<p> Nitrogen (N) management in Florida potato production is a major agronomic and environmental challenge due to coarse-textured sandy soils and seepage irrigation, which accelerate nutrient losses. Microbial biostimulants may enhance potato yield and nitrogen use efficiency in the sandy soils typical of northeast Florida, supporting both productivity and environmental stewardship. A two-year field study was conducted on two different sites to evaluate the interactive effects of five N fertilization rates (0-314 kg N ha^-1) and a microbial biostimulant on potato yield, tuber quality, soil N dynamics, and microbial biomass. Total and marketable yields increased quadratically with N fertilizer application, reaching a plateau around 205-208 kg N ha^-1. Total yield ranged from 17.8 Mg ha^-1 to 31.3 Mg ha^-1. Higher N inputs did not enhance yield, but increased subsurface nitrate concentrations, indicating a greater risk of leaching. Nitrogen use efficiency (NUE) indices were highest at moderate N rates (78-157 kg N ha^-1) and declined sharply with higher N fertilization. Microbial biomass carbon (MBC) decreased with increasing N while microbial biomass nitrogen (MBN) remained stable. The microbial biostimulant used in this study had no effects on yield, NUE, or microbial parameters. These findings highlight that potato production in northeast Florida is optimized at around 200 kg N ha^-1, above which both efficiency and environmental sustainability decline. Moreover, under sandy soils with low organic matter (OM), microbial biostimulants provided limited agronomic or microbial benefits. This study reinforces the importance of BMP-based N recommendations and indicates that soil properties such as soil OM and water management likely influence microbial dynamics in sandy systems.</p>