Intensive rice cultivation for a long time resulted in increasing soil degradation and less yield. This study aimed to evaluate effects of the combining reducing nitrogen fertilizer (N) with biochar amendment on soil chemical properties, rice growth parameters, and grain yield in the rice cultivation system in the Mekong Delta region, Vietnam (VMD). Field experiment was designed in the split-plot design with two factors, including N fertilizer (main plot) and biochar (sub-plot). Two N fertilizer rates were: (N50)—50 kg N ha–1 and (N100)—100 kg N ha–1, which is the farmer's practice. Biochar was amended with three rates: no applied biochar (B0), 5 t ha–1 (B5), and 10 t ha–1 (B10). The results indicated that reducing N fertilizer by 50% combined 5–10 t biochar ha–1 resulted in maintaining soil pH, soil electrical conductivity, soil organic carbon, cation exchange capacity, and rice biomass. Applying biochar at a rate of 5–10 t ha–1 significantly increased the available N, available P, and rice height compared to the treatment with no applied biochar (B0). Rice yield in the treatments applied with 5–10 t ha–1 was significantly higher than the treatment without the use of biochar by 11.6–14.7%. The findings of this study confirmed that reducing 50% N fertilizer combined with 5 t ha–1 or 10 t ha–1 of biochar could improve soil available N, available P, rice growth, and grain yield in intensive rice cultivation systems in the VMD region.

Reducing greenhouse gas emission by alternating the upland crop rotation in the Mekong Delta, Vietnam | Van Dung Tran, Kim Thu Nguyen, Nguyen Hoang Phuc Ho, Nguyen Thanh Lich Duong, Ngoc Minh Tam Vu, Thi Phong Lan Nguyen, Long Vu Van, Ben MacDonald | Agricultural Journals

The application of organic substrates can affect soil respiration, dehydrogenase (DH‐ase) activity, dissolved organic carbon (DOC), and humic acid (HA) fractions. This study aimed to evaluate the effects of five organic substrates in the organic fractions of degraded alluvial soil, acid sulfate soil, and sandy soils and the physicochemical properties of the soil. Soil samples were amended at a rate of 5 tons ha⁻¹ with (1) water hyacinth compost, (2) sugarcane filter cake compost, (3) biogas sludge‐rice straw compost, (4) vermicompost, and (5) sludge. The results showed that soil respiration and DH‐ase activity increased rapidly within the first 5 days of incubation, while the concentrations of DOC and HA decreased throughout the incubation period. The highest respiration and DH‐ase activity occurred after the application of vermicompost. DOC was found to be the highest in soils amended with sugarcane. The highest concentration of HA was observed with the application of sugarcane residues, regardless of the type of soil. The application of water hyacinth and biogas sludge stimulated cumulative HA only in the acid sulfate soil, while vermicompost improved HA only in the degraded soil. The largest stimulation in respiration and DH‐ase activity was observed in degraded and sandy soils, regardless of the type of amendment. In the acid sulfate soil (3.7 mg·C·g⁻¹), larger amounts of DOC and HA were observed than in both degraded (1.7 mg·C·g⁻¹) and sandy soils (1 mg·C·g⁻¹). However, DH‐ase activity was the lowest in acid sulfate soil.

Advocating proper phosphorus (P) fertilisation is necessary to save this limited natural resource and to save the investment in rice cultivation. This study aimed to evaluate changes in phosphorus availability, total phosphorus in soil, phosph...

This study aimed to investigate effects of nitrogen (N) fertilizer rates and inoculation of rice seeds with N-fixing bacterium Gluconacetobacter diazotrophicus on the growth parameters and yield of OM5451 and OM6976 rice varieties in the Vietnamese Mekong Delta region. Nitrogen fertilizer rates of 50 kg N.ha-1 and 100 kg N.ha-1 were used, with latter reflecting farmer practice. Three rice seed inoculation methods were also employed: Seeds soaked in water for 24 hours and allowed to stand for 30 hours (control) (B0); Seeds soaked in water for 24 hours and inoculated with G. diazotrophicus for 30 hours (B1); Seeds soaked with G. diazotrophicus in water for 24 hours and allowed to stand for 30 hours. Applying 50 kg N.ha-1 without combining with NFB bacterium in this experiment generally resulted in less tillers, shorter plants, a lower SPAD index, and lower grain yield. Combining G. diazotrophicus bacterium with reduced N fertilizer of 50 kg N.ha-1 demonstrated rice growth and yield may be maintained in both varieties compared to 100 kg N.ha-1. These results providing a firm foundation for future research of adding NFB to paddy soils to decrease the N fertilizer requirement.

Luân canh cây màu trên nền đất lúa được xem là phương pháp canh tác thay thế cho mô hình chuyên canh lúa kém bền vững trong tương lai. Đề tài được thực hiện nhằm đánh giá ảnh hưởng của mô hình luân canh lúa-dưa hấu đến khả năng cải thiện hàm lượng đạm (N) hữu dụng, ...