Effects of nitrogen fertilization and planting spacing on growth, yield, and militarine content of Bletilla striata cultivated in Northern Vietnam

Abstract

Bletilla striata (Thunb.) Rchb.f. is an important medicinal plant widely used in traditional Asian medicine for its hemostatic, anti-inflammatory, and wound-healing properties. However, limited information is available on agronomic practices that improve both rhizome yield and bioactive compound accumulation under Vietnamese cultivation conditions. This study evaluated the effects of nitrogen fertilization and planting spacing on growth performance, yield components, and militarine content of Bletilla striata. A split-plot field experiment arranged in a randomized complete block design with three replications was conducted in Sa Pa, Lao Cai Province, northern Vietnam, from 2022 to 2024. Nitrogen was applied at four levels: 0, 60, 90, and 120 kg N/ha. Three planting spacings were tested: 20 × 20 cm, 20 × 25 cm, and 20 × 30 cm. The results showed that nitrogen fertilization and planting spacing significantly influenced plant growth, rhizome yield, and militarine accumulation. The highest plant height (14.2 cm) was recorded under N2K1, while the maximum SPAD value (17.8) and leaf area (5.97 cm²) were observed under N3K3 and N1K3, respectively. The highest actual yield (3.7 t/ha) and militarine content (4.7 mg/g DW) were obtained under N2K2. Militarine accumulation increased with nitrogen application up to 90 kg N/ha but declined slightly at 120 kg N/ha, suggesting that excessive nitrogen input did not further enhance metabolite accumulation. These findings indicate that balanced nitrogen supply and appropriate planting spacing are important for improving both productivity and medicinal quality of Bletilla striata. The combination of 90 kg N/ha and 20 × 25 cm spacing appears to be a suitable cultivation strategy for Bletilla striata under northern Vietnamese conditions.