C. Stanghellini

Plant water relations as affected by osmotic potential of the nutrient solution and potential transpiration in tomato (Lycopersicon esculentum Mill.)

Summary The hypothesis that water flow into tomato fruits is affected similarly by osmotic potential of the nutrient solution and potential transpiration (shoot environment) via their effects on stem water potential, was tested through experiments carried out in two glasshouses where climate was controlled to maintain a desired potential transpiration rate (normal and depressed, respectively). This climate treatment was factorially combined with a root zone osmotic potential treatment, whereby two values of osmotic potential were compared in each experiment. Data showed that water uptake per unit leaf area was not affected by osmotic potential of the nutrient solution. The hydraulic resistance within the plant, deduced from measurements of leaf and stem water potential, was independent of the transpiration flow and was not affected by the osmotic potential of the nutrient solution. Water import into the fruit was affected by both treatments and was correlated with the water potential gradient between the stem and the fruit. Since fruit osmotic potential was relatively constant at a given concentration of the nutrient solution, the stem water potential appeared to be a good indicator of fruit growth rate.

Response of tomato plants to a step-change in root zone salinity, under two different transpiration regimes

The response of a tomato crop to a step-change in salinity was investigated under different potential transpiration conditions. A crop growing for 5 months under saline irrigation water (EC 9 dS m−1) was given thereafter a standard nutrient solution with an EC of 2 dS m−1. The previous effects of salinity were largely reversed, especially for fruits and leaves that had not yet reached the rapid growth phase. After a period of 8 weeks, the final weight of fruits reached that of “normal” (EC 2 dS m−1) fruits. There was a high incidence of fruit cracking, even greater in the low transpiration treatment than the high one. The peak incidence of cracking was in fruits that were harvested some 25 days after lowering the EC. The chance of cracking was positively affected by the increase in skin expansion rate due to a change in EC and further enhanced by reduced potential transpiration (high ambient humidity). New leaves formed after the EC was lowered were comparable with those grown in low EC, but leaves that were fully expanded at that moment did not respond to the change in EC.

Growing fresh food on future space missions: Environmental conditions and crop management

Highlights • Fresh food can be produced under limited space and energy conditions providing 11 kg m-2 week-1 (leafy greens, herbs, radish, tomato and cucumber).• Applying spread harvest (weekly harvesting the oldest leaves of leafy greens) and increasing plant density increases fresh food production.• The quality of leafy greens often deteriorated at higher light intensities (600 μmol m-2 s-1).• The presented crop growth recipes and management will be applied in a mobile test facility at the Neumayer III Antarctic research station.

The functional dependence of canopy conductance on water vapor pressure deficit revisited

Current research seeking to relate between ambient water vapor deficit (D) and foliage conductance (gF) derives a canopy conductance (gW) from measured transpiration by inverting the coupled transpiration model to yield gW = m − n ln(D) where m and n are fitting parameters. In contrast, this paper demonstrates that the relation between coupled gW and D is gW = AP/D + B, where P is the barometric pressure, A is the radiative term, and B is the convective term coefficient of the Penman-Monteith equation. A and B are functions of gF and of meteorological parameters but are mathematically independent of D. Keeping A and B constant implies constancy of gF. With these premises, the derived gW is a hyperbolic function of D resembling the logarithmic expression, in contradiction with the pre-set constancy of gF. Calculations with random inputs that ensure independence between gF and D reproduce published experimental scatter plots that display a dependence between gW and D in contradiction with the premises. For this reason, the dependence of gW on D is a computational artifact unrelated to any real effect of ambient humidity on stomatal aperture and closure. Data collected in a maize field confirm the inadequacy of the logarithmic function to quantify the relation between canopy conductance and vapor pressure deficit.

Technology for Rooftop Greenhouses

Rooftop greenhouses (RTGs) can generate significant advantages provided RTGs and buildings are connected in terms of energy, water and CO2 flows. Beyond the production of high-value crops, environmental benefits such as re-use of waste water, application of residual heat and absorption of carbon dioxide are derived from urban RTGs. Social benefits viz the creation of employment, social cohesion and so on are also important assets of RTGs. This chapter is focussed on RTGs technology. RTG share many common aspects with conventional greenhouses, but at the same time RTGs show attributes that should be discussed separately. Synergies such as using residual heat, rain water for irrigation, CO2 exchange, etc. are part of the common metabolism greenhouse-building. This chapter will concentrate on the available technology from conventional greenhouses which is more suitable for RTGs, particularly concerning greenhouse structure, covering materials, climate control and soilless cultivation systems.

GREENHOUSE DESIGN AND CLIMATE MANAGEMENT SUITABLE FOR SUBTROPICAL SUMMER CONDITIONS IN CHINA

Adaptation of greenhouse climate management strategy to local climate conditions is very important for the improvement of resource use efficiency of greenhouse crop production. The objectives of this study were to explore the alternatives of the existing greenhouse climate control policy under Chinese subtropical climate conditions, through simulation analysis. Based on the calibrated and validated the Greenhouse Process (KASPRO) model using experimental data from a Dutch Venlo-type glass greenhouse in Shanghai, China, scenario studies were carried out to investigate the possible responses of crop biomass production to affordable means of climate management. In this paper we limited the study to greenhouse ventilation capacity, and canopy size, in a greenhouse without injection of CO2. The results show that for a cucumber crop under the summer conditions typical of Shanghai, an average of 26 volume changes per hour is required, which, in view of the prevailing wind speed, is ensured by a ratio of roof window area to greenhouse floor area about 0.3 (it is about 0.1 in Holland, for instance). A LAI of 4 maximizes crop biomass production, when accounting for the balance of assimilation, respiration and also for the evaporative cooling. The results obtained in this study show that many local climate factors must be taken into account for an optimal management of greenhouse design, crop and climate, and that a greenhouse climate simulator is a good tool for this analysis. INTRODUCTION Glasshouses originated in the temperate zones of the Northern hemisphere, mainly for getting subtropical plants through relatively cold winters. Thanks to the increasing cheapness of plastic films, an enormous expansion of protected cultivations has taken place during the last 20 years in subtropical regions. Millions of hectares of unheated plastic structures have sprouted up in the Mediterranean region, southern United States and China, just to name the most important regions. Most are one-crop tunnels that are taken out as soon as climate conditions allow for unprotected growth. However, the need of increasing productivity is causing the quality (and the worth) of the structures to grow so much that the financial investment must be retrieved through multi-year use, with the challenge of growing protected crop also during the summer, when solar radiation heats the air inside the structure, and the cover prevents adequate exchange with the colder upper atmosphere. Getting rid of the heat load is the major concern for greenhouse climate management in such conditions. This can be realised by 1) reducing the income of radiation; 2) removing the extra heat through air exchange; 3) increasing the fraction of energy partitioned into latent heat. In order to explore means of relieving greenhouse heat load in hot summers, many researches on shading, natural ventilation and evaporative cooling, mainly for the Mediterranean regions, have been reported, whereas few researches on greenhouse cooling have been devoted to the areas with hot and humid summers. Most of the existing reports focus on explaining how those means affects greenhouse microclimate (Baille et Proc. IC on Greensys Eds.: G. van Straten et al. Acta Hort. 691, ISHS 2005 830 al., 1994; Hayashi et al., 1998; Boulard et al., 1999). Those studies demonstrated that shading (Bailey, 2000; Castilla, 2001; Baille et al., 2001) and evaporative cooling (Giacomelli et al., 1985; Al Massoum et al., 1998; Arbel et al., 1999; Montero, 2001; Kittas et al., 2001) are effective means for relieving greenhouse heat load, under dry and sunny summer climate conditions in the Mediterranean area. In subtropical areas where the summer is hot, humid and less windy (Table 1), shading and active evaporative cooling may not work as effectively as they do in the Mediterranean area. Willits (2000) studied the effectiveness of different cooling means in a greenhouse with tomato crops, under summer climate conditions in the Eastern United States, where the summer is hot and humid. The results show that shading (with a shadow screen) decreases greenhouse air temperature very little, and that the most effective means for reducing greenhouse air temperature were increasing canopy density, ventilation rate, and active evaporation cooling. Active evaporation cooling (sprinkling, misting, and water pad plus forced ventilation) which needs a large wet bulb depression to be effective, however, is more expensive due to the requirement of high quality water (for sprinkling and misting) and electricity (for forced ventilation). As Table 1 makes clear, summer climate in subtropical China is hot and humid, and the solar radiation is a lot lower than that in the Mediterranean region, due to a shorter day length in the summer, and more cloudiness (seasonal rainfall). Permanent greenhouse shading may greatly reduce the crop production wherever solar radiation is the factor limiting assimilation for a large fraction of the time. Under humid climate conditions, greenhouse evaporative cooling will not be as effective as under dry climate conditions. In addition, very few and inexpensive means are available (and affordable) for climate manipulation in most greenhouses in the Shanghai area and many others regions where development is presently taking place. In fact, only shading, natural ventilation and passive evaporative cooling are inexpensive ways to cool down the greenhouse. Wang et al. (2001) experimentally investigated cooling measures in a Chinese solar greenhouse. But both Willits (2000) and Wang et al. (2001) did not consider the response of crop production to those cooling measures, hence could not quantitatively optimise the cooling control. Therefore, there is a need to develop a blue-print for optimal management in such conditions, that is to assess how such inexpensive greenhouse cooling measures as natural ventilation, shading and passive evaporative cooling (crop transpiration) will affect crop production, under the summer climate conditions typical of subtropical China. To answer this question, scenario studies were carried out to investigate the possible responses of crop biomass production to greenhouse ventilation capacity and canopy size, for the hottest period of the year (July 15 to August, 15). MATERIALS AND METHODS The greenhouse (KAS, in Dutch) process (KASPRO) model was used in this study. The KASPRO model is constructed from modules describing the physics of mass and energy transport in the greenhouse enclosure, and a large number of modules that simulate the customary greenhouse climate controllers. Thus, the model takes full account of mutual dependencies between greenhouse characteristics and climate control. The simulation of the greenhouse physical processes comprises separate computation of convective and radiative heat exchange and also includes latent heat fluxes associated with evaporation. The climate controller of KASPRO enables climate management by means of heating, ventilation, de-humidification, moistening, shading, artificial illumination and carbon dioxide supply. For the full description of the KASPRO model, the readers are referred to de Zwart (1996). The KASPRO model was calibrated and validated in our previous study (Luo et al., 2005). Thereafter, a scenario analysis was done for the hottest period (July 15 to August, 15) in 2002, during which we had a cucumber crop in the greenhouse and data of both inside and outside climate. Weather conditions outside the greenhouse during the studied period are listed in Table 2. Carbon dioxide injection, a feature that greatly determines optimal ventilation rate, is seldom available in low-investment greenhouses, therefore we did not account for