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John A. Biernbaum, William Argo, and Janet Pumford

Unlike vegetable and fruit crops, where petiole analysis has been used for many years, root media analysis is the primary method of checking fertility status of container-grown flowering greenhouse crops. With the emphasis on lower constant water-soluble fertilizer rates to prevent nutrient runoff, petiole analysis may be a better indicator of N and K status. During Fall 1993, samples were collected from 10 flowering pot plant species subirrigated with either 50, 100, or 200 mg·liter–1 N and K concentrations. During Spring 1995, samples were collected from major bedding plant species and Easter lilies. Sap was extracted using a hydraulic press and nitrate and potassium were measured with the Cardy flat electrode ion meters. Sampling methods and protocols will be presented with results of sampling technique experiments. Floriculture plant nutrition researchers were contacted to identify other research in progress, potential applications, and possible concerns with using this technique. Further research needed will be identified.

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Mark V. Yelanich and John A. Biernbaum

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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William R. Argo and John A. Biernbaum

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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Mark V. Yelanich and John A. Biernbaum

`V-14 Glory' poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch) were fertilized at every irrigation with solutions containing 7, 14, or 28 mol N/m3 at four leaching fractions (LFs) of 0, 0.1 to 0.2, 0.3 to 0.4, or 0.5 to 0.6 or with subirrigation. The N applied ranged from 44 to 464 mmol/pot applied over 12 to 25 irrigations. Medium NO3-N and K concentrations and electrical conductivity were highest at the highest fertilizer concentration and lowest LF throughout cropping. Phosphorous concentration in the medium declined until week 12, when phosphoric acid was added for pH adjustment. Subsequently, medium P concentration was highest in treatments with the highest LF. Final shoot height, plant dry mass, and leaf area decreased as fertilizer concentration increased. Highest fresh mass, bract area, and shoot: root ratio were obtained with 14 or 28 mol N/m3 and a 0.55 LF or with 7 mol N/m3 and a 0.15 LF. Leaf N concentration was lower with subirrigation than with surface application. Leaf P and Mg were lower at higher LFs or with subirrigation, but leaf K was not influenced by the treatments.

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William R. Argo and John A. Biernbaum

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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William R. Argo and John A. Biernbaum

Hybrid impatiens (Impatiens Wallerana Hook. F.) were planted in six root media containing either 70% (by volume) rockwool, coir, or four types of sphagnum peat and 30% perlite. The six media varied in cation exchange capacities (CEC) (from 5 to 76 meq·L-1) and the amount of a dolomitic hydrated lime [Ca(OH)2 and Mg(OH)2 at 0 to 4.5 kg·m-3) required to obtain an initial pH of ≈6.0. Two additional treatments were produced by using a dolomitic carbonate lime (CaCO3 and MgCO3) at 8.4 kg·m-3 instead of the hydrated lime in two of the sphagnum peat media. Plants were subirrigated for 17 weeks using three nutrient solutions (NS) that contained at 200N-20P-200K mg·L-1 but had a variable NH4 : NO3 ratio and Ca2+ and Mg2+ content. The NS were designed to produce either acidic, neutral, or basic reactions in the medium. In media containing the hydrated lime, the NS was the primary factor controlling medium pH. However, within each NS treatment, the media did have some effect on buffering the pH over time. There was a linear increase in shoot-tissue Ca and Mg as the applied concentration of Ca2+ increased from 18 to 156 mg·L-1 and that of Mg2+ increased from 5 to 56 mg·L-1. Linear regression analysis of shoot-tissue Ca and Mg based on their concentration in the NS indicated a similar overall decrease in the Ca and Mg supply in all six root media over time. For plants grown in media containing the carbonate lime, shoot dry mass was similar to that of plants grown in the same media with hydrated lime. The presence of the carbonate lime in the media increased the pH buffering capacity against decreasing pH with the acidic and neutral NS but not against increasing pH with the basic NS. In the media containing the carbonate lime and given the acidic NS, root-medium and shoot-tissue Ca and Mg increased by weeks 12 and 17 compared to that of the same medium containing the hydrated lime. There were minimal differences in root-media and shoot-tissue Ca and Mg concentration between lime treatments when given the neutral or basic NS.

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William R. Argo and John A. Biernbaum

Using incubation and container culture with subirrigation for up to 28 days, three experiments were conducted with six liming materials of different particle sizes and six blended preplant nutrient charge (PNC) fertilizers. Liming material, particle size, and incorporation rate had an effect on the initial pH (3.5 to 6.1) and the final stable pH (4.8 to 7.8) with one type of Canadian sphagnum peat that did not contain an incorporated PNC. Saturated media extract (SME) Ca and Mg concentrations were <25 and 15 mg·liter-1, respectively, for both pulverized and superfine dolomitic lime at incorporation rates up to 7.2 kg·m-3. For the blended PNC fertilizers in media containing lime, initial electrical conductivity (EC) and SME nutrient concentrations ranged from (EC) 1.0 to 2.9 dS·m-1, (mg·liter-1) 60 to 300 N, 4 to 105 PO4-P, 85 to 250 K, 120 to 400 Ca, and 60 to 220 Mg. However, within two days, the rapid stratification of fertilizer salts within the pot caused macronutrient concentrations to increase in the top 3 cm of root medium (top layer) by an average of 180% and decrease in the remaining root medium in the pot (root zone) by an average of 57% compared to that measured in the medium at planting. Nutrient concentrations in the top layer continued to increase even when those in the root zone fell below acceptable levels recommended for an SME. The importance of fertilizer salt stratification within a pot lies in the reduced availability of nutrients to the plant and illustrates the limited persistence of the PNC fertilizers. Testing nutrients in container media several days after planting rather than in freshly mixed media may be more representative of the starting point for a nutritional management program.

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Mark V. Yelanich and John A. Biernbaum

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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Mark V. Yelanich and John A. Biernbaum

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.