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J. Norrie, M.E.D. Graham, and A. Gosselin

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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J. Charbonneau, Y. De, D.-A. Demers, M. Dorais, and A. Gosselin

The objective of the experiments was to compare the performance of metal halide (MH) and high-pressure sodium (HPS) lamps on growth and yield of vegetables. Four experiments with lettuce were carried out. The lettuce grown under HPS lamps had a head firmness higher than under MH lamps. The difference between the type of lamps on fresh weight was not very constant with the period of production. There was no interaction between lamp and cultivar. Two experiments were carried out with tomato in Spring and Fall 1991. For a tomato crop, the yield and quality of the fruit were not affected by the type of lamps. Photosynthesis and transpiration of tomato and pepper plants were measured under MH and HPS lamps. No significant differences were found between both lamps under two humidity conditions and four PPFs. Under high humidity conditions, transpiration under MH was higher than under HPS.

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J. Norrie, M.E.D. Graham, P.A. Dubé, and A. Gosselin

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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Y. Zhang, L. Gauthier, D. de Halleux, B. Dansereau, S. Yelle, and A. Gosselin

qA 3-year study was undertaken to quantify the effect of four greenhouse covering materials on energy consumption, microclimate, and the growth and production of cut flowers Matthiola incana (Stocks) and Antirrhinum majalis (Snapdragons) in the greenhouse. The four materials are single glass (GL), polyethylene (PE) + anti-fog 1-year polyethylene (AF1), polyethylene + antifog 3-year polyethylene (AF3), and polyethylene + anti-fog thermal polyethylene (AFT). The effect of thermal screen and supplementary lighting (60 μmol·m–2·s–1) also are discussed. This study indicated that AFT film is the most energy efficient material and AF3 film is the most transparent to photosynthetic active radiation (PAR). For stocks, good quality can be obtained in GL and AF3 in terms of spike length, stem diameter, as well as number of buds and flowers. The stocks in GL, however, always possess the highest photosynthetic capacity, regardless light treatment. For snapdragons, the growth and flowering in PE houses were significantly improved by supplementary lighting

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Eric A. Lavoie, Damien de Halleux, André Gosselin, and Jean-Claude Dufour

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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Anick R. Fournier, André Gosselin, John T.A. Proctor, Louis Gauthier, Shahrokh Khanizadeh, and Martine Dorais

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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F. Chéour, C. Willemot, J. Arul, Y. Desjardins, J. Makhlouf, P.M. Charest, and A. Gosselin

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.