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Controlled-release fertilizers (CRFs), a vegetable production best management practice in Florida, are soluble fertilizers (SFs) coated with a polymer, resin, or a hybrid of polymer coating sulfur-coated urea. In 1994, a Controlled Release Fertilizer Taskforce developed an accelerated temperature-controlled incubation method (ATCIM) to predict column-incubated CRF nitrogen (N) release for regulatory purposes. Determination of CRF field N release uses a field method such as a pouch field study, which requires multiple samples and high costs for laboratory N analysis. If the ATCIM may be used to predict CRF N release in the field, then vegetables growers will have a faster and lowercost method to determine N release compared with the pouch field method. Therefore, the objective of this study was to evaluate the correlation of the ATCIM and the pouch field method as a predictor of N release from CRFs in tomato production in Florida. In 2011 and 2013, 12 and 14 CRFs, respectively, were incubated in pouches placed in polyethylene mulched raised beds in Immokalee, FL, and extracted in the ATCIM during 2013. The ATCIM CRF results were used individually and grouped by release duration to create predicted N release curves in a two-step correlation process. The two-step processes predicted the percentage N release of individual CRF with R of 0.95 to 0.99 and 0.61 to 0.99 and CRFs grouped by release duration with R of –0.64 to 0.99 and –0.38 to 0.95 in 2011 and 2013, respectively. Modeling CRF N release grouped by release duration would not be recommended for CRF 180-d release (DR), because coating technologies behaviors differ in response to high fall soil temperature in polyethylene mulched beds. However, with further model calibration, grouping CRFs of 90 to 140 DR to simulate the CRF N release profile may allow the ATCIM to predict CRF N release without performing the pouch field method, which currently negated the usefulness of the ATCIM in a tomato production system. The majority of fresh-market tomato in south Florida is grown using subsurface or seepage irrigation as a result of low costs and simple operation (E.J. McAvoy, personal communication; Zotarelli et al., 2013). Seepage irrigation consists of managing a perched water table on a slowly permeable agrillic or spodic soil layer (Pitts et al., 2002). In seepage-irrigated fresh-market tomato (Solanum lycopersicum L.) production using soluble fertilizer sources, all the phosphorus and micronutrients plus 10% to 20% of the N and potassium (K) are applied broadcast in-row before bedding and the remainder of the N and K is applied after bed formation in two bands on the bed shoulders before plants are transplanted in the field (Carson and Ozores-Hampton, 2013). Repeated water table fluctuations, resulting from inadequate water table management or intense rainfall, may result in N leaching losses from 35% to 43% in tomato production in south Florida (Sato et al., 2012). Therefore, vegetable growers should maintain a steady water table to reduce N leaching during the crop season. In response to the Federal Clean Water Act of 1972 and the Florida Restoration Act of 1999, a series of agronomic and vegetable best management practices (BMPs) have been adopted by the Florida Department of Agriculture and Consumer Services (Bartnick et al., 2005). One BMP can be the use of CRFs, which are SFs encapsulated in a polymer, resin, or a hybrid of sulfur-coated urea occluded in a polymer coating (Bartnick et al., 2005; Trenkel, 2010). By definition, CRFs may increase N use efficiency compared with SF by protecting N against leaching below the root zone and becoming an environmental pollutant (Slater, 2010). Over the past 50 years, several CRF coating technologies have been developed and marketed, but no standard method to evaluate CRF manufacturer claims or performance existed for regulatory purposes in the United States (Sartain et al., 2004a, 2004b). Therefore, a task force was formed in 1994 to develop an ATCIM to predict CRF release duration. The task force developed a two-step correlation between ATCIM N release and N release from CRFs incubated in soil-filled polyvinyl chloride (PVC) columns in the laboratory (Carson and Ozores-Hampton, 2012; Medina et al., 2009; Sartain et al., 2004a, 2004b). The ATCIM-predicted PVC column incubated CRF N release with greater than 90% accuracy (Medina et al., 2009; Sartain et al., 2004a, 2004b). During the PVC column laboratory incubation, CRFs were maintained at a constant temperature and moisture content between leaching events; thus, CRFs were subjected to minimal variability compared with CRFs placed in the open field. In contrast, field studies are subject to variations resulting from diurnal temperature oscillation, weather pattern, and water table fluctuations (Medina, 2011). Therefore, because of field environment variability, correlation for regulatory purposes needs to be tested between ATCIM and laboratory-based PVC column-incubated CRFs (Carson and Ozores-Hampton, 2012). The field pouch method has been used to determine CRF N release in the field in several studies (Carson and Ozores-Hampton, 2012). The mesh pouches allow for contact between the soil and CRF prills, which may affect CRF N release because pouches with 1.2-mm openings had greater N release compared with pouches with 0.07-mm openings (Wilson et al., 2009). Although this method may be effectively used to determine N release rate from CRFs, the pouch method requires an entire growing season and numerous samples with high analysis costs (Carson and OzoresHampton, 2012). However, an ATCIM that predicts CRF field release may assist growers with the selection of a CRF with the correct release duration to be used in vegetable production with lower time and costs. The two-step CRF prediction method requires correlation of N release from an ATCIM and a long-term CRF incubation to determine CRF-specific N release coefficients. Therefore, to predict N release from a new CRF never tested in tomato production in Florida, a pouch field method would be required to correlate with the ATCIM. Consequently, if a pouch study were conducted, an ATCIM would not be needed to predict field N release. Thus, if CRFs were grouped by release duration to develop a CRF N release model, then perhaps CRF N release may be predicted without a field pouch study. Therefore, the objective of this study was to evaluate the correlation of the ATCIM and Received for publication 2 Sept. 2014. Accepted for publication 20 Oct. 2014. To whom reprint requests should be addressed; e-mail Ozores@ufl.edu. HORTSCIENCE VOL. 49(12) DECEMBER 2014 1575 the field pouch method as a predictor of N release from individual CRFs and CRF grouped by release duration in tomato production in south Florida. Material and Methods Accelerated temperature-controlled incubation method. Fourteen CRFs from Florikan ESA L.L.C. (Sarasota, FL), Agrium Advanced Technologies Inc. (Loveland, CO), ChissoAsahi Fertilizer Co. Ltd. (Tokyo, Japan), and Everris International B.V. (Dublin, OH) were tested during July 2013 using the ATCIM (Table 1) (Medina et al., 2009). A 30-g CRF sample was exposed to four increasingly aggressive (in length and temperature) extractions using 0.2% citric acid as a solvent during the course of 72 h. Extractions were 2 h at 25 C, 2 h at 50 C, 18 h at 55 C, and 50 h at 60 C (or 2, 4, 22, and 72 h, cumulatively). The extraction device had 16 jacketed chromatography columns; therefore, 14 CRFs and two isobutylidene diurea (31% N) samples as controls were extracted during each incubation cycle, which was replicated three times with CRFs randomized in each replicate. Extract N content was measured by pyrolysis and chemiluminescence using an Antek 9000 N analyzer (PAC Co., Houston, TX). The ATCIM N release data were subjected to analysis of variance and orthogonal contrasts using the general linear model procedure of SAS (Version 9.2; SAS Institute, Cary, NC). Data were presented as cumulative percentage N released (PNR). Field pouch method field study. Twelve and 14 CRFs extracted in the ATCIM were used in the pouch method field study during 2011 and 2013, respectively, in Immokalee, FL, on Basinger fine sand (hyperthermic Spodic Psammaquents) (Carson et al., 2013, 2014c). The CRFs were divided into two independent studies containing an equal number of CRFs (Table 1). The CRF fall mixes (M112, M168, and M224) were CRF and SF mixes that when applied at 1493 kg·ha supply 112, 168, and 224 kg·ha CRF N; however, the SF and fillers in the pouch may have affected the N release in 2011. Therefore, FLmix was added in 2013 containing CRF equivalents to the fall mixes that were composed of FL100, FL140, and FL180. All other treatments were individual CRFs. Fiberglass window screen (18 · 14 mesh) was cut into 15 · 30-cm rectangles, folded in half, and sealed on two sides. A CRF sample containing 3.5 g N was placed in the mesh pouch and the last side was sealed giving inside dimensions of 12.7 · 14 cm. The CRF pouches were buried flat at a 10-cm depth in the center bed of a three-bed, 1.5-m long plot. The pouches in the experimental unit, e.g., a set (six or seven) of pouches representing each CRF, were placed randomly in the plot. The plots were placed in a randomized complete block design with four replications and eight collection dates (Table 2). After pouch collection, the pouch contents were dried in a beaker at room temperature, placed in plastic bags, and stored until N analysis (Carson et al., 2012). To prepare the sample for analysis, the pouch contents were ground in 300 mL of deionized water using a blender (Model 36BL23; Waring Commercial, New Hartford, CT) to destroy the prill coating. The CRF samples were diluted to 500 mL with deionized water, filtered using Whatman no. 42 filter paper, and frozen at –20 C until analysis. In 2011, the samples were analyzed for total soluble N by pyrolysis and chemiluminescence usi

hortscience

Prediction of Controlled-release Fertilizer Nitrogen Release Using the Pouch Field and Accelerated Temperature-controlled Incubation Methods in Sand Soils