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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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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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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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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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Andrew Ristvey and John Lea-Cox

Nutrient release patterns from several different controlled-release fertilizers (CRF) were studied during the overwintering period of a long-term nutrient uptake, leaching, and loss study of Azalea (Rhododendron) cv. `Karen' and Holly (Ilex cornuta) cv. `China Girl', under sprinkler and drip irrigation. In Maryland, diurnal winter temperatures can vary from ≈10 °C to above 15 °C. Most growers, therefore, cover frames with opaque plastic for cold protection from November through April. This is also the period when many growers apply CRFs on those plant species that take more than 1 year to produce. Few data are presently available on the release patterns of CRFs under variable temperature conditions in late winter/early spring. We hypothesized that substrate temperatures warmer than 15–16 °C will result in CRFs releasing nutrients at a time when root systems are inactive, with a major loss of nutrients with the first few irrigations in Spring. This 105-day study quantified nitrogen (N) and phosphorus release patterns from four brands of CRF (Osmocote, Nutricote, Scotts High N, and Polyon) with 270- and 360-day release rates, under these conditions. Each CRF was top dressed onto blocks of 18-month-old holly or azalea (n = 112) in 11.5-L (3-gal) containers, at a (low) rate of 6.1 g N per container. Ten randomly selected pots from each treatment were sampled every 15 days using two sequential leachings of distilled water, for a target leaching fraction of 25%. Leachates were recovered and analyzed for nitrate and orthophosphate concentrations. Ambient canopy temperatures were recorded continuously with remote temperature (HoBo) sensors from which degree days above 15–16 °C were calculated and correlated with CRF release patterns.

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Raul I. Cabrera

Research supported by the New Jersey Agricultural Experiment Station. Publication No. D-12167-1-96. The skillful technical assistance of Linda Santos, David Liloia, and Pedro Perdomo is gratefully acknowledged. Fertilizers used in these studies

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Jeffery Pack and Chad Hutchinson

Potato production in the Tri-County Agricultural Area of northeast Florida accounts for nearly half of the state's $120 M, 18-K hectare annual crop. Concern over nitrate movement into watersheds from potato production have stimulated research into alternative fertilizer sources and practices. This study evaluated the potential of several controlled-release fertilizer (CRF) products to release nutrients over a 100-day growing season under field temperature and precipitation conditions. In 2003 and 2004, 6 and 3 CRF products were evaluated, respectively. Meshbags containing 3 g of product mixed with 200 g of soil were buried 15 cm below the top of the potato row. Meshbags were removed at 2-week intervals. Samples were dried and sieved to remove soil. Fertilizer prills were ground and mixed with DI water to dissolve residual fertilizer. Samples were analyzed for total N by the Dumas (combustion) method (2003) or for TKN (2004). In 2003, initial release (after 20 days) ranged from 23% to 85% for the six products. In 2004, initial release (after 9 days) ranged from 34% to 65% for the three products. In 2003, total N release from CRF prills after 104 days ranged from 72% to 99%. In 2004, total N release from samples ranged from 79% to 92% release after 91 days. The shape of the release curve described some release patterns comparable to water-soluble fertilizers while others exhibited sustained-release properties. If release characteristics are designed to match potato plant uptake requirements in time and quantity, CRF products may be used to reduce off-site N movement while maintaining potato production.

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Paul K. Murakami and Fred D. Rauch

Three formulations of an encapsulated urea product and one sulfur-coated urea were evaluated at 0 to 4 times the recommended rate on Chomaedorea elegans, Chomaedorea seifrizii, Chrysalidocarpus lutescens, Spathiphyllum `Tasson', and Rhapis excelsa against a standard controlled-release fertilizer at equal N rates. Each plant species responded differently to the fertilizer sources. Chomaedorea seifrizii and Spathiphyllum `Tasson' did not exhibit preferences for fertilizer source from top-growth measurements. Chomaedorea elegans, Chrysalidocarpus lutescens, and Rhapis excelsa growth measurements indicate that fertilizer source affected growth and quality of the plants. The general recommendation for foliage plant production is an equal ratio of ammoniacal to nitrate nitrogen sources. Economically, this ratio makes the fertilizer more expensive than other traditional fertilizers. The use of a controlled-release urea fertilizer has the benefit of being a cheaper source of N and would lower the cost of production, but results on the selected foliage plants indicate that the fertilizer composition is important in plant production.

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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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Daphne L. Richards and David Wm. Reed

material, fertilizer, and growing medium, respectively, and grant support from the Texas Ornamental Enhancement Program and The Fred C. Gloeckner Foundation, Inc. We thank Dr. George Fernandez, Dept. Applied Economics and Statistics, Univ. of Nevada