Abstract：【Objective】This study aims to investigate the effects of different irrigation levels on the growth dynamics of 'Zhong Hong Bei 7 hao' kiwiberry (Actinidia arguta) under substrate cultivation. The primary goal is to identify the most suitable water management strategy to enhance the growth performance of the kiwiberry. By evaluating various irrigation strategies, the study seeks to provide scientific recommendations and practical guidelines for optimizing substrate cultivation of kiwiberry. 【Methods】One-year-old kiwiberry plants were selected for the experiment,that were subjected to seven irrigation treatments based on substrate maximum water holding capacity (Saturated Moisture Content, SMC): 60%, 70%, 80%, 90%, 100%, 110%, and 120%. Each treatment was replicated three times to ensure statistical validity. On March 12, 2023, the kiwiberry plants grown from nursery bags were transplanted into a rain-shelter, using cylindrical nutrient bags with a diameter of 60 cm and a height of 60 cm for substrate cultivation. The planting density was 2 m * 3 m, and the plants were trained into a single main trunk with two lateral vines in a pinnate shape. After planting, survival rates were recorded, and growth metrics such as the length and thickness of the main trunk, primary vine, and fruiting branches, as well as leaves size, were measured post-tagging. The total net growth and growth increments between measurement intervals were compared across different treatments to assess the impact of irrigation levels on kiwifruit growth. Data analysis was conducted using One way ANOVA and LSD multiple comparison methods to determine the significant effects of different irrigation treatments on growth parameters.【Results】The study revealed that substrate water-holding capacity significantly affects the growth performance of kiwiberry. The net growth of the main trunk and primary vine increased significantly with higher substrate moisture levels (P＜0.05). Among the treatments, SMC-100%, SMC-110%, and SMC-120% showed the most pronounced effects, with net growth of the main stem's diameter reaching a highly significant level (P＜0.01). The SMC-110% treatment yielded the best results, with the net growth of the main trunk's diameter significantly higher than in the other treatments.Comparing the net growth increments between each measurement, when the substrate water-holding capacity was above SMC-60%, the net growth in the main stem's diameter showed significant increases during T2 (mid to late June), T4 (late July to mid-August), and T5 (late August to mid-September), indicating these as rapid growth periods. Similarly, T2, T4, and T5 were also identified as rapid growth phases for the primary vine. The net growth in length of the fruiting branches showed a trend of initially increasing and then decreasing with increasing substrate moisture levels. No significant differences were observed between the SMC-60% and SMC-120% treatments, indicating that the impact of irrigation levels on the length growth of the fruiting vine is quite complex. In contrast, the net growth in thickness of the fruiting vine increased significantly with higher substrate moisture levels, with notable differences between low irrigation treatments (e.g., SMC-60%, SMC-70%, SMC-80%) and sufficient irrigation treatments (e.g., SMC-100%, SMC-110%, SMC-120%) (P＜0.05).The net growth in diameter of the fruiting branch showed significant increases during T3 (early July) and T4 (July to mid-August), marking these periods as phases of rapid growth for the branch's diameter. Regarding leaf growth indicators, lower irrigation treatments (e.g., SMC-60%, SMC-70%, SMC-80%) resulted in better leaf performance compared to higher irrigation treatments (e.g., SMC-100%, SMC-110%, SMC-120%).The periods T2 and T6 were identified as phases of rapid growth for the leaves. The SPAD values and nitrogen content of the leaves were also affected to varying degrees by different substrate moisture levels. Within the same treatment, the trends in leaf SPAD values and nitrogen content were generally consistent. Notably, leaves under low moisture treatments showed a more rapid response in changes to SPAD values and nitrogen content. 【Conclusion】Different irrigation levels have a significant impact on the growth of kiwiberry. Considering the net growth increments across various growth indicators, the effects of SMC-110% and SMC-120% irrigation levels were notably superior to those of the other treatments. In substrate cultivation of kiwiberry, providing an appropriate amount of irrigation is crucial for enhancing plant growth, particularly in terms of main trunk diameter, primary vine growth, and leaf development. The study suggests that SMC-110% or SMC-120% irrigation levels should be adopted as water management strategies in practical cultivation to optimize growth. This approach not only improves cultivation efficiency but also provides valuable insights for future management practices.
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