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In the Vietnamese Mekong Delta, soil quality and crop yield are steadily declining under rice monocultures with three crops per year. The objective of this study was to evaluate the medium-term effects of rotating rice with upland crops and adding organic amendments on rice yield, and to relate this to soil quality. A field trial with split-plot design including two factors and three replicates was carried out from 2017 to 2020, over the course of nine consecutive cropping seasons. Crop rotations and organic amendments were applied as main-plot and subplot factors, respectively. The rotations were (1) rice–rice–rice (R–R–R), (2) soybean–rice–rice (So–R–R), and (3) sesame–rice–rice (Se–R–R), while organic amendment treatments included (i) no amendment (NO-AM), (ii) compost of rice straw and cow manure (RS+CM), and (iii) sugarcane compost (SGC); the composts were applied at a rate of 2.0 t ha−1. The rotation cycle started with the so-called spring–summer (SS) season, followed by the summer–autumn (SA) season and ending with the winter–spring (WS) season. Rice yield significantly (p < 0.05) increased under organic amendments after nine growing seasons (2019–2020 WS), with an increment of 5.1% for RS+CM (7.07 ton/ha) and 6.1% for SGC (7.14 ton/ha). Contrary to our expectation, rotations with upland crops did not significantly increase rice yield. Rice yield significantly and positively correlated with an integrated soil quality index–SQI (r = 0.85) for the topsoil (0–15 cm), but not for the subsoil (15–30 cm). The increased availability of soil nutrients (Si and marginally also P) and improved soil physical properties probably induced by organic amendments, along with other soil properties under study, cumulatively attributed to enhanced rice yield. Repeated organic amendments thus becomes an effective management practice in improving soil quality under rice-based systems and could be applied to sustain rice yield in rice-producing regions with similar soil types and climatic conditions. Use of a SQI involving several soil quality indicators enables us to quantify the overall importance of soil fertility for rice yield versus other factors, and it provides an effective means of quantifying the integrated effect of improved management. Moreover, integrating a wide range of soil quality indicators in a SQI ensures its applicability across diverse settings, including different crop rotations and various soil types. [ABSTRACT FROM AUTHOR]

This study was carried out to evaluate the fertility of rice soil and the effect of inorganic fertilizers combined with sugarcane filter cakes on rice yield in a protected dike area in Cho Moi district, An Giang province. The experiment consists of 4 treatments, and the dose of fertilizer in each treatment is (1) controlled according to the farmers' dosage (224 kg N + 148 kg P2O5 ha−1), (2) fertilize according to farmers + 6 tons/ha of cow manure composted with straw, (3) fertilizer according to farmers + 6 tons/ha of cow manure composted 15 cm deep, and (4) fertilize according to farmers + 2 tons/ha of organic fertilizer with sugarcane filter cakes. By analyzing the nutrient content of soil samples, it was found that inorganic fertilizers in combination with sugarcane residues improved soil fertility as reduced soil acidity and electrical conductivity, and increased organic matter, total nitrogen content, and exchangeable K. In addition, exchange and enriched exchangeable Mg achieved the highest rice yield, a statistically significant difference compared with organic fertilizer treatment with straw compost and inorganic fertilizer. However, the content of total P, available P, exchangeable Na, and Ca have not improved significantly. Therefore, applying inorganic fertilizers combined with sugarcane filter cakes is an excellent measure to help improve the supply of nutrients from the soil and increase rice yield in the dike land. [ABSTRACT FROM AUTHOR]

The study assesses steel slag fertilizer’s effect on rice yield on acid sulfate soil in Vinh Phuoc village, Tri Ton district, An Giang province. A fi eld experiment with three treatments was established by the randomized block method with three replications. The fertilizer dose applied in individual treatments was: (1) 3 tons/ha lime, (2) 3 tons/ha steel slag fertilizer, and (3) 3 tons/ha compost in the experiment. The farmers’ practice fertilizer rate of 131 kg N + 41 kg P2 O5 + 108 kg K2 O/ha was applied as the based treatment. Using steel slag fertilizer on acid sulfate soil at a dosage of 3 tons/ha in combination with inorganic fertilizers showed a tendency to improve soil chemical properties such as soil pH, EC, soil organic carbon (SOM) content, CEC, total P, available P, and exchangeable cations (K, Na, Mg) content. The slag fertilizer affected the growth of rice plants, thereby helping to increase the yield and yield components of rice compared to other treatments. The steel slag fertilizer has improved soil properties and rice yield, which was statistically signifi cantly different from other treatments. However, total nitrogen and calcium exchange content have not improved considerably. Therefore, applying inorganic fertilizers combined with steel slag fertilizer is an appropriate solution to enhance soil nutrients and increase rice yield. [ABSTRACT FROM AUTHOR]

This study evaluated nutrients removal from domestic wastewater by five plants in wetland roof systems (WR). The study plants includeArachis duranensis(1),Evolvulus alsinoides(2),Cosmos Bipinnuatus(3),Cyperus alternifoliusLinn (4), andPhilodendron hastatum(5). The WRs were acclimatized at hydraulic loading rates (HLR) of 220 m3/ha d and operated at HLR of 300 m3/ha d. The plants (1), (2), (4), and (5) had the ability to grow under the rooftop conditions with domestic wastewater as a nutrient source while the plant (3) was not suitable and dead after 20 d of operation. Generally,A. duranensis(1) andC. alternifoliusLinn (4) were the most suitable plants treating domestic wastewater under the conditions of WR. The average phosphorus removal efficiencies of (1) and (4) were approximately 75 and 89%, respectively, while the average nitrogen removal efficiencies were 69 and 92%. The phosphorus accumulation in plants (1) and (4) during operation was 20.4 and 29.4%, respectively, while the nitrogen accumulation was 21.5 and 93%. It is concluded thatC. alternifoliusLinn (4) has best nutrient removal among the study plants under the conditions of shallow bed WR treating domestic wastewater (24 ± 4 and 2.0 ± 0.4 kg TP/ha d). [ABSTRACT FROM PUBLISHER]

A marine fungus was isolated from the black tiger prawn Penaeus monodon at Nha Trang, Vietnam, on March 20, 2001 and named isolate NJM 0131. The fungus was identified as Haliphthoros milfordensis from the characteristics of asexual reproduction, and its physiological characteristics were investigated. Although the optimum temperature for growth of the isolate was 25°–30°C, the fungus grew at a wide range of temperatures (15°–40°C). H. milfordensis grew well in 50%–100% seawater, but poorly in PYG agar containing 1.0%–5.0% NaCl and KCl. The fungus grew at a wide range of pH (4.0–11.0) with the optimum pH value of 7.0–9.0. The isolate also showed pathogenicity to swimming crab larvae (Portunus trituberculatus) by artificial infection, but mortality was not high. This is the first report of disease in the black tiger prawn P. monodon in Vietnam caused by H. milfordensis. [ABSTRACT FROM AUTHOR]