Greenhouse Humidity Research Articles

Modeling greenhouse air humidity by means of artificial neural network and principal component analysis

A back propagation neural network (BPNN) based on principal component analysis (PCA) was proposed for modeling the internal greenhouse humidity in winter of North China. The environment factors influencing the inside humidity include outside air temperature and humidity, wind speed, solar radiation, inside air temperature, open angle of top vent and side vent, and open ration of sunshade curtain, which were all collected as data samples. Through PCA of these data samples, 4 main factors were extracted, and the relationship between the main factors and the original data was discussed. Taking the principal component values as the input of BPNN, the model showed a good performance. A comparison was made between the performances of the BPNN based on PCA and the stepwise regression method with 20 data samples which had not been used to establish the NN model, and the prediction of stepwise regression method was less accurate than the BPNN based on PCA.

시설원예 습도환경 제어를 위한 냉각식 제습기 개발

During the winter season in Korea, the relative humidity of greenhouse at night often exceeds 90% because air temperature inside the greenhouse is usually controlled using a heater with all of windows closed to minimize heat loss, thereby requiring the use of a dehumidifier that can maintain optimum humidity levels of <TEX>$70{\sim}80%$</TEX> to provide a good growth condition of crops. Also, such a high humid condition can cause the development of a pest, such as insects, fungi or diseases. However, the use of most conventional dehumidifiers for low temperature dehumidification is limited because their performance is degraded due to frost accumulation on the evaporator coil. This study was carried out to develop a refrigeratory-based dehumidifier suitable for low temperature dehumidification in greenhouse cultivation. The developed dehumidifier consists of a condenser and an evaporator installed separately so that relative and absolute humidity levels can be reduced when air passed through the condenser and evaporator, respectively. The prototype dehumidifier showed a dehumidification capacity of <TEX>$5{\sim}7kg/h$</TEX> when air with a temperature of <TEX>$15{\sim}25^{\circ}C$</TEX> and a relative humidity of <TEX>$70{\sim}95%$</TEX> came into the dehumidifier. Under the condition that either temperature or relative humidity was fixed, the amount of condensed water was proportional to the levels of both temperature and relative humidity.

Greenhouse Microclimate and Soilless Pepper Crop Production and Quality as Affected by a Fog Evaporative Cooling System

The influence of greenhouse humidity control on greenhouse microclimate, crop transpiration rate, and yield and fruit quality of a soilless grown pepper crop was studied in a greenhouse located at the coastal area of western Greece. Measurements were carried out during summer and autumn in two distinct greenhouse compartments involving: (1) no air humidity control and (2) a fog system operating when the relative humidity of the greenhouse air was lower than 80%. Under fog conditions, the greenhouse air and the crop leaf temperature were about 3°C lower than those measured under no fog conditions. The fog system allowed maintenance of the greenhouse air temperature under 30°C, while a maximum value of about 35°C was reached under no fog conditions. In addition, under fog conditions, the air vapor pressure deficit was lower than 2 kPa, even during the warmest part of the day, while under no fog conditions it reached values near 4 kPa. However, the transpiration rate was not affected to such an extent by fog as the air vapor pressure deficit, and under fog conditions it decreased by about 26%. This is attributed to the values reached by the bulk stomatal conductance, which were about 1.5 times higher under fog than under no fog conditions. The crop leaf area index values observed after the middle of the experimental period and later, under fog conditions, were higher than that observed under no fog conditions. Finally, the fog system enhanced the mean fruit weight and the percentage of marketable fruits but reduced appreciably the total number of fruits per plant. The free (titratable) acidity and the total soluble solids in the pepper fruit sap were slightly reduced by the fog cooling system, while the fruit size was increased. The use of a fog cooling system proved to be beneficial for summer crops of pepper grown under Mediterranean climatic conditions due to a favorable impact of the reduced vapor pressure deficit on both the mean fruit weight and the quality in terms of fruits graded Class I. Nevertheless, the high air humidity imposed by a cooling fog system may reduce the number of fruits per plant, thereby offsetting the benefits from the increased mean fruit weight in terms of total yield.

Effect of microclimate heterogeneity and ventilation system on entomopathogenic hyphomycete infection of Trialeurodes vaporariorum (Homoptera: Aleyrodidae) in Mediterranean greenhouse tomato

Collaborative research was conducted in the south of France to assess constraints related to both climate heterogeneity and ventilation systems on the control potential of a Lecanicillium muscarium-based formulation against whiteflies in Mediterranean greenhouses. Four series of small-scale greenhouse trials were performed in 2001 and 2002. Two applications at 4–5 day intervals of Mycotal were conducted on young larvae of the greenhouse whitefly, Trialeurodes vaporariorum, at the rate recommended by the manufacturer (ca. 1010 viable spores per liter of water suspension). The climatic heterogeneity was taken into account by comparing the fungus-induced mortality of nymphs located on lateral row plants to that of nymphs on center row plants. In spite of significant differences in air flows (0.7–1.2 and 0.3 ms−1, respectively) there was no effect on fungus efficacy (53–76% mortality). When comparing the influence of greenhouse equipment (sophisticated glasshouse vs. polyethylene-covered greenhouse), the fungus was not affected (89–96% mortality) in spite of significant differences in ventilation rates. The results confirmed that entomopathogenic Hyphomycetes have a strong potential for microbial control of whitefly larvae infesting tomato crops at moderate ambient humidity in Mediterranean greenhouses in spite of windy periods. These investigations confirmed that microclimatic conditions prevailing in the targeted insect habitat (under-leaf surface boundary layer) are greatly disconnected from that of both outside and inside the greenhouse. In northern Mediterranean greenhouses, non-stressed tomato crops provide unexpected favorable conditions for mycoinsecticide use against a phyllophagous insect.

Models to estimate phytomass accumulation of hydroponic lettuce

The protected and hydroponics cultivation are increasing in Brazil, demanding a better knowledge of crop performance in this environment. Plant dry matter accumulation as a function of solar radiation, temperature, relative humidity and other weather parameters in greenhouse is different when compared with field cultivation. With the purpose of proposing models to characterize the temporal variation of leaf and total dry matter production of hydroponics-grown lettuce (Lactuca sativa L.) and to determine the flowering period and the maximum dry matter accumulation rate as a function of plant relative development (relative degree-days), solar radiation and effective thermal index, two experiments (Spring and Autumn) were carried out in the greenhouse, at Santa Maria, Rio Grande do Sul State, Brazil. Growth and development models are useful in obtaining basic information on the plant &lt;FONT FACE=Symbol&gt;´&lt;/FONT&gt; environment interactions, maximizing the use of resources in greenhouse, as well as, to define the best form of crop management. The cultivar Vera was chosen as function of its earliness. Models were proposed to estimate the temporal variation of dry matter accumulation, where the best results for relative development were obtained using effective degree-days, characterizing the importance of the air temperature for the vegetative phase and the solar radiation for the reproductive. The yield and quality of the lettuce seeds evidenced a high potential of hydroponics technique.

Influence of Humidity and Greenhouse Microclimate on the Efficacy of &lt;I&gt;Beauveria bassiana&lt;/I&gt; (Balsamo) for Control of Greenhouse Arthropod Pests

Abstract This study investigated the influence of different humidity levels on percentage of infection by Beauveria bassiana (Balsamo) Vuillemin (Hyphomycetes) (Botanigard Emulsifiable Suspension formulation) on greenhouse insect and mite pests, and their commercially available biological control agents. The target insect and mite species were sprayed with B. bassiana and evaluated in petri dish trials under controlled environment conditions, on cucumber leaves under greenhouse crop conditions, and under fully sprayed greenhouse conditions. Results of this study showed that in petri dish trials, a humidity of 97.5% RH resulted in significantly higher percentage of infection (60–88.8%), while at 75 and 80% RH only 15.3–43.9% of the pest insects were infected. On leaf surfaces, the differences in ambient humidity did not cause as great of variations in percentage of infection as in the petri dish trials. Increasing greenhouse humidity by 15% RH caused an increase of 17–25% in percentage of infection. Under ...

INFLUENCE OF VAPOUR PRESSURE DEFICIT ON TOMATO CROP TRANSPIRATION

The effect of air VPD on the transpiration rate of a tomato crop (vs. Forteza) was studied in multispan greenhouses. Measurements were carried out during ontogeny in two greenhouses (i) without air VPD control (maximum VPD 2.5 – 4 kPa) and (ii) with a fog-system operating when air VPD was higher than 2 kPa. Transpiration rate was determined every ten minutes by weighing plants with an electronic balance. The leaf transpiration vs inside radiation relationship at high VPD was two-fold greater than at low VPD. However, leaf transpiration response to air evaporative demand was equal in both greenhouses. A multiple regression analysis, based on the simplified Penman-Monteith formula, was established between the measured transpiration rate and the radiative and advective components. Either at high or low VPD, the model gave a good prediction of the hourly water consumption, using the same multiple regression coefficients. This simplified model, that considers the influence of air VPD on the transpiration rate, can be used in different levels of greenhouse humidity control.

First Report of Leaf and Sheath Spot Caused by Rhizoctonia zeae Affecting Panicum tennesseense in Rhode Island.

Panicum tennesseense Ashe is a perennial, coarse-textured, cool-season grass (similar in appearance to many warm-seasoned grasses), which grows in the southern coastal areas of New England and is commonly found in home lawns, roadsides, and meadows. In August 2002, a large stand of P. tennesseense with significant leaf spotting was identified in Washington County, RI. Lesions were excised, surface sterilized with 0.6% sodium hypochlorite, and plated on one-half-strength potato dextrose agar (PDA). Cultures were incubated at 25°C, and mycelia quickly covered plates within 3 days. After 2 weeks in darkness, plates were covered with white, aerial mycelium. When placed under near-UV light, no aerial mycelium was produced, and mycelia were a salmon color. After 5 weeks, separate, spherical, 0.5-mm-diameter beige sclerotia were produced submerged throughout the media and turned red within a few days. Sclerotia were not produced in the absence of near-UV light. Spores were not produced, and right-angled branching, characteristic of Rhizoctonia spp., was observed. Monilioid hyphae were also produced in culture. At the optimal growth temperature of 32°C, mycelia grew an average of 33.6 mm/day. Cells were stained using safranin, and the number of nuclei observed within young hyphal cells was five or seven. On the basis of the described mycelial and sclerotial characterisitics, the isolated fungus was identified as Rhizoctonia zeae (1,2). To demonstrate pathogenicity, plugs of isolated fungi were cut from PDA plates, placed on leaf blades at the junction with leaf sheaths, and incubated in a greenhouse humidity chamber at an average temperature of 32°C and 80% humidity. After 3 days, significant disease was observed and included blighting of newly emerged shoots, blighting and spotting on leaf sheaths, and severe spotting on leaf lamina. Whereas Rhizoctonia solani has been reported as a pathogen on P. tennesseense, to our knowledge, this is the first report of R. zeae induced leaf and sheath spot on this host (1).

Analysis of strategies for reducing calcium deficiencies in glasshouse grown tomatoes: model functions and simulations

Energy saving measures can result in high levels of humidity in greenhouses which reduces transpiration resulting in calcium deficiency symptoms on tomato leaves with subsequent loss of yield and quality. Transpiration can be increased by lowering the saturation deficit. Control strategies need to be cost-effective so that the benefits are in excess of the costs of carrying out the dehumidification. The HORTITRANS model [Journal of Agricultural Engineering Research, 57 (1994) 23], which predicts the conditions inside a greenhouse, was modified to enable simulations to be carried out for a developing crop and to quantify the effects of high humidity on yield and quality. Saturation deficit set-points were determined so that the transpiration rate was equal to a minimum of 0.65 kg m −2 day −1, a value derived to be satisfactory from experiments. Simulations were carried out for sample single and double glazed greenhouses with dehumidification by ventilation and heating. The cost of dehumidification was high when the ventilators were widely opened and so ventilation rates were constrained by restricting the maximum angle of opening. For a double glazed house additional profit was greater when the saturation deficit was controlled during the period of daylight compared to continuous control. For the single glazed house, a maximum angle of opening of 3° produced an additional profit of 6 p m −2. One year in eight there was a loss. For the double glazed house, a maximum ventilator opening of 10° produced an average additional profit of 90 p m −2. The models can be used to study control strategies for other types of greenhouse structures in different climatic regions where short-term (hourly) meteorological data exists using local information on prices and costs.

キュウリの抑制栽培におけるハウス内の気温と湿度が生育に及ぼす影響

ハウス内の温度と湿度がキュウリの生育に及ぼす影響を明らかにすることを目的として，午前中を中心に昼の温度と相対湿度を30 ℃・60 %と25 ℃・40 %の2処理区を設けて抑制栽培を行った．さらに，摘心栽培，摘心摘花栽培およびつる下ろし栽培においては，30 ℃・60 %区で初期の果実肥大が促進され，第3次以降の側枝の発生が抑制された．一方，25℃・40 %区では果実肥大が緩慢となり，側枝の発生が促進され，その結果として全期間合計の収穫果実本数が増加した．しかし，生育後半の低温期において果実の上物率が低下した．

Viability and storage of bromeliad pollen

Several bromeliad species from two different subfamilies, were used to develop a reliable method to evaluate pollen viability. Pollen germination on a medium containing 20% sucrose, 0.001%H3BO3 and 0.5% agar was comparable to germination on a compatible stigma. Maximum germination was reached within 2 to 10 hours depending on the species. Based on this test, six species were considered as being good pollen donors with germination percentages between 49%and 83%. Furthermore, pollen from these species and cultivars could be stored in liquid nitrogen (–196 °C) without a considerable loss of viability. For all species, a dehydration period of 4 hours prior to cryopreservation and a rehydration period of 1 hour after cryostorage were essential. Greenhouse humidity influenced anther moisture content and cryostorability.

Manipulating Plant Moisture Conditions Using Greenhouse Highpressure Fogging

This study investigated greenhouse and plant surface microclimate for cucumber crops (Cucumis sativus) under high pressure overhead fogging. Overhead fogging maintained greenhouse humidity above its set point and avoided excessively low humidity conditions on sunny days. Fogging caused minimal to moderate changes in greenhouse air temperature in the fall depending on whether or not the leaves were sunlit or shaded. The temperature of sunlit leaves decreased by 1 to 1.5 °C (1.8 to 2.7 °F) under occasional fogging in the morning and by 3 °C (5.4 °F) under extensive fogging during noon hours. The temperature of fogged shaded leaves did not significantly change (&lt;1 °C) when compared to nonfogged shaded leaves. Leaf wetness duration (LWD) was extended when overhead fogging was used. The length of extended daytime wetness duration (LWDday) from 0800 to 1700 HR in the fogged greenhouse depended primarily on global radiation at the leaf level. A simulation model was developed to predict LWDday using daily integrated global radiation (Rsum) as the input.

Bumble bee (Hymenoptera: Apidae) activity and loss in commercial tomato greenhouses

AbstractActivity of bumble bees,Bombus impatiensCresson, was examined in commercial tomato,Lycopersicon esculentumMill. (Solanaceae), greenhouses in relation to greenhouse covering type, solar radiation, greenhouse temperature and humidity. Bumble bee activity was measured by photodiode monitors inserted into the entrance of the colonies. Colony sizes were monitored as an indicator of bee loss through gutter ventilation systems in relation to covering. Activity monitors were found to be a good predictor of actual bumble bee entrances and exits (r2= 0.85). Bumble bee activity was 94.0% greater under the ultravioltet (UV)-transmitting covering than under ones that transmitted less UV light. No relationship was found between bee activity and the amount of solar radiation or internal greenhouse humidity. Bee activity was weakly positively correlated with internal greenhouse temperature (r2= 0.18). Bee activity was not different during three periods of the day: morning, midday, and evening. The mean ± SE colony size under the UV-transmitting covering was 86.0 ± 2 bees per colony after 10 days within the greenhouses, compared with 36.4 ± 5.8 bees per colony under the other three types of covering. Our results suggest that bee activity is greatest and bee loss through gutter ventilation systems lowest in greenhouses made with coverings that transmit high levels of UV light.

Effect of misting on transpiration and conductances of a greenhouse rose canopy

The influence of greenhouse humidity control on the transpiration rate ( λE c), sensible heat flux ( H c) and bulk stomatal conductance ( g c) of a soilless rose canopy ( Rosa hybrida, cv. First Red) was studied in a greenhouse located in the coastal area of eastern Greece. Measurements were carried out during several days in the summer (i) without air humidity control and (ii) with a mist system operating when the relative humidity of the greenhouse air was lower than 75%. The diurnal course of g c was determined from the relation linking λE c to canopy-to-air vapour pressure deficit ( D c) or from inversion of the Penman–Monteith equation. The two ways of estimating g c were in good agreement, showing a significant increase of g c under mist conditions. Covariation of radiation and humidity during the day caused diurnal hysteresis in λE c and g c. The hysteresis phenomena were less marked when the mist system was operating. Normalising g c by radiation removed most of the hysteresis and indicated a curvilinear stomatal response to vapour pressure deficit. The analysis of the energy partition at the canopy showed high negative values of the Bowen ratio ( β≈−0.7) in both conditions, indicating that canopy transpiration played a major role in cooling the greenhouse atmosphere. The contribution of the mist system to total evaporative cooling was estimated to be about 20%, with only 40–50% of the mist water being effectively used in cooling. Calculation of the crop water stress index confirmed that the crop was less stressed under misting conditions. It was concluded that the prediction of short-term variations of λE c and g c in greenhouse environments must account for the magnitude and diurnal variation of air VPD.

022 Manipulation of the Greenhouse Microclimate to Improve the Efficacy of Entomopathogens for Control of Greenhouse Pests

Application of entomopathogenic fungi by inundative releases has been attempted for control of a wide range of insect pests, with generally poor results. This is largely because entomopathogens are often treated as direct substitutes for chemical insecticides and applied without an adequate knowledge of their interactions with the local environment. Humidity of greater than 90% RH has long been regarded as the a critical condition for germination and infection by the spores. With both temperature and humidity controlled, greenhouse crops offer an excellent potential for pest control using entomopathogens. The long-term maintenance of &gt;90% RH, however, is not standard practice in greenhouse production. This study explored the possibility of improving the efficacy of the fungi by temporarily changing greenhouse humidity without adversely affecting crop growth. The study included laboratory and greenhouse trials. In laboratory trials, four humidity levels of 75%, 80%, 89%, and 97.5% RH were evaluated over a 48-h period. Three commercial products of Beauveria bassiana were evaluated (Naturalis-O, Botanigard 22 WP, and Botanigard ES). Greenhouse pests of green peach aphid, melon aphid, western flower thrips, whitefly, and two-spotted spider mite were used as target insects. The infection rate of B. bassiana was found to increase when the sprayed adult insects were exposed to higher humidity levels with the maximum infection obtained at 97.5% RH. Percent infection and difference between humidity levels, however, were formulation- and host-dependent. The highest overall control efficacy was obtained by using Botanigard ES. Botanigard ES was highly effective to adult green peach aphid, melon aphid, and greenhouse whitefly at high humidities. Effects of B. bassiana against biological control agents for greenhouse vegetable crops were also evaluated. Greenhouse trials were conducted in two adjacent greenhouse compartment with high and low humidity conditions for 48 h, respectively, for selected pest insects to valid laboratory results.

Hydrogen and oxygen isotope ratios of tree-ring cellulose for riparian trees grown long-term under hydroponically controlled environments.

Saplings of three riparian tree species (alder, birch and cottonwood) were grown for over 5 months in a hydroponics system that maintained the isotopic composition of source water in six treatments, ranging from -120 to +180‰δD and -15 to +10‰δ18O. The trees were grown in two greenhouses maintained at 25°C and at either 40 or 75% relative humidity, creating differences in transpiration rates and leaf water isotopic evaporative enrichment. The cellulose produced in the annual growth ring was linearly related to source water with differences in both slope and offset associated with greenhouse humidity. The slope of the isotopic composition of source water versus tree-ring cellulose was less than 1 for both δD and δ18O indicating incomplete isotopic exchange of carbohydrate substrate with xylem water during cellulose synthesis. Tests using the outer portion of the tree-ring and new roots were similar and showed that the tree-ring values were representative of the cellulose laid down under the imposed environmental conditions. The fraction of H and O in carbohydrate substrate that isotopically exchange with medium water was calculated to be 0.36 and 0.42 respectively, and biochemical mechanisms for these observed fractions are discussed. A mechanistic model of the biochemical fractionation events for both δD and δ18O leading to cellulose synthesis was robust over the wide range of cellulose stable isotope ratios. The experimental results indicate that both water source and humidity information are indeed recorded in tree-ring cellulose. These results help to resolve some of the disparate observations regarding the interpretation of stable isotope ratios in tree-rings found in the literature.

Night-time greenhouse humidity control with a cooled wetness sensor

High night-time humidity in greenhouses may lead to the spread of fungal diseases. Traditionally, dehumidifying the greenhouse air in mild climates is accomplished by means of periodic ventilation. More efficient operation can be achieved by triggering ventilation with a humidity sensor or a wetness sensor. In this study, a thermoelectrically cooled wetness sensor was used to turn on a fan, a heater or a combination of both, to dehumidify a small experimental greenhouse. Increased sensor cooling increased the condensation safety margin, namely the difference between canopy temperature and the dew-point temperature of the greenhouse air. The safety margin was increased by about 0.8 K for every 1K of sensor cooling. The results show that the need for dehumidification increases with atmospheric humidity and decreases with wind speed (which promotes natural infiltration).

Effect of covering materials on energy consumption and greenhouse microclimate

The objective of the study was to conduct an extensive energy and microclimatic assessment of different greenhouse covering materials. Single glass (GL) and three types of double polyethylene (PE) claddings were compared. The double polyethylene cladding consisting of an anti-fog thermal film for the inner layer and a standard PE film for the outer layer was the most energy efficient. It had an average measured heat transfer coefficient ( U value) of 2.9 W m −2 K −1. The average U value for the other PE cladding was 3.4 W m −2 K −1. The use of thermal screens in the PE houses during the night reduced heat loss rates by 23–24%. The differences in climates under different claddings is presented in terms of PAR transmission and humidity levels. The measured average PAR transmission during the winter months (November–March) were 0.68, 0.62, 0.65 and 0.60 for glass, anti-fog 1-year, anti-fog 3-year and anti-fog thermal claddings, respectively. In the summer months (April–October) the values were higher. The average vapour pressure deficit in the double PE houses was found to be 0.2 kPa lower than under single glass during the winter season, but no significant difference was observed between various anti-fog films. The use of a thermal screen in a double PE houses caused only a slight increase in greenhouse humidity. The contribution of supplementary lighting to greenhouse heating demand is also presented and discussed.

Effect of Humidity on the Transpiration of Greenhouse Tomato Crops

Experiments were conducted in four independently controlled greenhouses. The purpose of these experiments was to measure the effect of humidity on transpiration and yields. Four different humidity treatments were evaluated: 1) high night and high day humidity levels (vapor pressure deficits &lt;0.4 kPa), 2) high night and low day humidity levels (VPD &gt;0.8 kPa), 3) high night and low day humidity levels, and 4) variable greenhouse humidity to maintain a set hourly transpiration rate. Transpiration rates were measured in the four greenhouses at 15-min intervals from Nov. 1993 to May 1994. Results show that high humidity reduces the hourly and daily transpiration levels significantly and has an impact on crop yields. Results also show that it is possible to regulate crop transpiration by calculating the transpiration rate for a set of VPD and solar radiation levels.

HORTITRANS, a Model for Predicting and Optimizing Humidity and Transpiration in Greenhouses

A new model is presented to predict humidity and transpiration directly as a function of the outside climate, with the particular objective of developing optimal control strategies for humidity in greenhouses. This model is of straightforward structure, while including the processes of transpiration, condensation, ventilation and humidification or dehumidification. The model allows the inside vapour pressure to be directly calculated as a function of the outside conditions and the greenhouse characteristics. It includes a linearized relationship for transpiration, which is a good approximation of a more detailed model. Condensation on the cladding is first calculated for the inside greenhouse air at saturation (100% relative humidity) and then corrected by a factor to account explicitly for the feedback effect of inside humidity on cladding temperature. Because of its simplicity, this model also explicitly determines the water and energy to be added to or extracted from the greenhouse air, in order to achieve given humidity or transpiration set-points. The HORTITRANS model predicted to within 8% vapour pressure, relative humidity, transpiration and condensation inside the greenhouse, when tested against measurements taken on a young and on a mature crop in a full-size greenhouse. The optimization of inside humidity shows that there is little need for dehumidification in a single glazed greenhouse. For double glazing, dehumidification could be cost effective at very low light levels, in particular just before sunset.