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Jinsheng Huang* and Sieglinde Snapp

Potassium (K) and boron (B) nutrition play an important role in control of tomato quality. To evaluate the interactive effects of K and B on yield and fruit quality in fresh market tomatoes, two-year field experiments were conducted in 2002 and 2003 in Southwest Michigan, using the industry standard cultivar `Mountain Spring' and recommended practices for irrigated, staked fresh market production. Six treatments evaluated three fertilizer regimes applied during fruit development (1N:1K, 1N:2K and 1N:3K) and two weekly B foliar sprays (none and 300 mg·L-1 B) at fruit set stage. Increasing K concentration in the fertilizer increased K content in both leaf and fruit tissue, but reduced calcium content in leaf tissue. 1N:3K fertilizer treatment increased tomato shoulder check incidence. The overall total percent shoulder check defect was 32.7%, 33.5% and 38.2% for 1N:1K, 1N:2K and 1N:3K fertilizers, respectively. Weekly B foliar spray increased both tomato marketable yield and fruit quality. Less shoulder check incidence was obtained with a foliar B spray. Boron foliar spray also increased K content in fruit tissue for 1N:1K and 1N:2K treatments. The 1N:2K plus B foliar spray is recommended for improving tomato yield and quality.

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JinSheng Huang and Paul V. Nelson

It is desirable to have a large root mass and compact shoot in the final stage of plug seedling production. Marigold `Discovery Orange' was grown for six weeks from sowing in a hydroponic system. Hoagland's all nitrate solution was used at 0.25X for the first three weeks and 0.5X for the final three weeks. P was applied continuously in the control and was eliminated for the first one or three weeks in the two stress treatments. Weekly mot and shoot dry weights indicated: a.) P stress caused an increase in root/shoot ratio with roots larger than in the control plants and b.) restoration of P after a P stress resulted in a rapid shift of root/shoot ratio back to the control level with final root and shoot weights less than in the control plants. A continuous marginal P stress or a stress near the end of seedling production is suggested. Tomato `Marglobe' was grown for five weeks and impatiens `Super Elfin White' for six weeks in a 3 sphagnum peat moss: 1 perlite substrate in 288 cell plug trays. Fertilizer was applied at every third watering at a zero leaching percentage. The control nutrient ratio (mM) was 5.4 NH4+ NO3: 0.5 PO4: 1.6 K while the low P treatments contained 0.15, 0.1, and 0.05 mM PO4 throughout the experiment. The root/shoot dry weight ratios increased in the low P treatments. Tomato plants at 0.15 and 0.1 mM P and impatiens plants at 0.15 mM P had larger roots than the control plants. A continuous stress at 0.15 mM PO4 appears promising.

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Jin-Sheng Huang and Paul V. Nelson

Salinity guidelines for seed germination substrates are extremely low and difficult to attain given the salinity contributions of components such as peatmoss, vermiculite, limestone, wetting agent, and nutrients. This study was conducted to determine the value of N, P, K, and S as pre-plant nutrients with the anticipation that some could be eliminated. Seed were sown in two similar experiments on 23 Mar. and 6 June 1995 in 288-cell plug trays containing a substrate of 3 sphagnum peat: 1 perlite (v/v) amended with 6 g dolomitic limestone and 1.5 g Esmigran micronutrient mix per liter. Test plants included impatiens `Accent Rose' (Impatiens wallerana L.) and gomphrena `Buddy' (Gomphrena globosa. L.) Six preplant treatments including none, all, or all minus one of the nutrients N, P, K, and S were applied, each at a rate of 100 mg·L–1, substrate, in a randomized complete-block design with three blocks. Post-plant fertilization with 13–0.9–10.8 at 50 mg N/L began 1 week after sowing and was increased to 100 mg N/L when the fourth true leaf appeared. Omission of pre-plant K and S did not result in any reduction in final plant size in impatiens and only a minor reduction in one of the two gomphrena crops. Omission of N and P consistently reduced final size of plants by a commercially significant amount. While K and S are not necessary, N and P should be considered in a pre-plant fertilizer for these crops. In each situation where shoot size was smaller the root/shoot ratio was unchanged.

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Jin-Sheng Huang and S.S. Snapp

The appearance of a fruit quality defect, shoulder check in fresh-market tomatoes (Lycopersicon esculentum Mill.), has devastated the Michigan industry, and caused sporadic concern elsewhere. The defect appears as a surface roughness that occurs primarily on the shoulder area of the fruit. The fruit appearance is damaged and storability is severely compromised. Microscopic inspection reveals that the surface roughness consists of many microscopic cracks that occur in parallel lines. Our objectives were to describe this defect and evaluate the role of weather conditions and fruit surface moisture in inducing it. Field experiments were conducted in 2001 and 2002 in Southwest Michigan, using the industry standard cultivar Mountain Spring and recommended practices for irrigated, staked fresh market production. The effects of fruit surface wetness and nutrition on quality were evaluated by comparing responses to a plastic rain shelter; Surround WP kaolin spray (to enhance surface wetness); a foliar spray of calcium (Ca at 2 g·L-1), boron (B at 300 mg·L-1), Ca plus B, water alone; and no treatment. A complementary greenhouse experiment investigated the effects of low and high rates of foliar sprays. A very consistent association was found between defect incidence and precipitation events that followed periods of hot, dry weather during rapid fruit expansion. Fruit quality was highest and incidence of defects least in fruit produced under plastic rain covers, with an average marketable yield of 62,270 vs. 44,340 kg·ha-1 for the control. A 28% reduction in defects was consistently associated with Ca + B sprays across harvests and years. In contrast, 18% more fruit had shoulder check defect with kaolin spray, a consistent increase in defect across years compared to control fruit. Greenhouse and field studies gave markedly similar results, except for a water spray control. Incidence of defect was consistently low with the highest rate of B foliar spray.

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Cheon-Young Song, Jin-Sheng Huang and Paul V. Nelson

The greenhouse industry successfully uses high NO3 fertilizers to produce plants with short, compact shoots. It is commonly assumed that NO3 results in compactness while NH4 or urea stimulate large shoot growth. However, high NO3 fertilizers contain little or no phosphate. Four sets of treatments were applied to five species of bedding plant plug seedlings in two experiments to differentiate the effects of N source vs. phosphate supply on growth. Seedlings were established on 20-4.4--16.6 fertilizer until 10 days into stage 3, when the following treatments began. Set 1: phosphate-P was held at 22 mg/L and total N at 100 mg/L with NH4 comprising 40%, 13%, 7%, or 0% of total N, the remaining being NO3. Differences in shoot size did not occur as a consequence of the shift in NH4:NO3 ratio. Set 2: N was supplied at a concentration of 100 mg/L from 40% NH4 plus 60% NO3 while PO4-P was varied over the series of concentrations of 21.9, 6.6, 3.3, and 0 mg/L. Set 3: the same as Set 2 except that N was supplied entirely as NO3. Height and weight of shoots in Sets 2 and 3 were positively related to PO4 supply. Set 4: three commercial fertilizers containing 0 PO4-P and 8, 13, or 20% of N in the NH4 form. Compact shoots developed in these treatments. When 22 mg phosphate-P/L was added to one of these fertilizers, compactness was reversed. Shoot suppression by high NO3 fertilizers was concluded to be a function of low phosphate and not N form.

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Paul R. Fisher, Jinsheng Huang and William R. Argo

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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Jinsheng Huang, Paul R. Fisher and William R. Argo

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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Jinsheng Huang, Paul R. Fisher and William R. Argo

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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Jinsheng Huang, Paul R. Fisher and William R. Argo

Unreacted residual limestone in the container substrate is key in buffering pH change over time. Our goal was to develop a substrate test protocol to measure residual lime [in units of CaCO3 equivalent (CCE)] by applying a strong mineral acid (HCl) to a substrate sample and measuring the evolved CO2 gas with a gasometric method based on a Chittick apparatus. In one experiment, CaCO3 was added to a substrate that had previously been neutralized to pH 7.35 with Ca(OH)2 so that there would be minimal CaCO3 reaction with the substrate at this high pH. The gasometric method was then used to estimate residual CCE. Measured CCE and applied CaCO3 were similar, indicating reliable CCE estimation. In a second experiment, a pH titration method was used to quantify the relationship between substrate-pH and milliequivalents of reacted base and provided an additional validation of the estimated reacted and residual CCE. The gasometric method demonstrated declining residual CCE over time as a dolomitic limestone reacted to raise substrate-pH and increasing residual CCE as applied CaCO3 concentration increased. Residual CCE in a substrate is an important property that should be considered for pH control and management in greenhouse crop production. Our results indicate that the gasometric system may be useful for optimizing lime application rate, lime source, or management of residual CCE during crop production.

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Jinsheng Huang, Paul R. Fisher and William R. Argo

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.