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  • Author or Editor: A. Gosselin x
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The main objective of this research was to produce a simulated model that permitted the evaluation of operating costs of commercial greenhouse tomato growers with respect to heating methods (hot air, hot water, radiant and heat pumps) and the use of artificial lighting for 1991 and 1992. This research showed that the main factors that negatively influence profitability were energy consumption during cold periods and the price of tomatoes during the summer season. The conventional hot water system consumed less energy than the heat pump system and produced marketable fruit yields similar to those from the heat pump system. The hot water system was generally more profitable in regards to energy consumption and productivity. Moreover, investment costs were less; therefore, this system gives best overall financial savings. As for radiant and hot air systems, their overall financial status falls between that of the hot water system and the heat pump. The radiant system proved to be more energy efficient that the hot air system, but the latter produced a higher marketable fruit yield over the 2-year study.

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The use of potential evapotranspiration (PET) estimates to identify irrigation timing for greenhouse tomatoes (Lycopersicon esculentum Mill.) grown in peat-based substrate was evaluated for a spring and fall crop. PET (using the Penman equation) was calculated from leaf, wet and dry bulb temperatures, and incident and reflected photosynthetic photon flux. Substrate matric potential (SMP) was monitored continuously using electronic tensiometers. Two irrigation starting setpoints (-4.5 and -6.5 kPa SMP) and two nutrient solution electrical conductivity (EC) treatments (1.5 and 3.0 dS·m-1) were factorially combined in a completely randomized design. Irrigation frequency was greater in treatments irrigated at -4.5 than at -6.5 kPa. The integral of calculated PET values was correlated with SMP for both experiments. Accumulated PET values were higher at the start of irrigation in the -6.5-kPa treatments for spring and fall crops. Nutrient solution EC did not influence irrigation frequency. Leaf pressure potential (LPP) was correlated to PET-predicted LPP (r 2 > 0.56) in plants subjected to high EC, low (-6.5 kPa) matric potential setpoint, or both treatments. PET and electronic tensiometer technology can be used jointly to improve irrigation management for tomatoes grown in peat-based substrates by more accurately responding to crop needs for water and nutrients.

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Water potential at soil-root interface (WPs-r) appears to be a good indicator of soil water availability to the plants. However, it is not easy to measure it routinely. Plant water status is more convenient to manage from bulk soil water potential (WPsoil) determination if a good relationship between WPsoil and WPs-r can be established. In order to elucidate this relationship in different substrates, three soil mixes: Mix-1) composted bark, peat, sand; Mix-2) peat, bark, sand, compost; and Mix-3) peat, sawdust, sand, were used with Prunus × cistena. Two-year-old field grown plants were placed in a greenhouse. After soil water was depleted to different levels, WPsoi1, xylem water potential (WPxylem). transpir-ation as well as stomatal conductance were measured using a portable gas exchange system. WPs-r was calculated from these measured data. Plants grown in Mix-2 kept higher WPs-r until WPsoil decreased to -24 KPa, while WPs-r in the plants grown in Mix-1 began to decrease at -5 KPa of WPsoil. Mix-3 showed a medium critical WPsoil for WPs-r to decrease. Since there was a better availab-ilty of soil water to the plants, plants in Mix-2 also showed higher WPxylem. Dynamic analysis showed that plants in Mix-2 kept better plant water status mainly by avoiding water stress. Plants in Mix-3 also avoided water stress, but it was, at least in part, attributed to less leaf area

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An automatic irrigation system was designed for use on green-house tomatoes growing in peat-based substrates. This system uses electronic tensiometers to monitor continuously substrate matric potential (SMP) in peat-bags. The system also uses the Penman equation to evaluate potential evapotranspiration (PET) through the acquisition of many greenhouse environmental parameters. Through a series of linear equations, estimates of PET are used in a computer-controller system to vary the electrical conductivity (EC) of irrigated nutrient solutions, as well as SMP setpoints at which irrigations are started. Such modifications to current irrigation management systems may improve fruit quality and reduce the risk of water stress during periods of high PET by irrigating more frequently with less-concentrated nutrient solutions. Conversely, during periods of low PET, irrigation is less frequent with more-concentrated nutrient solutions. Although no differences were found in fruit number or overall yield using variable nutrient solution EC, plant fresh weight was higher in those treatments. It is concluded that an integrated tensiometer-PET system may give increased precision to irrigation management and the control of crop growth in the greenhouse.

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Abstract

Controlled atmosphere (CA) conditions were assessed for long-term broccoli (Brassica oleracea L. Italica Group) storage. Broccoli was stored for 6 weeks at 1C under N2 containing the following percentages of CO2/O2: 0%/20%; 10%/20%; 6%/2.5%; I0%/2.5%; and 15%/2.5%. Color and chlorophyll retention was better under CA than in air. This improved retention was mainly due to increased CO2 concentration. Storage under CA also delayed the development of soft rot and mold. However, after 6 weeks of storage under an atmosphere containing 10% or more CO2, the rate of respiration increased simultaneously with the development of undesirable odors and physiological injury. Among the atmospheres tested, 6% CO2 and 2.5% O2 was the best for long-term (>3 weeks) maintenance of broccoli quality while avoiding physiological injury.

Open Access

Our objective was to determine the relationship between daily and seasonal changes in understory light, and growth of 1- and 2-year-old american ginseng plants cultivated in a broadleaf forest. Using hemispherical photography and spectroradiometry, understory light [total, direct, and diffuse photon flux density (PFD), and sunfleck durations] and light quality [ultraviolet (UV) and red to far red (R:FR)] were evaluated during two consecutive growing seasons. While shoot and root dry weight (DW), and taproot area of 1-year-old american ginseng plants were related to sunfleck durations, accounting for up to 56% of the variation, the relationship reached a plateau at 2 h·d-1 sunfleck durations for growth. In September, growth of 1- and 2-year-old plants exposed to <2 h·d-1 sunfleck durations was positively related to diffuse PFD (and total PFD for 1-year-old plants), accounting for up to 69% of the variation. In mid-season (July 2000), shoot and root growth, and leaflet area of 2-year-old american ginseng were correlated with light PFD and light quality (UV and R:FR), accounting for up to 88% of the variation. Generally, the results suggest that exposing 1- and 2-year-old american ginseng plants to higher diffuse PFD and <2 h·d-1 sunfleck durations increases yield.

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Effects of CaCl2 preharvest treatment on postharvest strawberry (Fragaria × ananassa) ripening and gray mold development were assessed. Two experiments were carried out in 1987 on two sites. In the first experiment, the effects of rate of application of CaCl2 and degree of fruit maturity at treatment were studied with the conventional cultivar Kent. In the second experiment, the influence of concentration and frequency of application of CaCl2 was investigated with day-neutral `Tribute'. Calcium treatment caused a significant increase in fruit and leaf Ca contents, which were closely correlated. The degree of fruit maturity at application and the frequency of treatment did not affect Ca concentration in the tissues. Several maturity criteria were measured during fruit storage in air at 4C. Anthocyanin and free-sugar contents and tissue electrical conductivity increased, while titratable acidity and firmness decreased. In both experiments, Ca treatment delayed ripening and gray mold development. The delay increased with increasing Ca concentration.

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