Seasonal variation-dependent biochar impacts on coastal acid-sulfate soil in paddy fields and the consequences on rice growth and yield

Utilizing eco-friendly and cost-effective amendments, like biochar produced from agricultural biomass wastes offers numerous benefits for ameliorating acid-sulfate soils in coastal regions. This study investigates seasonal variation and rice husk and longan biochar's impacts on soil properties, quality, and rice (Oryza sativa L.) growth and yield in acid-sulfate paddy fields during dry and rainy seasons. Five treatments (T) were tested: T1 (no biochar), T2 and T3 (10-tone and 20-tone rice-husk biochar ha⁻¹), and T4 and T5 (10-tone and 20-tone longan biochar ha⁻¹). Results showed that biochar improved soil properties with pH increasing by 3.2 % to 9.2 % and exchangeable Al decreasing by 7.7 % to 18.1 %, compared to T1, dependent on treatments and seasons. Soil quality index in biochar treatments increased by 30 %, 54 %, 26 %, and 16 % for T2, T3, T4, and T5, respectively, compared to T1 in the dry season. This season exhibited the highest grain weight (1.06 kg m⁻²) and total biomass (2.31 kg m⁻²) in T3, followed by T5, T2, T4, and T1. The rainy season benefits were less pronounced, likely due to leaching, suggesting more frequent applications may be necessary in high-rainfall regions. Liming effects and leaching in the rainy season were identified as primary mechanisms influencing soil quality and rice yield. Rice-husk biochar was more effective than longan biochar in mitigating soil constraints and enhancing rice yield. In short, biochar effectively ameliorates acid-sulfate soil constraints, improving rice yield and growth. However, rapidly diminishing effects during the rainy season necessitate further investigation for optimal application in high-rainfall regions.