Search

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.

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.

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

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.

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.

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

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.

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.

This study tested the hypothesis that soils with a deprived biodiversity due to metal pollution are less stable than non-polluted soils, containing a more diverse community. For this, soils were sampled from specific grasslands in the Netherlands that contain elevated heavy metal concentrations (Cu, Pb and Zn). Soils that showed the largest differences in metal concentrations were incubated in the laboratory using Terrestrial Model Ecosystems (TMEs). This approach enabled simultaneous measurement of structural (bacteria, nematodes, enchytraeids, earthworms) and functional parameters (nitrogen leaching, feeding activity, CO2 production, plant growth). The highest polluted soils showed a lower bacterial growth, and decreased enchytraeid and nematode biomass and diversity, hence a deprived community. More nitrate leached from high polluted soils, while all other functional endpoints did not differ. Additional stress application of zinc and heat was used to test the stability. Zinc treatment caused effects only in the higher polluted soils, observed at several moments in time for enchytraeids, CO2 fluxes and plant growth. Heat stress caused a large reduction in enchytraeid and earthworm biomass. Ammonium leaching was decreased by heat treatments in the most polluted soils, while CO2 was increased by heat in less polluted soils. Most effects were seen in the most polluted systems and it was concluded that they seem less stable.

In the present study a commercial CFD code was used in order to investigate the dispersion of a pesticide inside an arch type tunnel greenhouse with continuous side vents. The greenhouse was cultivated with a tomato crop planted in double rows, which, during the period of measurements had a height of 1.5 m. In parallel, measurements were carried out in order to experimentally determine the decay rate of pesticide concentration. Air samples were continuously taken at seven points inside the greenhouse (six air pumps and one gas analyser). In the 3D numerical model calculations were done for several wind directions and wind speeds, using the experimental values as boundary conditions. The final solution for every case of wind direction and wind velocity was obtained, firstly by a converge solution under steady – state condition; and secondly by an unsteady one, where at the time which equals to zero the air volume in the experimental greenhouse was considered to contain a mixture consisting of air and the used pesticide. The simulation results that were in the same order of magnitude with the experimental values only during the first 5-6 minutes of unsteady solution and only qualitatively good agreement for the rest time, while the decay process was simulated. Even if different wind characteristics, as boundary conditions, were introduced in the CFD model every minute, the agreement remained in a qualitative level, showing that the concentration of the pesticide inside the greenhouse is a function not only of the greenhouse ventilation rate but also of the pesticide evaporation-volatilisation rate from the greenhouse crop, soil and cover surfaces. As the simulation model almost always underestimates the concentration levels inside the greenhouse, more investigation has to be carried out in order to obtain better agreement between measured and estimated values of pesticide concentration inside the greenhouse

Concerning the greenhouse environment, the ultimate goal of an investigation would be to determine the climatic parameters for all locations in the study area. Objective of the present study is to analyse the distribution of air temperature and air velocity of an experimental greenhouse with tomato crop, equipped with fan and pad evaporative cooling system, using geostatistical methods. The main aspects of geostatistics in terms of theoretical background for understanding spatial correlation models and kriging applications are presented. The most common variogram models were fitted to the experimental data sets obtained during summer period from an experimental greenhouse equipped with fan and pad evaporative cooling system. The Kriging approach was applied using the semivariograms corresponded to these data sets. Finally, the prediction maps of air temperature and air velocity were produced in different height levels inside the tomato crop canopy showing a great variability. Geostatistic analysis may be applied to determine not just optimal spatial predictions but also probabilities associated with risk-based analysis in order to improve the suitability and efficiency of climatic controls systems in greenhouses.

Natural ventilation to discharge excess heat and vapour from the greenhouse environment has serious drawbacks. Pests and diseases find their way through the openings; carbon dioxide fertilisation becomes inefficient and the inescapable coupling of heat and vapour release results often in sub-optimal conditions for either temperature or humidity. The present trend, therefore, is to reduce ventilation as much as possible, also in Mediterranean conditions. This relies obviously on improved means for diminishing the heat load and proper use of cooling equipment. Especially the latter can combine the benefits of cooling the greenhouse air with serious energy conservation. However, opposite to the clear benefits there are also serious investments associated with active cooling of greenhouse. Therefore, there is a growing demand for some computational tool that enables quantitive comparisons between the vast number of alternatives with respect to the different components of (semi) closed greenhouse systems. The benefits in terms of improved production (quality, ornamental value and quantity) are quite difficult to quantify, due to the complexity of the biological processes involved. On the energy side of the balance, however, since the physics of greenhouses, climate controllers and horticultural hardware can be described very well, it is quite possible to develop such a tool for predicting the energy consumption of a (semi) closed greenhouse for a wide range of horticultural and outside climate conditions. This paper gives an outline of such a tool and discusses some results. Just as an illustration, a number of quantitative effects are shown of changing the fraction of closed green¬house surface in a 1 hectare enterprise that consists of closed and non-closed compartments. This analysis is made for both a Dutch climate situation and a Mediterranean weather data set.

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.

In the last 15 years a significant increase in greenhouse area has occurred in Mexico, from a modest 50 hectares in 1990 to over 2,000 hectares in 2004. The rapid increase in greenhouse area is a result of an attractive export market, USA. Mexican summer midday temperatures are well above crop optimum and cooling is needed if heat stress induced crop growth reduction is to be prevented. The objective of this study was to determine the effectiveness and feasibility of greenhouse cooling systems for tomato culture under desert, humid tropic and temperate Mexican weather conditions. These climate regions are represented by Mexicali, Merida and Huejutla respectively. The cooling systems included a variety of passive and active systems, which through an engineering design methodology were combined to suit the climate conditions of the 3 regions. The evaluation was conducted via simulation, taking into account the most important temperature effects on crop growth and yield. The results showed that the cooling systems were effective in decreasing heat stress to plants. Investment costs of greenhouse with cooling equipment were under USD 50 m-2 and operational costs were under USD 10 m-2 for all equipment combinations and treatments except for the humid tropic climate of Merida. Solutions for Merida were both economically and physically not feasible due to too high humidity levels. This model study clearly indicates that cooling is feasible in desert and moderate climate regions of Mexico but in humid tropic climate regions feasibility is a problem. Application of design methodology and design evaluation with help of simulation greatly contributed to pointing out effective and non-effective solutions to reduce heat stress in hot climates.

Fogging systems are increasingly used to cool greenhouses and prevent water stress. More recently, fogging systems are applied also in relatively low radiation environments (such as The Netherlands), for a better control of product quality than whitewashing and to reduce need for natural ventilation ¿ thus allowing for higher CO2 concentrations to be maintained in the greenhouse. Most commonly the steering of such systems is done by setting an upper limit to the deficit of specific humidity that, whenever exceeded, triggers the fogging system. In both cases, however, one may wonder whether static and pre-fixed set points are the most effective choice. In the experiment presented in this paper, fogging and venting were controlled with the purpose of steering crop transpiration. The desired transpiration rate was the input of an algorithm that calculated on-line the required humidity and air temperature set points in view of the current weather factors. The set points were then the input of a standard P-controller that calculated vent opening and time of operation of the fogging system. In this paper, the resulting climate and actuator control operations are discussed and compared with a similar greenhouse controlled in a traditional fashion. The study concluded that a desired crop transpiration rate (an all-round indicator of crop well-being) could be used to select dynamic set points for the climate control in a greenhouse equipped with a fogging system.

An experimental greenhouse equipped with fan and pad evaporative cooling is analysed using two different models. The first one consists of a numerical simulation approach applying a commercial CFD code. The main aspects of evaporative cooling systems, in terms of heat and mass transfer and both the external and internal climatic conditions were integrated to set up the numerical model. The crop (tomato) was simulated using the equivalent porous medium approach by the addition of a momentum and energy source term. The temperature and humidity of incoming air, the operational characteristics of exhaust fans and the pressure drop occuring in the pad, were specified to set up the CFD model. The second model considers the greenhouse as a heat exchanger. Based on greenhouse structural characteristics, external climatic conditions, pad efficiency and ventilation rate, the air temperature distribution is predicted. The results, concerning the air temperature, provided both by numerical and analytical model, were validated by experimental measurements obtained at a height level of 1.2 m above the ground in the middle of the crop canopy. The correlation coefficient (R2) between computational results and experimental data was at the order of 0.96 for the numerical model and 0.77 for the analytical one, with average percentage error of 3.5% and 7.6%, respectively. The analytical model proved to be a useful simple evaluation tool, but the numerical one provides a more accurate overview of the air flow in the greenhouse showing that fan and pad evaporative cooling system could be effectively parameterized in numerical terms, in order to improve system’s efficiency

The need for a closed and sustainable water system in greenhouse areas is stimulated by the implementation in the Netherlands of the European Framework Directive. The Dutch national project Kasza: Design of a Closed Water System for the Greenhouse Horticulture will provide information how the water system in a greenhouse horticulture area can be closed. In this paper the conceptual design of two systems to close the water cycle in a greenhouse area is described. The first system with reverse osmosis system can be used in areas where desalination is required in order to be able to use the recycle water for irrigation of all crops. The second system with advanced oxidation using UV and peroxide can be applied in areas with more salt tolerant crops and good (low sodium) water sources for irrigation. Both systems are financially feasible in new greenhouse areas with substantial available recycle water.

We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis (Pergande)) and the greenhouse whitefly (Trialeurodes vaporariorum (Westwood)). In such a one-predator¿two-prey system, indirect interactions can occur between the two pest species, such as apparent competition and apparent mutualism. Whereas apparent competition is desired because it brings pest levels down, apparent mutualism is not, because it does the opposite. Because apparent competition and apparent mutualism occurs at different time scales, it is important to investigate the effects of a shared natural enemy on biological control on a time scale relevant for crop growth. We evaluated the control efficacy of the predatory mites Amblyseius swirskii (Athias-Henriot) and Euseius ovalis (Evans) in cucumber crops in greenhouse compartments with only thrips, only whiteflies or both herbivorous insects together. Each of the two predators controlled thrips, but A. swirskii reduced thrips densities the most. There was no effect of the presence of whiteflies on thrips densities. Whitefly control by each of the two predators in absence of thrips was not sufficient, yet better with E. ovalis. However, whitefly densities in presence of thrips were reduced dramatically, especially by A. swirskii. The densities of predators were up to 15 times higher in presence of both pests than in the single-pest treatments. Laboratory experiments with A. swirskii suggest that this is due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control may be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population growth. This latter phenomenon deserves more attention in experimental and theoretical work on biological control and apparent competition.

The closed greenhouse is a new development in protected cultivation. As air is not ventilated to the outside environment, CO2-concentrations are higher than in conventional greenhouses, causing 15¿20% increased production. The question remained as to whether increased air flow rates in a closed greenhouse cause photosynthetic adaptation. This was evaluated in a tomato crop that was planted in the summer of 2005 in The Netherlands in regular greenhouse compartments, in which air tubes were placed low and high in the canopy. Photosynthesis light-response curves were established at these two heights at 400, 700 and 1000 ppm of air CO2. Increased CO2 concentration and a higher position in the canopy caused an increase of the maximum photosynthetic rate, confirming earlier knowledge. However, the pattern of air circulation did not change the photosynthesis light-response curve. This corresponded with the absence of differences in total dry matter production and cumulative fruit growth. The INTKAM tomato model adequately simulated growth and development. It is therefore concluded that the pattern of air circulation did not cause adaptation of the photosynthetic apparatus, and that yield increases are attributable to the instantaneous effects of elevated CO2-concentrations.

Energy conservation in horticulture can be achieved by allowing temperatures to fluctuate within predefined bandwidths instead of using rigid set points for heating and ventilation. In temperature integration, plants are supposed to compensate effects of temporarily deviations of the average temperature some time later by deviations in the opposite direction. However, little is still known on the effects of integration periods exceeding 1 day. In this study, effects of temperature integration on growth and development of single-stemmed cut rose plants were determined. Pruned rose shoots were placed in climate chambers in which light levels switched daily (2 days integration period) or weekly (14 days integration period) from high light intensity (300 μmol m −2 s −1 ) to low light (150 μmol m −2 s −1 ). Temperatures were kept continuously at 20 °C (control) or changed with the light intensity (phase, high temperature at high light intensity, low temperature at low light intensity) or changed opposite to the light intensity (counter phase). Bandwidths of temperature integration were 0, 6 or 10 °C. Under these conditions, buds grew out to harvestable shoots in approximately 45 days. At both integration periods, shoot length was significantly reduced with increasing bandwidths of temperature integration. Shoot dry weights were reduced when a bandwidth of 10 °C was applied. At both integration periods, rates of photosynthesis were primarily determined by light intensity. However, in the counter phase treatments, photosynthesis rate at high light and low temperature was reduced compared to the high light condition of the control. Under these conditions, starch content increased to approximately 10%, suggesting a feedback inhibition of the rate of photosynthesis. However, this did not (yet) affect plant growth or development.

The combined effects of electrical conductivity (an EC of 2.5 dS m-1 or 8 dS m-1 in the root zone) and fruit pruning (three or six fruit per truss) on tomato fruit quality were studied in a greenhouse experiment, planted in January 2005. Taste-related attributes [dry matter content (DM), total soluble solids content (SSC), titratable acidity (TA), glucose, fructose and citric acid content] and health-promoting attributes (lycopene, ß-carotene, vitamin C, and total antioxidant activity) of tomato fruits harvested on the vine from the fifth or tenth truss positions were determined. The quality of tomato fruits was improved by high EC. A high EC in the root zone increased the DM content, total SSC, TA, as well as glucose, fructose and citric acid contents. A significantly higher lycopene and ß-carotene content was also observed [on a fresh weight (FW) and dry weight (DW) basis] with a high EC in the root zone. The accumulation of different compounds that determine tomato fruit quality differed between the fifth and tenth truss. In particular, the lycopene content was reduced, whereas the ß-carotene content was increased in the tenth truss with respect to the fifth truss, most likely because of higher temperatures during ripening of the tenth truss. Fruit pruning increased fruit FW by 42% and positively influenced the DM content and total anti-oxidant activity, while a negative effect was observed on lycopene and citric acid contents (on a FW and DW basis). EC and fruit pruning both had a strong effect on fruit size; however, EC had a much stronger impact on taste and health-related fruit quality attributes. A small interaction between EC and fruit pruning was found for marketable yield, fructose and glucose content, fruit firmness, and P and Ca concentrations in fruits.

This paper describes the development of software (EOM) to provide a tool for commercial growers in order to determine the site-specific effects of energy saving investments. Results consist of energy use, crop production and an extensive economic overview. The core of the software is a scientific model (KASPRO) which simulates the greenhouse climate accurately and computes the resulting energy consumption. Instead of simply adding general (manufacturer) data about the energy potentials of investments, mutual influences of a combination of investments are taken into account automatically. With the software it is easy to determine both the energetic and economical effect of e.g. a changed illumination level, a double layered greenhouse cover or the use of bio fuel. Currently the software is available for tomato, freesia, kalanchoe and chrysanthemum growers

Soil grown greenhouse crops require high fertilisation rates. Combined with the common practice of over-irrigation, leaching of nutrients is a serious problem. In order to reduce the environmental impact, a `fertigation¿ model was developed as a decision support system for irrigation and fertiliser supply. The applicability in growers practice was evaluated during two years on commercial nurseries, growing chrysanthemum (Dendranthema grandiflorum). The evaluation was performed by comparison of the actual water and irrigation strategy of the growers with the strategy recommended by the model in a specific section within the same greenhouse. At one chrysanthemum grower a lysimeter was installed to measure water and nutrient leaching. The model performed well in general, without any yield or quality decline by using the model. The irrigation and the nitrogen surplus were decreased significantly compared to the growers standard and consequently reduced the environmental impact. The results indicate also that application of this model depends highly on the growers¿ attitude towards the environmental impact of irrigation and fertilisation at one hand and the avoidance of risks at the other

Temperature control on the basis of a crop¿s physiology offers advantages over a control that avoids strong climate fluctuations. The assimilate balance, defined as the ratio between the supply of and demand for assimilates, enables a radiation-dependent temperature regulation. The INTKAM crop growth model and KASPRO greenhouse model were coupled, and were combined with an optimization module to evaluate the potential of this regulation. The simulation study resulted for cucumber in all growing seasons in production increase or reduced energy consumption. Annual figures were 5.25 m3 m-2 gas reduction or 4.4 kg m-2 production increase. The underlying mechanisms include a more stable and greater dry matter partitioning to the fruits, and more stable fruit size, length and age.

A greenhouse cooling system with heat storage for completely closed greenhouses has been designed, based on the use of a fine wire heat exchanger. The performance of the fine wire heat exchangers was tested under laboratory conditions and in a small greenhouse compartment. The effects of the system on the environmental conditions (temperature and humidity distribution) in the greenhouse were simulated to decide on the final lay out of the system. Finally the system was implemented on a large scale in a pot plant greenhouse complex of 2500 m². The system is being tested under practical conditions and compared to a traditional heating and ventilation system in a comparable reference compartment of 2500 m². This paper describes the set up of the greenhouse system, the first simulation results achieved with the system with respect to environmental conditions and energy use.

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 ¿mol 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 ¿mol 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 CO2 on potential production. Maximum levels of 110, 64 and 168 kg m-2 year-1 were calculated for tomato, sweet pepper and cucumber, respectively.

This paper reviews the state of the art and future perspective of greenhouse mechanization. Driving forces for mechanization are identified. Dutch greenhouse crop production is used as an example. Analysis of a generic crop production process combined with a review of the state of the art in greenhouse mechanization revealed that the first phases of plant production such as seeding, cutting, grafting and transplanting as well as the final phase of crop production including sorting and packing the harvested produce are mechanised. Those tasks do not require much human intelligence and/or fast and accurate eye-hand coordination. The available machines are largely based on principles of industrial automation consisting of mechanical solutions with only a limited amount of sensors and `intelligence¿ used. The next ten years, the available line of machines will be redesigned, extended and optimised. The middle phase of crop production including crop maintenance and harvest does not show much automation yet. Maintaining the crop and harvesting do rely on human intelligence and ability and are much more difficult to automate. The next ten years will show the advent of the next generation machines that will be based on the principles of mechatronics and robotics, combining smart mechanical design with sensors and `artificial intelligence¿ to achieve the fast and accurate eye-hand coordination needed for these difficult tasks. This trend is supported by the commercial development of a strawberry harvester in Japan and a rose harvesting robot and tomato de-leafing robot in the Netherlands. It is concluded that the slow progress in the field of robotic harvesting is to a large extent due to uncertainty in the working environment of the robot as a result of biological variability and the typical structure of the growing systems used. Progress in the field of greenhouse robotics therefore will not only rely on innovations in the field of robot technology but also on necessary innovations in the field of growing systems and plant breeding to reduce variability and thus to simplify the task

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 CO2 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

The WET-sensor is a frequency domain dielectric sensor that measures permittivity, conductivity and temperature, which can be used for monitoring soil water content and electrical conductivity in horticulture. By using a specific model it measures pore water conductivity as well. However, under practical circumstances, large errors have been observed using the existing model. The purpose of this study was to obtain a empirical correction for this model and to investigate the nature of the errors, so horticultural growers can use the WET-sensor to measure pore water EC in-situ. Using 36 potted samples of sand, clay and peat, the relation between permittivity, bulk EC and pore water EC was studied in a laboratory over a temperature range from 19-22 oC and a pore water EC range from 4 ¿ 12 mS/cm. This resulted in an adaptation of the constant in the existing model and an extra second order polynomial correction factor. After temperature correction, an overall linear fit with a coefficient of 0.9948 was found at a reasonable correlation (0.79). Errors may occur up to ±40%, but for permittivity values larger than 20, errors have a maximum of ±15%. The overall standard deviation is 15%, which is in accordance with simulated results. For growers using relatively wet soils at water contents above 20%, the WET-sensor can be used to measure pore water EC in situ with a reasonable accuracy. Further study is needed to explore this correction at larger temperature ranges and for more soil types

A hitherto unknown single nucleocapsid nucleopolyhedrovirus (SNPV) with a unique property was isolated from larvae of the looper Chrysodeixis chalcites (Lepidoptera, Noctuidae, Plusiinae). Polyhedrin, lef-8, and pif-2 gene sequences were obtained by PCR with degenerate primers and used for phylogenetic analysis. ChchNPV belonged to class II NPVs and its polyhedrin sequence was most similar to that of class II NPVs of other members of the subfamily Plusiinae. Further genetic characterization involved the random cloning of HindIII fragments into a plasmid vector and analysis by end-in sequencing. A gene so far unique to baculoviruses was identified, which encodes a putative DNA repair enzyme: cyclobutane pyrimidine dimer (CPD) DNA photolyase (dpl). The transcriptional activity of this gene was demonstrated in both ChchNPV-infected C. chalcites larvae and infected Trichoplusia W High Five cells by RT-PCR and 5' and 3' RACE analysis. The possible role of this gene in the biology of the virus is discussed. (C) 2004 Elsevier Inc. All rights reserved.

Modelling quality in pot plants is still a weak feature in crop modelling research. This work aims at building a conceptual dynamic model for external quality (plant height and number of flower heads) in Kalanchoe blossfeldiana. Four experiments were conducted to quantify the effects of temperature and spacing schedules at two different planting dates. Five constant temperatures (18, 20, 22, 24 and 26°C) and nine spacing schedules, resulting from combinations of spacing at a given leaf area index (LAI: 1.6, 2, 3, 4 and 4.4) into a final plant density (31.1, 34.6, 43.4, 52.0 and 55.6 plants m-2) were studied. Stem length was modelled as the number of internodes (same as number of leaf pairs) times the average internode length. Plant height results from the stem length plus the uppermost pedicel length. The spacing schedules did not affect plant height, but total aerial dry mass (TDM, g plant-1), leaf area and number of flower heads were increased at earlier and wider spacing. In contrast, temperature had a significant effect on the average internode length (internode elongation rate linearly increased with temperature) and on the generative length (optimum response to temperature). However, internode appearance rate was not affected by temperature. Number of flower heads showed a positive linear relationship with TDM. Therefore, by simulating TDM the number of flower heads can be predicted. TDM was simulated based on the intercepted photosynthetic active radiation and light use efficiency. The reaction time showed a quadratic response to temperature, with a maximum rate of progress to flower at 23°C (10 days delay at 18°C). These modules need to be validated to form the basis of a year-round decision support system for Kalanchoe.

For testing phytotoxicity many methods have been developed. In this experiment some methods are compared. Tests with development of cucumber cotyledons, luminescence of bacteria, growth of duckweed and root growth of germinating seeds of kohlrabi and garden cress are compared. All tests were suitable but the bioassay where development of cucumber cotyledons is determined and the luminescence of bacteria were the most practicable. The different bioassays give comparable results but they cannot always be converted directly. The different bioassays can be used when in a short time results are needed or when experience has learned that e.g. phytotoxic substances can be expected from a certain production process. For a more robust general bioassay an adapted version of ISO 11269-2 (1995) standard for testing the soil quality looks promising, although the adaptations still have to be tested.

Green potato (Solanum tuberosum L.) tubers are rejected by the processing industry. Therefore their amount should be reduced to minimum. The objective of this study was to assess the reduction of greening of new French fry varieties in experiments conducted from 1998 to 2001 on ridge qualities like geometry and the compression and crumbling degree of the loose soil in the ridge. The experiments were mainly carried out on the experimental husbandry farm Westmaas on a Calcaric Fluvisol having a clay content of ca. 200 g kg−1. French fry potato varieties used were Agria and Fambo, whereas Bintje was used as a reference. Row spacings were 0.75 m (30 in.) and 0.90 m (36 in.). Net ridge size was determined by the internal height (distance between the plate and the top of the ridge) and by the width of the top of the ridge combined with planting near the surface of the plate. For the traditional French fry variety Bintje a reduction in greening was achieved by ridges having a gross size of 0.06–0.07 m2. New French fry potato varieties like Agria and Fambo, however, are characterized by higher yields, larger cluster widths and longer tubers than Bintje. These properties favor the greening of tubers and require adjustment of the ridge geometry. Increase of the internal height and of the top width were found to be crucial to reduce greening of tubers to minimum. An increase of the top width of standard 0.75 m ridges from 0.15–0.18 to 0.25 m combined with an internal height of 0.18–0.20 m was realized by the so-called plateau ridges. This ridge type required ca. 0.04 m deeper seedbed than the depth of the seedbed for standard 0.75 m ridges. Without deeper loosening of the seedbed such larger ridges could also be realized by an increase of row spacing to 0.90 m. Net yields of new French fry varieties of plateau and 0.90 m ridges were generally similar or higher than the yields of standard 0.75 m ridges with the same internal height. With 0.90 m ridges over-sizing occurred sometimes. Greening of new varieties of French fry potatoes was reduced to minimum by the new knowledge on ridge geometry: an increase of the internal ridge height to 0.18–0.20 m, a top width to 0.25 m and reduction of cracking by relatively coarse, non-compressed ridges.

In a 14 month pot experiment with Anthurium andreanum cv. Sonate, grown in soil-less medium in glasshouse conditions, burrowing nematode (Radopholus similis) population development and crop damage were investigated. At 9 days after transplanting, plants were inoculated with R. similis at four initial densities (Pi): 0, 100, 1000 and 10 000 per pot. Three to 5 months after inoculation R. similis populations reached maximum densities ranging from 59 000 to 112 000 per pot in roots and from 500 to 1150 per litre of drainage water. The greatest densities occurred at the smallest Pi. Subsequently, nematode populations decreased in the decreasing root mass. Fourteen months after inoculation, root systems of nematode-inoculated treatments were almost completely necrotic and root weights were reduced by 84-91% compared to those of non-inoculated plants. In response to the deteriorating root systems, plant vigour of all nematode-inoculated treatments declined tremendously and flower production was significantly less compared to non-inoculated plants at 6 months after inoculation. During the last 2 months of the experiment, reductions in flowers ranged from 46-70% (number), 30-53% (weight), 19-33% (stem length) and 15-31% (width). The total yield losses of these flower growth parameters, calculated over the 14-month experimental period, ranged from 18-33, 15-35, 9-19 and 6-15%, respectively. Greatest reductions occurred in plants in the treatment with the greatest Pi. In these conditions, the damage threshold was calculated to be equal to or fewer than 100 R. similis per pot.

Plants use diffuse light more efficiently than direct light. However, experimental comparisons between diffuse and direct light have been obscured by co-occurring differences in environmental conditions (e.g. light intensity). This study aims to analyse the factors that contribute to an increase in crop photosynthesis in diffuse light and to quantify their relative contribution under different levels of diffuseness at similar light intensities. The hypothesis is that the enhancement of crop photosynthesis in diffuse light results not only from the direct effects of more uniform vertical and horizontal light distribution in the crop canopy, but also from crop physiological and morphological acclimation. Tomato (Solanum lycopersicum) crops were grown in three greenhouse compartments that were covered by glass with different degrees of light diffuseness (0, 45 and 71 % of the direct light being converted into diffuse light) while maintaining similar light transmission. Measurements of horizontal and vertical photosynthetic photon flux density (PPFD) distribution in the crop, leaf photosynthesis light response curves and leaf area index (LAI) were used to quantify each factor's contribution to an increase in crop photosynthesis in diffuse light. In addition, leaf temperature, photoinhibition, and leaf biochemical and anatomical properties were studied. The highest degree of light diffuseness (71 %) increased the calculated crop photosynthesis by 7 center dot 2 %. This effect was mainly attributed to a more uniform horizontal (33 % of the total effect) and vertical PPFD distribution (21 %) in the crop. In addition, plants acclimated to the high level of diffuseness by gaining a higher photosynthetic capacity of leaves in the middle of the crop and a higher LAI, which contributed 23 and 13 %, respectively, to the total increase in crop photosynthesis in diffuse light. Moreover, diffuse light resulted in lower leaf temperatures and less photoinhibition at the top of the canopy when global irradiance was high. Diffuse light enhanced crop photosynthesis. A more uniform horizontal PPFD distribution played the most important role in this enhancement, and a more uniform vertical PPFD distribution and higher leaf photosynthetic capacity contributed more to the enhancement of crop photosynthesis than did higher values of LAI.

Background and Aims: Fruit set in indeterminate plant species largely depends on the balance between source and sink strength. Plants of these species show fluctuations in fruit set during the growing season. It was tested whether differences in fruit sink strength among the cultivars explained the differences in fruit-set patterns. Methods: Capsicum was chosen as a model plant. Six cultivars with differences in fruit set, fruit size and plant growth were evaluated in a greenhouse experiment. Fruit-set patterns, generative and vegetative sink strength, source strength and the source : sink ratio at fruit set were determined. Sink strength was quantified as potential growth rate. Fruit set was related to total fruit sink strength and the source : sink ratio. The effect of differences observed in above-mentioned parameters on fruit-set patterns was examined using a simple simulation model. Key Results: Sink strengths of individual fruits differed greatly among cultivars. Week-to-week fruit set in large-fruited cultivars fluctuated due to large fluctuations in total fruit sink strength, but in small-fruited cultivars, total fruit sink strength and fruit set were relatively constant. Large variations in week-to-week fruit set were correlated with a low fruit-set percentage. The source : sink threshold for fruit set was higher in large-fruited cultivars. Simulations showed that within the range of parameter values found in the experiment, fruit sink strength and source : sink threshold for fruit set had the largest impact on fruit set: an increase in these parameters decreased the average percentage fruit set and increased variation in weekly fruit set. Both were needed to explain the fruit-set patterns observed. The differences observed in the other parameters (e.g. source strength) had a lower effect on fruit set. Conclusions: Both individual fruit sink strength and the source : sink threshold for fruit set were needed to explain the differences observed between fruit-set patterns of the six cultivars

In greenhouse industry fertilizers as well as soil improvers are widely used. Fertilizers are mainly applied to optimize the physical-chemical conditions of the root environment and are used for growing in soils in situ as well as for growing in substrates. Soil improvers are materials solely added to soils in situ primarily to maintain or improve its physical properties, but it also can improve its chemical and biological properties. Thus the difference between fertilizers and soil improvers is somewhat diffuse.

In this paper the design and development of a new type of greenhouse with an integrated filter for reflecting near infrared radiation (NIR) and a solar energy delivery system is described. Especially the optical parts as the spectral selective film, the properties of the circular reflector and the efficiencies of photo voltaic cells are studied. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated. It has to block up to 35% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity. The second measure is the integration with a solar energy system. When the NIR reflecting coating is designed as a circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PhotoVoltaic (PV) cell in the focus point delivers electric energy. With a ray tracing computer program the optimal geometry of the reflector was designed with respect to the collecting efficiency. The PV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (geometric concentration factor of 30). The properties of different PV materials were investigated to find the optimal cell for this application. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. All parts are integrated in a 100m2 prototype greenhouse which will be applied for the proof of principle.

The word fertigation is derived by a composition from the words fertilization and irrigation and the action expressed by it is exactly what the word suggests: fertilization and irrigation in one activity. Since long years fertigation is a common practise in greenhouse industry. The development of this method of fertilizer supply originated from the fifties of the 20th century. In these years a beginning was made with drip irrigation and the small spots wetted by this type of irrigation did not offer any possibilities for top dressings by hand. Therefore with the introduction of drip irrigation also fertilizer diluters were introduced with which concentrated fertilizer solutions could be added to irrigation water streams. Different diluter systems have been developed, but the dilutions realised with these systems were not very precisely. This was not a strong handicap in the beginning, because the water irrigated was supplied by drip irrigation and did not touch the plant canopy. Thus, an accidental somewhat high concentration of fertilizers in the irrigation water did not affect the plant negatively. Afterwards, control and adjustments on the applied quantity of fertilizer always was possible and utmost, in that period the addition was still traditionally based on quantities of fertilizer per area. Later on, when overhead irrigation by sprinkler irrigation was developed, as a matter of course precise dilutions were required. This was essential for overhead sprinkling to prevent leaf damage by possibly high concentrations of fertilizers, as a result of an inaccurate function of the equipment. This precise addition of fertilizers was developed by on line measurement of the electrical conductivity (EC) of the irrigation water combined with injectors for the dosage of concentrated nutrient solution in the water stream. The increase of the EC in the irrigation water was used as a unit for the fertilizer concentration. The once attuned concentration is controlled by proportional adjustment of the injectors on basis of continuously measurements of the EC.

Nutrient solutions intended for plant growth are already used from the middle of the 19th century, when the importance of mineral elements for plant growth was made clear by Justus von Liebig. In advance, the nutrient solutions used to grow plants in so called “water cultures” had a simple composition and consisted of salts like KNO3, Ca(NO3)2, KHPO4, MgSO4, and a little Fe-compound (Hoagland and Arnon, 1950), thus, containing all the major elements and some Fe. The relative success with these solutions will be due to the not knowingly supplied micro nutrients from the impurities of the chemicals and fertilizers used to compose the solutions. It can be supposed that the impurities contained sufficient micronutrients, to prevent the crops grown from serious nutrient disorders. Knowledge about the necessity of micro nutrients for plant growth was mainly gathered in the first half of the 20th century (Marschner, 1997), when the purification of fertilizers and chemicals were improved. The first systematic description for the preparation of nutrient solutions was given by Hoagland and Arnon (1950) and since then in many publications reference is given to them, when one or another nutrient solution is used to grow plants in soilless cultivation systems.

Tissue tests are widely used in horticulture practice and have in comparison with soil or substrate testing advantages as well disadvantages in comparison with soil testing. One of the main advantages of tissue tests is the certainty that analysed nutrients in plant tissues are really present in the tissue analysed, while analytical data of soil and substrate testing only estimate the availability of nutrients to plants. There is no guarantee that nutrients determined in the root environment as available quantities will be absorbed by plants. Numerous factors can hinder or stimulate the uptake by plants of nutrients determined with soil and substrate testing as being sufficiently available for that. The best known example of such a hindrance or stimulation is the root zone temperature. Low root zone temperature generally reduces shoot tissue concentrations, whereby Ca, P and Mg are mostly more affected than N and K. But shoot tissue concentrations also can be negatively affected by evidently too high root zone temperatures. The effects differ for crops and growing conditions (Daskalaki and Burrage, 1998; Ikeda and Osawa, 1984; Moustafa and Morgan, 1984). Huge effects on nutrient concentrations in plant tissues occur, when crops are grown at root temperature far below the optimum for crop development (Ali et al., 1994). Another example of a factor that can affect the uptake of some minerals is the use of root stocks. The effect of grafting apparently differs for crops and probably rootstocks. Baas (1998) found for rose a stimulation of the uptake of B by grafting, while Edelstein et al. (2005) reported for melons a reduced B uptake for grafted plants when compared with non grafted. The effects also differ for elements. Cabrera (2002) using the same rootstock “Natal Briar” with roses like Baas (1998) found besides a higher uptake of B also higher uptakes of Cl, Na and Mg, while P, K and Fe were significantly decreased by grafting.

Laboratory tests, which give a reliable indication of the performance of the medium with respect to water, nutrient, and oxygen availabilities on the short and long term, are normally more cost-effective, and can be performed under standardized conditions with reference samples. It is therefore logical that analytical methods, mostly adopted from soil science analytical methods, have become available as part of the selection process of growing media and for setting soilless growing media standards. Such analyses can be physical, chemical, or biological. Methods of physical analysis include determination of bulk density, determination of porosity, measurement of particle size, water retention and air content, defining the rewetting curve, rehydration rate and hydrophobicity, measuring shrinkage, saturated hydraulic conductivity, unsaturated hydraulic conductivity, oxygen diffusion, penetrability, and determining hardness and stickiness. The chemical analysis determines the water-soluble elements (1:1.5 volume method, 1:3 substrate solution method, 1:5 method, and pour through method), exchangeable, semi- and non-water soluble elements (calcium chloride/DTPA method, 0.1 M barium chloride 1:1.5 volume method, and active manganese method), pH in loose media, nitrogen immobilization, and calcium carbonate content. Finally, the biological analysis determines the stability, potential biodegradability, heat evolution, and respiration rate by oxygen consumption. It employs the solvita test, weed test, and growth test.