, it will be discussed how greenhouse growers have to deal with the various constraints for fertilization management and which constraints have to be faced in the near future. The focus will be within the Dutch context. FERTILIZATION PRACTICE The current fertilization strategy in practice is characterized by a base dressing of compost, and in many cases also animal manure, before planting, partly to amend the soil Proc. First IC on Organic Greenhouse Hort. Eds.: M. Dorais and S.D. Bishop Acta Hort. 915, ISHS 2011 76 micro-organisms and maintain soil structure and partly for nutrient supply. Top dressings are applied throughout the growing season, using a variety of additional fertilizers like dried dairy and chicken manure, dried slaughterhouse waste (bloodmeal, feathermeal) or dried fertilizers derived from plant sources (e.g., remains from malt, sugar beet, ricinus industry). Occasionally, fertigation with liquid organic fertilizer which is dissolved in water with epsom salt or potassium sulphate is used to establish a certain electrical conductivity level (EC) to allow dosage rates to be automatically controlled. The rates applied are mainly based on soil analysis and the grower’s own experience (Janmaat and Cuijpers, 2005). From 2002 on, the fertilizer application and soil management was monitored at 8– 10 organic greenhouse companies. In some years, the total net crop nutrient removal was determined by fresh and dry weight of crop plants and plant tissue analysis aimed at estimating the mineral balance. The total available N was estimated using the mineralization model established by Janssen (1984). The greenhouse companies observed had intensive fruit vegetable crop rotations, consisting of tomato, cucumber and sweet pepper and a limited number of smaller crops like lettuce, cauliflower, beans and egg plant. Parts of these results have been described earlier (Cuijpers et al., 2008). The average total supplied N was much higher than the removal by the crop. At the same time, the N supplied was in the same order of magnitude as the estimated total available N, showing that the unavailable fraction of organic N in the yearly applied soil amendments was compensated by the decomposition of the soil organic matter versus the historic soil amendments (Fig. 1). The average application was about double the crop demand. Part of this excess will be lost by denitrification, the other part by leaching and a small fraction will be fixated in the stable organic matter pool. de Visser et al. (2006) showed that denitrification losses could be considerable; it was found to be responsible for as much as 25% of the total N balance output. For P, the results were also troubling; the total supply was almost three times the estimated crop removal, resulting in a significant P excess. Since leaching of P is not to be expected, the majority of P will have accumulated in the soil. The excessive P accumulation in organic greenhouse horticulture was observed previously (Voogt, 1999). Next to the N and P surpluses, it was established that the mutual ratio between N, P and K in the total organic fertilizer supply was not balanced with the ratio in the crop demand (Fig. 2). This was caused mainly by the relatively lower levels of K in compost and manure (45 and 50%, respectively), compared with the crop uptake (57%). Moreover, the portion of P in compost and manure (11%) is relatively much higher than the crop demand (6%). In addition, growers added more specific N fertilizers like blood and feathermeal to compensate for N losses not due to crop uptake but other processes in the N cycle, like denitrification (Cuijpers et al., 2005). REGULATIONS Dutch organic greenhouse production has to meet the following standards and regulations: A. The principal aims of organic production and processing, as formulated under IFOAM basic standards, are of course leading for organic greenhouse production. Within EU, the EU regulation for Organic Food (837/2007) is leading. This does not need further specification within this context; the fertilizers allowed are certified by SKAL, the Dutch certification body (Anonymous, 2002). B. Manure: resulting from the European Nitrate Directive, applicable since 1998. The application of manure is limited to the equivalent of 170 kg N ha yr. This also holds for any additional (dried) fertilizer derived from animal manure, even for the manure component in composts amended with manure like mushroom compost (Anonymous, 1986; Anonymous, 1997; Anonymous, 2010). C. Compost: Since 2008, the application of compost is regulated under the new fertilization law. Compost should contain at least 10% organic matter (dry matter) and must comply with the EU standards for heavy metals. There are no more limits in the applied quantity but these are restricted by the application standards for nutrients (D)

Growers and Dutch government have concluded a covenant in which they express the ambition to reduce the carbon footprint of greenhouse production in order to improve the energy neutrality of newly built greenhouses. Conditioned cultivation in (semi-)closed greenhouses is seen as one of the instruments to reach this goal. It is appointed in the covenant to arrive in 2011 at 700 ha and in 2020 at 2,500 ha semi-closed greenhouses. This paper describes the instruments used to monitor the results of conditioned cultivation in eight semi-closed greenhouses in practice. It addresses the monitoring process, the installations involved and highlights some of the measured data.

behind phenotypic differences and led to selection of genotypes having favourable traits. Continuous monitoring of environmental conditions has also become an accessible option. Rather than single trait evaluation, we would prefer smarter approaches capable of evaluating multiple, often correlated and time dependent traits simultaneously as a function of genes (QTLs) and environmental inputs, where we would The use of molecular breeding techniques has increased insight into the genetics like to include intermediate genomic information as well. In this paper, an exploratory QTL analysis over two environments was undertaken using available genetic and phenotypic data from segregating recombinant inbred lines (RIL) of pepper (Capsicum annuum). We focused on vegetative traits, e.g. stem length, speed of stem development, number of internodes etc. We seek to improve the estimation of allelic values of these traits under the two environments and determine possible QTL x E interaction. Almost identical QTLs are detected for each trait under the two environments but with varying LOD scores. No clear evidence was found for presence of QTL by environment interactions, despite differences in phenotypes and in magnitude of QTLs expression. Within the EU project SPICY (Voorrips et al., 2010 this issue), a larger number of environments will be studied and more advanced statistical analysis tools will be considered. The correlation between the traits will also be modelled. The identification of markers for the important QTL (Nicolaï et al., 2010 this issue) will improve the speed and accuracy of genomic prediction of these complex phenotypes

behind phenotypic differences and led to selection of genotypes having favourable traits. Continuous monitoring of environmental conditions has also become an accessible option. Rather than single trait evaluation, we would prefer smarter approaches capable of evaluating multiple, often correlated and time dependent traits simultaneously as a function of genes (QTLs) and environmental inputs, where we would The use of molecular breeding techniques has increased insight into the genetics like to include intermediate genomic information as well. In this paper, an exploratory QTL analysis over two environments was undertaken using available genetic and phenotypic data from segregating recombinant inbred lines (RIL) of pepper (Capsicum annuum). We focused on vegetative traits, e.g. stem length, speed of stem development, number of internodes etc. We seek to improve the estimation of allelic values of these traits under the two environments and determine possible QTL x E interaction. Almost identical QTLs are detected for each trait under the two environments but with varying LOD scores. No clear evidence was found for presence of QTL by environment interactions, despite differences in phenotypes and in magnitude of QTLs expression. Within the EU project SPICY (Voorrips et al., 2010 this issue), a larger number of environments will be studied and more advanced statistical analysis tools will be considered. The correlation between the traits will also be modelled. The identification of markers for the important QTL (Nicolaï et al., 2010 this issue) will improve the speed and accuracy of genomic prediction of these complex phenotypes

The ability to concentrate CO2 around Rubisco allows C-4 crops to suppress photorespiration. However, as phosphoenolpyruvate regeneration requires ATP, the energetic efficiency of the C-4 pathway at low photosynthetic flux densities (PFD) becomes a balancing act between primary fixation and concentration of CO2 in mesophyll (M) cells, and CO2 reduction in bundle sheath (BS) cells. At low PFD, retro-diffusion of CO2 from BS cells, relative to the rate of bicarbonate fixation in M cells (termed leakiness phi), is known to increase. This paper investigates whether this increase in phi could be explained by incomplete inhibition of photorespiration. The PFD response of phi was measured at various O-2 partial pressures in young Zea mays plants grown at 250 (LL) and 750 mu mol m-2 s-1 PFD (HL). phi increased at low PFD and was positively correlated with O-2 partial pressure. Low PFD during growth caused BS conductance and interveinal distance to be lower in the LL plants, compared to the HL plants, which correlated with lower phi. Model analysis showed that incomplete inhibition of photorespiration, especially in the HL plants, and an increase in the relative contribution of mitochondrial respiration at low PFD could explain the observed increases in phi.

Commercial protected cultivation of shade-tolerant pot-plants in The Netherlands has expanded enormously in the last decade. Typically, very low daily light integrals are applied (3-5 mol PAR m-2 day-1), which are achieved by use of heavy screening and application of a layer of chalk (CaCO3) on the outside of the greenhouse to increase reflection of incoming irradiance. Although these low daily light integrals are meant to avoid damage by high light intensities and/or high temperatures, it is clear that they carry a production penalty, since potential crop growth is directly related to the amount of light that can be captured and efficiently used. Additionally, it remains unclear whether current daily light integrals are too conservative, which would create room for optimisation. Recently, a number of experiments have been carried out to examine the possibilities and limitations for cultivation of several shade-tolerant pot-plants at higher daily light integrals. For most species, plants could be grown faster when more light was allowed. Also, a significant reduction in energy use for heating could be achieved if more natural irradiance was allowed to enter the greenhouse. However, use of more light required higher levels of relative humidity to avoid light damage. In this paper, we present a synthesis of experiments, as well as an outlook to further improvements.