Evaluation of Controlled Release Nitrogen Fertilizers and Irrigation Rate On Tomato Yield, Nitrogen Use Efficiency and Nitrate Leaching in South Florida.

Tomato (Lycopersicon esculentum Mill.) field experiment was conducted at the Tropical Research and Education Center, University of Florida. The soil was Krome very gravelly loam soil. The objective was to grow tomatoes in the field with controlled release fertilizers under two irrigation rates for evaluation of their growth, nitrogen use efficiency (NUE) and nitrogen (N) losses through leaching. The controlled release N fertilizers were Kingenta polymer coated urea 43-0-0 (PCU) and Kingenta polymer sulfur coated urea 34-0-0 (PSCU). Soluble N fertilizer (Ammonia nitrate) was included as one N source. N rate applied in each treatment was 200 lb N/ac. Two irrigation rates used were 5 cbar as the high irrigation rate (HW) and the 25 cbar as low irrigation (LW) respectively. Both tomato shoot biomass (dry weight) and shoot N accumulation increased from DAT 60 to 90 and decreased from DAT 90 to 136 for the three N treatments under the two irrigation rates. PSCU had the highest shoot biomass and shoot N accumulation at both of LW and HW at DAT 90. NUE from PSCU, PCU and AN were 51%, 43% and 45% at LW respectively and 56%, 43% and 46% at HW respectively. There was no significant difference in tomato fruit yield among the three N sources at LW. However, PSCU had a significantly higher yield than PCU and AN at HW. Increasing irrigation rate increased NO3-N leaching in the same N treatment. The amount of NO3-N leaching in declining order was AN> PSCU> PCU at both LW and HW. Field results indicated that the controlled release fertilizer (PSCU) improved tomato growth, enhanced NUE, increased tomato fruit yield and reduced NO3-N leaching.