Optimizing Rice Straw Biochar Production for Sustainable Soil Management in Thai Agriculture

Thesis Abstract

Thailand’s expanding rice agriculture generates significant quantities of rice straw, which is largely underutilized and often disposed of through open-field burning, contributing to environmental pollution and greenhouse gas emissions. This study addresses the pressing need to convert rice straw into biochar as a sustainable soil amendment to improve soil fertility and crop productivity while mitigating environmental impacts. The primary aim is to optimize the production parameters of rice straw biochar to enhance its agronomic benefits within Thai farming systems. Specific objectives include identifying optimal pyrolysis temperature and residence time, evaluating the influence of feedstock pre-treatment on biochar properties, and assessing the effects of biochar application on soil health and rice yield in smallholder plots. The study employed a mixed-methods research design comprising experimental laboratory analyses and field trials. The laboratory component involved conducting pyrolysis experiments on rice straw samples collected from three representative rice-growing communities in Chiang Mai Province, with a sample size of 50 biomass samples. The experimental design utilized a factorial arrangement with temperature levels of 400°C, 500°C, and 600°C, and residence times of 30, 60, and 90 minutes. The biochar produced was characterized through proximate and ultimate analyses, surface area assessment using Brunauer–Emmett–Teller (BET) analysis, and functional group identification via Fourier-transform infrared spectroscopy (FTIR). For field trials, a randomized complete block design was employed across three smallholder farms, with 30 plots per farm, comparing control soils with biochar application rates ranging from 5 to 20 t/ha. Data collection included soil chemical and physical property measurements (pH, cation exchange capacity, organic carbon, nutrient content) pre- and post-application, crop yield measurements at harvest, and farmer surveys on biochar production and application practices. Analytical techniques encompassed analysis of variance (ANOVA) to determine significant differences in soil and crop parameters across treatments, regression analysis to model relationships between production variables and biochar properties, and thematic analysis of qualitative data from farmer interviews. The theoretical framework integrated the Theory of Planned Behavior to understand adoption behaviors and the Soil Fertility and Sustainable Agriculture theories to contextualize biochar’s impact. Anticipated findings suggest that pyrolysis at 500°C for 60 minutes will produce biochar with optimal porosity, nutrient content, and stability, thus maximizing soil amendment benefits. Furthermore, pre-treatment methods, such as torrefaction, are expected to enhance biochar quality by increasing surface area and nutrient retention. Field results are projected to demonstrate significant improvements in soil pH, cation exchange capacity, and organic carbon content, coupled with increased rice yields by approximately 15-20% compared to controls. The study’s findings aim to fill a critical gap in localized biochar production protocols, linking laboratory optimization with field validation within the Thai agricultural context. This research contributes to knowledge by providing evidence-based guidelines for smallholder farmers and policymakers on effective rice straw-to-biochar conversion techniques tailored to local conditions. It integrates scientific rigor with socio-economic assessments, facilitating sustainable adoption pathways. The study concludes that optimized biochar production and application can serve as a practical strategy for enhancing soil health, reducing environmentally harmful practices like stubble burning, and improving rice productivity. It recommends scaling up controlled pilot projects, integrating biochar into existing extension services, and fostering policies that promote sustainable biomass valorization. Future research should explore long-term impacts, economic feasibility, and potential integration with other sustainable practices such as crop rotation and organic amendments.