Rehabilitation potential of post-coal mining landscapes for Brachiaria cultivation: Linking nutrient retention and nutrient availability indicators

Department of Agroecotechnology, Faculty of Agriculture, Mulawarman University, 75243 Samarinda, Indonesia

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Abstract

This study assessed the nutrient retention and nutrient availability characteristics of post-mining soils in the Decho 3 Pit Area and evaluated their suitability for Brachiaria cultivation. A composite soil sample representing 10 subsampling points (0-20 cm) was analyzed for pH, cation exchange capacity (CEC), base saturation (BS), organic carbon (OC), total nitrogen (N), available phosphorus (P), and exchangeable potassium (K). Because the dataset consisted of a single composite sample, a descriptive comparative approach was applied by contrasting measured values with established fertility benchmarks. The soils exhibited extreme acidity (pH 3.59), very low BS (4.49%), and low CEC (5.50 cmol(+)/kg), indicating weak nutrient retention capacity. Nutrient availability was also severely constrained, with N (0.08%), P (2.80 ppm), and K (0.08 cmol(+)/kg) falling far below moderate soil fertility thresholds. Quantitatively, all indicators were 40-90% lower than values commonly reported in rehabilitated post-mining soils. Land evaluation classified the site as S3nr,na (marginally suitable) for Brachiaria, with limitations driven by both nutrient retention and availability factors. The findings highlight that chemical amelioration is essential before Brachiaria can be effectively established. Practically, this study provides a diagnostic basis for prioritizing rehabilitation inputs in tropical post-mining landscapes.