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Mary M. Gachukia and Michael R. Evans

conductivity (EC), or phytotoxic levels of one or more mineral nutrients. Other materials evaluated as potential alternatives to perlite were too expensive or had unacceptably high bulk densities (i.e., calcined clay aggregates, gravel) that resulted in

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Ka Yeon Jeong, Claudio Pasian, and David Tay

There is limited information on optimal substrate EC level for begonia species (noncultivated hybrids). The objective of this study was to evaluate the response of six species to different substrate EC in a greenhouse. Begonia albopicta, B. cucullata var. cucullata, B. echinosepala var. elongatifolia, B. holtonis, B. fuchsioides (red) and B. fuchsioides (pink) plants were propagated by stem cuttings, and transplanted into plastic pots using a soilless mix. Five concentrations (20, 80, 200, 400, and 600 mg·L-1 N) of 17–5–17 fertilizer were applied as irrigation water to derive the five substrate EC levels. This experiment was a factorial randomized complete-block design. Substrate EC was measured weekly using the PourThru method and averaged for each treatment of each species. Inflorescence number, the longest stem length, SPAD readings, leaf area, and dry weight of each plant were measured as growth parameters. There were significant responses to substrate EC level and species on begonia growth parameters. The highest growth parameters of B. albopicta and B. cucullata were obtained at EC 5.7 and 6.6 mS·cm-1, respectively. The maximum growth of B. echinosepala and B. holtonis was observed at 2.6 and 3.0 mS·cm-1, respectively. B. fuchsioides, grown at 1.2 mS·cm-1, had the best growth parameter values. As EC level increased, SPAD value for B. fuchsioides (pink) and B. holtonis also increased. The highest SPAD reading was observed at EC 3.7 mS·cm-1 for B. albopicta, EC 6.6 mS·cm-1 for B. cucullata, EC 2.6 mS·cm-1 for B. echinosepala, and EC 4.1 mS·cm-1 for B. fuchsioides (red). Plant mortality of several begonia species was observed when grown at EC value above 6.4 or below 4.4 mS·cm-1.

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Michael R. Evans, Johann S. Buck, and Paolo Sambo

determine and compare the substrate pH, EC, and primary macronutrient status of three ground PBH products to sphagnum peat over time in a greenhouse environment and to determine if these chemical properties were within acceptable ranges for use in substrates

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Huan-Ying Yao, Ren-Shih Chung, Sheng-Bin Ho, and Yao-Chien Alex Chang

collected and tested for pH and electrical conductivity (EC) by a pH and EC meter (IQ170; IQ Scientific Instruments, Carlsbad, CA), and the volume of leachate collected was also measured. The experiment was conducted in a completely randomized design with 20

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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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Johann S. Buck, Chieri Kubota, and Merle Jensen

the ion concentration of nutrient solution is electrical conductivity (EC) of the nutrient solution. One disadvantage of increasing fruit TSS by increasing nutrient solution EC is reduction in fruit yields. Increasing the EC to greater than 2.3 dS·m −1

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Ajay Nair, Mathieu Ngouajio, and John Biernbaum

compost had 27.5% organic matter, 7.2 dS·m −1 EC (in a 1:1 v:v water extract), and 5.27 pH (in a 1:1 v:v water extract). The nutrient content was 459, 1, 45, 810, 585, 192, 169, and 235 mg·kg −1 of nitrate-N, ammonium-N, P, K, calcium, magnesium, sodium

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Xiuming Hao and Athanasios P. Papadopoulos

Poor tomato fruit quality in summer time (soft fruit, cracking, and russetting) is a major greenhouse production problem in North America. To improve tomato quality and yield, especially under summer conditions, four EC treatments were applied to a tomato crop grown in rockwool in summer and fall of 1999 at the Greenhouse and Processing Crops Research Centre, Harrow, Ont., Canada. The four fertigation solution EC treatments were 1) constant low EC at 2.54 mS·cm-1, 2) constant high EC at 3.82 mS·cm-1, 3) diurnal EC variation (1 to 5 mS·cm-1) with a 24-h average of 2.54 mS·cm-1 and 4) diurnal EC variation (1 to 7 mS·cm-1) with a 24-h average of 3.82 mS·cm-1. For diurnal EC variation, the plants were fed with low EC in the morning and around noon, and high EC in the afternoon and night. High EC (3.82 mS·cm-1, constant or 24-h average for diurnal variation) treatments, in comparison to the recommended EC (2.54 mS·cm-1) treatments, improved tomato fruit quality by reducing fruit cracking, and increasing percentage of grade #1 fruit, fruit firmness, soluble solid and dry-matter content. However, the constant high EC treatment resulted in smaller fruit size and lower yield. Diurnal EC variation with a high EC average (24-h average: 3.82 mS·cm-1) did not reduce fruit size and yield, and reduced fruit russetting. Therefore, a diurnal fertigation EC variation strategy-supplying low EC solution in the morning and noon and high EC solution in the afternoon and night, with an overall 24-h average of 3.82 mS·cm-1, may be used to improve tomato fruit quality.

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Min Wu and Chieri Kubota

Manipulation of the electrical conductivity (EC) of the hydroponic nutrient solution has been studied as an effective method to enhance flavor and nutritional value of tomato fruit. The objective of this research was to quantitatively understand the accumulation of lycopene, soluble sugars, and the degradation of chlorophyll in fruits as affected by EC and EC application timing relative to fruit ripeness stages. `Durinta' tomato was grown hydroponically inside the greenhouse under two EC (2.3 and 4.5 dS·m-1). The high EC treatment began immediately after anthesis (HEC treatment) or 4 weeks later (DHEC treatment), when fruits had reached maximum size, but still were green. Fruits were harvested weekly beginning 2 weeks after anthesis, until they reached red ripe stage. The chlorophyll concentration in tomato fruits showed no difference between treatments when compared at the same ripeness stages. The lycopene concentration of red ripe tomato fruits in HEC and DHEC treatments was 29% greater than that in low EC control (LEC treatment). However, there was no significant difference in lycopene concentration between HEC and DHEC. Both DHEC and HEC increased total soluble solid concentration (TSS) of red ripe tomato fruits compared with those grown in LEC; while the DHEC showed an increase of fruit TSS of 12%, the HEC had a greater enhancement of TSS of 19%. In addition, the fruit ripeness was accelerated under high EC, regardless of the timing of treatment. High EC treatment at early and mature green fruit developmental stages enhanced both fruit TSS and lycopene concentration; however, the nutrient solution EC effect on lycopene concentration was not dependent on the time of application during fruit development.

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Marc van Iersel

Ebb- and-flow irrigation is an economically attractive subirrigation method that reduces labor costs and eliminates runoff from greenhouses. The effects of fertilizer concentration on growth of subirrigated pansy (Viola ×wittrockiana Gam.) and the leachate electrical conductivity (EC) and pH were quantified, using two growing media. Leachate EC increased as the EC of the fertilizer solution increased from 0.6 to 3.6 dS·m–1 (70 to 530 mg·L–1 N). The leachate EC was fairly constant over time when the EC of the fertilizer solution was 0.6 dS·m–1, while it increased throughout the experiment at higher fertilizer concentrations. MetroMix 300 leachate consistently had a higher EC than did MetroMix 500. Leachate pH of both growing media was similar throughout the growing season. The pH decreased over time and was lower with higher fertilizer concentrations. Optimal plant growth occurred with a fertilizer EC of 1.2 or 1.8 dS·m–1, and a leachate EC between 1.5 and 4 dS·m–1. Increasing the concentration of the fertilizer solution resulted in increased shoot tissue levels of P and Mn and decreased tissue levels of K, Mg, and Na. The results of this study indicate that pansy is not very sensitive to the EC of the growing medium and can be grown successfully in a closed subirrigation system.