Mulberry (Morus spp.) is resilient to water deficit conditions, and the high protein content of its leaves means they can be used as forage. Therefore, it could be a valuable resource for alleviating the animal feed crisis, but it is crucial that its high productivity and stable traits are sustained to achieve this. We conducted a 2-year field experiment in the North China Plain (NCP), which investigated different irrigation levels (W1 = 15 mm, W2 = 30 mm) and genotypes (Feng Yuan No. 1, Feng Chi). This study demonstrates that using water-saving irrigation coupled with selected genotypes can increase the leaf yield and protein content. We measured various physiological and ecological indicators of mulberry, including the leaf area, fresh leaf weight, dry leaf weight, net photosynthetic rate, leaf water use efficiency (WUE_L) under limited irrigation, protein content, and yield. The results from both years indicate that, under deficit irrigation conditions, Feng Yuan No. 1 exhibited drought resistance while maintaining relatively high and stable growth traits. When the irrigation amount was increased (W2 = 30 mm), the net photosynthetic rate and leaf water use efficiency of Feng Yuan No. 1 were significantly better than those of Feng Chi. Additionally, Feng Yuan No. 1 combined with the W2 irrigation treatment led to a higher protein content of leaves (19.98 g/100 g and 21.19 g/100 g) and greater yield of leaves and branches (9.79 t·ha⁻¹ and 11.19 t·ha⁻¹) in the two years. Furthermore, under deficit irrigation conditions, Feng Yuan No. 1 effectively compensated for yield losses caused by water scarcity.

This study aimed to establish an integrated variety–technology cultivation pathway for the new forage mulberry variety ‘Fengyuan No. 1’, linking salt tolerance mechanisms with practical application. A systematic investigation was conducted via a pot experiment with a 0–5‰ NaCl gradient and a field trial comparing three cultivation modes: Ridge Planting (RP), Furrow Planting (FP), and Flat-Bed Planting (FBP). Key findings are as follows. (1) The salt tolerance threshold was clearly defined: a 100% survival rate at salinity ≤ 4‰ (with no injury symptoms at ≤3‰), and 5‰ identified as the lethal threshold (33.33% survival). Salt stress triggered a resource reallocation strategy, increasing the leaf-to-stem fresh weight ratio from 1.53 (0‰) to 2.78 (5‰) to prioritize leaf photosynthetic function. Stable leaf circularity (0.83–0.87) indicated morphological stress resistance. (2) Optimized cultivation pathways were identified: FBP was the core pathway for maximizing biomass accumulation (root, stem, and leaf fresh weights were 5.0, 2.3, and 1.5 times those of RP, respectively) and resulted in the lowest leaf Na⁺ accumulation (124 mg/kg), making it suitable for lightly to moderately saline–alkali land (≤4‰). FP served as an effective pathway for salt avoidance and height promotion (plant height: 113.18 cm). RP constituted a specialized pathway for high-quality forage, yielding the highest crude protein content (23.3 g/100 g). (3) Cultivation modes significantly affected functional components; FBP activated alkaloid DNJ synthesis (215.16 mg/kg), whereas RP and FP increased osmolyte GABA accumulation (~586 mg/kg). In conclusion, this study integrates a complete technical pathway from salt tolerance mechanism analysis to diversified cultivation options, providing a systematic variety–technology solution for the industrial development of forage mulberry on coastal saline–alkali land.

The shortage of high-quality forage and the need for alternative protein sources are critical challenges for livestock production in northern China, where cold winters and saline–alkaline soils limit crop options. Mulberry (Morusalba L.) is a promising high-protein forage, yet few varieties have been bred for these conditions. Here, we report the breeding of ‘Fengyuan No. 1’, developed through systematic evaluation of 31 mulberry accessions for five forage traits, followed by a 4 × 3 factorial crossing design using four female parents (‘8036’, ‘Dahongpao’, ‘Jinqiang 63’, ‘Hongguo 2’) and three male parents (‘Nongsang 14’, ‘Yu 2’, ‘Yiyuan Huanglu’) selected based on comprehensive evaluation and complementary agronomic traits. Among the nine hybrid families with sufficient seed, family X01 (‘8036’ × ‘Nongsang 14’) ranked first in a three-year (2011–2013) comprehensive evaluation of growth traits using membership function analysis and was subsequently named ‘Fengyuan No. 1’. Multi-location (Shandong, Anhui, Shaanxi) field trials (2018–2021) with ‘Fengchi’ as the control showed that ‘Fengyuan No. 1’ achieved an average annual leaf yield of 12,596.48 kg DM·ha⁻¹ (+14.20%) and total branch–leaf biomass of 25,341.95 kg DM·ha⁻¹ (+13.36%). Leaf crude protein reached 30.87% on a dry matter basis (+25.64% vs. control). Silage prepared from this variety exhibited excellent fermentation quality (pH 4.10) and a relative feed value of 272.46, exceeding alfalfa silage standards. The variety maintained 100% survival at 0.4% NaCl and a 13.74% biomass advantage over the control on saline–alkaline field soils, with winter-desiccated shoot tips reduced by 53%. These results establish ‘Fengyuan No. 1’ as an elite forage mulberry for the Yellow River Basin and similar ecoregions.