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Polymer coated urea fertilizers provide a gradual release of nitrogen in forest fertilization, and may have better nutrient use efficiency than conventional nitrogen fertilizers. Leaching of applied nitrogen is of particular concern in the Lower Suwannee Valley where surficial groundwater is close to the surface and soils are prone to nutrient leaching. Three rates of polymer coated urea (PCU) plus triple super phosphate fertilizer (25, 50, 125 lb N and 25 lb P), a diammonium phosphate (DAP) plus urea standard treatment (50 lb N and 25 lb P) and a non-fertilized control were compared in a nine-year-old slash pine plantation near Live Oak, Florida. Changes in soil nitrogen at various depths to 183 cm and changes in soil solution nitrogen concentration at 30 cm depth were monitored over time. Volatile losses of ammonia were measured using two trap methods. From 2 through 4 weeks after fertilization, nitrate concentrations in soil solution were significantly greater for the DAP plus urea standard treatment than for the same rate of nitrogen from PCU (50 lb N/acre). In this same period, the high PCU rate (125 lb N/acre) had significantly greater nitrate concentration in soil solution than all other treatments through week 13. From 2 through 8 weeks, there was a significant interaction between raking and fertilization treatments. In raked plots at weeks 4 and 8, nitrate concentrations for the middle rate of PCU were not significantly different than the non-fertilized control, whereas the DAP plus urea standard was. However, in non-raked plots, nitrate concentration for the DAP plus urea standard was not significantly different from the control and nitrate concentration with the middle PCU rate was significantly less than the DAP plus urea standard at week 4. Ammonia volatilization results after first sampling reported differences between the middle PCU rate and DAP plus standard urea with larger ammonia concentrations from the PCU, but no significance between raking treatments. |