Impact of nitrogen fertilizer concentrations on growth, yield, and nutrient use efficiency of wolfberry (Lycium barbarum L.) in Northwestern China

Nitrogen (N) management is critical for improving productivity and nutrient-use efficiency in substrate-based soilless wolfberry cultivation; therefore, this study aimed to quantify the effects of nutrient-solution N concentration on vegetative growth, nutrient uptake, fruit yield, fruit quality, and nutrient-use efficiency, and to identify an optimal N level for fertigation management. A controlled two-year experiment (2023-2024) was conducted in arid northwestern China with four N concentrations (250, 300, 350, and 400 mg L^-1) applied via drip fertigation, with three replicates per treatment. Moderate N supply (350 mg L^-1, T3) enhanced vegetative growth and nutrient uptake and produced the highest yield (2759.65 kg ha^-1 in 2023 and 2930.93 kg ha^-1 in 2024), while also improving 100-berry weight and quality-related traits, including β-carotene, crude protein, and essential amino acids. In contrast, the highest N level (400 mg L^-1, T4) did not further increase yield and was associated with lower nutrient-use efficiency; NUE, PUE, and KUE were higher under low-to-moderate N inputs and declined under high N. An entropy weight-TOPSIS evaluation further ranked T3 as the best overall treatment when multiple indicators were jointly considered, suggesting that optimizing nutrient-solution N concentration to around 350 mg L^-1 can improve yield and fruit quality while maintaining nutrient-use efficiency under the tested soilless cultivation conditions.