Effects of Mung Bean Residue Return and Biochar Amendment Combined with Reduction in Inorganic Fertilizer on Rice Yield and Nutrient Uptake: A Case Study in Mekong Delta, Vietnam

Abstract

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.