Soil Moisture Dynamics and Groundwater Quality under Oil Palm Cultivation in Tropical Peatlands
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Universiti Malaysia Sarawak
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Oil palm plantation (OPP) establishment on peatland requires drainage, soil compaction as pre-requisite and fertilizer application for high oil palm yield. However, the effect of these activities on the environment is still understudied, particularly in OPP under tropical peatlands. Hence, to ensure sustainable oil palm production, this study evaluates soil moisture dynamics and groundwater quality under oil palm plantation on tropical peatland. A field-based comparative study was conducted at twelve sampling points (Q1-Q12) within an OPP planted on peat soil and grouped according to planting year, with an adjacent drained secondary forest (DSF) used as a control. Soil bulk density (BD), water table (WT), and soil moisture content (SMC) were measured at depths of 0–100 cm to evaluate the influence of compaction and drainage. Long-term groundwater quality data (2011–2017) were combined with post-replanting data (2021–2022) to assess changes in groundwater nutrients associated with plantation activities. Results showed that soil BD was lowest in the DSF (0.03–0.14 g cm⁻³), suggesting the effect of high total C and N, and minimal soil compaction compared to OPP zones. Significant differences in SMC obtained via the Least Significant Difference (LSD) test were observed between OPP sites and the DSF at 10–40 cm depth (p < 0.05), demonstrating the influence of soil compaction. Across plantation areas, SMC increased with depth due to peat submergence below the WT. Groundwater monitoring indicated higher concentrations of K⁺ and Cl⁻ in the OPP compared to the DSF, consistent with fertilizer leaching. Elevated groundwater pH and NO₃⁻ concentrations following replanting suggest reduced soil organic matter and adsorption capacity following land clearing and altered redox conditions. Correlation and regression analyses revealed that SMC was significantly related to groundwater electrical conductivity, PO₄³⁻, Cl⁻, K⁺, and NH₄⁺ concentrations. Overall, the findings indicate that SMC dynamics, regulated by soil compaction and iii drainage, play a key role in controlling nutrient transport from peat soils to groundwater. These results highlight the importance of integrated soil and water management strategies to support sustainable oil palm production on tropical peatlands.