Effects of Source on the Nitrogen Uptake, Allocation Patterns, and Performance of Strawberry (Fragaria × ananassa...

Nitrogen (N) is an essential determinant of strawberry growth and productivity. However, plants exhibit varying preferences for sources of nitrogen, 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, and use efficiency, as well as the plants' growth, for '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 and distribution and total N concentration among the treatments. Sole NH₄⁺ promoted early N uptake and accelerated flowering, while NO₃^- enhanced vegetative growth and later-stage nitrogen use efficiency (NUE). The application of combined NO₃^- and NH₄⁺ 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 the sources of N in 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.