Fruit orchards in the Vietnamese Mekong Delta (VMD) are severely degraded due to many factors, such as low organic matter content, soil acidification, and poor soil management. Organic manures are ...considered to be a soil conservation measure that decreases soil degradation and acidity. This study aimed to evaluate the impacts of soil organic amendments on the improvement of soil fertility and pomelo productivity. Two soil amendments, namely, chicken manure (CM) and cow dung (CD), were investigated for a period of three years at three pomelo orchards. The soil quality was assessed in two depths (0–20 and 20–50 cm), including the soil pH, electrical conductivity (EC), total nitrogen (Ntot), available phosphorus (Pavail), soil organic matter (SOM), bulk density (BD), and exchangeable cations (Ca, Mg, and K). The results indicated that CD and CM improved soil fertility in topsoil layer (0–20 cm) due to an increase in soil pH, SOM, exchangeable Ca, Ntot, and Pavail. In addition, soil BD significantly reduced after CD and CM were supplied in the three consecutive years of study. The soil quality properties that significantly affected pomelo yield were SOM, Ntot, Pavail, and soil BD. Thus, these soil qualities may be considered as key factors for determining and assessing soil quality in fruit orchards in the VMD. More studies on the influence of organic manures on nutrient uptake and pomelo fruit quality are warranted.
Soil acidity is an important factor affecting crop productivity in the tropics. The soil of the Vietnamese Mekong Delta has high acidity, deficient levels of exchangeable bases, and low fertility. ...This study aimed to evaluate soil amendments’ role in improving soil fertility, soil acidity, and pomelo yield cultivated in raised beds. The field trial was carried out in Hau Giang Province consecutively over 3 years from 2018 to 2020. Four treatments were used, namely control, biochar (5 ton·ha−1·year−1), lime (2 ton·ha−1·year−1), and compost (5 ton·ha−1·year−1). All treatments applied the same amount of NPK fertilizers at rates of 400 kg·N, 300 kg·P2O5, and 400 kg·K2O·ha−1·year−1. Physicochemical properties of the topsoil (0–20 cm) and subsoil (20–40 cm) and fruit yield were investigated. The results showed that biochar or compost application increased soil pH, soil organic matter (SOM), and exchangeable cations and decreased soil bulk density (BD), improving soil fertility and fruit yield in the raised beds. Applications of biochar or compost resulted in about 1.5-fold higher fruit yield than that of chemical fertilizer alone. The average profit increased to USD 1,672 ha−1 after applying biochar and compost in the three-year experiments. Biochar and compost amendments have a positive effect on reducing soil acidity and soil BD, elevating SOM, supplying available Ca2+ and Mg2+, improving soil fertility, enhancing fruit yield, and increasing profit.
Cover crops and mulching can ameliorate soil porosity and nutrient availability, but their effects on the physical characteristics and nutrients in the raised bed soils are unclear.
The field ...experiment was conducted in a pomelo orchard from 2019 to 2021, with an area of 1,500 m
. The treatments included control (no cover crop), non-legume cover crop (
L.), legume cover crop (
Krabov & W.C. Gregory), and rice straw mulching (
L.). At the end of each year (2019, 2020, and 2021), soil samples were collected at four different layers (0-10, 10-20, 20-30, and 30-40 cm) in each treatment. Soil bulk density, soil porosity, and the concentration of nutrients in the soil were investigated.
The results revealed that soil bulk density at two depths, 0-10 and 10-20 cm, was reduced by 0.07 and 0.08 g cm
by rice straw mulch and a leguminous cover crop, thus, increasing soil porosity by ~2.74% and ~3.01%, respectively. Soil nutrients (Ca, K, Fe, and Zn) at topsoil (0-10 cm) and subsoil (10-20 cm) layers were not significantly different in the first year, but those nutrients (Ca, K, Fe, and Zn) improved greatly in the second and third years.
Legume cover crops and straw mulch enhanced soil porosity and plant nutrient availability (Ca, K, Fe, and Zn). These conservation practices best benefit fruit orchards cultivated in the raised bed soils.
The available phosphorus (P) in acid sulfate soils (ASSs) is low because of fixation by aluminum (Al) and iron (Fe), resulting in decreased P use efficiency and crop yield. At present, the use of ...dicarboxylic acid polymer (DCAP) coated on P fertilizer is expected to improve P use efficiency and plant productivity. However, the influence of DCAP on P solubility and on the yield of sweet potato cultivated in acidic soils has not been elucidated. Thus, the aimed of this study was to evaluate the effect of the use of DCAP-coated P fertilizer on the availability and nutrient uptake of P as well as the yield of sweet potato. Under the greenhouse condition, the use of DCAP significantly improved P availability (~3 mg P kg
), increasing tuber diameter and length by ~0.5 and ~1.0 cm, respectively. Thus, the productivity of sweet potato in the treatment 40-kg P
O
and 60-kg P
O
ha
coated with DCAP was higher by about 100 g pot
than that in the same rate of P fertilizers (40- and 60-kg P
O
ha
) not coated with DCAP. In the field experiment, P accumulation (82.7 kg P
O
ha
) and tuber yield (22.0 t ha
) in the treatment of DCAP-coated with 60-kg P
O
ha
were not significantly different compared with that in the treatment of 80-kg P
O
ha
(82.1 kg P
O
and 21.7 t ha
, respectively). Furthermore, the use of DCAP combined with 75% P fertilizer increased the P availability by the same amount as that with the use of 100% P fertilizer. Hence, the use of DCAP reduced about 25% of the chemical P fertilizer applied in soil.
Foliar application is a popular technique to supply mineral nutrients to crops. It also enhances nutrient use efficiencies, especially under limited soil fertility or restricted environmental ...conditions. This study aimed to evaluate the influence of foliar application of phosphorus (P) with potassium (K), magnesium (Mg), and zinc (Zn) on the nutrient uptake, yield, and fruit quality of pomelo. The experiments were conducted between 2018 and 2021 in three different sites of alluvial soils, including four treatments, namely, control (without foliar fertilization), FF1 (containing P, K, and Mg), FF2 (P, K, Mg, and Zn), and FF3 (Zn). The results indicated that the P, K, and Mg concentrations in leaves and fruits were significantly enhanced after the spraying of solutions FF1 and FF2 compared with the control and FF3. The application of FF1 and FF2 greatly improved the fruit quality, and the fruit yield response was as high as 4.0-5.0 t ha−1. Foliar Zn application (FF3) increased the Zn concentration in leaves, but there was no improvement in fruit Zn content, fruit quality, and yield compared to the control treatment. The results indicate that FF1 or FF2 could be used as a sustainable fertilizer strategy for pomelo trees because of its ability to improve the leaf and fruit nutrient concentration and enhance the fruit quality and productivity of pomelo.
Durian is one of the most valuable and expensive fruits in Vietnam and Southeast Asia. Leaf nutritional disorders are considered to be causes of reductions in fruit yield and quality. However, ...studies on the nutritional balance in durian leaf are limited. In this study, we used the DRIS method for leaf limitation nutrient diagnosis at the stage 2 months before durian flowering. Our objectives were to (i) establish DRIS norms for the macronutrients (N, P, K, Ca, Mg, and S) in durian leaf and (ii) determine nutrient value ranges that are insufficient or excessive in durian production. A total of 180 leaf samples were collected and examined from 90 durian orchards cultivated on alluvial soils in the Vietnamese Mekong Delta. The results indicate that DRIS establishment for durian was highly reliable due to the significant positive correlation (r > 0.5) among nutrient indices. The limiting nutrients in durian leaf at the investigation stage were S, Mg, Ca, and P, where S and Mg were the most deficient. The optimal ranges of nutrients in durian leaf were determined and recommended in this study. Further studies are necessary to validate the efficiency of DRIS using nutrient omission trials under durian cultivation.
Abstract
Acid soils contain high concentrations of aluminum and ferrous ions, which limit crop growth and the available plant nutrients. The current work was to determine the effects of bio-organic ...fertilizer (BOF) application on soil quality and the growth of blueberry cultivated in acid soil. A completely randomized block design was arranged, with four doses of BOF (0, 2, 4, and 6 t ha
–1
yr
–1
). Each treatment was carried out with four replicates. In the present work, soil quality properties such as pH, soil organic matter, available phosphorus, total nitrogen, aluminum (Al
3+
), and iron (Fe
2
+) were measured. Additionally, the influence of organic fertilizer on the growth of blueberry (plant height, number of shoots, and leaves) was also investigated. The results indicated that both the rates of BOF (4 and 6 t ha
−1
yr
–1
) significantly improved soil organic matter and available phosphorus. Also, BOF application greatly decreased the soil concentrations of Al
3+
and Fe
2
+ compared to the control treatment. Similarly, 12 months after planting, the number of shoots and leaves was improved in the pots with BOF compared to that without BOF addition. From the results of this study, we recommend using BOF as the best measure for enhancing soil health and blueberry growth.
Alternate wetting and drying (AWD) irrigation is projected to replace continuous flooding (CF) irrigation for rice production in parts of the Mekong delta area during the dry season. A dry season ...field experiment was conducted in Mekong delta alluvial soil to compare N cycle processes and agronomic parameters under AWD and CF water management schemes. 15N-labeled urea was applied in microplots to follow the fate of fertilizer N. The major loss of fertilizer N occurred through ammonia volatilization amounting to 21% and 13% of the applied N in the AWD and CF treatments, respectively. Ammonia volatilization was largely controlled by soil and floodwater pH which determined the NH3/NH4+ ratio. Irrespective of water management, 10–12% of the fertilizer N could be recovered from the top soil (0–15 cm) after harvest, whereas 10% of fertilizer N accumulated in deeper soil horizons (15–50 cm). Even though the loss of fertilizer N through nitrification-denitrification was 6 fold higher under AWD than CF (0.22 versus 0.04 g N m−2) it only removed 2.5% of the applied fertilizer and was thus quantitatively insignificant. Overall, net N mineralization and potential nitrification in the top soil were stimulated by the AWD treatment, whereas the difference in water management practice did not affect N uptake by the plants, aboveground biomass, or grain yield. Fertilizer N contributed only around 20% of the N uptake by the plants probably because the soil was rich in N, which was deposited during the preceding flooding season. Although based on data from one dry season crop only, our study indicates that future implementation of AWD irrigation is unlikely to adversely affect crop yields by loss of fertilizer N in intensive rice production systems in the Mekong delta.
► NH3 volatilization was responsible for the major gaseous N loss of fertilizer N. ► Denitrification was increased six-fold by AWD, but was still quantitatively insignificant. ► Approx. 10% of fertilizer N accumulated in deeper soil horizons (15–50 cm). ► AWD did not affect rice yield or fertilizer N loss.
To grow fruit plants, farmers in the Vietnamese Mekong Delta (VMD) must use raised bed constructions to avoid waterlogging during the rainy season. This study aimed to evaluate the effects of the age ...of the raised beds on the soil physicochemical properties of longan orchards located in the VMD. Two raised bed systems were evaluated: a young bed constructed 10 years ago and an old bed constructed 42 years ago. Soil samples were collected from five different soil layers (0–20, 20–40, 40–60, 60–80, and 80–100 cm) with four replicates per layer. Soil samples were tested for pH, electrical conductivity (EC), available phosphorus (AP), total nitrogen (TN), soil organic matter (SOM), exchangeable cations (Ca
2+
, K
+
, Mg
2+
, and Na
+
), cation exchange capacity (CEC), bulk density (BD), soil porosity, available water-holding capacity (AWC), particle composition (sand, silt, and clay), and size. The soil pH was approximately 1.0 units lower in the old bed compared to the young bed at depths of 0–20 and 20–40 cm. The BD was higher in the old bed (0.15 g cm
−3
) than in the young bed at a soil depth of 0.4 m. SOM, AP, exchangeable cations (Ca
2+
, Na
+
, and Mg
2+
), AWC, and soil porosity were significantly lower in both the topsoil (0–20 cm) and subsoil (20–40 cm) layers in the old bed than in the young bed. In particular, the SOM, AP, AWC, and soil porosity contents in the old bed decreased by 18%, 20%, 15%, and 17%, respectively, compared with those in the young bed at soil depths of 0–40 cm. Therefore, cultivating raised bed soil for a longer period significantly reduced the soil exchangeable cations, porosity, and fertility of the surface and subsurface soils. Based on these results, farmers should use soil conservation practices, such as cover crops, rice straw mulching, and soil amendments in their orchards to mitigate topsoil degradation.
We report a superspreading event of severe acute respiratory syndrome coronavirus 2 infection initiated at a bar in Vietnam with evidence of symptomatic and asymptomatic transmission, based on ...ministry of health reports, patient interviews, and whole-genome sequence analysis. Crowds in enclosed indoor settings with poor ventilation may be considered at high risk for transmission.
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