Effect of nocturnal ventilation on the occurrence of Botrytis cinerea in Mediterranean unheated tomato greenhouses

Botrytis cinerea is the causal agent of grey mould disease which is one of the most important diseases affecting tomato crops in unheated greenhouses. Nocturnal ventilation is a technique that can be used to reduce relative humidity inside unheated greenhouses. The main objectives of this research were to investigate the effect of ventilation management on the environmental conditions and on the disease severity, to develop and validate a model which could predict disease severity and to present a warning system. Experiments were conducted in two plastic greenhouses. Two natural ventilation treatments were randomly assigned to the greenhouses. One was nocturnal ventilation (NV), with the vents open during the day and night, while the other was classical ventilation (CV), in which the vents were open during the day and closed during the night. A tomato crop was grown directly in the soil between the end of February and the end of July during two crop seasons. Climatic data were measured with three meteorological stations, averaged and recorded on an hourly basis. The number of diseased leaflets were counted and removed from the greenhouse. In the NV greenhouse a significant reduction of air humidity and disease appearance was observed. A warning system was developed and can be a useful tool for helping to decide on appropriate actions and the correct timing to avoid conditions that favour disease development. For a more practical application, disease risk levels were defined as a function of the duration of periods with RH > 90%

Natural ventilation of greenhouses. Comparison of measured and predicted ventilation rates.

Ventilation is one of the most important tools for controlling the greenhouse climate. The air exchange between inside and outside of a greenhouse influences the environmental conditions such as temperature, humidity and carbon dioxide concentration of the enclosure which affect the development and production of the crop. In winter, ventilation must remove the excess water vapour while during summer cooling is the main reason for ventilation. Natural ventilation is the result of the action of two natural forces, wind and thermal buoyancy. Some models of natural ventilation are described. Various techniques have been used to determine ventilation and leakage rates such as tracer gas and energy balances. The energy balance is based on the energy removed by ventilation from the greenhouse as a way of preventing excessively high temperatures. Tracer gas techniques are based on mass balances and are used mostly to measure ventilation rates directly in greenhouses. It seems that the tracer gas technique gives greater accuracy than the energy balance at low ventilation rates. The difficulty of using the energy balance is the large number of variables involved and the required accuracy in their measurement. In this study, ventilation rate was measured using the decay tracer gas method for leeward ventilators opened to 10 and 20%. It was found that wind speed had a strong influence on ventilation rates and a linear relation was obtained. Ventilation rates were predicted using the energy balance method and a model based on wind and buoyancy forces proposed by Boulard and Baille (1995), assuming that total ventilation is due to the combined effect of both natural forces. It was found that the energy balance gives better results for higher ventilator apertures. In the case of the model based on wind and buoyancy forces good agreement was obtained between measured and predicted ventilation rates for both ventilator positions

Nocturnal Ventilation For Controling Greenhouse Humidity and Botrytis Cinerea Severity In Unheated Tomato Greenhouses

Grey mould disease is one of the most important diseases affecting crops grown in unheated greenhouses, where ventilation is the main technique used to control inside environmental conditions. The main goal of this investigation was to study the influence of nocturnal ventilation on the humidity conditions in unheated tomato greenhouses and the consequences for Botrytis cinerea control. Experimental work was realised at the High Institute of Agronomy in Lisbon in two identical adjacent double-span greenhouses covered with three layer co-extruded plastic film. Two different natural ventilation treatments were randomly assigned to the greenhouses, being one treatment nocturnal or permanent ventilation (PV), with the vents open during the day and night and the other classical ventilation (CV), in which the vents were open during the day and closed during the night. Inside the nocturnally ventilated greenhouse air humidity was significantly reduced comparing with the classical ventilated greenhouse. Also, it was observed a great contribution to reducing disease severity on tomato leaves caused by B. cinerea

Comparion of humidity conditions in unheated tomato greenhouses with different natural ventilation management and implications for climate and Botrytis cinerea control

The objective of the research was to investigate the influence of nocturnal ventilation on the humidity conditions in unheated tomato greenhouses and the consequences for Botrytis cinerea control. Experiments were carried out at the Instituto Superior de Agronomia in Lisbon in two identical adjacent double-span greenhouses covered with three layer co-extruded film. The climate was controlled by natural ventilation, using continuous apertures located on the roof and side walls over the entire length of the greenhouses. Two different natural ventilation treatments were randomly assigned to the greenhouses. One treatment was permanent ventilation (PV), with the vents open during the day and night, while the other was classical ventilation (CV), in which the vents were open during the day and closed during the night. A spring tomato crop (Lycopersicon esculentum Miller), cultivar Zapata was grown directly in the soil between the end of February and the end of July. The growing technique was the usual for greenhouse tomatoes in Portugal. Trickle ferti-irrigation tubes were located between each two rows of plants. Climatic data were measured with three meteorological stations, one located in the centre of each greenhouse and one outside. All data were averaged and recorded on an hourly basis using two data logger systems. The number of leaflets with lesions caused by B. cinerea were counted and removed from the greenhouse from the randomly selected groups of plants. A significant reduction of air humidity occurred in the nocturnally ventilated greenhouse. Nocturnal or permanent ventilation was shown to give a great contribution to reducing disease severity on tomato leaves caused by B. cinerea. Nocturnal ventilation management is an environmental control technique which can be used as a prophylactic control measure, since it reduces the severity of B. cinerea on tomato crops grown in unheated greenhouses, enabling a reduction in chemical use and lowering both production costs and environmental impacts

Measuring and Modelling Transpiration Versus Evapotranspiration of a Tomato Crop Grown on Soil in a Mediterranean Greenhouse

The main sources of water vapour in a greenhouse are plant transpiration and the evaporation of water from soil (evapotranspiration). These processes are influ- enced by environmental factors such as solar radiation and water vapour pressure deficit, as shown by the Penman-Monteith equation. Most previous studies have been conducted in Northern countries and with soiless crops, which means that they only refer to transpiration. In Mediterranean greenhouses many crops are still grown on soil, so evaporation adds another component to the water vapour balance. The purpose of this study was: 1 – to measure the evapotranspiration (soil and crop) and transpiration (crop), of a tomato crop grown on a heavy soil using a lysi- meter; 2 – to develop models as a function of the inside solar radiation and water vapour pressure deficit; 3 – to validate the models using data from different days and 4 - to compare the models. Experiments were conducted in a Mediterranean unheated greenhouse covered with co-extruded PE-EVA-PE film, with a soil grown tomato crop, located in Lisbon. The orientation was east-west and ventilation was achieved by continuous apertures located on the side walls over its entire length. Trickle ferti-irrigation tubes were located between each two rows of plants. Climatic parameters, such as dry and wet bulb air temperatures, crop and leaf temperatures and solar radiation were measured and recorded using a data logger. Information on the evolution of the crop was also recorded. To compute evapotranspiration and transpiration a lysimeter was used and data of irrigation, drainage and soil moisture content were recorded. For the evalua- tion of the transpiration, the lysimeter was covered with a plastic film to prevent evaporation from the soil. To develop the models, data were recorded over periods of several days at different stages of plant development and another set of data from different periods was used for model validation. Comparison between measured and estimated data shows good agreement for both models. Differences between transpiration and evapo- transpiration were very small, which reveals that, under the conditions experienced, evaporation from the soil can be neglected when trickle ferti-irrigation is used

Development of a Warning System for Controlling Botrytis cinerea in Unheated Tomato Greenhouses

Botrytis cinerea is the causal agent of grey mould disease which is one of the most important diseases affecting tomato crops in unheated greenhouses. As a prophylactic measure growers usually apply large quantities of chemical fungicides for its control. Nocturnal ventilation is an effective way to reduce high relative humidity inside greenhouses and can be a useful tool to minimise chemical use in unheated greenhouses. The main purpose of this research was to develop a warning system which provides useful information about how and when to act to avoid or at least minimise disease occurrence. Experiments were carried out at the Instituto Superior de Agronomia in Lisbon in two identical adjacent double-span plastic greenhouses. Two different natural ventilation treatments were randomly assigned to the greenhouses. One was permanent ventilation (PV), with the vents open during the day and night, while the other was classical ventilation (CV), in which the vents were open during the day and closed during the night. Spring tomato crops (Lycopersicon esculentum ‘Zapata’) were grown directly in the soil between the end of February and the end of July for two years. Air dry and wet bulb temperatures were measured using ventilated psychrometers. All data were averaged and recorded on an hourly basis using two data logger systems. The number of leaflets with lesions caused by B. cinerea were counted and removed from the greenhouses from the randomly selected groups of plants. A warning system, defining disease risk levels based on disease severity was developed and can be a useful tool for technicians, advisors and growers, helping them to decide on appropriate actions and the correct timing to avoid favourable conditions for disease development. For a more practical and immediate application, disease risk levels were defined as a function of the time duration with RH >90%. This approach may help to reduce the number of chemical sprays, with unquestionable economic and environmental benefits

Performance aspects of a seawater greenhouse

Performance aspects of a seawater greenhous

Comparison of the climatic conditions and tomato crop productivity in Mediterranean greenhouses under two different natural ventilation management systems

This study was based on experiments with a tomato crop, carried out in two Mediterranean unheated greenhouses, located at the Instituto Superior of Agronomia, Lisbon. The main objective was to compare the behaviour of internal air parameters such as air temperature and relative humidity and the likelihood of condensation on the greenhouse cover in two greenhouses with different management of natural ventilation. The influence of the internal climate on plant development and productivity was also determined by the number of opened flowers and set fruits per truss, and also the harvest rate. One greenhouse had permanent ventilation (PV) during the day and night while the other had classical ventilation (CV), in which the vents were closed during the night and open during the day. During the growing season, measurements were made of dry and wet bulb air temperatures, plastic cover temperature, plant temperature, global radiation, PAR radiation, soil temperature and wind speed, and recorded using a data logger. Also, information on the evolution of the crop was recorded. Internal air temperature, relative humidity and water vapour pressure deficit data were analysed and compared between the two greenhouses. Dew point temperature was computed and compared with the plastic cover temperature to find out if, and when, condensation occurred. Ventilation rates were estimated and related to internal air conditions. he relative humidity was lower in the PV greenhouse during the night due to the higher ventilation rate. Condensation on the plastic cover was more severe in the CV greenhouse and inversions of the air temperature were also more frequent. Lethally low temperatures did not occur in either of the greenhouses. The PV greenhouse had a higher tomato fruit production but this difference was not statistically significant. On the CV greenhouse the harvest started one week earlier due to heat accumulation after closing the vents in the afternoon

Sensitivity analysis of the seawater greenhouse

Sensitivity analysis of the seawater greenhous

High resolution study of the spatial distributions of abyssal fishes by autonomous underwater vehicle

On abyssal plains, demersal fish are believed to play an important role in transferring energy across the seafloor and between the pelagic and benthic realms. However, little is known about their spatial distributions, making it difficult to quantify their ecological significance. To address this, we employed an autonomous underwater vehicle to conduct an exceptionally large photographic survey of fish distributions on the Porcupine Abyssal Plain (NE Atlantic, 4850?m water depth) encompassing two spatial scales (1–10?km2) on and adjacent to a small abyssal hill (240?m elevation). The spatial distributions of the total fish fauna and that of the two dominant morphotypes (Coryphaenoides sp. 1 and C. profundicolus) appeared to be random, a result contrary to common expectation but consistent with previous predictions for these fishes. We estimated total fish density on the abyssal plain to be 723 individuals km?2 (95% CI: 601–844). This estimate is higher, and likely more precise, than prior estimates from trawl catch and baited camera techniques (152 and 188 individuals km?2 respectively). We detected no significant difference in fish density between abyssal hill and plain, nor did we detect any evidence for the existence of fish aggregations at any spatial scale assessed