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.

This study aimed to assess the co-incorporation of mung bean residue and rice husk biochar with reduced NPK fertilizer rates on rice yield and nutrient uptake in the subsequent rice crop. A field experiment was conducted in five treatments (T1 to T5). In the spring–summer (SS) of 2023, rice was cultivated and its straw was burned (T1), while mung bean was cultivated and its residue was incorporated (T2 to T5). In the next summer–autumn crop (SA), rice was cultivated with different levels of inorganic fertilizers. T1 was added with the conventional fertilizer (95 kg N, 45 kg P₂O₅, and 35 kg K₂O ha⁻¹). T2 included the same amount of NPK fertilizer as T1 with mung bean incorporation. In T3 to T5, rice husk biochar was amended at a rate of 10 Mg ha⁻¹ before SA. In T3, inorganic fertilizers were reduced by 30% of N and 50% of P₂O₅ and K₂O; in T4, by 15% of N, 30% of P₂O₅ and K₂O; and in T5, by 15% of N only. The rice grain yield was 26.6–35.3% significantly higher in T3, T4, and T5 compared to T1. P accumulation in straw and grain was significantly higher in T3, T4, and T5 than in T1. Furthermore, K accumulation in grain was markedly higher in T3, T4, and T5. No significant differences were observed in any of the soil chemical properties among treatments at harvest in SA. This study highlights that the combination of residue incorporation and biochar may substitute a part of chemical fertilizers and contribute to more sustainable rice production.

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.

Những tác động của các tiến trình tự nhiên và sử dụng đất làm thay đổi đặc tính đất. Nghiên cứu đánh giá sự thay đổi đơn vị bản đồ đất thông qua đặc tính và hình thái phẫu diện đất làm cơ sở cho sử dụng đất đai hiệu quả. Tổng hợp tư liệu, khảo sát đất theo tuyến với 20 điểm khoan sâu 2 m, 3 phẫu diện đất điển hình, 15 mẫu đất tầng mặt và 30 phiếu điều tra được thực hiện. Kết quả chỉnh lý bản đồ đất tỷ lệ 1/25.000 có 2 nhóm đất chính được xác lập gồm Gleysols (đất phù sa mới) và Plinthosols (đất phù sa cổ) với 5 đơn vị bản đồ đất. So với bản đồ đất 2016, đất phèn hoạt động nặng tăng 1,2%; đất phèn tiềm tàng nông thay đổi thành phèn tiềm tàng trung bình chiếm 97,6%. Phẫu diện đất được phân hóa mạnh có tầng phèn, tầng kết von và tầng chứa vật liệu sinh phèn. Tầng đất canh tác có nhiều chất hữu cơ chiếm gần 64%. Với sự thay đổi này thể hiện đất đai còn tiềm năng cho canh tác. Sử dụng đất và biện pháp quản lý phù hợp cần được nghiên cứu thực hiện để khai thác và sử dụng đất hiệu quả tại huyện Mộc Hóa, tỉnh Long An.

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 relate it 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), followed by summer–autumn (SA) and ended with the winter–spring (WS) season. Rice yield significantly (P < 0.05) increased by 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 = 0.86) 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. Use of a SQI involving several soil quality indicators enables to overall quantify the 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.

The objective of this study was to evaluate the effects of land preparation methods and iron-coated (Fe-coated) rice seeds on the growth, yield, and Fe uptake of rice in alluvial soils in the Mekong Delta region. The experiment was conducted in the 2020 summer-autumn cropping season under the triple rice cultivation system in Chau Thanh district, An Giang province. The field experiment was designed as a randomized complete block design (RCBD) with six treatments and four replications. The treatments were: (T1) puddled + water seeding + Fe-coated seeds; (T2) non-puddled + dry seeding + Fe-coated seeds; (T3) zero-tillage + non-puddled + dry seeding + Fe-coated seeds; (T4) puddled + water seeding + sprouted + non-Fe-coated seeds; (T5) puddled + wet seeding + sprouted + non-Fe-coated seeds; and (T6) puddled + transplanting + sprouted + non-Fe-coated seeds. The results showed that changes in the land preparation, planting method, and Fe-coated seeds did not significantly affect the number of tillers, plant height, yield components, soil chemical properties, grain yield, or Fe uptake of the rice plants and grains. However, the T3 and T6 treatments tended to have higher grains yields (5.86-5.90 tons ha-1), and higher total Fe content in grains (93.0-94.3 mg kg-1) and rice plants (83.1-84.0 mg kg-1). The findings from this study confirmed that the new planting method using zero-tillage + non-puddled + dry seeding + Fe-coated seeds can maintain the germination rate, growth, and grain yield of rice.