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Donald J. Merhaut*, Joseph Albano, Eugene K. Blythe, and Julie Newman

Release patterns of ammonium, nitrate, phosphorus, potassium, calcium, magnesium, iron, manganese and zinc were measured during an eleven month period for four types of Controlled Release Fertilizers (CRF): Apex 17-5-11, Multicote 17-5-11, Nutricote 18-6-8 and Osmocote 24-4-9. Rate of fertilizer incorporation was 2.3 kg/m3 of nitrogen. Media consisted of 50% composted forest products, 35% ¼%-3/4% pine bark and 15% washed Builder's sand. The media was also amended with 0.60 kg/m3 of dolomite. Fertilizer was incorporated into the media with a cement mixer and placed into 2.6-L black polyethylene containers. Containers were placed on benches outside. Air and media temperature were monitored throughout the 11-month period. Containers were irrigated through a ring-dripper system. Leachate was collected twice weekly. Leachate electrical conductivity, pH, and nutrient content were measured weekly. Significant differences in the nutrient release patterns were observed between fertilizer types throughout much of the experimental period. Release rates were significantly greater during the first 20 weeks of the study compared to the last 20 weeks of the study, regardless of the fertilizer type.

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Chad Hutchinson* and Eric Simonne

Potato (Solanum tuberosum L.) production best management practices (BMPs) are under development for the Tri-County Agricultural Area (TCAA; St. Johns, Putnam, and Flagler counties) near Hastings, Fla. BMPs are designed to reduce nitrate non-point pollution in the St. Johns River from the |8000 ha in potato production in the TCAA. Research to develop a controlled release fertilizer (CRF) program to help growers meet the current nitrogen rate BMPs was conducted during the 2003 season. A randomized complete block experiment with four replications was conducted at the Plant Science Research and Education Unit in Hastings, Fla. The treatments were no nitrogen control, ammonium nitrate (168 and 212 kg N/ha) and three CRF products blended at different ratios (168 kg N/ha). Total tuber yields for `Atlantic' for the no nitrogen, and 168 and 212 kg N/ha ammonium nitrate treatments were 11.5, 23.4, and 36.4 MT/ha. The best combination of the three CRF products were a ratio of 33:33:33 with a 40 day, 75 day, 120 day release period, respectively. Total yield for this blend was 42.2 MT/ha. Specific gravities for tubers in all four treatments were 1.060, 1.072, 1.078, and 1.082, respectively. Percent of tubers with hollow heart four all four treatment were 8.1, 18.2, 20.0, and 6.4% respectively. Percent of tubers with internal heat necrosis four all four treatments were 20.6, 8.1, 20.6, and 6.3%, respectively. The CRF treatment produced significantly more tubers than the ammonium nitrate treatment at the same nitrogen rate. Quality of the tubers in the CRF treatment was higher than tubers from the no nitrogen control and ammonium nitrate treatments. Research will continue to optimize the CRF program for potato production in Florida.

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Timothy K. Broschat

( Ogden et al., 1987 ). Controlled-release fertilizers (CRFs) have been very effective in supplying plant nutrient needs and minimizing the loss of environmentally problematic ions such as nitrate nitrogen (NO 3 -N) and phosphate phosphorus (PO 4 -P

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Mary Jane Clark and Youbin Zheng

Micros controlled-release fertilizer, applied at six rates. Data are means of five replicates. Where effect of fertilizer rate was significant ( P < 0.05), lines indicate the calculated regression, otherwise no lines are shown. Despite the natural yellow

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R. Kasten Dumroese

Juniperus scopularum Sarg. (Rocky Mountain juniper) and Potentilla fruticosa L. `Gold Drop' (gold drop potentilla) plants grown in containers had similar or better morphology, higher nitrogen concentrations and contents, and higher N-use efficiency when grown with liquid fertilizer applied at an exponentially increasing rate as compared to the same amount of N applied via controlled-release fertilizers. More importantly, plants grown with a half-exponential rate were similar to those grown with controlled-release fertilizer but with a higher N-use efficiency, indicating that this type of fertilization may be a method for reducing the amounts of applied nutrients in nurseries and subsequent nutrient discharge.

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D. Joseph Eakes and John W. Olive

Two 8- to 9- month [Nutricote 20-7-10 (Type 270) and Osmocote 18-6-121 and two 12- to 14- month [Nutricote 20-7-10 (Type 360) and Osmocote 17-7-121 controlled release fertilizers were preplant incorporated into a 3:1 pine bark:peat moss medium during two potting dates (April 12 and June 6, 1991) at the rate of 1.5 kg N/m. Plant growth of two woody ornamentals, 'Green Luster' Japanese holly and 'Fashion' azalea, and monthly medium solution electrical conductivity (EC) were determined. Growth index [GI = (height + width at widest point + width perpendicular to widest point)/3] response to fertilizer treatment was species specific. Nutricote 20-7-10 (type 360) produced the largest GIs for holly, while GIs for azalea were not affected 420 days after initiation (DAI) of the test. Plants potted in April had greater GIs than those potted in June for the two plant species 420 DAI, regardless of fertilizer type. Osmocote 18-6-12 and 17-7-12 controlled release fertilizers had the greatest medium solution ECs from 90 to 180 DAI.

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T.L. Prince, H.K. Tayama, T.A. Prince, N.R. Bhat, and S.A. Carver

Controlled-release fertilizers (CRF), Nutricote 14N–6.2P-11.6K or Osmocote 14N-6.2P-11.6K, at the recommended rate (1×) and at half that rate (0.5×) plus 200 mg/l N of Peter's 20N-4.4P-16.6K water soluble fertilizer at every irrigation were applied to potted chrysanthemums cv. `Bright Golden Anne' and `Torch'. Production and postproduction quality was evaluated. CRF applications (1×) resulted in reductions of plant height (-10%), plant diameter (-17%), leaf area (-35%), and leaf dry weight (-47%), but did not affect number of flowers compared to plants receiving only water soluble fertilizer. Application of water soluble fertilizer with CRF (0.5×) increased foliar nutrient levels above water soluble fertilizer application alone, or above either CRF (1×). CRF applications (1×) resulted in improved floral longevity (up to +8 days) and flower color rating (up to +54%), and less foliar senescence (up to -45%) than the water soluble fertilizer application alone, or either of the CRFS (0.5×) used with water soluble fertilizer.

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Mark H. Brand

Information on fertility optimization for container-grown ornamental grasses is limited. For ornamental grasses, growers are concerned with the degree of flowering, number of tillers, and height and width of the plants as well as other growth or ornamental components. Pennisetum alopecuroides divisions potted into 8.5-L containers were grown outdoors in a container nursery from May through September. The potting medium used was a 3 aged pine bark: 2 peatmoss: 1 sand nursery mix (by volume), amended with dolomitic lime 3 kg/yard3. Sierra 17-6-10 plus minors, 8 to 9 month controlled-release fertilizer (CRF) was top dressed at 20, 30, 40, 50, or 60 g/container. Foliage height increased linearly with increasing CRF rate. Flower height increased to a maximum at 40 g of CRF per container and then decreased with higher levels of CRF. Basal plant width exhibited a quadratic response to CRF rate, reaching a maximum at 40 g of CRF per container. The greatest number of flowers and tillers were obtained using 50 g of CRF per container. Maximizing the number of flowers is important for marketing of Pennisetum, since this plant is grown primarily for its flowering.

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Stephen K. O'Hair and Tiangen Wang

Controlled-Released Fertilizer (CRF) has a great potential for applications in the nursery container industry. However, the specific mechanisms of the control are proprietary. The longevity claimed by manufacturers are unclear. The longevity of one CRF is claimed to be 2 to 3 months at 80 °F, resulting in a deviation of 30%. Thus, the actual release rate will have a 30% deviation from the claimed longevity. A preliminary study was conducted to test the longevity of two types of RCFs. 1.00 g (7.7% NO- 3-N, fast release) and 1.30 g (5.9% NO- 3-N slow release) of CRF was added to 500 ml distilled water in separate flasks and stirred continuously at a low speed during measurement period. A nitrate electrode and a reference electrode were set in the solution. The nitrate electrode responded to the increase in nitrate concentration caused by nitrate release from he CRFs. The response analog signal from the nitrate sensor was input to a 16-bit analog/digital converter with 1-minute interval for each measurement. The results indicated that 9% of the nitrate from the fast CRF (2- to 3-month longevity) was released in 10 hours. About 11.5% of the nitrate from the slow CRF (8- to 9-month longevity) was released in 260 hours. Based on the observed release rates, a 2- to 3-month longevity CRF will last about 111 hours in the stirred distilled water at room temperature. A CRF with 8 to 9 month longevity will last about 94.2 days. Even though field conditions are different from the experimental conditions, the real longevity of CRF in the fields may have to be further investigated. In the tropical southern Florida climate, the release rates of nutrients from CRFs are likely to be enhanced.

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Raul I. Cabrera and Pedro Perdomo

Herbaceous perennials are the hottest item in the ornamental industry, yet relatively little is known about the most appropriate management and cultural practices for many of these species. The response of selected perennials to controlled-release fertilizer (CRF) rates was evaluated in this study. Liners of Coreopsis `Early Sunrise' and `Zagreb', Astilbe `Bridal veil', Hemerocallis `Stelladoro', Phlox `Franz Shubert', and Rudbeckia `Goldstrum' were transplanted to 5.7-L pots filled with a 2 peat: 1 perlite (v/v) medium amended with dolomite and Micromax (2 and 0.6 kg·m-3, respectively). Plants were topdressed with Osmocote 18N-2.7P-10K at rates of 0, 1.8, 3.6, 5.3, 7.1 (industry standard) and 8.9 kg·m-3, and grown over a 3-month period. Plant biomass and quality ratings (including chlorophyll levels) followed an asymptotic behavior with CRF applications for Coreosis `Early Sunrise' and Astilbe `Bridal veil', leveling at ≈1.8 kg·m-3. The rest of the species showed increases in plant growth and quality with CRF rates of 1.8-3.6 kg·m-3, followed by sharp, and significant, reductions at higher CRF rates. Observations of optimum growth and quality at CRF rates 1/2 to 3/4 below commercial recommendations were partially attributed to the use a peat medium, with relatively higher nutrient holding characteristics in relation to the more common pine bark mixes. This observation was confirmed the following season, where plants grown in a 4 pine bark: 1 sand medium (v/v) required higher CRF rates to have similar growth and quality responses to those grown in a 4 peat: 1 bark: 1 sand medium (v/v).