Long Van Nguyen

Aims: Intensive agricultural practices have led to severe soil degradation in the Central Highlands of Vietnam. Integrating legumes as cover crops is a promising strategy to restore soil fertility via biological nitrogen fixation (BNF). Arachis pintoi has been increasingly promoted in Vietnam for adoption as a cover crop but the diversity and efficiency of its native rhizobial partners remain poorly documented. This study assessed the diversity of indigenous rhizobial strains nodulating A. pintoi in the Central Highlands of Vietnam and evaluated their symbiotic efficiency and ability to support plant growth under greenhouse conditions. Methods and results: Nodule occupancy was analyzed by Restriction Fragment Length Polymorphism and 16rDNA sequencing was performed for representative strains of each group. Seven distinct profiles were found, all identified as Bradyrhizobium spp. While the diversity of rhizobia was relatively similar across both provinces, nodule occupancy varied markedly between locations. Strains from IGS 04 group dominated in Dak Lak (66.3%), whereas IGS 01 was the most prevalent group in Gia Lai (78.3%). A greenhouse trial was conducted to assess the performance of the different rhizobial groups. Inoculation significantly improved plant growth and nitrogen levels compared to uninoculated treatment. Plants inoculated with IGS 03 and IGS 06 groups exhibited the highest performance, exceeding that of the positive control. Conversely, IGS 01 and IGS 07 strains demonstrated the poorest symbiotic efficiency. Conclusions: These results highlight the critical need to select high-efficiency native strains for bioinoculants to maximize BNF potential and support the long-term sustainability of perennial agroecosystems in Vietnam.

Long NV, Do N, Anh NTV, Hanh DTN, Cuong VC, Ngoc NQ, Van NTC. 2025. Soil acidification and nutrient imbalance under intensive black pepper plantations in the Central Highlands of Vietnam. Asian J Agric 9: 906-916. Black pepper, Vietnam's most valuable spice crop, is concentrated in the Central Highlands, where it plays a significant role in global supply, yet its long-term productivity is increasingly constrained by soil degradation. However, production is increasingly threatened by soil degradation and rising disease pressure. To evaluate substantial constraints, the soil fertility in 150 intensive black pepper plantations across Dak Lak, Dak Nong, and Gia Lai was assessed based on key physicochemical properties. Results revealed three critical constraints: (i) strong to very strong soil acidification (pH 3.55-6.40), (ii) low Cation Exchange Capacity (CEC 2.50-14.50 Cmolc kg-¹), and (iii) pronounced nutrient imbalances. Excessive phosphorus occurred in 82% of samples, while potassium deficiency affected up to 57.6% of plantations, with calcium and magnesium ratios varying substantially among provinces. Organic matter levels were generally adequate but unevenly distributed. Correlation and principal component analyses highlighted soil pH and organic matter as the primary regulators of nutrient availability. Notably, Dak Lak exhibited the strongest acidity and lowest CEC, Dak Nong showed more balanced fertility with higher CEC, and Gia Lai displayed higher nutrient levels but greater variability among farms. These constraints collectively reduce nutrient efficiency, weaken crop resilience, and intensify vulnerability to soilborne diseases. Practical interventions should therefore prioritize correcting acidity, enhancing buffering capacity, and managing nutrients in a balanced manner to sustain productivity and safeguard soil health. The findings provide an essential evidence base for soil restoration and sustainable intensification of black pepper cultivation in Vietnam's Central Highlands.