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-mm2 openings had greater N release compared with pouches with 0.07-mm2 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 Ozores-Hampton, 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 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.
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