Fresh-market tomato comprised 16% of the harvested vegetable area and 23% of Florida vegetable production with 11,700 ha harvested and a market value of $268 million in 2012 [U.S. Department of Agriculture (USDA), 2013]. The Federal Clean Water Act of 1972 and the Florida Restoration Act of 1999 codified the maintenance and improvement of water quality for human consumption, wildlife habitat, crop irrigation, etc. (Bartnick et al., 2005). To improve polluted water bodies, the Florida Department of Agriculture and Consumer Services adopted a series of best management practices, which includes the use of CRF (Bartnick et al., 2005). Controlled-release fertilizers are SFs occluded in a polymer, resin, sulfur, or a polymer covering a sulfur-coated urea that protect nutrients against leaching from the root zone to become an environmental pollutant (Slater, 2010; Trenkel, 2010).
Approximately 40% of the Florida fresh-market tomato industry uses seepage irrigation as a result of low operating costs and straightforward use (E.J. McAvoy, personal communication; Zotarelli et al., 2013). In seepage irrigation, ground or surface water pumped into a series of canals creates a water table perched on a slowly permeable layer (agrillic or textural). Growers maintain the top of the water table at 0.4 to 0.6 m below the bed surface to irrigate the crop by capillarity (Smajstrla and Muñoz-Carpena, 2011). Oscillation in the water table causes nutrient leaching, primarily nitrate–nitrogen (NO3–-N) and potassium (K+); thus, a stable water table must be sustained (Sato et al., 2009).
Producers of seepage-irrigated tomato use raised beds covered with polyethylene mulch and the gradient fertilizer system, in which fertilizers are applied BIR before bed formation and banded on the bed shoulders (BBS) after bed formation (Geraldson, 1980; Liu et al., 2012). The UF/IFAS recommends that 100% of the P and micronutrients and 10% to 20% of the N and K+ be BIR. The remaining 80% to 90% of the N and K+ should be placed BBS. The UF/IFAS-recommended fertilizer rates for tomato production are 224 kg·ha−1 N and P and K fertilization based on calibrated soil test results (Olson et al., 2012). Additional N fertilizer applications are recommended as a result of leaching rainfall, defined as 76 mm of rainfall in 3 d or 102 mm of rainfall in 7 d, extended harvest season, or low LTN or petiole sap NO3–-N concentrations (Olson et al., 2012).
When polymer-coated urea (PCU) was placed as the only N source BIR or BBS in plasticulture tomato production, similar or lower total marketable tomato yields, respectively, were found compared with SFs at a similar N rate in two single-year studies (Ozores-Hampton et al., 2009). The reduced yields were likely the result of low PCU N release when BBS. To increase soil NO3–-N content, Ozores-Hampton et al. (2009) placed PCU and SF N (80% CRF:20% SF N ratio) BIR at 168 kg·ha−1 N, which resulted in similar tomato yields compared with the UF/IFAS SF recommendation during a winter production season. However, high plant mortality and reduced plant biomass were associated with high NH4+-N soil concentration from the PCU (Ozores-Hampton et al., 2009). To overcome the NH4+-N toxicity, a “hybrid fertilizer system” was created that contains 50% to 80% of the N as CRF placed BIR with the remaining N as SF BBS. Use of this system, in a single-year study, resulted in similar marketable tomato yields when CRF KNO3 was applied at equal or 25% reduced N rates compared with SF (Ozores-Hampton et al., 2009). A recent study, Carson et al. (2014), confirmed these results in a 2-year study. However, CRF KNO3 is more costly compared with CRF-urea (E. Ellison, personal communication). Because microbial activity increases with temperature (Frederick, 1956), perhaps detoxification of ammonium released from CRF-urea may be accelerate during the fall season compared with the winter, which may allow for use of CRF-urea.
Soil fumigation and staggered plantings extend the time CRFs are in the ground releasing nutrients before planting. For instance, a soil fumigant application requires a 2- to 3-week period between bed formation (and fumigation) and planting, and staggered plantings allowing for continual harvest may increase the production season by 3 weeks (Noling et al., 2012). Therefore, the extended production season must be considered in selection of CRF release duration (Carson and Ozores-Hampton, 2013). However, soil temperatures higher or lower than the CRF manufacturer’s nutrient release determining temperature will decrease or increase the release duration, respectively (Carson and Ozores-Hampton, 2013). For instance, Carson et al. (2013) found that the release duration of 90-, 120-, and 180-d release CRFs was shortened by 46% to 69% as a result of high soil temperatures that averaged 25.1 °C in white polyethylene mulch raised beds during a fall season. Thus, the objective of this research was to evaluate the effects of CRF N rate, source [mixed N (54% NH4+, 46% NO3–) compared with urea-N], release duration, and bed placement on marketable tomato yield, LTN content, post-season soil N content, and post-harvest fruit firmness and color during the fall.
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