ASHS 2015 Annual Conference

Florida had the second largest fresh-market tomato production in the United States, with a value of $455 million and 10,700 ha harvested in 2013. Despite the development of Best Management Practices and the existence of University of Florida/Institute of Food and Agricultural Sciences (UF/IFAS) irrigation and fertilizer recommendations, growers often tend to apply fertilizers above recommended rates. Lack of confidence in the recommendations, limited knowledge on how to implement recommendations, and limited data on actual crop nutrient uptake and efficiency are the possible explanations for this practice. Therefore, objective of the study was to evaluate nitrogen (N) rate effects on tomato plant growth, fruit yield, N, phosphorus (P), and potassium (K) uptake and plant partitioning. The study was conducted on seepage-irrigated tomato, in a commercial farm located in Immokalee, FL, during the 2006 spring season. The UF/IFAS N-recommended rate (224 kg·ha^-1) was compared with a grower-commercial rate (358 kg·ha^-1). Both rates were applied pre-plant and incorporated at bedding with 61 and 554 kg·ha^-1 of P and K fertilizer, respectively. Plant growth was determined at 30, 60, 90, and 120 days after planting (DAP) by measuring roots, stems, leaves and fruit biomass. Plant tissues were analyzed to determine total N, P, and K content and uptake. Fruit yield was measured on 10 plants per plot for three consecutive harvests. At 120 DAT total plants biomass was 11.5% higher in the grower-commercial N rate than with UF/IFAS N rate. Total N, P, and K uptake were 250.4, 55.6 and 285 kg·ha^-1 in plants grown with the grower-commercial N rate and were 23.3%, 5.2% and 22.5% lower in the UF/IFAS N rate, respectively. In terms of nutrient partitioning, at 30 and 60 DAP, leaves and stems represented the major allocation for N, P, and K accounting for 90% of the nutrients uptake. While at 90 and 120 DAP, more than 50% of the N, P and K were allocated to the fruits. The higher nutrient uptake observed with the grower-commercial N rate resulted in 14.4% higher tomato yield (107.6 Mg·ha^-1) as compared to the UF/IFAS N rate. However, at grower-commercial N rate, N use efficiency, expressed as crop productivity per kg of applied N was 28.4% lower than UF/IFAS rate (300 versus 420 kg of fruits per kg of N). Thus, further investigations with higher N rates than UF/IFAS recommended rate must include an environmental and economic analysis to be considered a viable BMP.