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Cristian Moya, Eduardo Oyanedel, Gabriela Verdugo, M. Fernanda Flores, Miguel Urrestarazu, and Juan E. Álvaro

. Table 2. Fertigation parameters and nutrient emissions to environment of nutrient solutions with different electrical conductivity (EC) levels (dS·m −1 ) used for tomato cultivation during the crop cycle. Water uptake decreased dramatically with

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Hui-lian Xu, Laurent Gauthier, and André Gosselin

`Capello' tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in peat-based substrate (70% sphagnum peat and 309'. perlite, by volume) and supplied with nutrient solutions of high (4.5 mS·cm-1) or low (2.3 mS·cm-1) electrical conductivity (EC) under high (95% ± 5%) or low (55% ± 8% of capillary capacity) soil water conditions. Three weeks after treatments started, stomatal transpiration (TRst) and cuticular transpiration (TRcu) rates were measured by three methods: 1) analyzing TRst and TRcu from a water retention curve obtained by drying excised leaves in air under a photosynthetic photon flux (PPF) of 400 μmol·m-1·s-1, 2) analyzing TRst and TRcu from a transpiration decline curve obtained by measuring transpiration rates after cutting the leaf from the stem of the dehydrated plant in the gas-exchange system, and 3) measuring transpiration rates under light and in dark respectively using the gas-exchange method. TRst and TRcu were decreased by high EC and/or low soil water content. For method 1, the transpiration decline curve shows two distinct phases: the initial steep slope that indicates TRst and the gently sloped section that indicates TRcu. Both slopes were lower for high EC and/or water-stressed plants compared to the control (low EC and high soil water content). The tangent lines of these two phases of the curve intersect at one point (t, w). The value oft that indicates the time for stomatal closure was longer and the value of w that indicates the critical tissue water level for stomatal closure was lower for high EC and/or water-stressed plants. In method 2, the initial rate of total transpiration was higher in high EC and/or water-stressed plants. Leaf wax content increased, especially under high EC stress. This suggests that increased deposition of wax prevents water loss from the cuticle. A delay in complete stomatal closure, complete closure at lower RWC, and reduced TRcu or an increase in wax deposit were adaptations to water and salinity stresses in tomato plants under our controlled environmental conditions.

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Catherine S.M. Ku and David R. Hershey

Abbreviations: EC, electrical conductivity EC a , EC of the applied solution; EC e , EC of a saturated medium extract; ET, evapotranspiration; LF, leaching fraction; LR, leaching requirement; M a , mass of pot after irrigation when at container

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Catherine S.M. Ku and David R. Hershey

Abbreviations: EC, electrical conductivity; EC a , EC of the applied solution; EC e , EC of a saturated medium extract; ET, evapotranspiration; LF, leaching fraction; LI, leaching intensity; LR, leaching requirement; M a , mass of pot after

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Ryo Matsuda, Chieri Kubota, M. Lucrecia Alvarez, and Guy A. Cardineau

, and total leaf area at the end of experiment and rates of stem elongation and leaf development of transgenic tomato grown at conventional (control) or high electrical conductivity (EC); n = 3–6. Table 2. Mean net photosynthetic rate ( P n

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Simon Chrétien, André Gosselin, and Martine Dorais

In order to improve fruit quality under the Northern climatic growing conditions prevailing in Quebec, Canada (lat. 47°N, long. 71°W), a greenhouse tomato (Lycopersicon esculentum Mill. cv. Blitz) spring production experiment was conducted using several irrigation regime and electrical conductivity (EC) levels. The irrigation regime treatments were a function of the global solar radiation, with three thresholds applied to each EC treatment. The irrigation thresholds (KJ·m–2) were 1) 468, 2) 540, and 3) 612. Two EC treatments were used: 1) control EC (2.0 to 3.5 mS·cm–1) and 2) 30% higher EC than the control (2.6 to 4.6 mS·cm–1), which was raised by adding NaCl to 12 mmol·L–1. Plant water potential in summer and in the fall and plant growth after 6 months were not affected by irrigation or EC treatments. Raising the EC increased the Na content of reproductive and vegetative parts and decreased the N concentration of the vegetative parts. The highest EC improved fruit quality by reducing the incidence of fruit cracking. Although marketable yields were not affected by EC (P = 0.09) or irrigation regime (P = 0.08) treatments, higher EC during March to September increased (P ≤ 0.01) the proportion of Class 2 fruit by reducing fruit size.

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Jong-Goo Kang and Marc W. van Iersel

toxicities ( Dubey, 1996 ). Researchers previously have reported that higher than recommended leachate electrical conductivity (EC) can reduce plant growth ( Gislerød and Mortensen, 1990 ; James and van Iersel, 2001 ; Kang and van Iersel, 2001 ; Nemali and

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Holly L. Scoggins and Marc W. van Iersel

Growing medium electrical conductivity (EC) is used in laboratory analysis and greenhouse production as a measure of the nutrient content of the growing medium. Fast, accurate ways to measure growing medium EC will make it easier to determine EC and maintain it within a suitable range for a particular crop. Several probes have been developed that can be inserted directly into the growing medium of container-grown crops for measurement of EC. We tested the sensitivity of four in situ EC probes (Field Scout, HI 76305, WET sensor, and SigmaProbe) at a range of temperatures, substrate volumetric water contents (VWC), and fertilizer concentrations. The HI 76305 probe was highly sensitive to temperature, while the WET sensor was temperature-sensitive at high ECs above its normal operating range. The probes responded differently to increasing VWC. The SigmaProbe and WET sensor measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water become more diluted as VWC increases. EC readings of the HI 76305 and Field Scout probes, which measure the EC of the bulk substrate (growing medium, water, and air combined) increased with increasing water content as the added water helps conduct the current of these meters. At a VWC above 35%, there was little effect of VWC on EC readings of all probes. The EC measured with the various in situ probes differed slightly among the probes but was highly and positively correlated with all three of the standard solution extraction methods [pour-through, 1:2 dilution, and saturated media extract (SME)] over the range of fertilizer concentrations at a given temperature and VWC. These results make it possible to convert substrate EC guidelines that have been established for any of the three standard methods for use with the in situ probes, though our results indicate the substrate VWC must be above 35% for the interpretation to be valid. The in situ probes are a viable alternative for measurements of substrate EC and eliminate the step of substrate solution extraction, thus simplifying data collection.

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Erin M.R. Clark, John M. Dole, and Jennifer Kalinowski

added to DW with an EC of 0.4, 1.0, 1.5, 2.75, or 4.75 dS·m –1 . Solution pH was measured ( Table 1 ). Table 1. Electrical conductivity (EC) values used to determine the effect of EC on vase life of three cultivars of cut rose stems. Salts were

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Ariana P. Torres, Michael V. Mickelbart, and Roberto G. Lopez

container-grown crops. There are three accepted methods for monitoring substrate pH and electrical conductivity (EC) on-site: the pour-through (PT), the saturated media extract, and the 1:2 water:substrate (v/v) suspension test (1:2) ( Camberato et al., 2009