The effects of ¹⁵N-labeled fertilizer applied to mature summer-bearing red raspberry (Rubus idaeus L.) plants were measured over two years. Four nitrogen (N) treatments were applied singularly at 0, 40, or 80 kg·ha⁻¹ of N in early spring (budbreak), or split with 40 kg·ha⁻¹ of N (unlabeled) applied at budbreak...