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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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John D. Lea-Cox*, Andrew G. Ristvey, and David S. Ross

Many agronomic and horticultural studies on nutrient uptake and use-efficiency have indicated, in general, that agricultural crops are poor competitors for nitrogen (N) and phosphorus (P) in soil-based systems, with estimates of overall nutrient efficiency being less than 50% for N and 10% for P. Low efficiencies are due to losses from leaching, runoff, gaseous emissions and soil fixation, but uptake efficiency is also affected by rate and timing (i.e. seasonal effects) of applications. Controlled-release fertilizers (CRF's) have been promoted as a technology that can slowly release nutrients; the release rate is most often a function of prill coating and temperature. There are few data in the ornamental literature that have directly compared the total uptake efficiency of CRF's to soluble fertilizer sources. From 1999-2002, we collected three annual N and P budgetary datasets, comparing two species (Rhododendron cv. azalea and Ilex cornuta cv.`China Girl') with different growth rates and hence nutrient requirements. Plant N and P uptake efficiencies were usually less than 20% of the total applied, but all datasets included a significant soluble fertilization component. In 2003, a new study with Ilex cornuta cv.`China Girl' was initiated, where nutrients were supplied only from two CRF sources, as we want to determine whether this technology can significantly increase nutrient uptake efficiency at similar rates. A preliminary analysis of the data indicate that total N and P uptake efficiencies between different CRF sources were similar, but leaching losses between sources varied during the growing season. It appears that the primary determinant of uptake efficiency is not source material or timing, but the overall rate of nutrient application.

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Thomas A. Obreza and Robert E. Rouse

Controlled-release N (CRN) fertilizer is receiving interest as a possible nutrient best management practice (BMP) for Florida citrus production, but grower acceptance will be limited until cost decreases and familiarity with CRN materials increases. The objective of this study was to compare long-term citrus production resulting from N fertilizer programs containing isobutylidene diurea (IBDU) or methylene urea (MU) with a conventional water-soluble N fertilizer program to determine the magnitude of horticultural utility provided by CRN. We applied N to a newly planted `Hamlin' orange (Citrus sinensis L. Osbeck) orchard using three sources (100% ammonium nitrate (AN); a 50/50 mixture of AN/IBDU; a 60/40 mixture of AN/MU) at four rates (0.25, 0.5, 1.0, and 2.0 or 1.5 times the recommended annual rate) in factorial combination, and continued for 7 years. During this period, AN was applied 31 times vs. about 15 times for CRN-containing fertilizers. We measured fruit yield, juice quality, and total soluble solids (TSS) yield in years 4 through 7 and found that they generally were not affected by N source, especially when year-to-year variation was taken into account. In year 7, fruit and TSS yields of well-fertilized trees reached 153 and 9.2 kg/tree, respectively. Maximum 4-year cumulative fruit and TSS yields (486 and 27.6 kg/tree, respectively) occurred at an N rate of 200 kg/ha. Maximum juice quality occurred at 180 kg N/ha. We feel the CRN materials tested could be used successfully in a nutritional BMP program that would maintain high yields while potentially decreasing N loss to the environment.

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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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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).

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Kimberly A. Klock-Moore and Timothy K. Broschat

Growth of hand-watered and subirrigated `Ultra Red' petunia (Petunia ×hybrida Hort.) and `Super Elfin Violet' impatiens (Impatiens wallerana Hook.f.) plants were compared when grown using four controlled-release fertilizer rates and four fertilizer placements in the pot. Furthermore, the amount of NO3-N leached from hand-watered plants was compared to amount captured by subirrigation system. Before planting, Osmocote (14N-6.2P-11.6K) (4 month release) was either topdressed (TD), layered in the middle of the pot (M), layered at the bottom of the pot (B), or incorporated throughout (I) the substrate at 1.25, 2.5, 5.0, or 7.5 kg·m-3 (oz/ft3). Shoot dry mass of petunia plants was similar between both irrigation systems and among the four fertilizer placements. Subirrigated petunias fertilized with 2.5 kg·m-3 had similar shoot dry mass as hand-watered petunias fertilized with 7.5 kg·m-3. Hand-watered impatiens had greater shoot dry mass than subirrigated impatiens. Hand-watered impatiens also had greater shoot dry mass in pots with fertilizer at TD, M, or I than with fertilizer at B, but no difference in growth was observed in subirrigated impatiens among the different fertilizer placements. Finally, significantly more NO3-N was leached from hand-watered plants than was captured with the subirrigation systems.

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Wayne L. Schrader

California vegetable and strawberry growers are expecting legislation which will limit their use of fertilizers and water by crop, acreage, and season. An increasing number of growers are adopting drip irrigation, which affords the opportunity for more precise control of water and nitrogen nutrition. Many growers, however, lack the skills and time necessary to manage and monitor water and fertilizer applications effectively in drip irrigation. Consequently, the need for quick, easy, and reliable methods to manage nitrogen fertility with drip irrigation has increased. Two trials were conducted to evaluate the effectiveness of granular controlled release nitrogen fertilizers in fields where excessive water use had been eliminated by using tensiometers and ET data to manage irrigations. A range of management options for maximizing yield and quality in vegetable and strawberry production with reduced nitrogen and water inputs will be discussed.

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Timothy K. Broschat

Five-gram (0.18 oz) samples of two controlled-release fertilizers (CRFs), Osmocote 15N–3.9P–10K (8–9 month) (OSM) and Nutricote 18N–2.6P–6.7K (type 180) (NUTR), were sealed into polypropylene mesh packets that were placed on the surface of a 5 pine bark: 4 sedge peat: 1 sand (by volume) potting substrate (PS), buried 10 cm (3.9 inches) deep below the surface of PS, buried 10 cm below the surface of saturated silica sand (SS), or in a container of deionized water only. Containers with PS received 120 mL (4.1 floz) of deionized water three times per week, but the containers with SS or water only had no drainage and were sealed to prevent evaporation. Samples were removed after 2, 5, or 7 months of incubation at 23 °C (73.4 °F) and fertilizer prills were crushed, extracted with water, and analyzed for ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), phosphorus (P), and potassium (K). Release rates of NO3-N were slightly faster than those of NH4-N and both N ions were released from both products much more rapidly than P or K. After 7 months, OSM prills retained only 8% of their NO3-N, 11% of their NH4-N, 25% of their K, and 46% of their P when averaged across all treatments. Nutricote prills retained 21% of their NO3-N, 28% of their NH4-N, 51% of their K, and 65% of their P. Release of all nutrients from both fertilizers was slowest when applied to the surface of PS, while both products released most rapidly in water only. Release rates in water only exceeded those in SS, presumably due to lower rates of mass flow in SS.

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Eric H. Simonne and Chad M. Hutchinson

Best management practices (BMPs) for vegetable crops are under development nationwide and in Florida. One goal of the Florida BMP program is to minimize the possible movement of nitrate-nitrogen from potato (Solanum tuberosum) production to surface water in the St. Johns River watershed without negatively impacting potato yields or quality. Current fertilizer BMPs developed for the area focus on fertilizer rate. Controlled-release fertilizers (CRF) have long been a part of nutrient management in greenhouse and nursery crops. However, CRFs have been seldom used in field-vegetable production because of their cost and release characteristics. Nutrient release curves for CRFs are not available for the soil moisture and temperature conditions prevailing in the seepage-irrigated soils of northern Florida. Controlled-leaching studies (pot-in-pot) in 2000 and 2001 have shown that plant-available nitrogen (N) was significantly higher early in the season from ammonium nitrate, calcium nitrate and urea compared to selected CRFs. However, N release from off-the-shelf and experimental CRFs was too slow, resulting in N recoveries ranging from 13% to 51%. Cost increase due to the use of CRFs for potato production ranged from $71.66 to $158.14/ha ($29 to $64 per acre) based on cost of material and N application rate. This higher cost may be offset by reduced application cost and cost-share pro-grams. Adoption of CRF programs by the potato (and vegetable) industry in Florida will depend on the accuracy and predictability of N release, state agencies' commitment to cost-share programs, and CRFs manufacturers' marketing strategies. All interested parties would benefit in the development of BMPs for CRFs.