Abstract

The scarcity of resources has constrained the supply of conventional feedstuffs for livestock production. Consequently, mulberry (Morus spp.), known for its high protein content and bioactive compounds, has been developed as a promising alternative feed. However, the optimal water–fertilizer ratio for cultivating feed mulberry and the underlying physiological and agronomic mechanisms remain poorly understood. To address this, a two-year field experiment (2023–2024) was conducted to investigate the effects of water–fertilizer coupling on feed mulberry yield, water use efficiency (WUE), and soil quality. This experiment employed a split-plot design with three irrigation levels (I1 = 45, I2 = 90, and I3 = 135 mm) and four fertilizer rates (F1 = 0, F2 = 150, F3 = 225, and F4 = 300 kg·ha−1). The results demonstrated the following: (1) The variation trends in SWC were consistent with those of soil available N, P, and K contents. Under water–fertilizer coupling, the total water consumption peaked in the I3F3 treatment, with values of 639.9 mm and 703.5 mm in the two years, respectively. (2) The I3F3 treatment produced both the highest yield (37.19 and 41.66 t·ha−1) and the highest leaf N, P, and K contents among all treatments. (3) Water and fertilizer use efficiencies exhibited parabolic trends in response to increasing irrigation and fertilizer inputs. The highest agronomic nitrogen efficiency (AEN) was observed in I2F2. (4) The AMOS 26 model further revealed that soil nutrient content had the strongest direct positive effect on yield (standardized coefficient = 0.68), followed by total water consumption (0.33). And irrigation significantly enhanced soil nutrient availability (standardized coefficient = 0.29). In summary, the I3F3 combination achieved the highest yield and water use efficiency, whereas the I2F2 treatment exhibited the highest AEN. This trade-off suggests that the optimal strategy depends on management objectives (yield maximization vs. resource conservation) in the North China Plain.

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