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John A. Cline and Eric J. Hanson

Abbreviation: RH, relative humidity. 1 Current address: Horticulture Research International, Crop Science-Perennial Crops Division, East Malling, Kent ME19 6BJ, England. 2 Associate Professor. We acknowledge the Michigan Agricultural Experiment

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Eric W. Kerschen, Caleb Garten, Kimberly A. Williams, and Melanie M. Derby

Environmental Research, Manhattan, to quantify the effect of root medium evaporation and plant transpiration on relative humidity. This layout was used for each of 12 runs of the experiment. All measurements are in feet; 1 ft = 0.3048 m. Test stand. The test

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Brian A. Krug, Brian E. Whipker, Ingram McCall, and Jonathan Frantz

Boron moves passively into plants from the roots to the shoots through the transpiration stream through the xylem ( Jones, 1991 ; Kochian, 1991 ; Kohl and Oertli, 1961 ; Raven, 1980 ). Relative humidity can be a major factor influencing the rate

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Dominique-André Demers, Martine Dorais, and Athanasios P. Papadopoulos

russeting was more severe in the summer than in the fall and spring seasons, suggesting a possible implication of climatic conditions [light, temperature, relative humidity (RH)]. Huang and Snapp (2004) found that shoulder check, a disorder similar to

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Wenjie Ma, Wen Liang, and Bing Zhao

lowercase letters indicate significant differences between R . ‘Fen Zhenzhu’ and R . ‘Zhuangyuan Hong’ at the same relative air humidity, and different uppercase letters indicate significant differences between treatments of the same Rhododendron

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Scott B. Lukas, Joseph DeFrank, Orville C. Baldos, and Ruijun Qin

, therefore the water volumes to produce their saturated salt solutions were based on the LiCl calibration. Table 3. Desiccation chamber relative humidity (RH) calibration using saturated lithium chloride. The optimal RH level of 12.5% was obtained by adding 6

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Ahmad Shirazi and Arthur C. Cameron

The feasibility of controlling relative humidity in modified atmosphere packages using compounds possessing Type III sorption isotherm behavior was studied. Ten grams each of dry sorbitol, xylitol, NaCl, KCl, or CaCl2 sealed with one maturegreen tomato (Lycopersicon esculentum L.) fruit at 20C in simulated packages for 48 days resulted in stable relative humidities of ≈75%, 80%, 75%, 85%, and 35%, respectively. Relative humidity was a function of the ratio of chemical to fruit mass. Relative humidities within control packages were in the range of 96% to 100% throughout the experiments. A simple system that uses spunbonded polyethylene pouches for the application of this humidity control method to packages is described. The storage life of packaged red-ripe tomato fruit at 20C was extended from 5 days using no pouch to 15 to 17 days with a pouch containing NaCl, mainly by retardation of surface mold development.

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Jianhua Zhang and Miller B. McDonald

The accelerated aging vigor test subjects seeds to high temperatures (41°C) and relative humidity (about 100%) for short durations (usually 72 hours). These recommendations, however, have been developed for large-seeded agronomic crops and may be too severe for small-seeded flower crops that deteriorate rapidly during storage such as impatiens. We examined the effect of aging regime duration (48, 72, and 96 hours) and temperature (38 and 41°C) as well as relative humidity using three saturated salt solutions (KCl–87% RH, NaCl–76% RH, and NaBr–55% RH) on two commercial impatiens seed lots differing in seed vigor but not percentage germination. The greatest differences in percentage germination after 4 days were found among the treatments of 48 hours for KCl, 72 hours for NaCl, and 96 hours for NaBr. While any of these saturated salt solutions may be used in a commercial situation to determine impatiens seed vigor, we suggest that a total 7-day test period consisting of 72 hours aging at 41°C using saturated NaCl with germination being determined 4 days after aging is most convenient.

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H. Chris Wien and David S. de Villiers

Tipburn is a necrosis of the rapidly expanding young leaves of lettuce, caused by a localized Ca deficiency that is a major constraint to raising productivity of hydroponically-grown leaf lettuce. Root pressure is thought to be important in distributing calcium to young tissue that is not transpiring rapidly in crops such as cabbage, tomato and strawberry. Since root pressure is enhanced by high relative humidity (RH), experiments were conducted with two cultivars of leaf lettuce to determine if regulating relative humidity during the day or night would influence tipburn incidence. Lettuce was grown hydroponically in a glass-covered greenhouse. Plants were transferred to ponds of 1 × 2 m size, starting at about day 25 from sowing. Four ponds containing 42 plants each were subjected to ambient or elevated RH, either during the day, or at night, or at both times. Each pond was covered by a clear polyethylene ventilated canopy, to ensure maintenance of the desired RH condition. The experiment was conducted five times. In three experiments, tipburn developed in 3 or 7 days, depending on the cultivar. The disorder was most severe in ponds whose atmosphere was constantly humid, followed by the treatment that provided humid days and dry nights. Treatments which provided dry conditions, either during the day, or continuously, were least affected. In two experiments, ambient RH rose above 70%, and the differential effect of humidity on tipburn incidence was no longer evident. Both cultivars reacted similarly to the treatments, even though `Winter Density' developed the disorder 4 days before `Batavian'. The results imply that root pressure is less important than transpiration in distributing Ca to the edges of young leaves of leaf lettuce.

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D. Mortley, P. Loretan, C. Bonsi, W. Hill, and C. Bonsi

An experiment was conducted in environmental growth chambers to study the response of sweet potato to relative humidity (RH). Twenty-four vine cuttings of `TI-155' sweet potato were planted in growth channels in a modified half Hoagland's solution using the nutrient film technique. Plants were exposed to constant RH levels of 50% or 85%. Temperature regimes of 20/22 C were maintained during the light/dark periods with an irradiance level of 600 umol m-2 s1, and a 14 hr/10 hr photoperiod. Plants were harvested 120 days after planting and yield data was taken. High RH (85%) resulted in significant increases in number of storage roots/plant, storage root fresh and dry weight, single leaf photosynthesis and stomatal conductance than at 50% RH. Foliage dry weight and leaf temperature was higher at 50% than 85% RH.