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Robusta coffee is the largest cash crop in Vietnam and intensive farming practices significantly increased coffee production in recent decades. However, applications of fertilizers and pesticides significantly reduced the soil biodiversity and increased the incidence of soil soil-borne pests and diseases, mainly nematodes and Fusarium. Crotalaria pallida is a legume that can excrete nematicide compounds to control the populations of Pratylenchus and Meloidogyne in soils. However, the efficacy of the practice to reduce nematode incidence remains unknown. As this nematicide effect is produced by the complex legume-rhizobial interactions, it is important to have C. pallida nodulated with effective strains of rhizobia. At this stage, however, there is very limited knowledge about the genetic diversity of native rhizobia nodulating C. pallida in Vietnam. The objective of our study is to investigate the phylogenetic diversity of rhizobia nodulating C. pallida intercropped with coffee trees from five different farms in the Gia Lai province. The genetic diversity of native rhizobia strains was identified by Polymerase Chain Reaction/Restriction Fragment Length Polymorphism of the Inter Genic Spacer (IGS) between rDNA 16S and 23S obtained with Msp I and Hae III restriction enzymes. The phylogenetic positions of strains were determined by using 16S rRNA sequencing. Our results identified 11 different IGS Groups within a total of 88 strains isolated from 125 nodules (25 nodules/farm). Strains for these different IGS groups were sequenced and the results showed that Bradyrhizobium strains (B. arachidis, B. liaoningense, B. elkanii, and Bradyrhizobium sp.) and Rhizobium strains (R. multihospitium and R. tropici) were able to nodulate C. pallida. The screening of potential elite inoculum strains from the 88 isolates will be performed in field trials with C. pallida intercropped in young-replanted coffee plantations in the Central Highlands to determine their efficacy for controll

Legume crops have long played a major role in sustainable cropping systems in Southeast Asia, representing up to 44% of the total cropped area in Myanmar for example. However, in Vietnam, due to increasing population pressure and demand for agricultural land, the current agricultural system is dominated by intensive practices that include conventional tillage, mono-cropping and overuse of mineral fertilizers. Farmers in Northern Vietnam (Yen Bai province) rely on intensive monocropping fields of maize and cassava whilst facing serious issues of soil erosion and loss of natural soil biodiversity. Cowpea (Vigna unguiculata L.) is highly valued by farmers as it is locally consumed and easily sold at local markets at a good price. To reduce the damages caused by mono-cropping cassava, the intercropping cassava-cowpea system was tested by farmers and the impacts on soil health were assessed. Our results showed intercropping significantly enhanced macrofauna richness and evenness, increased diversity and abundance of soil microfauna as well as the abundance and richness of the total bacterial communities. Nodulation of cowpeas intercropped with cassava or maize in 2 districts showed that the natural nodulation of the legume plants remained limited regardless of the soil characteristics, seasons and landscape. Native strains were isolated, screened for their symbiotic effectiveness and successfully tested under field conditions to compensate for the total absence of commercial rhizobial inoculants for cowpeas on the market. The high expansion rate of intercropping with cowpeas shows the high adoption level of these agroecological practices by local farmers and justifies our current efforts to scale it up. Future projects will focus on further testing and legume intercropping promotion and dissemination to increase soil health and farmer incomes in mountainous regions of Vietnam.

Vietnam is leading the growth of black pepper worldwide, accounting for more than one-third of the global production. However, this is achieved by the intensive use of chemical fertilizers and pesticides, causing pollution to the environment and reduction of soil health. Overall, it favors the development of soil-borne pathogens, such as Fusarium, Phytophthora, and Pythium/Phytopythium. Arachis pintoi is a legume that can contribute to biological nitrogen fixation (BNF), due to its symbiosis with rhizobia. It is widely planted as a cover crop to reduce soil erosion, suppress weeds, control several pests and soil-borne diseases. For instance, in Vietnam, A. pintoi has been intercropped with black pepper to enhance soil health and sustain the yield. However, its impacts on reducing weeds, pests and soil-borne pathogens remain largely unknown. Meanwhile, limited information is available about the rhizobia nodulating A. pintoi in Vietnam. In this study, we investigated the impact of A. pintoi intercropped in black pepper plantations in Gia Lai and Dak Lak provinces in the Central Highlands in Vietnam. Soil samples were analyzed, and the results showed that plantations intercropped with A. pintoi significantly improved the total nitrogen. Besides, nodules of A. pintoi from these provinces were collected and screened for their rhizobial strains. The intergenic spacer (IGS 16-23S) region of the rhizobial DNA was amplified by PCR, and restriction was digested with two enzymes (MspI and HaeIII) to group rhizobia based on their restriction profiles. During the initial phase of our project, 38 strains have been isolated from 108 nodules and grouped into 13 different groups. The objective is to identify elite strains associated with A. pintoi and to formulate effective rhizobial inoculants to allow effective BNF by this legume, hence, reducing the need for fertilizer inputs, and assisting in soil health restoration of black pepper plantations.

Legume crops have long played a major role in sustainable cropping systems in Southeast Asia, representing up to 44% of the total cropped area in Myanmar for example. However, in Vietnam, due to increasing population pressure and demand for agricultural land, the current agricultural system is dominated by intensive practices that include conventional tillage, mono-cropping and overuse of mineral fertilizers. Farmers in Northern Vietnam (Yen Bai province) rely on intensive monocropping fields of maize and cassava whilst facing serious issues of soil erosion and loss of natural soil biodiversity. Cowpea (Vigna unguiculata L.) is highly valued by farmers as it is locally consumed and easily sold at local markets at a good price. To reduce the damages caused by mono-cropping cassava, the intercropping cassava-cowpea system was tested by farmers and the impacts on soil health were assessed. Our results showed intercropping significantly enhanced macrofauna richness and evenness, increased diversity and abundance of soil microfauna as well as the abundance and richness of the total bacterial communities. Nodulation of cowpeas intercropped with cassava or maize in 2 districts showed that the natural nodulation of the legume plants remained limited regardless of the soil characteristics, seasons and landscape. Native strains were isolated, screened for their symbiotic effectiveness and successfully tested under field conditions to compensate for the total absence of commercial rhizobial inoculants for cowpeas on the market. The high expansion rate of intercropping with cowpeas shows the high adoption level of these agroecological practices by local farmers and justifies our current efforts to scale it up. Future projects will focus on further testing and legume intercropping promotion and dissemination to increase soil health and farmer incomes in mountainous regions of Vietnam.

Salinity is one of the most devastating abiotic stresses hampering the growth and production of rice. Nine indole-3-acetic acid (IAA)-producing salt-tolerant plant-growth-promoting rhizobacteria (ST-PGPR) were inoculated into Thai jasmine rice (Oryza sativa L.) variety Khao Dawk Mali 105 (KDML105) seedlings grown under different concentrations of NaCl (0, 50, 100, and 150 mM). The ST-PGPR strains significantly promoted the growth parameters, chlorophyll content, nutrient uptake (N, P, K, Ca, and Mg), antioxidant activity, and proline accumulation in the seedlings under both normal and saline conditions compared to the respective controls. The K+/Na+ ratio of the inoculated seedlings was much higher than that of the controls, indicating greater salt tolerance. The most salt-tolerant and IAA-producing strain, Sinomonas sp. ORF15-23, yielded the highest values for all the parameters, particularly at 50 mM NaCl. The percentage increases in these parameters relative to the controls ranged from >90% to 306%. Therefore, Sinomonas sp. ORF15-23 was considered a promising ST-PGPR to be developed as a bioinoculant for enhancing the growth, salt tolerance, and aroma of KDML105 rice in salt-affected areas. Environmentally friendly technologies such as ST-PGPR bioinoculants could also support the sustainability of KDML105 geographical indication (GI) products. However, the efficiency of Sinomonas sp. ORF15-23 should be evaluated under field conditions for its effect on rice nutrient uptake and growth, including the 2AP level.

Tea is a very important cash crop in Vietnam as it provides crucial income and employment for farmers in poor rural areas. Unfortunately, the dominance of long-term, conventional tea cultivation has caused severe soil health degradation and environmental pollution. At the same time, as tea production may provide a better net income compared with other annual crops such as rice and vegetables, farmers have been converting parts of their allocated land to cultivate tea plants. Little is known about the benefit of agroecological management as an alternative to conventional tea management practices, and thus, there is a need to understand how it can improve tea yields, quality and the livelihoods of the farmers. Conducted in Northern Vietnam from 2019 to 2022, this study examined the impacts of agroecological tea management practices on soil health indicators, tea yield and quality, and net income of tea farmers. We showed that agroecological management practices significantly enhanced soil organic matter by 0.8% and soil pH by 0.5 units on average. Conversely, conventional management based on chemical fertilizer applications, significantly increased soil total nitrogen by 0.15%–0.2%. No significant differences were observed between soil texture and other soil chemical characteristics. Soil biological parameters were also significantly higher in agroecological tea soil and root samples than in conventional tea plots. Average AMF frequency and intensity of the agroecological tea roots were 98% and 37%, respectively, compared with 73% and 15% of the conventional tea roots. Likewise, soil macrofauna and mesofauna abundance in the agroecological tea plantations was 76 individuals/m2 and 101 individuals/100 g fresh soil on average, respectively, while that of conventional tea farms were 34 and 63 individuals/100 g fresh soil, respectively. Interestingly, a comparison between the converted and nonconverted lands did not show any significant effect of the conversion on soil ph