Studies were conducted over a 5 year period on fine sandy loam soil to determine the importance of N mineralization rate on grapefruit (Citrus paradisi) production under subtropical conditions. Grapefruit trees grown on soils with mineralization rates greater than 0.47 ppm N/day produced near maximum yields during the first 3 years that young trees were in production but did not supply enough N after trees were large and fruit yields were above 16 MT/ha. Soil mineralizing 0.65 ppm N/day supplied enough N to produce 72% of the yield produced by trees fertilized with application of 148 kg N/ha.