An experiment in a second rotation acacia hybrid (Acacia mangium × A. auriculiformis) clonal plantation in central Vietnam examined factors determining total wood production and its apportionment to sawlog and pulpwood. Growth and stand characteristics were compared with those in nearby plantations owned by small growers. The experimental site was on sloping land damaged and eroded by war and previous land use. The soil was shallow, with 20–30% laterised stones by volume and had lost part of the A horizon. Mean annual increment (MAI, in standing merchantable volume over bark) of the first rotation at age 8.8 years was 17 m³ ha⁻¹ y⁻¹. In the second rotation at age 7.6 years it was 20 m³ ha⁻¹ y⁻¹. Application of P fertiliser at three rates ranging from 14 to 86 kg ha⁻¹ increased stem diameter over the second rotation although stand volume response to P was not significant by rotation end. Potassium (14 kg ha⁻¹) gave no growth response. Growth rate was similar under weed control by herbicide and manual means. MAI increased progressively from 16.5 m³ ha⁻¹ y⁻¹ at the hilltop to 25.0 m³ ha⁻¹ y⁻¹ at the lowest part of the experiment; slope position influenced growth more than management practices. Key soil properties, pH, N, Bray-1 P and organic C were maintained from the first to the second rotation. With simple management practices including conservation of site organic matter and early stand management, appropriate for local small growers, the second rotation yielded 46% of harvested volume as sawlogs and the balance as pulpwood. Although small growers achieved similar growth rates, their current management regime does not yield sawlogs. They can influence the log categories produced and stand value through changes to stocking rate, stand management and rotation age.

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.

The overuse of chemical fertilizers under adverse conditions endangers the sustainability of agriculture. A biological approach should be investigated to address this issue. Therefore, this study aimed to detect the potency of purple non-sulfur bacteria that can fix nitrogen (N) (PNSB-fN) Rhodobacter sphaeroides in soil N fertility, plant N uptake, growth, and rice yield. In brief, an experiment was conducted to check whether the biofertilizer containing PNSB-fN strains can improve rice yield and soil fertility under a highly saline acidic condition. A randomized complete block design was used with four replicates on saline soil in An Bien-Kien Giang, Vietnam. The first factor was the N fertilizer level, i.e., (i) 100%, (ii) 75%, (iii) 50%, and (iv) 0%; the second factor was the PNSB-fN (R. sphaeroides), i.e., (i) the control, (ii) S01, (iii) S06, and (iv) combined S01–S06. In the results, supplying PNSB-fN increased NH₄⁺ compared with the control, i.e., 104.7–112.0 mg NH₄⁺ kg⁻¹ compared with 94.0 mg NH₄⁺ kg⁻¹ in season 1 and 35.9–38.0 mg NH₄⁺ kg⁻¹ compared with 34.2 mg NH₄⁺ kg⁻¹ in season 2. Additionally, by supplying each PNSB-fN strain, the soil Na⁺ and plant Na in culm leaf and grain were decreased in comparison with those in treatments without PNSB-fN. The total N uptake was also enhanced by the PNSB-fN compared with the control. Moreover, supplying PNSB-fN improved the crop height, panicle length, panicle quantity pot⁻¹, grain quantity panicle⁻¹, filled spikelet rate, and grain yield compared with the control. Ultimately, in extremely saline soil, the mixture of PNSB-fN not only improved soil fertility and reduced soil salinity but also replaced 25% of chemical N fertilizer to ensure sustainable agriculture. This newly developed biofertilizer was potent in not only improving the rice and soil health in the locality but also performing the same under similar conditions around the globe.

Acid-sulfate soils and overuse of chemical fertilizers have been obstacles to sustainable agriculture. The variation of fertilization due to poor soil fertility has remarkably affected the yield gap and the quality of the environment, so an optimal fertilizing rate should be formulated. Therefore, this study aimed at (i) detecting obstacles in soil characteristics reducing pineapple yield between farms and (ii) assessing the effects of NPKCaMg fertilizers on soil fertility, uptakes, and pineapple yield. The on-farm experiment was carried out according to site-specific nutrient management (SSNM) arranging in acid-sulfate soil for pineapple, including (i) no fertilizers used; (ii) NPKCaMg: fully fertilizing with nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg); (ii) PKCaMg: fertilizing without N; (iii) NKCaMg: fertilizing without P; (iv) NPCaMg: fertilizing without K; (v) NPKMg: fertilizing without Ca; (vi) NPKCa: fertilizing without Mg; and (vii) FFP: farmers’ fertilizing practice. The result of the principal component analysis revealed that the soil had low availability of N, P, and K nutrients. Available P concentration was negatively correlated with concentrations of Al³⁺, Fe²⁺, and total Mn, whose correlation coefficients were −0.34 to −0.59, −0.52 to −0.74, and −0.63 to −0.70, respectively. Fertilizing NPKCaMg obtained the highest result in the uptakes of N, P, K, Ca, and Mg, which were 289.1–327.4, 25.4–29.3, 137.4–166.0, 41.9–48.9, and 39.8–43.1 kg ha⁻¹, respectively. Fertilizing by SSNM has increased pineapple yield by 22.9 %–44.9 % compared to the FFP. This fertilizer formula should be transferred to the local farmers in order not only to enhance productivity, but also to limit the damage of chemical fertilizers on the environment. Moreover, this formula should be tested globally in other places that share similar soil characteristics.

Fruit rot seriously damages pomelo production. Given concerns regarding the safety of chemical agents, biological alternatives are becoming more preferable. Therefore, the experiment aimed to (i) identify the pathogens causing pomelo fruit rot disease and (ii) select Trichoderma spp. strains controlling the determined pathogens in Ben Tre, Vietnam. Three pathogenic fungal strains isolated from diseased pomelo fruits were selected. The three pathogenic fungal strains were randomly injected into 9 healthy pomelo fruits. The strain PCP-B02-A2 led to a completely rotten fruit on day 17 after infection, while strains PCP-B02-B2 and PCP-B03-A1 had infected spots whose lengths were 17.5 and 28.1 mm, became larger, and eventually led to the whole fruit rot. The pathogens were identified by the internal transcribed spacer (ITS) technique as Colletotrichum gloeosporioides PCP-B02-A2, Pseudopestalotiopsis camelliae sinensis PCP-B03-A1, and P. chinensis PCP-B02-B2. Twenty-five Trichoderma spp. strains were isolated. The ITS technique identified four strains, including Trichoderma asperellum TP-B01, T. harzianum TP-B08, T. harzianum TP-B09, and T. asperellum TP-C25. The PCP-B02-A2 strain had antagonism at 66.7–68.7%, while those of PCP-B02-B2 and PCP-B03-A1 were 64.2–71.1% and 55.7–57.4%, respectively.