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A portable, nondispersive infrared (NDIR) gas analyzer was modified to measure the concentration of CO2 and water vapor in small gas samples. A 2-mL gas sample was taken from a series of sealed flasks partially filled with a saturated solution of chemicals known to produce various levels of relative humidity (RH). The modified NDIR instrument quantified water vapor content by its absorption at 2.59 μm. Peak height was displayed on a strip chart recorder and a standard curve constructed. At a specific temperature, the vapor pressure (VP) and vapor pressure difference (VPD) were calculated for sweet pepper (Capsicum annuum L., cv. Mazurka) fruit packed in trays that were covered with plastic films having several levels of perforations. Water loss from the fruit was highly correlated with VPD inside the packages. The modified NDIR instrument has an advantage over other instruments used to measure RH because it can rapidly and simultaneously determine the concentration of water vapor and CO2 in a single injection of a small gas sample.

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Authors: , , , and

In commercial production of greenhouse cucumber, moderate water stress is often undetectable until plants show severe wilting. The purpose of this study was to establish a noncontact, early detection method for such moderate stress before visual wilting takes place. An infrared imaging system including an infrared camera, a personal computer, and necessary image processing software was placed in a greenhouse with the camera elevated and viewing the plant canopy. Selected plants, each in a bag of sawdust growing medium, were subjected to water stress by removing irrigation tubes from the growing medium. The infrared images obtained from a crop canopy displayed an increase in foliar temperature of stressed plants, which were located among normally watered (control) plants in the same greenhouse. Increased foliar temperatures of stressed plants occurred 1 to 3 days before wilting was observed. When visual wilting occurred, the stress treatment was stopped and irrigation was resumed within the same day. Cucumber plants showed no crop loss after one cycle of moderate stress. Repeated moderate stress caused yield loss. The potential applications of this nondestructive, noncontact detection method in plant science research and in commercial greenhouse production will be discussed.

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