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Hui-lian Xu, Laurent Gauthier, and André Gosselin

Tomato plants were grown in peatmoss-based substrate and supplied with nutrient solution of high (4.5 mS·cm–1) or low (2.3 mS·cm–1) electrical conductivity (EC) under high (95%) or low (55% of capillary capacity) substrate water content (SWC) to examine the effects of high EC and low SWC on growth and physiology. Salts were allowed to accumulate in the substrate for 7 weeks. Both high EC and low SWC significantly decreased dry matter production (DMP) and fruit yield (FY). Fruit harvest index was lower in high EC- or low SWC-treated plants. Decrease in marketable FY was attributed to both the decrease in total FY and the increase in small and abnormal (cracked and rot) fruits. Both high EC and low SWC decreased photosynthesis (PN) and leaf water potential (ΨL). However, chlorophyll content and respiration were increased by high EC under both high and low SWC. Water consumption based on both whole plant and unit of leaf area was decreased by high EC and low SWC. ΨL and transpiration were depressed by high EC and low SWC, especially at midday. There was a significant positive correlation between fruit yield and water consumption. The effects of high EC and low SWC were additive on most of the variables. Decreases in ΨL might ultimately account for water consumption reduction, PN depression, and FY decrease.

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Elizabeth Herrera, Nicolas Tremblay, and André Gosselin

Transplants of angelica (Angelica archangelica L.), horehound (Marrubium vulgare L.), and thyme (Thymus vulgaris L.) were grown in multicompartment trays with five proportions of compost (0%, 15%, 30%, 45%, 60%) mixed to peatmoss and perlite. Plants were fertilized with different electrical conductivity (EC) levels of the nutrient solution (0, 1, and 2 mmho/cm). Horehound and thyme plants were transplanted in the field to measure the residual effects of treatments on dry matter yields and level of active substances. The three medicinal plants showed increased shoot and root dry weights as well as leaf mineral content (some nutrients) when proportion of compost and EC of nutrient solution were higher. The optimal combinations of compost and fertilization treatments on plants growth varied between species. Residual effects of treatments applied in greenhouse on shoot dry matter weight of horehound and thyme plants were observed until the 9th and 12th week, respectively, after transplantation. Treatments also affected active substance levels in horehound plants in field. Organic fertilization management influenced growth, yield in the field and level of certain active substances of the harvested parts of medicinal plants.

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Julie P. Newman, Joseph P. Albano, Donald J. Merhaut, and Eugene K. Blythe

Release characteristics of four different polymer-coated fertilizers (Multicote, Nutricote, Osmocote, and Polyon) were studied over a 47-week period in a simulated outdoor, containerized plant production system. The 2.4-L containers, filled with high-fertility, neutral-pH substrate, were placed on benches outdoors to simulate the environmental conditions often used for sun-tolerant, woody perennials grown in the southwestern United States. Container leachates were collected weekly and monitored for electrical conductivity, pH, and concentrations of NH4 +N, NO3 N, total P, and total K. Concentrations of most nutrients in leachates were relatively high, but fluctuated frequently during the first third of the study period, and then gradually decreased and stabilized during the last 27 weeks. Osmocote often resulted in greater NH4 + and total inorganic N concentrations in leachates than other fertilizers during weeks 1 through 5, whereas Multicote produced higher NH4 + in leachates than most of the other fertilizer types during weeks 9 through 12. Overall, total P concentrations were greater with Multicote during a third of the experimental period, especially when compared with Osmocote and Polyon. Differences were also observed among treatments for leachate concentrations of K, with Polyon and Multicote fertilizers producing greater K concentrations in leachates compared with Osmocote during several weeks throughout the experimental period. Leachate concentrations of NO3 N and P from all fertilizer types were usually high, especially from week 5 through week 30.

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Donald J. Merhaut, Eugene K. Blythe, Julie P. Newman, and Joseph P. Albano

Release characteristics of four types of controlled-release fertilizers (Osmocote, Nutricote, Polyon, and Multicote) were studied during a 47-week simulated plant production cycle. The 2.4-L containers containing a low-fertility, acid-based substrate were placed in an unheated greenhouse and subjected to environmental conditions often used for production of azaleas and camellias. Leachate from containers was collected weekly and monitored for pH, electrical conductivity, and concentrations of NH4 + N, NO3 N, total P and total K. Leachate concentrations of all nutrients were relatively high during the first 10 to 20 weeks of the study, and then gradually decreased during the remaining portion of the experiment. Differences were observed among fertilizer types, with Multicote often resulting in higher concentrations of N, P, and K in leachates compared to the leachates from the other fertilizer types during the first half of the study. Concentrations of NO3 and P from all fertilizer types were often above permissible levels as cited in the federal Clean Water Act.

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Holly L. Scoggins, Paul V. Nelson, and Douglas A. Bailey

Substrate solution testing is an essential management tool for greenhouse plug production. Current methods of plug solution extraction and testing can be confounded by subjective aspects of their techniques. The press extraction method (PEM) developed at North Carolina State University offers a convenient and timely method of solution extraction. The rooting substrate is brought to container capacity and after a period of one hour, pressing the plug surface with a finger or thumb is sufficient to expel the solution. This series of experiments serves to quantify possible variation that may occur in pH, Electrical conductivity (EC), and nutrient analysis from differing manual extraction forces. A modified press was designed to apply a range of force [53, 71, 89, 106, and 124 N (5.0, 6.7, 8.3, 10.0, and 11.6 lb/inch2)], and sampling protocol consistency was verified. For all three experiments, the range of extraction forces within a single fertilizer rate did not significantly affect solution pH or EC. When testing included a range of fertilizer rates, results were significantly different among the fertilizer rates, demonstrating the method's ability to detect changes in pH and EC resulting from increases in fertility levels. Nutrient analysis (NO3 -, NH4 +, P, K, Ca, Mg, Na, B, Cu, Fe, Mn, and Zn) of solution extracted from two different rooting substrates (peat-based and coir-based) showed no differences within substrates for the range of force treatments.

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Joseph P. Albano, James Altland, Donald J. Merhaut, Sandra B. Wilson, and P. Chris Wilson

Scientific, Orion 4 Star) calibrated with 1413 µS·cm −1 standard (Fisher Scientific, Traceable Conductivity Standard 09-328-11). Experimental design and statistical analysis. Experimental units (containers/plants) were arranged on a greenhouse bench using a

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Fátima Medina-Lara, Ramón Souza-Perera, Manuel Martínez-Estévez, Manuel O. Ramírez-Sucre, Ingrid M. Rodríguez-Buenfil, and Ileana Echevarría Machado

plants per sample and soil type were grouped and mixed for use in the chemical analyses. The physico-chemical analyses of the soil and plant tissue were conducted by NUTRELAB. The parameters measured for soil were pH and electrical conductivity (EC

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Melanie L. Welles, David E. Hartley, and Steven E. Newman

The purpose of this experiment was to examine the effects of various root-zone temperatures and pH on Impatiens ×hybrida, New Guinea impatiens `Celebration Orange.' Greenhouse growers need to be cognizant of the root-zone medium pH, as New Guinea impatiens are sensitive to nutrient toxicities at low pH. It is thought that limestone at low root-zone medium temperatures is not quickly activated, leading to toxicities. The objectives of this project were to determine: the effect of root-zone medium pH on foliar symptoms of iron and manganese toxicity; and the effective rates and grind size of limestone on root-zone medium pH. Various rates of limestone and different grind sizes were incorporated into a sphagnum peat moss-based medium at a range of temperatures. This experiment used a two-way thermogradient plate to maintain varying, but stable root-zone medium temperatures, ranging from 12 to 42 °C. Plant growth as well as root-zone medium pH was monitored. Changes in root-zone medium pH were monitored over time. Results indicated that the addition of moderate or high rates of limestone, 6 or 3 kg·m-3, provided stable root-zone media pH over the course of time. Both limestone grind sizes at 325 and 100–200 mesh provided satisfactory starting and ending pH values for healthy New Guinea impatiens growth, especially between the root-zone temperatures of 30 and 18 °C. Higher and lower temperature extremes inhibited root growth, resulting in lower quality plants.

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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.