Nitrogen (N) is often the primary limiting factor in strawberry (Fragaria ×ananassa Duch.) production. Optimizing N fertilization is crucial for maximizing economic returns while minimizing environmental pollution risks. This study aimed to determine cultivar- and growth stage-specific optimum N rates for winter strawberry production in a subtropical sandy soil. Three field experiments (Expt. 1, 2, and 3) were conducted in west-central Florida, with four cultivars [‘Florida Brilliance’ (Brilliance), Florida MedallionTM (Medallion), Florida PearlTM (Pearl 109), and Florida Pearl® (Pearl 66)] and five N rates (0, 0.56, 1.12, 2.24, and 3.36 kg·ha–1·d–1). Different N rates were applied during Weeks 3–8 (early growth) in Expt. 1, Weeks 9–14 (mid-growth) in Expt. 2, and Weeks 15–20 (late growth) in Expt. 3, with a baseline rate of 1.12 kg·ha–1·d–1 outside the treatment period. All experiments concluded at the end of Week 20, with total N application rates ranging from 94 to 235 kg·ha–1. Model fitting revealed cultivar- and growth stage-specific yield responses to N rates. In Expt. 1, the best-fit models were linear for Brilliance, Medallion, and Pearl 109, with maximum yield increases of 102%, 109%, and 71%, respectively. For Pearl 66, the best-fit model was quadratic, with a maximum yield increase of 126% at 3.34 kg·ha–1·d–1. In Expt. 2, Medallion maintained a linear response with a maximum yield increase of 90%, whereas Brilliance followed a quadratic model, with a maximum yield increase of 70% at 2.27 kg·ha–1·d–1. Pearl 109 and Pearl 66 followed exponential plateau models, reaching 90% of their respective maximum yields with 89% and 73% increases at 1.64 and 2.09 kg·ha–1·d–1, respectively. In Expt. 3, no cultivar exhibited a significant model fit. Agronomic N use efficiency (ANUE, kg yield increase per kg N applied) showed contrasting results. In Expt. 1, only Pearl 109 exhibited a significant model fit, with a linear reduction of up to 30%. In Expt. 2, Medallion showed no significant model fit, whereas the other three cultivars reduced ANUE linearly by 27% to 38%. In Expt. 3, all cultivars followed exponential decay models, with maximum reductions of 57% to 63%. These results suggest that Medallion is the most responsive to N fertilization, while Pearl 109 is the least. Moreover, N fertilization efficiency could be improved by increasing its distribution during the early and mid-season growth stages and limiting late-season inputs.
