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  • Author or Editor: Paul Fisher x
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Medium-pH above 6.4 is a common cause of micronutrient deficiency for container-grown plants, and technologies are required to correct an excessively high medium-pH. The objective was to quantify the dose response from application of several acidic materials that have been recommended for lowering medium-pH in soilless media. A 70% peat/30% perlite (by volume) medium was mixed with a preplant nutrient charge, a wetting agent and 1.5, 1.8, 2.1, or 2.4 kg·m-3 of a dolomitic hydrated lime resulting in four starting pH levels ranging from 6.4 to 7.6. Aluminum sulfate (17% Al) at 1.8-28.8 g·L-1, flowable elemental sulfur (52% S) at 3.55-56.8 mL·L-1, ferrous sulfate (20.8% Fe) at 1.8-28.8 g·L-1, Seplex-L organic acid at 0.32-5.12 mL·L-1, sulfuric acid (93%) at 0.08-2.56 mL·L-1, 21.1N-3.1P-5.8K water-soluble fertilizer at 50-400 mg·L-1 N (potential acidity 780 g CaCO3 equivalents/kg), and a deionized water control were applied at 60 mL per 126-cm3 container with minimal leaching as a single drench (except repeat sulfuric acid applications at 0.08 or 0.16 mL·L-1 and 21.1N-3.1P-5.8K treatments that were applied about every 3 days). Medium-pH and electrical conductivity (EC) were tested over 28 days using the saturated medium extract method using deionized water as the extractant. One day after application, aluminum sulfate, ferrous sulfate, and sulfuric acid lowered pH by up to 3 pH units at the highest concentrations and medium-pH remained fairly stable for the following 27 days. Flowable sulfur lowered pH gradually over the course of the experiment by up to 3.3 pH units, with no difference across the wide range in concentrations. Organic acid had minimal impact on medium-pH, and 21.1N-3.1P-5.8K did not lower medium-pH despite the fact that all nitrogen was supplied in the ammonium and urea form. At recommended concentrations, chemicals tested raised medium-EC, but not above acceptable levels for plant growth. The highest rates of aluminum and ferrous sulfates, and sulfuric acid, however, increased medium-EC by 2.0 dS·m-1 on day 1. Medium-pH-responses to acid-reaction chemicals would be expected to vary in commercial practices depending on additional factors such as lime type and incorporation rate, water alkalinity, media components, and plant interactions.

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The objective was to systematically quantify the dose response from applications of several alkaline materials recommended for raising pH in acidic media. A 70 peat: 30 perlite (by volume) medium was mixed with a pre-plant nutrient charge, a wetting agent, and between 0 and 1.5 kg·m3 of a dolomitic hydrated lime resulting in six starting-pHs between 3.4 and 6.4. The supernatant from a solution of Ca(OH)2, 2.5 to 40 mL·L-1 of a flowable dolomitic limestone suspension, 99.5% KHCO3 between 0.6 to 9.6 g·L-1, 85% KOH between 0.056 and 0.56 g·L-1, 15N-0P-12K water-soluble fertilizer at 50 to 400 mg·L-1 N, and a distilled water control were applied at 60 mL per 126-mL container with minimal leaching as a single drench (except the 15N-0P-12K that was applied about every three days). All chemicals increased medium-pH within one day, and pH remained stable until day 28 except for Ca(OH)2 which showed a 0.2 unit decrease in pH from day 1 to 28. The Ca(OH)2 and KOH drenches raised medium-pH by less than 0.5 units, and there was a slight decrease in pH from the 15N-0P-12K for starting-pHs lower than 5.0. Flowable dolomitic lime and KHCO3 raised pH by up to 2 pH units, averaged across starting pHs and 1-28 days after application. The effect on medium-pH increased as concentration of flowable lime and KHCO3 increased. Effect of flowable lime was greater (up to 2.9 units) at lower starting-pHs, whereas KHCO3 was less affected by starting-pH. Medium-EC increased by <0.6 dS·m-1 following single applications of all solutions.

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Our objective was to quantify the stem-elongation patterns of several Oriental and Asi-florum lily cultivars to develop graphical tracking charts where actual crop height can be compared visually against a target growth curve. Oriental lilies (`Mona Lisa' and `Stargazer') were grown in research greenhouses at Michigan State Univ. (MSU) during 1994 and 1995. Asi-florum lily cultivars (`Centurion', `LA-87', `Non-stop', `Salmon Queen', and `Salzburg') were grown at MSU in 1995. Plants received constant 20 °C from emergence to flower in 1995, and constant 15, 18, 21, 24, or 27 °C in 1994. Elongation of Oriental lily plants followed a sigmoid pattern. Oriental lily cultivars elongated rapidly after emergence until 60% of the relative time between dates of emergence and first open flower, at which time plants had achieved ≈82% (`Stargazer') or 85% (`Mona Lisa') of their final height; elongation then exhibited a plateau phase. In contrast to the Oriental lilies, Asi-florum cultivars consistently exhibited a more constant elongation rate throughout the growing period. Simplified graphical tracking curves were developed based on the patterns of elongation and were programmed into a computer decision—support system (`UNH FloraTrack'). The graphical tracking curves were tested by growing `Stargazer', `Mona Lisa', and four Asiflorum cultivars (`Donau', `Dream', `Moneymaker', `Spirit') at the Univ. of New Hampshire and MSU during 1997 to height specifications of 51 to 56 cm (including a pot height of 15 cm). Sumagic growth retardants were applied as a prebulb dip at 5 ppm and as a foliar spray at 3 ppm when plant height was above the target curve. Final height targets were achieved using this method. E-mail prf@hopper.unh.edu; phone, (603) 862-4525.

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Easter lily bulbs are harvested in fields in northern California and southern Oregon, packed in cases, and shipped to distributors and growers. The greenhouse forcer then cools the bulbs at 40–45°F for 6 weeks. This cold period is needed to vernalize the bulbs and to assure that the plants will later flower uniformly. Bulbs that have been cooled for longer or shorter lengths of time respond differently. The objective of this study was to determine the optimal storage temperature regime for the bulbs dug during the early part of the 3-week bulb-harvest period. Twelve groups of bulbs at various storage temperature regimes were evaluated as to their performance during greenhouse forcing. The variables that were considered were: 1) bud count, 2) variability of flowering date, 3) earliness of flowering date, 4) variability of Visible Bud date, and 5) variability of final plant height. An index was developed to evaluate the degree to which each variable impacted the production during the forcing phase. We found that the best protocol for bulb growers is to dig the bulbs and then hold them at cool (>45°F) ambient temperatures for a week. Temperatures higher than the high 65°F should be avoided. If the bulbs will be stored just 1 more week, then they can stay at this temperature; otherwise, the bulbs should be cooled down to, and held at, 42 to 45°F.

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The objective was to develop indices to describe reactivity of different lime particle size fractions with respect to pH change in horticultural substrates. Particle size efficiency (PSE) was calibrated from pH responses for separated six lime particle size fractions (>850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm) from three calcitic limes, and seven dolomitic limes, based on their increase in substrate pH relative to reagent grade CaCO3 when mixed in a sphagnum peat substrate at 5 g CaCO3 equivalents per liter of peat. The fineness factor (FF) was calculated for a liming material by summing the percentages by weight in each of the six size fractions multiplied by the appropriate PSE. The effective calcium carbonate equivalence (ECC) of a limestone was the product of the FF and the acid neutralizing value (NV) in CaCO3 equivalents. Reliability of the parameters for FF and ECC were then validated in two experiments, using 29 unscreened carbonate and hydrated lime sources, including the 10 calibration limes. In one experiment, 1 L of peat was blended at 5 g of lime (i.e., not corrected for differences in NV between limes). In the second experiment, 5 g CaCO3 equivalents for each lime, corrected for NV, were blended with 1 L of peat (a different peat source), using the same 29 lime sources. Both FF and ECC were positively correlated with the corresponding substrate-pH changes, with P < 0.001 and r 2 from 0.87 to 0.93. This calibration of PSE, FF, and ECC can improve limestone selection and application rate for the short term response and fine limestone sources used in horticulture.

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Limestone is incorporated into horticultural substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual”? lime. In horticulture, lime reactivity is currently measured empirically in batch tests, whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the non-limed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

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Lime sources vary in their reactivity depending on particle size, surface area and crystalline structure, and chemical composition. Current horticultural practice for testing lime reactivity and the appropriate lime rate is through batch trials where lime is incorporated into growing media. Our objective was to test a laboratory approach that would provide a rapid analytical test on reactivity of lime sources, and could eventually be applied to measuring unreacted (residual) lime in container media. Four moles HCl was added to a lime sample, and the volume of CO2 released over time was measured in a burette. Three lime types were tested, including reagent grade CaCO3, and two pulverized dolomitic limestones used in horticultural media. 100% of CaCO3 reacted in less than a minute after acid addition, whereas only 79.8% and 49.5% of the two commercial lime samples had reacted after 10 minutes. The time required for 50% of the two commercial lime samples to react was 5 and 10 minutes, respectively, whereas it took 20 and 60 minutes, respectively, for 95% neutralization. Reaction rates in the laboratory test correlated with the time required to achieve a stable pH level when limes were incorporated into a peat substrate. The reagent-grade CaCO3 raised pH more rapidly (within 7 days) and to a higher level (maximum pH 7.5 at 9 g of lime per liter of peat) compared with the dolomitic lime sources. It may be possible to establish a lime reactivity index, for example, based on CO2 release after 10 minutes, and thereby provide a rapid screening of limes. Further gasometric analysis of lime types used in horticultural substrates is therefore needed.

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The objective of this study was to develop reactivity indices to describe the pH response for liming materials incorporated into container substrates. Three reactivity indices [particle size efficiency (PSE), fineness factor (FF), and effective calcium carbonate equivalence (ECC)] were developed based on lime particle size distribution and lime neutralizing value (NV) in CaCO3 equivalent. Six lime particle size fractions (2000 to 850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm) separated from each of three calcitic limes and seven dolomitic limes were used to calibrate PSE, and were based on the increase in substrate pH (ΔpH) incited by the particle size fraction relative to reagent grade CaCO3 when mixed in a sphagnum peat substrate at 5 g CaCO3 equivalents per liter of peat. PSE for calcitic carbonate limes at day 7 (short-term pH response) were 0.13, 0.40, 0.78, 0.97, 1.00, and 1.00 for 2000 to 850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm particle fractions, respectively. Other PSE values were described for dolomitic carbonate limestones and for long-term pH response, and PSE was modeled with a function over time. FF was calculated for a liming material by summing the percentages by weight in each of the six size fractions multiplied by the appropriate PSE. ECC rating of a limestone was the product of its NV and FF. ECC multiplied by the applied lime incorporation rate could be used to predict substrate-pH response. Estimated PSE values were validated in two experiments that compared expected and observed substrate pH using 29 unscreened carbonate and hydrated lime sources blended with peat. Validation trials resulted in a close correlation and no bias between expected and observed pH values. Revised PSE values are useful to evaluate the reactivity of different limestone sources for container substrates given the fine particle size, short crop duration, and pH sensitivity of many container-grown crops.

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Paclobutrazol is a plant growth retardant commonly used on greenhouse crops. Residues from paclobutrazol applications can accumulate in recirculated irrigation water. Given that paclobutrazol has a long half-life and potential biological activity in parts per billion concentrations, it would be desirable to measure paclobutrazol concentration in captured irrigation supplies. However, there are no standard protocols for collecting this type of sample. The objective of this research was to determine if sample container material or storage temperature affect paclobutrazol stability over time. In two experiments, paclobutrazol was mixed in concentrations ranging from 0.04 to 0.2 mg·L−1 and stored in polyethylene, clear glass, or amber glass containers at temperatures of either 4 or 20 °C. Paclobutrazol concentration was measured at 3, 14, and 30 days after the start of each experiment. Across the two experiments, there were no consistent trends in reduction of paclobutrazol concentration with respect to container material or storage temperature. In the first experiment, there was an average of 5% reduction across all treatments from day 0 to 30, whereas in the second experiment, concentration did not decrease over the 30-day time period. These data suggest that paclobutrazol is stable in collected water samples for at least 30 days, and that either glass or polyethylene containers are suitable for collecting greenhouse water samples for analysis of paclobutrazol concentration. A minimum volume of 100 mL was determined to be the optimum to analyze water samples with diverse paclobutrazol concentrations.

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Floriculture species differ in their effect on substrate-pH and the resulting substrate micronutrient availability in container production. The objective was to quantify effects of floriculture plant species on substrate-pH. In a growth chamber factorial experiment, 15 floriculture species were grown in 70%:30% by volume peat:perlite substrate and fertilized with nutrient solutions containing 100 mg·L−1 N and NH4 +-N:NO3 -N nitrogen ratios of 0:100, 20:80, or 40:60. The relationship between substrate-pH and milliequivalents (meq) of acid or base per unit volume of substrate was quantified by titration with hydrated dolomitic lime or HCl. After 33 days, species and solution type effects on substrate-pH and estimated meq of acid or base produced were evaluated. Final substrate-pH ranged from 4.83 for geranium in 40:60 solution to 6.58 for lisianthus in 0:100 solution, compared with an initial substrate-pH of 5.84. This change in substrate-pH corresponded with a net meq of acid or base produced per gram of tissue dry mass gain (NMEQ) ranging across solutions and species from 1.47 of base for lisianthus in the 0:100 solution to 2.10 of acid for coleus in the 40:60 solution. With the 0:100 solution, geranium produced the greatest NMEQ of acid (0.07), whereas lisianthus produced the greatest NMEQ of base (1.47). Because all N in the 0:100 solution was in the NO3 anion form, meq of both anions and cations taken up by plant roots could be calculated based on tissue analysis. With the 0:100 solution, species that took up more anions than cations into plant tissue tended to have a more basic effect on substrate-pH, as would be expected to maintain electroneutrality. Data were used to estimate the percent NH4 +-N of total N in a nutrient solution that would be neutral (results in no substrate-pH change) for each species. This neutral percent NH4 +-N of total N ranged from ≈0% (geranium) to 35% (pentas). Species were separated into three clusters using k-means cluster analysis with variables related to NMEQ and anion or cation uptake. Species were clustered into groups that had acidic (geranium and coleus), intermediate (dusty miller, impatiens, marigold, new guinea impatiens, petunia, salvia, snapdragon, and verbena), or basic (lisianthus, pansy, pentas, vinca, and zinnia) effects on substrate-pH. Evaluating the tendency to increase or decrease substrate-pH across a range of floriculture species, and grouping of plants with similar pH effects, could help predict NH4 +:NO3 ratios for a neutral pH effect and assist growers in managing substrate-pH for container production.

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