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  • Author or Editor: John A. Biernbaum x
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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 constructed to describe nitrogen dynamics in the root zone of subirrigated container-grown chrysanthemum was used to develop and test nitrogen fertilization strategies. The model predicts the nitrogen concentration in the root zone by numerical integration of the rates of nitrogen applied, plant nitrogen uptake, and nitrogen movement to the medium top layer. The three strategies tested were constant liquid N fertilization, proportional derivative control (PD) based upon weekly saturated medium extraction (SME) tests, or PD control based upon daily SME tests. The optimal concentration of N to apply using a single fertilization concentration was 14 mol·m–3, but resulted in greater quantities of N being applied than if PD controller strategies were used. The PD controllers were better able to maintain the predicted SME concentration within 7 to 14 mol·m–3 optimal range and reduce the overall sample variability over time. Applying 14 mol·m–3 N at every irrigation was found to be an adequate fertilization strategy over a wide range of environmental conditions because N was applied in excess of what was needed by the plant.

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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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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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Impatiens were planted in media containing either hydrated or carbonate dolomitic lime and subirrigated for 17 weeks using four irrigation water qualities (IWQ) and three water-soluble fertilizers (WSF). Micronutrients (Fe, Mn, Zn, Cu, B, and Mo) were incorporated into all root media at planting with fritted trace elements (FTE 555) at 0.07 kg·m–3 and were added to all WSF treatments with a commercially available chelated material (Compound 111) at a constant 50 mg·liter–1. Root-medium pH obtained from the various IWQ/WSF solutions at 4, 8, 12, and 17 weeks after planting were used to determine relationships with shoot tissue micronutrient concentrations. Tissue Fe concentrations decreased linearly as root-media pH increased from 5.0 to 8.5. Below pH 5.0, the tissue Fe concentration increased at a rate indicating greater nutrient availability in the root medium. However, between pH 4.0 and 7.5, tissue Fe was within acceptable levels. A linear relationship also was found with tissue Zn and B, but without the rate increase below a pH of 5.0. Tissue Mn decreased to a minimum as the rootmedium pH increased from 4.0 to 6.0 and increased again as the root medium pH increased from 6.0 to 8.5. Tissue Mo concentrations increased as root medium pH increased. Tissue Cu concentrations were unaffected by medium pH.

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Impatiens were grown in media containing either hydrated or carbonate dolomitic lime and subirrigated for 17 weeks with four irrigation water qualities (IWQ) and three water-soluble fertilizers (WSF). The WSF concentration was 14N–0.6P–5K mol·m–3 but contained either 50%, 25 %, or 3 % NH4-N. After 8 weeks, rootmedium pH ranged from 4.5 to 8.0. In general, the higher the percent NH4-N content of the WSF, the lower the root-medium pH, although there were significant interactions between IWQ and lime type with WSF on root-medium pH. With the same WSF, the concentration of NH4-N measured in the root media depended on root-medium pH. For example, with WSF containing 50% NH4-N, root-medium pH with the various IWQ ranged from 4.5 to 6.0, and media NH4-N ranged from 5.0 to 0.1 mol N/m3. Tissue N concentrations were higher with the higher NH4: NO4 ratio WSF at all four sampling dates. The effect of IWQ on tissue N resulted from the root-medium pH effects produced by the various IWQ/WSF combinations. Shoot fresh and dry weights were unaffected by the NH4: NO3 ratios in the WSF.

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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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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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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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