Effects of Source on Nitrogen Uptake, Allocation Patterns and Performance of Strawberry (Fragaria × ananassa Duch.): A 15N-Tracer Study

Nitrogen (N) is an essential determinant of strawberry growth and productivity. However, plants exhibit varying preferences for nitrogen sources, which ultimately affects its use efficiency. Thus, it is imperative to determine the preferred N source for the optimization of indoor strawberry production. This study employed the ¹⁵N-tracer technique to investigate the effects of N sources on N uptake, distribution, use efficiency and growth of 'Praratchatan 80' strawberries in a greenhouse. Five treatments were applied: T1 (5.0 mM ¹⁵NO₃⁻), T2 (2.5 mM ¹⁵NO₃⁻ + 2.5 mM NH₄⁺), T3 (5.0 mM ¹⁵NH₄⁺), T4 (2.5 mM ¹⁵NH₄⁺ + 2.5 mM NO₃⁻), and T5 (N-free, control) in a completely randomized design. Significant (p < 0.05) differences were observed in N uptake, distribution, and total N concentration among treatments. Sole NH₄⁺ promoted early N uptake and accelerated flowering, while NO₃⁻ enhanced vegetative growth and later-stage N use efficiency (NUE). The combined NO₃⁻ and NH₄⁺ application was most efficacious, balancing the benefits of both N forms. NO₃⁻ treatment enhanced ¹⁵NUE by 46% compared to NH₄⁺, and mixed N sources demonstrated superior and consistent ¹⁵NUE over time. NH₄⁺ alone or with NO₃⁻ expedited flowering by 20 days compared to sole NO₃⁻ and N-free treatments. This study elucidates the importance of N sources for optimizing strawberry growth and flowering, providing a foundation for developing tailored N management strategies. Future research should focus on refining mixed N application ratios and timings, exploring molecular mechanisms of N metabolism, and evaluating long-term impacts on strawberry production sustainability.