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Holly L. Scoggins

Little taxa-specific information is available regarding the nutrition needs of container-grown herbaceous perennials. The goal was to determine optimum fertilizer concentrations and corresponding substrate testing values for greenhouse production of 10 taxa. Astilbe chinensis (Maxim.) Franch. & Savat.`Purpurkerze', Campanula carpatica Jacq. `Deep Blue Clips', Coreopsis verticillata L.`Golden Gain', Gaura lindheimeri Engelm. & Gray, `Siskiyou Pink', Heucherasanguinea Engelm. `Mt St. Helens', Lamium maculatum L. `White Nancy', Penstemon ×hybridus Hort. `Sour Grapes', Perovskia atriplicifolia Benth. `Longin', Salvia nemerosa L. `Blue Hill', and Veronica × Hort. `Goodness Grows' were grown for 10 weeks with 15N–7P–14K at four rates (50, 150, 250, and 350 mg·L–1 N) of constant liquid feed. Substrate pH and soluble salts levels were measured weekly using the pour-through extraction method. In analysis of all taxa, most effects [quality, shoot dry weight, pH and electrical conductivity (EC)] varied by rate × taxa. Though higher levels of fertilizer produced the largest plants in some cases, satisfactory quality was also attained with a lower rate. Quality and pH were negatively correlated for a few genera but most showed no relationship. Results of this study indicate not all taxa tolerate increased fertilizer levels and that the herbaceous perennials studied could be grouped by nutritional needs. Furthermore, target ranges for EC can be developed based on dry mass and quality ratings.

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Paolo Sambo, Franco Sannazzaro, and Michael Evans

In order to evaluate alternative rooting media as a substitute to sphagnum peat in tomato transplant, fresh rice hulls (2 and 4 mm particle size), perlite, and peat were compared. In the same experiment, four nutrient solutions differing in electrical conductivity [(EC) 2.5, 3.5, 4.5 and 6.0 mS/cm], but not in nutrient content, were used. Seed of tomato (Lycopersium esculentum L.) `Brigade' (ASGROW) were sown in 55 × 35 × 6.5 cm polystyrene transplant trays containing 336 cells (15 mL) and filled with the root substrates. The trays were placed in a glass-glazed greenhouse. Trays were kept under intermittent mist for 6 days and then fertilized twice per week with 2.6 L per tray of solution. A split-plot design with three replications was used with nutrient solution serving as the main plot and root substrates serving as the subplots. During the growing cycle (once a week) and when plants were ready to transplant (16 cm tall, with an average of five to seven true leaves), stem diameter, hypocotyl length, plant height, number of true leaves, fresh shoot weight, and dry shoot weight were measured. Also at transplant, root fresh and dry weight and above- and below-ground biomass were analyzed to determine N, P, K, Ca, Mg, Fe, and Mn content. Plants grown in rice hulls were as marketable as those in peat, but showed a higher content in N, K, and Mn. Increased nutrient solution affected not only dry matter accumulation, but also stem diameter and plant hight, which were greater in plants grown with high EC.

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Norman E. Pellett and David A. Heleba

Most of 36 crabapple and 19 other woody plant taxa demonstrated the ability, when dormant, to grow a continuous row of callus along the cambial region on split-stem pieces within 5 to 7 days of incubation at 25 °C. The ability to grow callus after freezing tests was compared with discoloration and electrical conductivity for determining laboratory freeze injury to selected taxa. Hardiness levels were determined using the procedures of callus growth, discoloration, and electrical conductivity after freezing stem pieces of Jack crabapple [Malus baccata (L.) Borkh. `Jacki'], pink bud Sargent crabapple [M. sargentii Rehd. `Rosea'], Mary Potter crabapple [Malus sp. `Mary Potter'], and snowberry mountainash [Sorbus discolor (Maxim.) Maxim.]. Sampling dates for laboratory freezing tests were chosen to represent midwinter cold hardiness and partial hardiness of either late fall or early spring. There was a high correlation between discoloration and callus ratings for most plants; however, the two methods usually did not identify the same critical temperature (T50) for injury. The critical temperatures identified by callus growth was often 3 to 6 °C lower than for discoloration. For many taxa, callus growth was easier to see than discoloration of cambium and phloem, providing a less subjective evaluation of injury. TTC (2,3,5-triphenyl tetrazolium chloride) treatment was sometimes useful to identify callus growth that died after forming. The critical temperature (Tc), the highest temperature at which relative electrical conductivity differed significantly from the control temperature, was higher in most cases, indicating less cold hardiness than the T50 for callus and discoloration. The callus procedure may have value for evaluating injury to the cambial zone from freezing and other plant stresses because it determines the ability of the plant to continue growth.

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Robert L. Green, Laosheng Wu, and Grant J. Klein

Summer decline of annual bluegrass (Poa annua L.) putting greens is a major concern of golf course superintendents. Low soil water infiltration rates and high concentrations of salts in the root zone are contributing factors. This study was conducted to determine the effects of summer cultivation treatments on field infiltration rates of water, soil salinity, oxygen diffusion rates (ODR), bulk density, total and air-filled porosity, and root weight density. This research was conducted during two summer seasons (1996 and 1997) on a practice putting green located at Industry Hills Golf Courses, City of Industry, Calif. The green was constructed to U.S. Golf Association (USGA) specifications in 1978. Cultivation treatments consisted of: 1-3) water injection cultivation (WIC) applied with a Toro HydroJect every 21 d (raised position), and every 14 or 21 d (lowered position); 4) solid tine cultivation (STC) applied every 14 d; and 5) no cultivation (check). Results showed WIC and STC significantly increased field infiltration rates of water and lowered overall soil electrical conductivity of the extract (ECe) at depths of 2.5 to 7.5 cm and 7.5 to 15.0 cm in the root zone. The effects of WIC, raised position, did not differ significantly from those of STC, but infiltration rates of water were greater on all rating dates. Cultivation treatments had no significant effects on overall soil ODR, bulk density, and porosity or on overall root weight density.

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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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Harvey J. Lang

Analysts of potting media for pH and electrical conductivity (EC) can be a useful tool for monitoring the nutritional status of greenhouse grown plants. This research examined the variability associated with procedures involved in the determination of pH and EC in greenhouse potting media. Three commonly used methods, the 1:5 dilution, the 1:2 dilution and the saturated media extract, were examined on several different commercial potting media. Because of the different dilution volumes used, there were significant differences in pH and EC between the three methods for all media tested. Within each method, results varied baaed on whether readings were taken in the slurry, solution phase, or extract, with extracts resulting in consistently higher pH, but lower EC values. There was a significant effect of medium-solution equilibration time on both pH and EC, with variability decreasing after 30 minutes of equilibration. Samples taken from the upper half of pots had higher EC readings than those collected from the bottom half of pots only on plants fertilized with N concentrations greater than 200 ppm. There was also slight variability between the different calibrated instruments used in determining pH and EC. Details of each study along with grower recommendations will be discussed.

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Martin P.N. Gent

Solution electrical conductivity (EC) and the supply of nitrate in proportion to other elements (nitrate supply ratio) should effect tissue composition of lettuce (Lactuca sativa L.) grown in hydroponic solution. These parameters were varied in several series of successive plantings in greenhouses in the northeast United States. In 1996, when the treatments differed only in EC, 0.65 and 0.9 dS·m-1, but not in nitrate supply ratio, leaf tissue had more nitrate and total reduced-N and lettuce grew faster in the solution with higher EC. Over four series of plantings in 1997 and 1998, the nitrate supply ratio of a low-N treatment was only 60% of that for a high-N treatment, and EC was varied from 1.2 to 2.0 dS·m-1. In 1997 and 1998, tissue nitrate was lower in the low-N treatment only when EC was less than in the high-N treatment. However, under irradiance greater than 10 MJ m-2 per day, the lower EC also slowed growth. Stepwise regression over data from all experiments showed leaf nitrate was primarily a function of EC, and a term that described the interaction between irradiance and EC. Due to selective uptake by the plants, the ratio of elements in the recirculating solution differed from the ratio in which they were supplied. Under irradiance less than 10 MJ m-2 per day and solution EC greater than 1.5 dS·m-1, nitrate accumulated in solution to a concentration greater than expected from simple dilution of the concentrates. Tissue nitrate was also related to solution nitrate, increasing by 0.08-0.09 mg·g-1 dry weight per 1 mg·L-1 increase in solution nitrate. To prevent a rise in tissue and solution nitrate under low irradiance, both solution EC and nitrate supply ratio had to be reduced by about one-third, compared to the conditions required for rapid growth under high irradiance.

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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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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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Carey Grable, Joshua Knight, and Dewayne L. Ingram

with a wider range of release rate. The objective of this study was to determine the effects of four formulations of CRF, including two with new polymer coating technology, on leachate pH and electrical conductivity (EC), and plant growth of two species