Arundo donax L. (giant reed) is a perennial rhizomatous grass with high drought and salinity tolerance, making it a promising low-input bioenergy crop. However, the understanding of the combined effects of irrigation and nitrogen application in salinized soil on physiological adaptations and biomass allocation is still limited. In this study, we conducted a three-factor orthogonal pot experiment with four levels per factor in 2023 and 2024 as follows: salinity (S0: non-saline, S1: low salinity, S2: moderate salinity, S3: high salinity); irrigation amount (W0: 605, W1: 770, W2: 935, W3: 1100 mm); and nitrogen application (N0: 0, N1: 60, N2: 120, N3: 180 kg/ha). This resulted in 14 irrigation-nitrogen-salinity combined treatments. The results showed the following: (1) Irrigation, nitrogen and salinity significantly affected leaf dimensions, photosynthetic rate, plant height, biomass allocation and dry matter of the total plant (p < 0.05). (2) Significant coupling interactions were observed between salinity and irrigation, as well as between nitrogen and irrigation, affecting leaf morphology, plant height, leaf dry matter and total biomass accumulation; a coupling interaction of salinity and nitrogen was found to affect the leaf area, root, stem and leaf dry weight. (3) The S0N2W2 treatment produced the highest dry biomass, which was 2.2 times higher than for the S3N2W2 treatment. (4) Under moderate-salinity conditions (S2), biomass allocation favored stems and leaves, whereas under high-salinity conditions (S3) biomass allocation shifted towards leaves, followed by stems and roots. A combination of 935 mm irrigation amount and 120 kg/ha nitrogen (N2W2) under S1 and S2 is recommended to optimize biomass production. Our study provides practical irrigation and nitrogen management strategies to enhance A. donax cultivation on marginal saline lands, supporting climate-resilient bio-economy initiatives.

This work involves the development of a hydrodynamic fertilizer injector (HFI), which uses an integrated axial-flow turbine (AFT) and a diaphragm pump to absorb liquid fertilizer. Three structural parameters—the number of impellers (M₁), average number of blades per impeller (M₂), and arrangement pattern (M₃)—are considered, and 12 AFT designs are developed. Using a combination of CFD numerical simulations and hydraulic performance testing, the response of the AFT output power (P), blade negative pressure (NP), and fertilizer injection flow rate (Q_inj) to structural parameters and inlet pressure (H) is investigated. The results show that the normalized root mean square error between the simulated outlet flow rate (Q_s) and the measured flow rate (Q_m) is 5.1%, indicating high accuracy in the grid motion simulation method. P increases first and then decreases with the increase in impeller speed (n). The maximum P (P_max) ranges from 150.1 to 201.4 W. P_max increases with H, decreases with increasing M₁ and M₂, and shows little change with M₃. At H = 0.14 MPa, M₁ and M₂ have a significant influence, and at H ≥ 0.14 MPa, M₁ becomes the most significant factor (p < 0.05). Low-speed flow and negative pressure cavitation zones at the leading edge of the blade suction surface cause flow blockage and affect the lifespan of the AFT. These regions decrease in size as H increases but increase with M₁. The negative pressure (NP) decreases as M₂ increases. When M₁, M₂, and M₃ are 2, 3, and identical (D33), the P_max of the AFT is maximized, increasing by 6.7% to 33.5% compared with those of the other combinations. The Q_inj of D33, D34, D43, and D44 at H = 0.12~0.18 MPa range from 288.6 to 847.3 L/h, which is 38.7% to 461.0% higher than that of domestic and international venturi injectors. When considering cavitation issues and the manufacturing cost of the AFT mold, D44 may be chosen. Although its Q_inj is 7.0% lower than that of D33, NP is reduced by 37.9%. These findings provide a basis for the development of the HFI with AFT as the driving unit.

Arundo donax L. (giant reed) is a perennial rhizomatous grass with high drought and salinity tolerance, making it a promising low-input bioenergy crop. However, the combined effects of irrigation and nitrogen application in salinized soil on physiological adaptations and biomass allocation are still limited. In this study, we conducted a three-factor orthogonal pot experiment with four levels per factor in 2023 and 2024: salinity (S0: non-saline, S1: low salinity, S2: moderate salinity, S3: high salinity); irrigation amount (W0: 605, W1: 770, W2: 935, W3: 1100 mm); and nitrogen application (N0: 0, N1: 60, N2: 120, N3: 180 kg/ha). This resulted in 14 irrigation-nitrogen-salinity combined treatments. The results showed the following: (1) Irrigation, nitrogen and salinity significantly affected leaf dimensions (length, width, area and leaf elongation rate, specific leaf weight), photosynthetic rate, plant height, biomass allocation and dry matter of total plant (p < 0.05). (2) Significant coupling interactions were observed between salinity and irrigation, as well as between nitrogen and irrigation, affecting leaf width, leaf elongation rate,plant height,leaf dry matter and total biomass accumulation; coupling interaction of salinity and nitrogen were found to have effect on leaf width, leaf area, leaf fresh weight, root, stem and leaf dry weight. (3) The S0N2W2 treatment produced the highest dry biomass (44.76 ± 0.68 g/plant), which was 2.2 times higher than the S3N2W2 treatment (20.13 ± 0.50 g/plant). (4) Under moderate salinity conditions (S2), biomass allocation favoured stems (42.70%, mean values of 2023 and 2024) and leaves (39.53%, mean values of 2023 and 2024), whereas under high salinity conditions (S3) biomass allocation shifted towards leaves, followed by stems and roots. A combination of 935 mm irrigation amount and 120 kg/ha nitrogen (N2W2) in S1 and S2 is recommended to optimise biomass production. Our study provides practical irrigation and nitrogen management strategies to enhance A. donax cultivation on marginal saline lands, supporting climate-resilient bio-economy initiatives.