A COMPOSITE SOIL QUALITY INDEX INTEGRATING CHEMICAL FERTILITY AND PHYSICAL MATURITY INDICATORS FOR TROPICAL PEAT SOILS IN MAHAKAM TENGAH, EAST KALIMANTAN
Keywords:
Soil quality index, peat fertility, decomposition, composite indicator, mahakam tengahAbstract
Individual soil properties each capture only one dimension of peat condition, so composite soil quality indices (SQI) that integrate multiple chemical and physical indicators are increasingly used to support peatland restoration prioritization. This study developed a composite SQI for tropical peat soils within the Kedangrantau–Sabintulung Peat Hydrological Unit (KHG), Mahakam Tengah, Kutai Kartanegara, East Kalimantan, by combining a Nutrient Fertility Index (NFI: pH, total N, total P, total K, and C:N ratio) and a Physical Maturity Index (PMI: bulk density and porosity) derived from composite peat samples at three villages (Liang Buaya, Tunjungan, and Sabintulung). Each indicator was normalized to a 0–1 scale using min-max scoring and combined with equal weighting, following the additive soil quality index framework. Liang Buaya had the highest NFI (0.600) but the lowest PMI (0.000); Sabintulung showed the reverse pattern (NFI = 0.325, PMI = 1.000); and Tunjungan was intermediate on both axes (NFI = 0.557, PMI = 0.340). The composite SQI (mean of NFI and PMI) was 0.300, 0.449, and 0.662 at Liang Buaya, Tunjungan, and Sabintulung, respectively. This pattern reveals a consistent inverse relationship between chemical nutrient fertility and physical decomposition maturity across the three villages: the least physically decomposed site was chemically most fertile, while the most physically decomposed site was the most nitrogen-constrained despite comparatively higher phosphorus and potassium availability. Because this trade-off is invisible in any single indicator, the composite framework provides a practical, transparent basis for differentiating conservation versus restoration priorities across villages in this degraded KHG, pending validation with a larger, principal-component-weighted sample.
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