Effects of Oil Palm–derived Biochar on Plant Nutrient Availability and Phosphorus Solubility in an Acid Sulfate Paddy Soil

Abstract

Oil palm cultivation has been extended to acid sulfate paddy soils in the Thailand’s central plain. Palm oil industry, however, produced several of the biomass wastes that are potentially utilized as a soil amendment. This research aimed at investigating impacts of oil palm biochar (OPB) on chemical properties, plant nutrient availability and phosphorus (P) fractions in an acid paddy soil (Rangsit series: Rs). Four treatments were included the soil incubated with OPB at the respective rates of 0, 0.5, 1.0 and 2.0 ton/rai under saturated conditions. Results from a 16–week incubation revealed that soil OPB incorporation slightly increased pH, and increased the amounts of Bray–II–extractable P, CaCl₂–extractable Si, and NH₄OAc–extractable bases. Results from the P fractions using a five–step sequential extraction demonstrated that P associated with poorly crystalline Fe oxides (F3, 81%) and crystalline Fe oxides (F4 = 9.5%) were the major P fractions in the studied soil. Fractions of P bound to Al oxides (F2, 6.7%), P bound to CaCO₃ (F5, 2.8%) and soluble and loosely bound P (F1, 0.035%) occurred at minor extents. The OPB application increased P in the fraction F1 that is the most available fraction to plant. This study highlights a potential role of OPB in enhancing the availability of P, K and Si in acid sulfate paddy soils under saturated conditions.