05711nam a2200277 4500 260505b2024 bx d|||g m||| 00| 0 eng d Universiti Teknologi Brunei eng UTB UTB 120 REPORT THESIS & DISSERTATION RTDS 428 Awangku Syazwan bin Pengiran Sulaiman author Effect Of Plant Residue On the Improvement Of Soil Properties In Arabic Acidic Oil / Awangku Syazwan bin Pengiran Sulaiman Bandar Seri Begawan : Universiti Teknologi Brunei , ©2024 . xv,187 pages : charts ; 30cm. Thesis submitted for the degree of Doctor In Philosophy ABSTRACT Soil acidity is a widespread constraint across both temperate and tropical regions, which poses significant challenges to sustainable crop production due to excess H* concentration, nutrient depletion, and toxicity from heavy metals/metalloids. Addressing this issue is crucial for reclaiming and revitalising acidic soil for agricultural use. Among various approaches, the application of plant residues — such as crop straw and fresh plant material — offers a sustainable and resource-efficient strategy in repurposing agricultural and underutilized plant biomass for soil acidity management. The present thesis comprises four research chapters, which integrate a global meta-analysis and a series of controlled laboratory incubation experiments, exploring the potential of plant residue and the derived biochar to improve the chemical properties of acidic soil. In the first phase of the research, a meta-analysis of published literature was conducted to quantify the effect of plant residue incorporation on acid soil pH. This analysis established a consensus that plant residue significantly increases soil pH, with the strongest liming effect observed in extremely acidic soil (pH 3.5 - 4.4) compared to moderately or slightly acidic soil (pH > 5.5). Importantly, the study identified, for the first time, critical thresholds for plant alkalinity (≥ 80 cmol kg") and plant total nitrogen (N; ≥ 10 g kg ) to achieve optimal pH improvement. Building on the insights from the meta-analysis, the second phase of the research focused on a particularly challenging subtype of acid soil —acid sulfate soil. The soil, sampled from a rice field in Brunei Darussalam, was independently amended with plant residues of Melastoma malabathricum and Dicranopteris linearis, with dolomite serving as a comparison and unamended soil as a control. While both plant residues led to significant improvements in soil properties, the effects were modest and insufficient to alleviate the soil chemical constraints, particularly when compared to dolomite treatment. This suggests that the plant resides are not viable stand-alone amendments for acid sulfate soil. The subsequent experiment built upon the preceding laboratory investigation and explored the combined applications of dolomite with both plant residues and their derived biochar products for a more effective outcome. Biochar was produced by subjecting the plant resides to thermal decomposition in a laboratory muffle furnace at 300, 500, and 700 °C for 2h. The findings revealed greater improvements in soil chemical properties from the combined application of dolomite with biochar compared to dolomite-only treatment and dolomite-plant residue combination. Moreover, the study also found previously undocumented antagonistic interactions between dolomite and biochar in enhancing soil exchangeable magnesium (Mg) and available N. These findings suggest potential trade-offs in soil properties that must be considered, which could have practical implications in selecting appropriate amendment combinations for specific soil improvement objectives. The final phase of the research evaluated the effect of wheat straw-derived biochar on the chemical properties of slightly acidic soil from Canada. This investigation specifically examined the influence of pyrolysis conditions - pyrolysis temperatures (350, 500, and 650°C) and retention times (1 and 2h) - as well as application rates (5 and 10 t ha) and placement methods (thorough mixing vs. surface broadcasting) of wheat straw biochar. Biochar addition notably increased soil available phosphorus (P) and potassium (K), with the magnitude of these effects varying based on pyrolysis conditions and application rates. Intriguingly, surface broadcasting of wheat straw biochar resulted in greater soil N availability compared to thorough mixing, highlighting the significance of placement method in influencing soil N dynamics. Collectively, the findings of this thesis advance the understanding of the interplay between plant-based amendments and acid soil properties. The results provide a strong foundation and proof-of-concept for identifying promising strategies and recognizing the limitations of certain treatments. These insights are also crucial for refining future soil amendment practices and developing context-specific, field-applicable solutions for managing the fertility and productivity of acid soil. Thesis (Degree) - Universiti Teknologi Brunei, 2024 Universiti Teknologi Brunei Thesis Universiti Teknologi Brunei Final Year Report Soil acidity Management Biochar Acid sulfate soils Brunei Professor Dr. Guillermo Hernandez-Ramirez Supervisor lc 0 RTDS Reports, Thesis & Dissertation 850646: 002481 c.1_UTB Universiti Teknologi Brunei 24058 24058 0 0 lc 0 0 UTB UTB Level 2 2025-10-05 Universiti Teknologi Brunei 0 UTB 120 REPORT THESIS & DISSERTATION, RTDS 428 850646 2026-05-05 2025-10-05 RTDS Reg. No. 002481_UTB [RTDS 428]