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Florida had the largest fresh-market tomato (Solanum lycopersicumL.) production in the United States, with a value of $437million and 13,355 ha harvested in 2014. Despite the development of Best Management Practices (BMPs) and University of Florida/Institute of Food andAgricultural Sciences (UF/IFAS) fertilizer recommendations, tomato growers often use fertilizer rates above the recommended ones, especially when seepage irrigation is used and a longer growing season is foreseen. If a mass balance of N–P–K partitioning could be made in field conditions, a better understanding of nutrition applications could be reached. Therefore, a field study was conducted on seepage-irrigated tomato on a commercial farm in southwest Florida, during the spring and winter season of 2006 to evaluate the nitrogen (N) rate and season effects on tomato plant growth, fruit yield, N, phosphorous (P), and potassium (K) accumulation and use efficiency. The UF/IFAS N-recommended rate (224 kg·ha) was compared with a commercial grower (CG) rate (358 kg·ha). Both N rates were incorporated at bedding with 61 and 553 kg·ha of P and K, respectively. Fruit yield and plant growthweremeasured and roots, stems, leaves, and fruit samples were analyzed to determine total N, P, and K content and accumulation in different plant parts. Nutrient recovery (REC) and the partial factor of productivity of applied nutrients (PFP) were calculated for eachN rate. In the spring, 120 days after transplanting, plants dry biomasswas 11.5% higher (P = 0.01) in the CG N rate than with UF/IFAS N rate, while no significant differences were observed in the winter season. In the spring, N, P, andK accumulation were 250, 56, and 285 kg·ha in plants grown with CGN rate and were significantly lower (23%, 5%, and 23%, respectively) with the UF/IFAS N rate, respectively. In the winter, total N accumulation was 231 kg·ha in plants fertilized at CGN rate and significantly lower (16%) with the UF/IFAS N rate. N rate did not significantly affect P and K accumulation, which were on average 64 and 312 kg·ha, respectively. Marketable fruit yield was significantly higher (P = 0.03) with CGN rate than with UF/IFAS N rate (91.1 vs. 81.5Mg·ha), and was significantly higher (P = 0.03) in the spring than in the winter (100.8 vs. 71.8 Mg·ha). The NREC was significantly higher (P = 0.01) with the UF/IFAS N rate than with CG N rate and was not significantly affected (P = 0.94) by seasons. The PFPN was significantly higher (P = 0.001) with the UF/IFAS N-rate than with CGN-rate, and was significantly higher (P = 0.04) in the spring than in the winter season. These results suggest that current UF/IFAS N recommendations are more conservative of N and this should lead to reduced leaching potential but, UF/IFAS recommendations must be season specific due to the difference in environmental conditions of fruit maturation in cooler weather of the winter season compared with a warmer environment of the spring season. Fresh-market tomato is the most important vegetable crop in Floridawith a harvested area of 13,355 ha and a production value of $437 million in 2014 (USDA, 2015). Florida accounted for 34% of the national freshmarket tomato harvested area and 39% of the national crop value (USDA, 2015). Florida tomato production is concentrated in the central and southern areas of the state on low water-holding capacity sandy soils. Tomatoes are grown on raised polyethylene-mulched beds, using predominately subsurface (seepage) irrigation (Dukes et al., 2010). Seepage irrigation consists of managing a perched water table on top of a slowly permeable soil layer (‘‘spodic layer’’) located at 0.90 to 1.50mdepth.Water is pumped from the ground or surface reservoirs into a series of canals and ditches and is delivered to the plants by capillarity (Smajstrla and Mu~noz-Carpena, 2011). This irrigation method is widely used by Florida tomato’s growers for its low technology and operating costs (Zotarelli et al., 2013). An additional benefit of seepage irrigation is the possibility to raise the water table near the soil surface as an attempt to increase air temperature of few degrees during freezing events (OzoresHampton et al., 2010). However, drainage of water after the freeze event or excessive rainfall may remove substantial amounts of nutrients from the root zone. In seepageirrigated tomato crops, Sato et al. (2012) estimated losses of N and K over 40% and 35% of initial N and K available, respectively. Moreover, seepage irrigation requires large amounts of water, and has an average water use efficiency of 30% to 50% (Locascio, 2005). Seepage irrigation is hence considered one of the least efficient irrigation methods and its use raises several concerns for its potential negative impact on the environment (Ozores-Hampton et al., 2012; Simonne et al., 2010). In seepage-irrigated crops, all the nutrients N, P, and K are applied 100% at bed formation; 20% to 25% of N and K and 100% of P and micronutrients are broadcast applied into the bed as the ‘‘bottommix’’; the remaining 80% to 75% of N and K are applied in two grooves of 5 to 7 cm depth in the bed shoulders as the ‘‘hot mix’’ (Olson et al., 2005). As water moves upward into the root zone by capillarity, nutrients are slowly dissolved and made available for the crop (Sato et al., 2009a, 2009b). However, rainfalls events, water table rises for frost protection, and/or poor watermanagement may cause surface runoff, denitrification or leaching of nutrients out of the root zone, with consequent negative impact on crop productivity and groundwater and surface water quality (Cockx and Simonne, 2014; Sato et al., 2009a, 2009b; Simonne and Morgant, 2005). In an effort to reduce water pollution and improve the crop water and nutrient use efficiency (NUE), and in response to the Federal Total Maximum Daily Load mandate described in the Federal Clean Water Act (U.S. Environmental Protection Agency, 2010), the Florida Department of Agriculture and Consumer Services (FDACS) and the UF/ IFAS have developed and implemented BMPs. BMPs are cultural practices that aim at reducing the environmental impact of crop production while maintaining yields (FDACS, 2005), and ‘‘fertilization’’ and ‘‘irrigation’’ are Received for publication 9 July 2015. Accepted for publication 2 Sept. 2015. Corresponding author. E-mail: fdigioia@ufl.edu. 1636 HORTSCIENCE VOL. 50(11) NOVEMBER 2015 two important cultural practices addressed in the BMPs. Current UF/IFAS fertilization recommendations for tomato grown in Florida are based on preplanting soil tests for P, K, and micronutrients, with a blanket N rate of 224 kg·ha for all growing seasons (fall, winter, and spring), tomato types (round, Roma, or grape), soil types (spodic or well-drained soils), and irrigation methods (drip or seepage; Olson et al., 2005). The recommendations allow for supplemental applicationsofNandK1) after a leaching rainfall event (defined as 76mmof rain in 3 d or 102mm in 7 d), 2) when the results of foliar analysis or petiole sap testing are ‘‘low,’’ or 3) in case of extended harvest seasons (Olson et al., 2005). Despite these BMP recommendations, some tomato producers still apply N rates that range between 290 and 470 kg·ha of Nwhich is well above the UF/IFAS-recommended rate (Cantliffe et al., 2009). These higherN ratesmay be ‘‘justified’’ by: 1) the longer crop seasons (16, 20, or 18 weeks in south Florida for fall, winter, and spring plantings compared with 13 weeks in north Florida for spring plantings), 2) temporary water table rises during heavy rainfall periods and/or for frost protection events, and 3) the soil moisture conditions, more conducive to denitrification (Simonne and Morgant, 2005; Simonne and Ozores-Hampton, 2006). Although, studies on tomato yield response to N rates have been documented in the past and recently compiled by Hochmuth and Hanlon (2014), few studies have estimated the crop N, P, and K accumulation and partitioning, or have used the principle of the critical N concentration (%Ncrit), defined as the minimum N concentration in the aerial biomass required for maximum growth (Greenwood et al., 1991), to evaluate the UF/ IFAS N recommended rate. Yet, very few studies have evaluated and compared tomato crop N response in different growing seasons, which seem to have a big influence on the crop productivity and thus on the demand of nutrients (Ozores-Hampton et al., 2006; Scholberg et al., 2000). Therefore, a field study was conducted in southwest Florida on seepage-irrigated tomatoes comparing the UF/IFAS N rate (224 kg·ha) and a CG N rate (358 kg·ha) for two different (spring and winter) seasons to 1) evaluate the N rate and season effects on plant growth and fruit yield; 2) determineN, P, andK partitioning and accumulation in roots, stem, leaves, and fruits; 3) estimate the crop REC, the partial factor of PFP, and the potential return of nutrients to the soil with the crop residue; 4) analyze a posteriori the crop N status and fertilizer management following the principle of the %Ncrit and using the N nutrition index (NNI) proposed by Lemaire et al. (1989). Materials and Methods Experimental site, treatments application, and growing conditions. Two trials were conducted on seepage-irrigated tomato during the spring and winter growing seasons of 2006 in a commercial farm located near Immokalee, FL (26 25#11##N, 81 25#19##W). Soil types were typical Florida sandy soils in both trials: poorly drained Holopaw fine sand (loamy, siliceous, active, hyperthermic Grossarenic Endoaqualf) and Oldsmar fine sand (sandy, siliceous, hyperthermic Alfic Arenic Alaquod) for the spring and winter season, respectively (Sato et al., 2009a). For both trials, fertilizer treatments consisted of two N rates: the UF/ IFAS N recommended rate of 224 kg·ha and a CG rate of 358 kg·ha. Nitrogen rates were applied in pretransplanting and incorporated at bedding with 61 and 553 kg·ha of P and K fertilizer, respectively.

hortscience

Effects of Nitrogen Rates on Nitrogen, Phosphorous, and Potassium Partitioning, Accumulation, and Use Efficiency in Seepage-irrigated Fresh Market Tomatoes