Agriculture in the Global South is innately susceptible to climatic variability and change. In many arid and semi-mountainous regions of the developing world, drought is regularly cited as a significant threat to agricultural systems. The objective of this study is to assess the impacts of climate change on drought and land use and land cover (LULC) change in a semi-mountainous region of the Vietnamese Mekong Delta. We assessed previous drought trends (1980–2020) and future drought in the context of climate change, in accordance with three selected scenarios from the Coupled Model Intercomparison Project Phase 6 global climate models which have recently been released by the Intergovernmental Panel on Climate Change (IPCC) (2021–2060) using the Standardized Precipitation Index (SPI). The change of land use for the period 2010–2020 was then assessed and the associated climatic variability explored. The results show that for the period 1980–2019, SPI 3 responds quickly to changes in precipitation, whereas SPI 9 showed a clear trend of precipitation over time. The first longest duration occurrence of drought for SPI 3, SPI 6, and SPI 9 patterns were respectively 15–16, 21, and 25 months at Chau Doc station, and respectively 11, 14–15, and 16–17 months at Tri Ton station. Future precipitation and both maximum/minimum temperatures are projected to increase in both the wet and dry seasons. In addition, for all-time series scales and climate change scenarios, the levels of drought were slight, followed by moderate. In the future, the humidity at Chau Doc station is expected to decrease, while the occurrence of drought events is expected to increase at Tri Ton station, particularly in SPI 6 patterns (110 drought events in 1980–2020, and up to 198 drought events in the future). Moreover, between 2010–2020, the agricultural land area was seen to decrease, replaced by non-agricultural land uses that were found to increase by 22.4%. Among the agricultural land area, forestry, rice crops, and upland rice were found to reduce by 7.5, 16.0, and 21.2%, respectively, while cash crops and perennial crops increased by 26.4% and 170.6%, respectively. Amongst other factors, it is concluded that the variability of climate has led to drought and thus impacted on the conversion of LULC in the study area. Due to low economic efficiency, changing climate conditions, and a lack of irrigated water, the area of rice crops, forestry, aquaculture, and upland rice decreased, replaced by land for orchards for fruit production and other cash crops.

Potassium (K) is immobilized within the clay minerals, making it unavailable for plant use. Therefore, the current study aimed to (i) select isolates of purple nonsulfur bacteria that can dissolve K (K-PNSB) and (ii) evaluate the production of plant-growth-promoting substances by the K-PNSB isolates. The results revealed that from in-dyked alluvial soils in hybrid maize fields, 61 K-PNSB isolates were obtained under the pH 5.50 conditions. The total dissolved K content (K_dis) by the 61 K-PNSB isolates fluctuated from 56.2 to 98.6 mg L⁻¹. Therein, three isolates, including M-Sl-09, M-So-11, and M-So-14 had K_dis of 48.1–48.8 mg L⁻¹ under aerobic dark condition (ADC) and 47.6–49.7 mg L⁻¹ under microaerobic light condition (MLC). Moreover, these three isolates can also fix nitrogen (19.1–21.5 mg L⁻¹ and 2.64–7.24 mg L⁻¹), solubilize Ca-P (44.3–46.8 mg L⁻¹ and 0.737–6.965 mg L⁻¹), produce indole-3-acetic acid (5.34–7.13 and 2.40–3.23 mg L⁻¹), 5-aminolevulinic acid (1.85–2.39 and 1.53–2.47 mg L⁻¹), siderophores (1.06–1.52 and 0.92–1.26 mg L⁻¹), and exopolymeric substances (18.1–18.8 and 52.0–56.0%), respectively, under ADC and MLC. The bacteria were identified according to their 16S rDNA as Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11, and Rhodospeudomonas palustris M-So-14. These potential bacteria should be further investigated as a plant-growth-promoting biofertilizer.

Under the effects of saltwater intrusion from rising sea water levels, climate change, and socioeconomic issues, the Nga Nam district in Vietnam has suffered damage to its agriculture and changes in agricultural land use. This study aimed to investigate the factors that influenced land use changes and to propose approaches to limit the changes in agricultural land use. The damage caused by saltwater intrusion on agricultural production was evaluated via the use of secondary data collected from the Department of Infrastructure Economics of the Nga Nam district in the period of 2010–2021. The results show that during the 2010–2015 period, agricultural production areas were affected in 2010, 2012, and 2015. In the period of 2015–2021, the trend of saltwater intrusion along the damaged area remarkably decreased due to the work of saltwater-preventing structures. In this period, the area of annual plants increased, while that of fruit trees decreased. In the area comprising annual plants, the area using the triple rice land use type converted into an area using the double rice and double rice–fish ones. Lands for fruit trees transitioned from mixed farming to specialized farming to raise the economic efficiency for farmers. These changes were affected by four main factors: the physical factor, the economy, society, and the environment. The environmental and economic factors were seen to play the most important role as drivers of changes in land use. The factors of saltwater intrusion and acid-sulfate-contaminated soil, consumer markets, floods, drought, profit, and investments were noted to be significant drivers in agricultural land use change. Thus, both structural and non-structural approaches are suggested to inhibit the safeguard changes in the future.