Nitrogen volatilization and mineralization in a sandy entisol of Florida under citrus

Increasingly nitrate nitrogen (NO3-N) is found in excess of maximum contaminant limit (MCL) in groundwater adjacent to citrus production areas of central Florida. Understanding of fate of N in the environment following the application of fertilizers is critical to improve nutrient uptake efficiency, minimize nutrient losses and reduce the adverse effects on the groundwater. A study evaluated ammonia volatilization (NH3) and effects of ammonium nitrate (AN) and urea (UR) on N budget of citrus trees on a sandy Entisol. Dry granular N fertilizers were surface applied to irrigated 'Hamlin' orange trees. Ammonia volatilization was evaluated using a semi-open NH3 trapping system with and without additional air circulation, while net N mineralization and leaching losses were evaluated using in situ incubations with polyvinyl chloride (PVC) columns. Significant N losses by NH3 volatilization were observed from applied N fertilizers, which accounted for up to 13% of applied N as AN, and 33% as UR with additional air circulation in the collection chamber. These values were significantly greater than those observed with no additional air circulation. Maximum rates of NH3 volatilization occurred within 5 d after fertilizer application and were greater during the day than during the evening. This study demonstrated that fertilizer use efficiency is reduced due to increased gaseous losses of NH3 when urea is used, and that N fertilization affects soil N mineralization in a short time period after fertilizer application. Fertilization decreased N mineralization and increased the amount of soil microbial biomass N during incubation. Leaching of N accounted to 13% of applied N during a 90-d period.