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Timothy K. Broschat

Release rates for 13 commercially available soluble and controlled-release K fertilizers were determined in sand columns at 21C. Potassium chloride, KMgSO4, and K2CO3 were leached completely from the columns within 3 or 4 weeks. Osmocote 0N-0P-38.3K, Multicote 9N-0P-26.7K, the two S-coated K2SO4 products, and Nutricote 2N-0P-30.8K Ty 180 all had similar release curves, with fairly rapid release during the first 20 to 24 weeks, slower release for the next 10 to 12 weeks, and virtually no K release thereafter.

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Ka Yeon Jeong and James E. Altland

), and stored in a growth chamber set to 20 °C (left) or 40 °C (right) during 180-d storage period. Substrates were also either not amended with fertilizer (control), or amended with 0.59 kg·m −3 N of a controlled release fertilizer (CRF) (Osmocote 18N–1

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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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Christopher J. Currey and Roberto G. Lopez

Angelonia ‘AngelFace White’ and ‘Sundancer Pink’, Nemesia ‘Bluebird and Raspberry Sachet’, and Petunia ‘Cascadia Marshmallow pink’ cuttings 28 d after inserting cuttings into substrate containing 0, 3, 6, 12, or 24 g controlled-release fertilizer (CRF

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Mary Jane Clark and Youbin Zheng

overall appearance for five container-grown nursery crops in Sept. 2013 following transplant on 15 May 2013 and fertilized with six rates of nitrogen (N) incorporated from an 8–9 month release 19N–2.6P–10.8K plus minors, controlled-release fertilizer (CRF

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Mongi Zekri and Robert C.J. Koo

Controlled-release sources of N and K were compared with soluble sources on young `Valencia' orange trees (Citrus sinensis [L.] Osb.). The effects of these fertilizers on leaf mineral concentration, soil chemical analysis, and tree growth were evaluated for 3 years. Soluble fertilizers were generally more readily available but had shorter residual effects on leaves and soil than controlled-release fertilizers. In the top 30 cm of soil, the plots treated with controlled-release N had 23% more total N than those treated with soluble N sources, while the plots fertilized with controlled-release K contained 56% more extractable K than those that received soluble K. Different effects on leaf and soil N between the two controlled-release N sources, sulfur-coated urea (SCU) and methylene urea (MU), were also found. With the use of controlled-release fertilizers, application frequency was reduced from a total of 15 to six applications with no adverse effects on tree growth, leaf mineral composition, or soil fertility during the first 3 years. Combining soluble and controlled-release fertilizers in a plant nutrition program offers an economical and effective strategy for citrus growers.

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Shiv K. Reddy

Various methods are used to evaluate the release characteristics of coated, controlled-release fertilizers. These methods include measuring the nutrients released into water or remaining in the prills or measuring the growth and nutrient content of the plants grown. Such methods do not show the release mechanism of the fertilizers. A simple test was developed that actually shows how nutrients are released from coated fertilizer prills that contain potassium. When prills of commercial products were placed in 1.5% aqueous solution of sodium tetraphenyl boron, potassium released from the prills combined with sodium tetraphenyl boron and formed a white precipitate. The precipitate patterns revealed that some new prills had large cracks or imperfect coating, thus releasing their nutrients instantly and prematurely. Over time, individual prills within the same fertilizer showed different release behaviors—from no release to release through tiny holes in the coating to release by rupture or bursting of the coating. This test is particularly useful for detecting coating defects during manufacture or subsequent damage to coating, as during incorporation of the prills into growing media. (Provisional patent application filed for this method.)

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J.J. Ferguson and F.S. Davies

Young `Hamlin' orange trees [Citrus sinensis (L.) Osbeck] were fertilized six times/year with water-soluble N fertilizer at recommended rates (0.20, 0.34, and 0.38 kg N/tree per year) and with controlled-release fertilizer one time/year [Osmocote, IDBU, and a 44.5% urea-N fertilizer coated with a sulfonated ethylene-propylene-diene polymer (Sherritt, Inc.)] at 0.04, 0.06, and 0.08 kg N/tree per year for years 1, 2, and 3, respectively. There were no differences in trunk diameter, tree height, or tree rating among treatments in any year, although there was a slight reduction in tree rating for some trees with biuret symptoms in the Sherritt treatment in year 2. Leaf nitrogen content was acceptable for all treatments in all 3 years, except for the Osmocote treatment in year 2, which had low to deficient levels. Levels of other nutrients were all within acceptable ranges, except for low potassium levels for the Osmocote in year 2. There were no significant differences in yields of young trees in year 3, the first bearing year. Given its 44.5% N analysis, the total amount of Sherritt controlled-release fertilizer applied to young citrus trees was 4% that of the standard, water-soluble fertilizer and from 39% to 45% that of the two other controlled-release fertilizers in years 1, 2, and 3.

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Tom Yeager and Geri Cashion

Container plant runoff NO3-N levels varied with sampling time and were periodically higher than the 10-ppm federal drinking water standard during 4.5 months following fertilizer application, even though controlled-release fertilizers Nutricote 18N-2.6P-6.6K Osmocote 18N-2.6P-10K, Prokote 20N-1.3P-8.3K, and Woodace 19N-2.6P-10K were used. Leachate collected from containers had a higher NO3-N level than runoff regardless of sampling time. Leachate NO3-N ranged from 278 ppm for Nutricote 3.5 months after application to 6 ppm for Prokote 1 week after application.

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C.A. Sanchez

Lettuce produced in the desert typically shows large yield responses to N fertilization. However, concern about the potential threat of nitrate-N to ground-water has prompted additional studies aimed at developing improved N management practices. Field experiments were conducted between 1992 and 1995 to evaluate the response of crisphead lettuce to controlled-release N fertilizer (CRN). The use of CRN was compared to a soluble N fertilizer applied preplant (PP), and a soluble N fertilizer applied in split-sidedress applications (SD). Rates of N fertilizer application ranged from 0 to 300 kg·ha–1. Lettuce generally showed significant responses to N rate and N management practice. However, response to management practice varied by site-season. When conditions for N loss were high, SD and CRN management strategies were superior. However, in other site-seasons, SD management sometimes resulted in inferior head quality and marketable yield when compared to other management strategies. Data averaged over six site-seasons shoed improved yield and quality to CRN management strategies compared to PP and SD strategies.