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  • Author or Editor: John A. Biernbaum x
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Impatiens were planted into peat-based media containing two dolomitic liming materials [Ca(OH)2·Mg(OH)2 at 1.8 kg·m–3 or CaCO3·MgCO3 at 8.4 kg·m–3] and subirrigated for 17 weeks using four irrigation water qualities (IWQ) with varied alkalinity, Ca2+, Mg2+, and SO4-S content and three water-soluble fertilizers (WSF) with varied NH4:NO3 ratio, Ca2+, Mg2+, and SO4-S content. After 8 weeks, medium pH ranged from 4.5 to 8.5. Lime type did not affect the long-term increase in medium pH, Ca2+, and Mg2+ concentrations with IWQ/WSF solutions containing low NH4-N and high Ca2+ and Mg2+ concentrations. The carbonate lime did buffer the medium pH, Ca2+, and Mg2+ concentrations with IWQ/WSF solutions containing high NH4-N and low Ca2+ and Mg2+ concentrations. With both lime types, there was a linear increase in tissue Ca and Mg as the applied concentrations increased from 0.5 to 4.0 mol·m–3 Ca2+ and 0.3 to 3.0 mol·m–3 Mg2+ with the various IWQ/WSF. The relationship was similar for both lime types up to week 8, after which tissue Ca and Mg decreased with the hydrated lime and low solution Ca2+ and Mg2+. Relationships were also developed between the applied SO4-S concentration and tissue S and medium pH and tissue P.

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Hybrid impatiens (Impatiens wallerana Hook. F.) were planted into media containing two dolomitic liming materials {hydrated [Ca(OH)2 and Mg(OH)2] or carbonate (CaCO3 and MgCO3) lime} and subirrigated for 17 weeks with four irrigation water sources (IWS) and three water-soluble fertilizers (WSF). The WSF contained 200N–20P–200K mg·L-1 but varied in NH4 +-N content (50%, 25%, or 3%, respectively). Depending on the IWS and lime type used in the media, root-medium pH ranged from 4.5 to 6.0, 4.8 to 7.1, and 6.0 to 8.5 when treated with WSF containing either 50%, 25%, or 3% NH4 +-N, respectively, between 8 and 17 weeks after planting. The accumulation of NH4 +-N and NO3 --N in the root medium was different for treatments receiving the same WSF and depended on root-medium pH. The critical root-medium pH for NH4 +-N accumulation was between 5.4 and 5.7, and for NO3 --N, accumulation was between 5.3 to 5.9. Above this pH, minimal NH4 +-N concentrations were measured in the medium, even with 50% or 25% NH4 +-N WSF, while below this pH, NH4 +-N began to accumulate in the medium with a corresponding decrease in the NO3 --N concentration. The NH4-N: NO3-N ratios in the WSF had minimal effect on shoot fresh and dry weights. Tissue N concentration was higher with the higher NH4-N : NO3-N ratio WSF at all four sampling dates. There was a linear relationship between higher tissue N and lower root-medium pH with the same WSF, possibly due to differences in the ratio of NH4-N: NO3-N actually taken up by the plant.

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`V-14 Glory' poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch) were grown in five root media using top watering with 20% leaching for 112 days. Root media with a high water-holding capacity required fewer irrigations and fertilizer applications than those with a lower water-holding capacity. However, similar amounts of water were applied and leached with both types of root media over the entire experiment. The reduction in the number of fertilizations was compensated for by an increase in the amount (volume) of fertilizer applied at any one irrigation. The greatest differences in root-media nutrient concentrations were found between the top 2.5 cm (top layer) and the remaining root medium within the same pot (root zone). After 58 days, when fertilization with water-soluble fertilizer (28.6N–0P–8.5K mol·m–3) was stopped, nutrient concentrations in the top layer were 3 to 6 times greater than those in the root zone for all five root media tested. For the final 42 days of the experiment after fertilization was stopped, nutrient concentrations in the root zone remained at acceptable levels in all root media. The nutrients contained in the top layer may have provided a source of nutrients for the root zone once fertilization was stopped.

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A model was constructed to dynamically simulate how the nitrogen concentration changes in the root zone of a pot grown chrysanthemum. The root zone concentration of nitrogen is predicted at any time during the crop by predicting the root zone contents of nitrogen and water. The root zone content of nitrogen is predicted by integrating the rates of nitrogen applied, taken up by the plant and entering the top layer of the pot. The root zone water content is predicted by integrating the rates of water applied, evaporated from the media surface and transpired by the plant. Simple models were constructed to predict the various rate processes. For example the rate of nitrogen uptake was modeled as a function of the dry mass accumulation and was broken down into demands of nitrogen by the plant for maintenance of the current dry mass and for support of new growth. Dry mass accumulation was modeled as a function of the amount of PPF which could be intercepted by the plant. The model was validated using plants grown in growth chambers and greenhouses at various PPF levels and fertilizer concentrations. The model will be used to test the risks involved in using various fertilizer strategies and to develop more efficient fertilization strategies.

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The influence of fertilizer concentration and leaching volume on the quantity of applied N and water that were leached from a container-grown poinsettia crop (Euphorbia pulcherrima Willd.) was investigated. The NO3-N quantity leached after 71 days increased with higher NO3-N application rates (7, 14, or 28 mol NO3-N/m3) and higher leaching volumes; it ranged from 0.03 g NO3-N [7 mol·m-3, 0.00 container capacity leached (CCL)] to 7.65 g NO3-N (28 mol·m-3, 1.0 CCL). The NO3-N concentration for saturated media extracts increased with lower leaching volumes and higher fertilizer concentrations. For example, when 7 mol NO3-N/m3 was applied, NO3-N in the medium was 27.1 mol NO3-N/m3 when 0 CCL was used, but it was 8.6 mol NO3-N/m3 when 1.0 CCL was used. Shoot height and dry mass were not affected by the treatments. Leaching treatments also did not influenced leaf area, but leaf area was larger at 7 compared to 14 or 28 mol NO3-N/m3.

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Hybrid impatiens were grown in 15 cm pots containing one of six root medium. After seven weeks, plant available water holding capacity (AWHC) was measured as the difference between the drained weight of the plant and pot after a one hour saturation and the weight of the pot when the plant wilted. Water absorption potential (WAP) was calculated as the capacity of each root medium to absorb applied irrigation water up to the AWHC and was measured at two moisture levels with top watering (two leaching fractions), drip irrigation (two leaching fractions) and flood subirrigation. Top watering moist media (initial AWHC = 35%) with leaching fractions of 30+ % was me most efficient method of rewetting media and was the only irrigation method tested to obtain WAP's of 100%. In comparison, flood subirrigation was the least efficient method of rewetting media with WAP of 27% for dry media (initial AWHC = 0%), and obtained a total WAP of 55% for moist media (initial AWHC = 23%). In media comparisons, the incorporation of a wetting agent into a 70% peat/30% bark mix at planting increased the WAP compared to the same media without a wetting agent with nine of the ten irrigation treatments.

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The evaporation of water is a major source of water loss from potted plants which can be eliminated by placing a barrier at the exposed surface of media in the pot. To better understand the effect of reducing surface evaporation on growth and media nutrient concentration, 15 cm subirrigated poinsettias were produced with and without a pot cover. Both treatments received the same quantity of fertilizer, 75 mg·week-1 N for a total of 13 fertilizations. Uncovered pots received 12 more irrigations than pots with covers (20 vs. 32). Sixteen weeks after planting, covered plants had significantly less leaf area (2175 vs 2628 cm2), bract area (1655 vs 2137 cm2), height (24.1 vs 27.6 cm), fresh mass (116 vs 144 g) and dry mass (17 vs 20 g) than uncovered plants. Concentrations of N, P, K, Ca and Mg and EC (4.23 vs 2.65 mS·cm-1) were higher in the root-zone of covered plants than in uncovered plant. Covering the media surface did reduce the EC and the concentrations of N, P, K, Ca and Mg in the top layer (eg 13.47 mS·cm-1 vs 15.74 mS·cm-1) but stratification of salts to the top layer still occurred. Fertilizer salts in the top layer were shown to be less available to the plant than those in the root zone.

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Four experiments were conducted with six liming materials of different particle sizes and six commercially available blended preplant nutrient charge (PNC) materials in the laboratory and in container culture with subirrigation for durations up to twenty-eight days. Liming material, particle size, and incorporation rate affected both the initial and final stable pH of one type of peat without an incorporated PNC. Saturated media extract (SME) Ca2+ and Mg2+ concentrations were below the acceptable recommended concentrations for both pulverized and superfine dolomitic lime at incorporation rates up to 7.2 kg·m-3. For the blended PNC materials, initial N, P, K+, Ca2+, and Mg2+ concentrations for five of the six PNC materials were at or above the optimal concentrations recommended for an SME, but did not remain persistent in the root zone. A large percentage of all nutrients tested moved from the root zone into the top 3 cm (top layer) of the pot within two days after planting. Nutrient concentrations in the top layer continued to increase even when nutrient concentrations in the root zone fell below acceptable levels for an SME. The importance of this fertilizer salt stratification within the pot lies in the reduced availability of nutrients to the plant.

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Abstract

A crop of Calceolaria herbeohybrida Voss, was grown from December 1979 through March 1980 using a 16-week production schedule and nightbreak lighting to accelerate flowering. A second crop was grown from March through June 1980 without lighting. Root-zone heating of 20° to 22°C increased shoot fresh and dry weights and flower number but had no effect on days to anthesis. Plants at ambient (10° to 12°) root-zone temperature were of poor quality and underdeveloped; while plants with root-zone heating were well-developed with an adequate number of flowers. Root-zone heating was less effective for the March to June crop.

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Medium CO2 and O2 partial pressures were measured at three locations [3.8 (top layer), 7.5 (middle layer), and 10.3 (bottom layer) cm below the rim] in 15-cm-tall pots containing flowering chrysanthemums [Dendranthem×grandiflorum (Ramat.) Kitamura] grown in one of three root media. Average ambient medium CO2 and O2 partial pressures were 63 Pa and 21 kPa, respectively, and were similar in the three sampled layers in root media with an average moisture content of 50% to 60% of container capacity. Within 10 minutes after a drip-irrigation application of well water containing a titratable alkalinity to pH 4.5 of 320 mg CaCO3/liter, the partial pressure of medium CO2 increased to ≤1600 Pa and medium O2 decreased to 20.5 kPa in the top and middle layers of the pot. With subirrigation, medium CO2 partial pressures increased to ≤170 Pa and medium O2 remained at 21 kPa. When reverse-osmosis purified water (titratable alkalinity to pH 4.5 of <20 mg CaCO3/liter) was used instead of well water, the large increase in medium CO2 did not occur, indicating that the bicarbonate alkalinity in the irrigation water was the source of CO2. The high medium CO2 partial pressure measured after irrigation was not persistent; within 180 minutes, it returned to levels averaging 45% higher (100 Pa) than that measured before the irrigation. Medium O2 also had returned to ambient levels 180 minutes after the irrigation.

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