Improving our understanding of plant N-uptake dynamics is critical for increasing nitrogen uptake efficiency (NUE) and is a prerequisite for minimizing N leaching on vulnerable soils. The objective of our research was to determine the effect of residence time of N-fertilizer on N-uptake and NUE of bell peppers. Plants were grown in large (32 L) PVC Soil-N Uptake Monitoring (SUM) systems during the spring of 2004 and 2005 at Gainesville, FL. Nitrogen application rates were based on standard IFAS recommendation using weekly fertigations with potassium nitrate complemented with a N-depleted complete nutrient solution. Residence times (RT) were 24, 72 and 168 hours prior to weekly removal of residual soil N via application of 3 porevolumes of water combined with a partial (15 cbar) vacuum. Plant N-uptake was calculated by comparing weekly N recovery from planted columns with non-planted (reference) columns. Plant N-uptake and NUE were very low during the first three weeks. Towards the end of vegetative growth period (63 DAP) and the end of the growing season (84 DAP), NUE were 6%, 26% and 36% vs 18%, 73% and 89% for the 24, 72 and 168 RT treatments, respectively. Cumulative plant N-uptake was 21, 76 and 106 kg N/ha for the 24, 72 and 128 hours RT treatments, respectively. Corresponding plant dry weight were 20.5, 51.5 and 70.0 g/plant. It is proposed that NUE during initial growth was limited by low root N interception capacity and crop N demand. More frequent fertigation may thus be beneficial during initial growth. Although uptake efficiencies appear to be greatest towards the end of the growing season, this may also be related to a reduction in N application rate. Enhancing NUE on sandy soils thus will also require improved synchronization between N application and daily crop N-requirements in addition to increasing RT.